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{{Short description|NASA program for public suggestions for MRO images}}
{{Short description|NASA program for public suggestions for MRO images}}
{{Too many images|date=November 2024}}

'''HiWish''' is a program created by NASA so that anyone can suggest a place for the [[HiRISE]] camera on the [[Mars Reconnaissance Orbiter]] to photograph.<ref>{{cite web |url=http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily |access-date=January 10, 2011}}</ref><ref>{{Cite web|url=http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter|title=Take control of a Mars orbiter|date=28 August 2018 }}</ref><ref>{{Cite web|url=http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html|title=HiWishing for 3D Mars images, part II}}</ref> It was started in January 2010. In the first few months of the program 3000 people signed up to use HiRISE.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref><ref>{{cite web|url=http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|access-date=20 November 2018}}</ref> The first images were released in April 2010.<ref>{{cite web |url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |access-date=January 10, 2011 |archive-url=https://web.archive.org/web/20120312073722/http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |archive-date=March 12, 2012 |url-status=dead }}</ref> Over 12,000 suggestions were made by the public; suggestions were made for targets in each of the 30 quadrangles of Mars. Selected images released were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>
'''HiWish''' is a program created by NASA so that anyone can suggest a place for the [[HiRISE]] camera on the [[Mars Reconnaissance Orbiter]] to photograph.<ref>{{cite web |url=http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily |access-date=January 10, 2011}}</ref><ref>{{Cite web|url=http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter|title=Take control of a Mars orbiter|date=28 August 2018 }}</ref><ref>{{Cite web|url=http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html|title=HiWishing for 3D Mars images, part II}}</ref> It was started in January 2010. In the first few months of the program 3000 people signed up to use HiRISE.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref><ref>{{cite web|url=http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|access-date=20 November 2018}}</ref> The first images were released in April 2010.<ref>{{cite web |url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |access-date=January 10, 2011 |archive-url=https://web.archive.org/web/20120312073722/http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |archive-date=March 12, 2012 |url-status=dead }}</ref> Over 12,000 suggestions were made by the public; suggestions were made for targets in each of the 30 quadrangles of Mars. Selected images released were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>


==Glacial features==
==Glacial features==


{{Main|Glaciers on Mars}}
Some landscapes look just like glaciers moving out of mountain valleys on Earth. Some have a hollowed-out appearance, looking like a glacier after almost all the ice has disappeared. What is left are the moraines—the dirt and debris carried by the glacier. The center is hollowed out because the ice is mostly gone.<ref>{{cite journal | last1 = Milliken | first1 = R. | last2 = Mustard | first2 = J. | last3 = Goldsby | first3 = D. | year = 2003 | title = Viscous flow features on the surface of Mars: Observations from high-resolution Mars Orbiter Camera (MOC) images | journal = J. Geophys. Res. | volume = 108| issue = E6 | page = 5057 | doi = 10.1029/2002JE002005 | bibcode = 2003JGRE..108.5057M }}</ref> These supposed alpine glaciers have been called glacier-like forms (GLF) or glacier-like flows (GLF).<ref>{{cite journal | last1 = Arfstrom | first1 = J | last2 = Hartmann | first2 = W. | year = 2005 | title = Martian flow features, moraine-like ridges, and gullies: Terrestrial analogs and interrelationships | journal = Icarus | volume = 174 | issue = 2 | pages = 321–335 | doi = 10.1016/j.icarus.2004.05.026 | bibcode = 2005Icar..174..321A }}</ref> Glacier-like forms are a later and maybe more accurate term because we cannot be sure the structure is currently moving.<ref>{{cite journal | last1 = Hubbard | first1 = B. | last2 = Milliken | first2 = R. | last3 = Kargel | first3 = J. | last4 = Limaye | first4 = A. | last5 = Souness | first5 = C. | year = 2011 | title = Geomorphological characterisation and interpretation of a mid-latitude glacier-like form: Hellas Planitia, Mars | journal = Icarus | volume = 211 | issue = 1 | pages = 330–346 | doi = 10.1016/j.icarus.2010.10.021 | bibcode = 2011Icar..211..330H | doi-access = free }}</ref>


Some landscapes look just like glaciers moving out of mountain valleys on Earth. Some have a hollowed-out appearance, looking like a glacier after almost all the ice has disappeared. What is left are the moraines—the dirt and debris carried by the glacier. The center is hollowed out because the ice is mostly gone.<ref>{{cite journal | last1 = Milliken | first1 = R. | last2 = Mustard | first2 = J. | last3 = Goldsby | first3 = D. | year = 2003 | title = Viscous flow features on the surface of Mars: Observations from high-resolution Mars Orbiter Camera (MOC) images | journal = J. Geophys. Res. | volume = 108| issue = E6 | page = 5057 | doi = 10.1029/2002JE002005 | bibcode = 2003JGRE..108.5057M }}</ref> These supposed alpine glaciers have been called glacier-like forms (GLF) or glacier-like flows (GLF).<ref>{{cite journal | last1 = Arfstrom | first1 = J | last2 = Hartmann | first2 = W. | year = 2005 | title = Martian flow features, moraine-like ridges, and gullies: Terrestrial analogs and interrelationships | journal = Icarus | volume = 174 | issue = 2 | pages = 321–335 | doi = 10.1016/j.icarus.2004.05.026 | bibcode = 2005Icar..174..321A }}</ref> Glacier-like forms are a later and maybe more accurate term because we cannot be sure the structure is currently moving.<ref>{{cite journal | last1 = Hubbard | first1 = B. | last2 = Milliken | first2 = R. | last3 = Kargel | first3 = J. | last4 = Limaye | first4 = A. | last5 = Souness | first5 = C. | year = 2011 | title = Geomorphological characterisation and interpretation of a mid-latitude glacier-like form: Hellas Planitia, Mars | journal = Icarus | volume = 211 | issue = 1 | pages = 330–346 | doi = 10.1016/j.icarus.2010.10.021 | bibcode = 2011Icar..211..330H | doi-access = free }}</ref>
{{Main|Glaciers on Mars}},


{{wide image|ESP 028352 2245glacier.jpg|600px|align-cap=center|Martian glacier moving down a valley, as seen by HiRISE under HiWish program.}}|
{{wide image|ESP 028352 2245glacier.jpg|600px|align-cap=center|Martian glacier moving down a valley, as seen by HiRISE under HiWish program}}


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
Image:Wide view of glacier showing image field.JPG|Possible glacier flowing down a valley and spreading out on a plain. Rectangle shows a portion that is enlarged in the next image.
Image:Wide view of glacier showing image field.JPG|Possible glacier flowing down a valley and spreading out on a plain. Rectangle shows a portion that is enlarged in the next image.
Image:Glacier close up with hirise.JPG|Enlargement of the area in the rectangle in the previous image. This area would be called a moraine in an alpine glacier on Earth.
Image:Glacier close up with hirise.JPG|Enlargement of the area in the rectangle in the previous image. This area would be called a moraine in an alpine glacier on Earth.
Image:Hollows as seen by hirise under hiwish program.jpg|Well-developed hollows of concentric crater fill, as seen by HiRISE under the HiWish program.
Image:Hollows as seen by hirise under hiwish program.jpg|Well-developed hollows of concentric crater fill, as seen by HiRISE under the HiWish program
44410 2195glacier.jpg|[[Glacier]] on a crater floor, as seen by HiRISE under HiWish program. The cracks in the glacier may be crevasses. There is also a gully system on the crater wall.

44410 2195glacier.jpg|[[Glacier]] on a crater floor, as seen by HiRISE under HiWish program The cracks in the glacier may be crevasses. There is also a gully system on the crater wall.
ESP 045560 2230wideglacier.jpg|Glacier coming out of valley, as seen by HiRISE under HiWish program. Location is rim of [[Moreux Crater]]. Location is [[Ismenius Lacus quadrangle]].

ESP 045560 2230wideglacier.jpg|Glacier coming out of valley, as seen by HiRISE under HiWish program Location is rim of [[Moreux Crater]]. Location is [[Ismenius Lacus quadrangle]].
</gallery>
</gallery>


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==Possible pingos==
==Possible pingos==


{{see also|pingo}}
{{see also|Pingo}}

The radial and concentric cracks visible here are common when forces penetrate a brittle layer, such as a rock thrown through a glass window. These particular fractures were probably created by something emerging from below the brittle Martian surface. Ice may have accumulated under the surface in a lens shape; thus making these cracked mounds. Ice being less dense than rock, pushed upwards on the surface and generated these spider web-like patterns. A similar process creates similar sized mounds in arctic tundra on Earth. Such features are called "pingos," an Inuit word.<ref>{{cite web|url=http://www.uahirise.org/ESP_046359_1250|title=HiRISE - Spider Webs (ESP_046359_1250)|website=www.uahirise.org|access-date=20 November 2018}}</ref> Pingos would contain pure water ice; thus they could be sources of water for future colonists of Mars. Many features that look like the pingos on the Earth are found in Utopia Planitia (~35-50° N; ~80-115° E).<ref>Soare, E., et al. 2019.
The radial and concentric cracks visible here are common when forces penetrate a brittle layer, such as a rock thrown through a glass window. These particular fractures were probably created by something emerging from below the brittle Martian surface. Ice may have accumulated under the surface in a lens shape; thus making these cracked mounds. Ice being less dense than rock, pushed upwards on the surface and generated these spider web-like patterns. A similar process creates similar sized mounds in arctic tundra on Earth. Such features are called "pingos", an Inuit word.<ref>{{cite web|url=http://www.uahirise.org/ESP_046359_1250|title=HiRISE - Spider Webs (ESP_046359_1250)|website=www.uahirise.org|access-date=20 November 2018}}</ref> Pingos would contain pure water ice; thus they could be sources of water for future colonists of Mars. Many features that look like the pingos on the Earth are found in Utopia Planitia (~35-50° N; ~80-115° E).<ref>Soare, E., et al. 2019.
Possible (closed system) pingo and ice-wedge/thermokarst complexes at the mid latitudes of Utopia Planitia, Mars. Icarus. https://doi.org/10.1016/j.icarus.2019.03.010</ref>
Possible (closed system) pingo and ice-wedge/thermokarst complexes at the mid latitudes of Utopia Planitia, Mars. Icarus. https://doi.org/10.1016/j.icarus.2019.03.010</ref>
<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
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There is great deal of evidence that water once flowed in river valleys on Mars. Pictures from orbit show winding valleys, branched valleys, and even meanders with [[oxbow lakes]].<ref>Baker, V. 1982. The Channels of Mars. Univ. of Tex. Press, Austin, TX</ref> Some are visible in the pictures below.
There is great deal of evidence that water once flowed in river valleys on Mars. Pictures from orbit show winding valleys, branched valleys, and even meanders with [[oxbow lakes]].<ref>Baker, V. 1982. The Channels of Mars. Univ. of Tex. Press, Austin, TX</ref> Some are visible in the pictures below.


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
WikiESP 034082 1375channel.jpg|Channel on floor of Newton Crater, as seen by HiRISE under HiWish program.
WikiESP 034082 1375channel.jpg|Channel on floor of Newton Crater, as seen by HiRISE under HiWish program
ESP 037045 2235channel.jpg|Branched channel, as seen by HiRISE under HiWish program.
ESP 037045 2235channel.jpg|Branched channel, as seen by HiRISE under HiWish program
File:ESP 054919 1465channels.jpg|Channel, as seen by HiRISE under HiWish program
File:ESP 054919 1465channels.jpg|Channel, as seen by HiRISE under HiWish program
WikiESP 033729 1410stream.jpg|Branched channel, as seen by HiRISE under HiWish program.
WikiESP 033729 1410stream.jpg|Branched channel, as seen by HiRISE under HiWish program
WikiESP 039594 1365oxbow.jpg|[[Oxbow lake]], as seen by HiRISE under HiWish program

WikiESP 039594 1365oxbow.jpg|[[Oxbow lake]], as seen by HiRISE under HiWish program.

WikiESP 035449 2100stream.jpg|Valleys as seen by HiRISE under HiWish program
WikiESP 035449 2100stream.jpg|Valleys as seen by HiRISE under HiWish program
WikiESP 039997 2170channels.jpg|Channel in Arabia, as seen by HiRISE under HiWish program

WikiESP 039997 2170channels.jpg|Channel in Arabia, as seen by HiRISE under HiWish program.

ESP 042924 2195channel.jpg|Channel system that travels through part of a crater, as seen by HiRISE under HiWish program
ESP 042924 2195channel.jpg|Channel system that travels through part of a crater, as seen by HiRISE under HiWish program
Image:ESP_025336channels.jpg|Channels, as seen by HiRISE under HiWish program. Stream appears to have eroded through a hill.
Image:ESP_025336channels.jpg|Channels, as seen by HiRISE under HiWish program. Stream appears to have eroded through a hill.
ESP 045779 1730meander.jpg|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program. Location is [[Memnonia quadrangle]].
ESP 045779 1730meander.jpg|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program. Location is [[Memnonia quadrangle]].

File:ESP 057410 1445channelinvalley.jpg|Channel on floor of valley, as seen by HiRISE under HiWish program. Location is [[Eridania quadrangle]].
File:ESP 057410 1445channelinvalley.jpg|Channel on floor of valley, as seen by HiRISE under HiWish program. Location is [[Eridania quadrangle]].

45837 2245channel.jpg|Close view of channel in [[Ismenius Lacus quadrangle]], as seen by HiRISE under HiWish program
45837 2245channel.jpg|Close view of channel in [[Ismenius Lacus quadrangle]], as seen by HiRISE under HiWish program

45916 2205hanging.jpg|Channel with hanging valley in Ismenius Lacus quadrangle, as seen by HiRISE under HiWish program
45916 2205hanging.jpg|Channel with hanging valley in Ismenius Lacus quadrangle, as seen by HiRISE under HiWish program
ESP 048582 1845hangingvalleys.jpg|Hanging valleys in [[Aram Chaos]], as seen by HiRISE under HiWish program
ESP 048582 1845hangingvalleys.jpg|Hanging valleys in [[Aram Chaos]], as seen by HiRISE under HiWish program

ESP 045864 2160channels.jpg|Wide view of channels in Ismenius Lacus quadrangle, as seen by HiRISE under HiWish program
ESP 045864 2160channels.jpg|Wide view of channels in Ismenius Lacus quadrangle, as seen by HiRISE under HiWish program
</gallery>
</gallery>
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Streamlined shapes represent more evidence of past flowing water on Mars. Water shaped features into streamlined shapes.
Streamlined shapes represent more evidence of past flowing water on Mars. Water shaped features into streamlined shapes.


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 045897 1645streamlined.jpg|Streamlined feature, as seen by HiRISE under HiWish program. Location is [[Memnonia quadrangle]].

ESP 045897 1645streamlined.jpg|Streamlined feature, as seen by HiRISE under HiWish program Location is [[Memnonia quadrangle]].
ESP 050856 1445channels.jpg|Channel, as seen by HiRISE under HiWish program. Streamlined shapes are indicated with arrows. Location is the [[Phaethontis quadrangle]].
ESP 050856 1445channels.jpg|Channel, as seen by HiRISE under HiWish program Streamlined shapes are indicated with arrows. Location is the [[Phaethontis quadrangle]].
</gallery>
</gallery>


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="190px" heights="180px">
ESP 045860 2085streamlined.jpg|Wide view of streamlined shapes in [[Amenthes quadrangle]], as seen by HiRISE under HiWish program
ESP 045860 2085streamlined.jpg|Wide view of streamlined shapes in [[Amenthes quadrangle]], as seen by HiRISE under HiWish program
ESP 045860 2085streamlinedbottom.jpg|Close view of streamlined shapes, as seen by HiRISE under HiWish program Arrow indicates the direction of past flowing water.
ESP 045860 2085streamlinedbottom.jpg|Close view of streamlined shapes, as seen by HiRISE under HiWish program. Arrow indicates the direction of past flowing water.
ESP 045860 2085streamlinedmiddle.jpg|Close view of streamlined shapes, as seen by HiRISE under HiWish program
ESP 045860 2085streamlinedmiddle.jpg|Close view of streamlined shapes, as seen by HiRISE under HiWish program
ESP 045860 2085streamlinedtop.jpg|Close view of streamlined shapes, as seen by HiRISE under HiWish program
ESP 045860 2085streamlinedtop.jpg|Close view of streamlined shapes, as seen by HiRISE under HiWish program
ESP 045860 2085streamlineduppertop.jpg|Close view of streamlined shapes, as seen by HiRISE under HiWish program
ESP 045860 2085streamlineduppertop.jpg|Close view of streamlined shapes, as seen by HiRISE under HiWish program
45860 2085close.jpg|Close view of streamlined shape, as seen by HiRISE under HiWish program
45860 2085close.jpg|Close view of streamlined shape, as seen by HiRISE under HiWish program
ESP 052677 2075streamlined.jpg|Streamlined shapes, as seen by HiRISE under HiWish program Location is the [[Elysium quadrangle]].
ESP 052677 2075streamlined.jpg|Streamlined shapes, as seen by HiRISE under HiWish program. Location is the [[Elysium quadrangle]].
</gallery>
</gallery>


==New Crater==
==New crater==
<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
29565 2075newcratercomposite.jpg|HiRISE images showing discovery of a new crater with HiWish program
29565 2075newcratercomposite.jpg|HiRISE images showing discovery of a new crater with HiWish program
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Many locations on Mars have sand [[dune]]s. The dunes are covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. Many martian dunes strongly resemble terrestrial dunes but images acquired by the High-Resolution Imaging Science Experiment on the Mars Reconnaissance Orbiter have shown that martian dunes in the north polar region are subject to modification via grainflow triggered by seasonal {{CO2}} [[sublimation (phase transition)|sublimation]], a process not seen on Earth. Many dunes are black because they are derived from the dark volcanic rock basalt. Extraterrestrial sand seas such as those found on Mars are referred to as "undae" from the [[Latin]] for waves.
Many locations on Mars have sand [[dune]]s. The dunes are covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. Many martian dunes strongly resemble terrestrial dunes but images acquired by the High-Resolution Imaging Science Experiment on the Mars Reconnaissance Orbiter have shown that martian dunes in the north polar region are subject to modification via grainflow triggered by seasonal {{CO2}} [[sublimation (phase transition)|sublimation]], a process not seen on Earth. Many dunes are black because they are derived from the dark volcanic rock basalt. Extraterrestrial sand seas such as those found on Mars are referred to as "undae" from the [[Latin]] for waves.


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
34745 34694combdunes.jpg|Dunes in two craters, as seen by HiRISE under the HiWish program.
34745 34694combdunes.jpg|Dunes in two craters, as seen by HiRISE under the HiWish program
Image:ESP 034956 1745dunescraters.jpg|Dunes among craters, as seen by HiRISE under HiWish program. Some of these are barchans.
Image:ESP 034956 1745dunescraters.jpg|Dunes among craters, as seen by HiRISE under HiWish program. Some of these are barchans.
ESP 023561dunes.jpg|Dunes on a crater floor, as seen by HiRISE under HiWish program. Most of these are barchans. Box shows location of next image. Location is the [[Eridania quadrangle]].
ESP 023561dunes.jpg|Dunes on a crater floor, as seen by HiRISE under HiWish program. Most of these are barchans. Box shows location of next image. Location is the [[Eridania quadrangle]].
ESP 023561dunesclose.jpg|Dunes on a crater floor, as seen by HiRISE under HiWish program. Most of these are barchans. Note: this is an enlargement of the center of the previous image.
ESP 023561dunesclose.jpg|Dunes on a crater floor, as seen by HiRISE under HiWish program. Most of these are barchans. Note: this is an enlargement of the center of the previous image.
Esp 037367 1340bdunes.jpg|Dunes, as seen by HiRISE under HiWish program. Location is [[Eridania quadrangle]].
Esp 037367 1340bdunes.jpg|Dunes, as seen by HiRISE under HiWish program. Location is [[Eridania quadrangle]].

ESP 043821 2555dryice.jpg|Defrosting dunes and ice in troughs of polygons, as seen by HiRISE under HiWish program
ESP 043821 2555dryice.jpg|Defrosting dunes and ice in troughs of polygons, as seen by HiRISE under HiWish program
ESP 043821 2555dryicecolor.jpg|Color view of defrosting dunes and ice in troughs of polygons, as seen by HiRISE under HiWish program
ESP 043821 2555dryicecolor.jpg|Color view of defrosting dunes and ice in troughs of polygons, as seen by HiRISE under HiWish program
43821 2555defrostingdune.jpg|Defrosting surface, as seen by HiRISE under HiWish program Frost is disappearing in patches from a dune. The trough boundaries around the polygon shapes still contain frost; hence they are white. Note: the north side (side near top) has not defrosted because the sun is coming from the other side.
43821 2555defrostingdune.jpg|Defrosting surface, as seen by HiRISE under HiWish program. Frost is disappearing in patches from a dune. The trough boundaries around the polygon shapes still contain frost; hence they are white. Note: the north side (side near top) has not defrosted because the sun is coming from the other side.

ESP 044861 2225dunes.jpg|Wide view of dunes in [[Moreux Crater]], as seen by HiRISE under HiWish program
ESP 044861 2225dunes.jpg|Wide view of dunes in [[Moreux Crater]], as seen by HiRISE under HiWish program
ESP 045822 1680dunes.jpg|Dunes in [[Mare Tyrrhenum quadrangle]], as seen by HiRISE under HiWish program
ESP 045822 1680dunes.jpg|Dunes in [[Mare Tyrrhenum quadrangle]], as seen by HiRISE under HiWish program
45822 1680dunesclose.jpg|Close view of dunes in [[Mare Tyrrhenum quadrangle]], as seen by HiRISE under HiWish program
45822 1680dunesclose.jpg|Close view of dunes in [[Mare Tyrrhenum quadrangle]], as seen by HiRISE under HiWish program
45822 1680color.jpg|Close, color view of dunes in [[Mare Tyrrhenum quadrangle]], as seen by HiRISE under HiWish program Ripples are visible on dune surface.
45822 1680color.jpg|Close, color view of dunes in [[Mare Tyrrhenum quadrangle]], as seen by HiRISE under HiWish program. Ripples are visible on dune surface.
File:55097 1455dunescolor.jpg|Close, color view of dome sand dunes, as seen by HiRISE under HiWish program
File:55097 1455dunescolor.jpg|Close, color view of dome sand dunes, as seen by HiRISE under HiWish program

</gallery>
</gallery>


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Some of the targets suggested became possible sites for a Rover Mission in 2020. The targets were in [[Firsoff (crater)]] and [[Holden (Martian crater)|Holden Crater]]. These locations were picked as two of 26 locations considered for a mission that will look for signs of life and gather samples for a later return to Earth.<ref>[http://marsnext.jpl.nasa.gov/workshops/index.cfm NASA.gov]</ref><ref>{{cite web|url=http://hirise.lpl.arizona.edu/ESP_039404_1820|title=HiRISE - Candidate Landing Site for 2020 Mission in Firsoff Crater (ESP_039404_1820)|website=hirise.lpl.arizona.edu|access-date=20 November 2018}}</ref><ref>Pondrelli, M., A. Rossi, L. Deit, S. van Gasselt, F. Fueten, E. Hauber, B. Cavalazzi, M. Glamoclija, and F. Franchi. 2014. A PROPOSED LANDING SITE FOR THE 2020 MARS MISSION: FIRSOFF CRATER. http://marsnext.jpl.nasa.gov/workshops/2014_05/33_Pondrelli_Firsoff_LS2020.pdf</ref>
Some of the targets suggested became possible sites for a Rover Mission in 2020. The targets were in [[Firsoff (crater)]] and [[Holden (Martian crater)|Holden Crater]]. These locations were picked as two of 26 locations considered for a mission that will look for signs of life and gather samples for a later return to Earth.<ref>[http://marsnext.jpl.nasa.gov/workshops/index.cfm NASA.gov]</ref><ref>{{cite web|url=http://hirise.lpl.arizona.edu/ESP_039404_1820|title=HiRISE - Candidate Landing Site for 2020 Mission in Firsoff Crater (ESP_039404_1820)|website=hirise.lpl.arizona.edu|access-date=20 November 2018}}</ref><ref>Pondrelli, M., A. Rossi, L. Deit, S. van Gasselt, F. Fueten, E. Hauber, B. Cavalazzi, M. Glamoclija, and F. Franchi. 2014. A PROPOSED LANDING SITE FOR THE 2020 MARS MISSION: FIRSOFF CRATER. http://marsnext.jpl.nasa.gov/workshops/2014_05/33_Pondrelli_Firsoff_LS2020.pdf</ref>


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 039404 1820landingsitetop.jpg|Layers in Firsoff Crater, as seen by HiRISE under HiWish program Note: this image field can be found in the previous image of the layers in Firsoff Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter).
ESP 039404 1820landingsitetop.jpg|Layers in Firsoff Crater, as seen by HiRISE under HiWish program. Note: this image field can be found in the previous image of the layers in Firsoff Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter).
ESP 039404 1820landingsiteclose.jpg|Close-up of layers in Firsoff Crater, as seen by HiRISE Note: this is an enlargement of the previous image of Firsoff Crater.
ESP 039404 1820landingsiteclose.jpg|Close-up of layers in Firsoff Crater, as seen by HiRISE. Note: this is an enlargement of the previous image of Firsoff Crater.
Wikiesp 039404 1820landingdustfield.jpg|Layers in Firsoff crater with a box showing the size of a football field. Picture taken by HiRISE under HiWish program.

Wikiesp 039404 1820landingdustfield.jpg|Layers in Firsoff crater with a box showing the size of a football field Picture taken by HiRISE under HiWish program.
Wikiesp 039404 1820landingfir.jpg|Layers and faults in Firsoff Crater, as seen by HiRISE under HiWish program. Arrows show one large fault, but there are other smaller ones in the picture.
Wikiesp 039404 1820landingfir.jpg|Layers and faults in Firsoff Crater, as seen by HiRISE under HiWish program. Arrows show one large fault, but there are other smaller ones in the picture.
ESP 026126 1530delta.jpg|Part of delta in [[Holden (Martian crater)|Holden Crater]], as seen by HiRISE under HiWish program. Holden crater is a possible landing site for a Mars Rover scheduled for 2020.<ref>Golombek, J. et al. 2016. Downselection of landing Sites for the Mars 2020 Rover Mission. 47th Lunar and Planetary Science Conference (2016). 2324.pdf</ref>

ESP 026126 1530delta.jpg|Part of delta in [[Holden (Martian crater)|Holden Crater]], as seen by HiRISE under HiWish program Holden crater is a possible landing site for a Mars Rover scheduled for 2020.<ref>Golombek, J. et al. 2016. Downselection of landing Sites for the Mars 2020 Rover Mission. 47th Lunar and Planetary Science Conference (2016). 2324.pdf</ref>
26126 1530deltalayers.jpg|Close view of previous image showing layers, as seen by HiRISE under HiWish program and enlarged with HiView
26126 1530deltalayers.jpg|Close view of previous image showing layers, as seen by HiRISE under HiWish program and enlarged with HiView
</gallery>
</gallery>


==Landscape features==
==Landscape features==
<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
Image:Troughs in Elysium Planitia.JPG|Troughs to the East of Albor Tholus, as seen by HiRISE under the HiWish program.
Image:Troughs in Elysium Planitia.JPG|Troughs to the East of Albor Tholus, as seen by HiRISE under the HiWish program
Image:Troughs showing blue in Elysium Planitia.JPG|Portion of a trough (Fossae) in [[Elysium Planitia]], as seen by HiRISE under the HiWish program. Blue indicates possible seasonal frost.
Image:Troughs showing blue in Elysium Planitia.JPG|Portion of a trough (Fossae) in [[Elysium Planitia]], as seen by HiRISE under the HiWish program. Blue indicates possible seasonal frost.
ESP 043963 1550landslide.jpg|Landslide in a crater, as seen by HiRISE under HiWish program Image from [[Iapygia quadrangle]].
ESP 043963 1550landslide.jpg|Landslide in a crater, as seen by HiRISE under HiWish program. Image from [[Iapygia quadrangle]].
ESP 045016 2080mesas.jpg|Wide view of Buttes and Mesas, as seen by HiRISE under HiWish program. Location is [[Elysium quadrangle]].

ESP 045016 2080mesas.jpg|Wide view of Buttes and Mesas, as seen by HiRISE under HiWish program Location is [[Elysium quadrangle]].
45016 2080mesas2.jpg|Buttes and mesas, as seen by HiRISE under HiWish program. Note: this is an enlargement of the previous image.
45016 2080mesas.jpg|Mesas, as seen by HiRISE under HiWish program. Note: this is an enlargement of a previous image.

45016 2080mesas2.jpg|Buttes and mesas, as seen by HiRISE under HiWish program Note: this is an enlargement of the previous image.
45016 2080mesas.jpg|Mesas, as seen by HiRISE under HiWish program Note: this is an enlargement of a previous image.
</gallery>
</gallery>


==Dark slope streaks==
==Dark slope streaks==


{{see also|Dark slope streaks}}
{{Main|Dark slope streak}}
<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
Image:ESP_036956_1895layers.jpg|Layers and dark slope streaks, as seen by HiRISE under HiWish program
Image:ESP_036956_1895layers.jpg|Layers and dark slope streaks, as seen by HiRISE under HiWish program
Esp 036851 1995mesastreaks.jpg|Dark slope streaks on mesa, as seen by HiRISE under HiWish program Location is [[Amazonis quadrangle]].
Esp 036851 1995mesastreaks.jpg|Dark slope streaks on mesa, as seen by HiRISE under HiWish program. Location is [[Amazonis quadrangle]].
Image:25609layersstreak.jpg|Close-up of some layers under cap rock of a pedestal crater and a dark slope streak, as seen by HiRISE under HiWish program

Image:25609layersstreak.jpg|Close-up of some layers under cap rock of a pedestal crater and a dark slope streak, as seen by HiRISE under HiWish program.

Image:Streaks22919.jpg|Dark slope streaks and layers near a pedestal crater, as seen by HiRISE under the HiWish program. Arrows show the small starting points for the streaks.
Image:Streaks22919.jpg|Dark slope streaks and layers near a pedestal crater, as seen by HiRISE under the HiWish program. Arrows show the small starting points for the streaks.

44802streaks.jpg|Dark slope streaks on mound in [[Lycus Sulci]] in [[Diacria quadrangle]], as seen by HiRISE under HiWish program
44802streaks.jpg|Dark slope streaks on mound in [[Lycus Sulci]] in [[Diacria quadrangle]], as seen by HiRISE under HiWish program
ESP 045435 2055troughlayers.jpg|Layers in trough and dark slope streaks, as seen by HiRISE under HiWish program Location is [[Amazonis quadrangle]].
ESP 045435 2055troughlayers.jpg|Layers in trough and dark slope streaks, as seen by HiRISE under HiWish program. Location is [[Amazonis quadrangle]].
</gallery>
</gallery>


==Recurrent slope lineae==
==Recurrent slope lineae==


Recurrent slope lineae are small dark streaks on slopes that elongate in warm seasons. They may be evidence of liquid water.<ref>{{cite journal | last1 = McEwen | first1 = A. | display-authors = etal | year = 2014 | title = Recurring slope lineae in equatorial regions of Mars | journal = Nature Geoscience | volume = 7 | issue = 1 | pages = 53–58 | doi = 10.1038/ngeo2014 | bibcode = 2014NatGe...7...53M }}</ref><ref>{{cite journal | last1 = McEwen | first1 = A. | display-authors = etal | year = 2011 | title = Seasonal Flows on Warm Martian Slopes | journal = Science | volume = 333 | issue = 6043| pages = 740–743 | doi = 10.1126/science.1204816 | pmid = 21817049 | bibcode = 2011Sci...333..740M | s2cid = 10460581 }}</ref><ref>{{cite web|url=http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|access-date=20 November 2018}}</ref> However, there remains debate about whether water or much water is needed.<ref>{{Cite journal |doi=10.1126/sciadv.abe4459 |title=Martian subsurface cryosalt expansion and collapse as trigger for landslides |year=2021 |last1=Bishop |first1=J. L. |last2=Yeşilbaş |first2=M. |last3=Hinman |first3=N. W. |last4=Burton |first4=Z. F. M. |last5=Englert |first5=P. A. J. |last6=Toner |first6=J. D. |last7=McEwen |first7=A. S. |last8=Gulick |first8=V. C. |last9=Gibson |first9=E. K. |last10=Koeberl |first10=C. |journal=Science Advances |volume=7 |issue=6 |pmid=33536216 |pmc=7857681 |bibcode=2021SciA....7.4459B |s2cid=231805052 }}</ref><ref>Bishop, J., et al. 2021. Martian subsurface cryosalt expansion and collapse as trigger for landslides. Science Advances. Vol. 7, no. 6, eabe4459 DOI: 10.1126/sciadv.abe4459</ref><ref>{{Cite web|url=https://www.newscientist.com/article/2266632-lines-on-mars-could-be-created-by-salty-water-triggering-landslides/|title = Lines on Mars could be created by salty water triggering landslides}}</ref>
Recurrent slope lineae are small dark streaks on slopes that elongate in warm seasons. They may be evidence of liquid water.<ref>{{cite journal | last1 = McEwen | first1 = A. | display-authors = etal | year = 2014 | title = Recurring slope lineae in equatorial regions of Mars | journal = Nature Geoscience | volume = 7 | issue = 1 | pages = 53–58 | doi = 10.1038/ngeo2014 | bibcode = 2014NatGe...7...53M }}</ref><ref>{{cite journal | last1 = McEwen | first1 = A. | display-authors = etal | year = 2011 | title = Seasonal Flows on Warm Martian Slopes | journal = Science | volume = 333 | issue = 6043| pages = 740–743 | doi = 10.1126/science.1204816 | pmid = 21817049 | bibcode = 2011Sci...333..740M | s2cid = 10460581 }}</ref><ref>{{cite web|url=http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|access-date=20 November 2018}}</ref> However, there remains debate about whether water or much water is needed.<ref>{{Cite journal |doi=10.1126/sciadv.abe4459 |title=Martian subsurface cryosalt expansion and collapse as trigger for landslides |year=2021 |last1=Bishop |first1=J. L. |last2=Yeşilbaş |first2=M. |last3=Hinman |first3=N. W. |last4=Burton |first4=Z. F. M. |last5=Englert |first5=P. A. J. |last6=Toner |first6=J. D. |last7=McEwen |first7=A. S. |last8=Gulick |first8=V. C. |last9=Gibson |first9=E. K. |last10=Koeberl |first10=C. |journal=Science Advances |volume=7 |issue=6 |pmid=33536216 |pmc=7857681 |bibcode=2021SciA....7.4459B |s2cid=231805052 }}</ref><ref>Bishop, J., et al. 2021. Martian subsurface cryosalt expansion and collapse as trigger for landslides. Science Advances. Vol. 7, no. 6, eabe4459 DOI: 10.1126/sciadv.abe4459</ref><ref>{{Cite web|url=https://www.newscientist.com/article/2266632-lines-on-mars-could-be-created-by-salty-water-triggering-landslides/|title = Lines on Mars could be created by salty water triggering landslides}}</ref> <ref>{{cite web | url=https://www.uahirise.org/ESP_023184_1335 | title=HiRISE &#124; Transient Slope Lineae Formation in a Well-Preserved Crater (ESP_023184_1335) }}</ref>


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 049955 1665rslbox.jpg|Wide view of part of Valles Marineris, as seen by HiRISE under HiWish program Box shows location of recurrent slope lineae that are enlarged in next image.
ESP 049955 1665rslbox.jpg|Wide view of part of Valles Marineris, as seen by HiRISE under HiWish program. Box shows location of recurrent slope lineae that are enlarged in next image.
49955 1665rslcolorarrows.jpg|Close, color view of recurrent slope lineae, as seen by HiRISE under HiWish program Arrows point to some of the recurrent slope lineae <ref>Stillman, D., et al. 2017. Characteristics of the numerous and widespread recurring slope lineae (RSL) in Valles Marineris, Mars. Icarus. Volume 285. Pages 195-210</ref>
49955 1665rslcolorarrows.jpg|Close, color view of recurrent slope lineae, as seen by HiRISE under HiWish program. Arrows point to some of the recurrent slope lineae <ref>Stillman, D., et al. 2017. Characteristics of the numerous and widespread recurring slope lineae (RSL) in Valles Marineris, Mars. Icarus. Volume 285. Pages 195-210</ref>
</gallery>
</gallery>


==Layers==
==Layers==
Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers.<ref>{{cite web|url=http://hirise.lpl.arizona.edu?PSP_008437_1750 |title=HiRISE &#124; High Resolution Imaging Science Experiment |publisher=Hirise.lpl.arizona.edu?psp_008437_1750 |access-date=2012-08-04}}</ref> Layers can be hardened by the action of groundwater. {{Main|Groundwater on Mars#Layered terrain}},
Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers.<ref>{{cite web|url=http://hirise.lpl.arizona.edu?PSP_008437_1750 |title=HiRISE &#124; High Resolution Imaging Science Experiment |publisher=Hirise.lpl.arizona.edu?psp_008437_1750 |access-date=2012-08-04}}</ref> Layers can be hardened by the action of groundwater. {{Main|Groundwater on Mars#Layered terrain}}


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
Line 175: Line 155:
</gallery>
</gallery>


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
File:60331 1880mound.jpg|Layered mound on floor of Danielson Crater, as seen by HiRISE under HiWish program
File:60331 1880mound.jpg|Layered mound on floor of Danielson Crater, as seen by HiRISE under HiWish program

File:60331 1880layerscolortop2.jpg|Close, color view of layers and dark dust on floor of Danielson Crater, as seen by HiRISE under HiWish program
File:60331 1880layerscolortop2.jpg|Close, color view of layers and dark dust on floor of Danielson Crater, as seen by HiRISE under HiWish program
File:60331 1880layersclosecolor4boulders.jpg|Close, color view of layers and dark dust on floor of Danielson Crater, as seen by HiRISE under HiWish program. Boulders are visible in the image.

File:60331 1880layersclosecolor4boulders.jpg|Close, color view of layers and dark dust on floor of Danielson Crater, as seen by HiRISE under HiWish program Boulders are visible in the image.
File:60331 1880layerscolorfaults.jpg|Close, color view of layers and dark dust on floor of Danielson Crater, as seen by HiRISE under HiWish program. Faults are indicated with arrows.
File:60331 1880widefault.jpg|Close view of layers on floor of Danielson Crater, as seen by HiRISE under HiWish program. Some faults are visible in image.

File:60331 1880layerscolorfaults.jpg|Close, color view of layers and dark dust on floor of Danielson Crater, as seen by HiRISE under HiWish program Faults are indicated with arrows.

File:60331 1880widefault.jpg|Close view of layers on floor of Danielson Crater, as seen by HiRISE under HiWish program Some faults are visible in image.

</gallery>
</gallery>


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
Image:ESP_024807whitebutte.jpg|Light toned butte on floor of crater, as seen by HiRISE under HiWish program. Arrows show outcrops of light toned material. Light toned material is probably sulfate-rich and similar to material examined by Spirit Rover, and it once probably covered the whole floor. Other images below show enlargements of the butte. Location is [[Margaritifer Sinus quadrangle]].
Image:ESP_024807whitebutte.jpg|Light toned butte on floor of crater, as seen by HiRISE under HiWish program. Arrows show outcrops of light toned material. Light toned material is probably sulfate-rich and similar to material examined by Spirit Rover, and it once probably covered the whole floor. Other images below show enlargements of the butte. Location is [[Margaritifer Sinus quadrangle]].
24807whitebuttei.jpg|Enlargement of white butte, as seen by HiRISE under HiWish program Box shows size of a football field.
24807whitebuttei.jpg|Enlargement of white butte, as seen by HiRISE under HiWish program. Box shows size of a football field.
24807 1755whitebuttezoomed.jpg|Closer view towards top of white butte, as seen by HiRISE under HiWish program Box shows size of a football field.
24807 1755whitebuttezoomed.jpg|Closer view towards top of white butte, as seen by HiRISE under HiWish program. Box shows size of a football field.
24807 1755whitebuttetop.jpg|Top of white butte, as seen by HiRISE under HiWish program Box shows size of a football field.
24807 1755whitebuttetop.jpg|Top of white butte, as seen by HiRISE under HiWish program. Box shows size of a football field.
</gallery>
</gallery>


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
Image:ESP 036510 1735layers.jpg|Layered terrain in [[Aeolis quadrangle]], as seen by HiRISE under HiWish program.
Image:ESP 036510 1735layers.jpg|Layered terrain in [[Aeolis quadrangle]], as seen by HiRISE under HiWish program.
ESP 045029 1785moundlayers.jpg|Wide view of layered terrain, as seen by HiRISE under HiWish program Location is northeast of Gale Crater in [[Aeolis quadrangle]].
ESP 045029 1785moundlayers.jpg|Wide view of layered terrain, as seen by HiRISE under HiWish program. Location is northeast of Gale Crater in [[Aeolis quadrangle]].
45029 1785layerswide.jpg|Close view of mound with layers, as seen by HiRISE under HiWish program Note: this is an enlargement from the previous image.
45029 1785layerswide.jpg|Close view of mound with layers, as seen by HiRISE under HiWish program. Note: this is an enlargement from the previous image.
45029 1785layersclose.jpg|Close view of mound with layers, as seen by HiRISE under HiWish program Note: this is an enlargement from a previous image.
45029 1785layersclose.jpg|Close view of mound with layers, as seen by HiRISE under HiWish program. Note: this is an enlargement from a previous image.

Image:ESP_028353layers.jpg|Layers in Arabia, as seen by HiRISE under HiWish program.
Image:ESP_028353layers.jpg|Layers in Arabia, as seen by HiRISE under HiWish program.
Image:ESP 044507 1880layersdanielson.jpg|Wide view of part of Danielson Crater, as seen by HiRISE under HiWish program
Image:ESP 044507 1880layersdanielson.jpg|Wide view of part of Danielson Crater, as seen by HiRISE under HiWish program
Image:44507 1880longlayers.jpg|Enlargement of previous image of Danielson Crater, as seen by HiRISE under HiWish program The box represents the size of a football field.
Image:44507 1880longlayers.jpg|Enlargement of previous image of Danielson Crater, as seen by HiRISE under HiWish program. The box represents the size of a football field.
Image:44507 1880bouldersclose.jpg|Close-up of layers in Danielson Crater, as seen by HiRISE under HiWish program—boulders are visible, as well as dark sand
Image:44507 1880bouldersclose.jpg|Close-up of layers in Danielson Crater, as seen by HiRISE under HiWish program—boulders are visible, as well as dark sand

43376 1710layersclose.jpg|Close-up of layers in trough south of Ius Chasma, as seen by HiRISE under HiWish program
43376 1710layersclose.jpg|Close-up of layers in trough south of Ius Chasma, as seen by HiRISE under HiWish program
042055 1580layersclose.jpg|Close-up of layers in Lotto Crater, as seen by HiRISE under HiWish program
042055 1580layersclose.jpg|Close-up of layers in Lotto Crater, as seen by HiRISE under HiWish program
ESP 043824 2180layers.jpg|Layers, as seen by HiRISE under HiWish program. Location is [[Tempe Terra]].

ESP 043824 2180layers.jpg|Layers, as seen by HiRISE under HiWish program Location is [[Tempe Terra]]
43824 2160layers.jpg|Layers, as seen by HiRISE under HiWish program. Location is [[Tempe Terra]] Note: this is an enlargement of the previous image.
43824 2160layers.jpg|Layers, as seen by HiRISE under HiWish program Location is [[Tempe Terra]] Note: this is an enlargement of the previous image.
</gallery>
</gallery>
<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
46234 1845layersclose.jpg|Close view of layers, as seen by HiRISE under HiWish program At least one layer is light-toned which may indicated hydrated minerals.
46234 1845layersclose.jpg|Close view of layers, as seen by HiRISE under HiWish program. At least one layer is light-toned which may indicated hydrated minerals.
46234 1845layerstop.jpg|Close view of layers, as seen by HiRISE under HiWish program
46234 1845layerstop.jpg|Close view of layers, as seen by HiRISE under HiWish program
</gallery>
</gallery>
This group of layers that are found in a crater all come from the [[Arabia quadrangle]].
This group of layers that are found in a crater all come from the [[Arabia quadrangle]].


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 047421 1890nicelayers.jpg|Wide view of layers in crater, as seen by HiRISE under HiWish program parts of this image are enlarged in other images that follow.
ESP 047421 1890nicelayers.jpg|Wide view of layers in crater, as seen by HiRISE under HiWish program. Parts of this image are enlarged in other images that follow.
47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program Box shows the size of a football field.
47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.
47421 1890layeredterrain.jpg|Close view of layers, as seen by HiRISE under HiWish program Box shows the size of a football field.
47421 1890layeredterrain.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.
47421 1890layers5buttes.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

47421 1890layers5buttes.jpg|Close view of layers, as seen by HiRISE under HiWish program Box shows the size of a football field.

47421 1890layersbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program
47421 1890layersbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program

47421 1890layersbuttesclose.jpg|Close view of layers, as seen by HiRISE under HiWish program
47421 1890layersbuttesclose.jpg|Close view of layers, as seen by HiRISE under HiWish program

47421 1890layerssuperclose.jpg|Close view of layers, as seen by HiRISE under HiWish program
47421 1890layerssuperclose.jpg|Close view of layers, as seen by HiRISE under HiWish program
47421 1890pointed butte.jpg|Close view of layers, as seen by HiRISE under HiWish program
47421 1890pointed butte.jpg|Close view of layers, as seen by HiRISE under HiWish program
Line 235: Line 203:


This next group of layered terrain comes from the Louros Valles in the [[Coprates quadrangle]].
This next group of layered terrain comes from the Louros Valles in the [[Coprates quadrangle]].
<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 048980 1725layers.jpg|Wide view of layers in [[Louros Valles]], as seen by HiRISE under HiWish program
ESP 048980 1725layers.jpg|Wide view of layers in [[Louros Valles]], as seen by HiRISE under HiWish program
48980 1725layersclose2.jpg|Close view of layers in Louros Valles, as seen by HiRISE under HiWish program Note this is an enlargement of a previous image.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles, as seen by HiRISE under HiWish program. Note this is an enlargement of a previous image.
48980 1725layers.jpg|Close view of layers in Louros Valles, as seen by HiRISE under HiWish program. Note this is an enlargement of a previous image.

48980 1725layers.jpg|Close view of layers in Louros Valles, as seen by HiRISE under HiWish program Note this is an enlargement of a previous image.
48980 1725layersclose.jpg|Close view of layers in Louros Valles, as seen by HiRISE under HiWish program. Note this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles, as seen by HiRISE under HiWish program. Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros Valles, as seen by HiRISE under HiWish program Note this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles, as seen by HiRISE under HiWish program Note this is an enlargement of a previous image.
</gallery>
</gallery>


==Layers in Ice Cap==
==Layers in ice cap==


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 052405 2595icelayers.jpg|Layers in northern ice cap with an angular unconformity, as seen by HiRISE under HiWish program
ESP 052405 2595icelayers.jpg|Layers in northern ice cap with an angular unconformity, as seen by HiRISE under HiWish program
52405 2595icelayers.jpg|Close view of layers in northern ice cap, as seen by HiRISE under HiWish program. Arrows point to an angular unconformity.

52405 2595icelayers.jpg|Close view of layers in northern ice cap, as seen by HiRISE under HiWish program Arrows point to an angular unconformity.

ESP 052405 2595icelayersclosecolor.jpg|Close, color view of layers in northern ice cap, as seen by HiRISE under HiWish program
ESP 052405 2595icelayersclosecolor.jpg|Close, color view of layers in northern ice cap, as seen by HiRISE under HiWish program

File:ESP 054515 2595icecaplayers.jpg|Layers exposed in northern ice cap, as seen by [[HiRISE]] under HiWish program
File:ESP 054515 2595icecaplayers.jpg|Layers exposed in northern ice cap, as seen by [[HiRISE]] under HiWish program
File:ESP 054515 2595icecaplayerspartial.jpg|Close view of layers exposed in northern ice cap, as seen by HiRISE under HiWish program
File:ESP 054515 2595icecaplayerspartial.jpg|Close view of layers exposed in northern ice cap, as seen by HiRISE under HiWish program

</gallery>
</gallery>


==Gullies==
==Gullies==
'''Martian gullies''' are small, incised networks of narrow channels and their associated downslope [[sediment]] deposits, found on the planet of [[Mars]]. They are named for their resemblance to terrestrial [[gully|gullies]]. First discovered on images from [[Mars Global Surveyor]], they occur on steep slopes, especially on the walls of craters. Usually, each gully has a [[Dendritic drainage#Drainage patterns|dendritic]] ''alcove'' at its head, a [[Alluvial fan|fan-shaped]] ''apron'' at its base, and a single thread of incised ''channel'' linking the two, giving the whole gully an hourglass shape.<ref name="Malin, M. 2000">{{cite journal | last1 = Malin | first1 = M. | last2 = Edgett | first2 = K. | year = 2000 | title = Evidence for recent groundwater seepage and surface runoff on Mars | journal = Science | volume = 288 | issue = 5475 | pages = 2330–2335 | doi = 10.1126/science.288.5475.2330 | pmid = 10875910 | bibcode = 2000Sci...288.2330M }}</ref> They are believed to be relatively young because they have few, if any craters.
'''Martian gullies''' are small, incised networks of narrow channels and their associated downslope [[sediment]] deposits, found on the planet of [[Mars]]. They are named for their resemblance to terrestrial [[gully|gullies]]. First discovered on images from [[Mars Global Surveyor]], they occur on steep slopes, especially on the walls of craters. Usually, each gully has a [[Dendritic drainage#Drainage patterns|dendritic]] ''alcove'' at its head, a [[Alluvial fan|fan-shaped]] ''apron'' at its base, and a single thread of incised ''channel'' linking the two, giving the whole gully an hourglass shape.<ref name="Malin, M. 2000">{{cite journal | last1 = Malin | first1 = M. | last2 = Edgett | first2 = K. | year = 2000 | title = Evidence for recent groundwater seepage and surface runoff on Mars | journal = Science | volume = 288 | issue = 5475 | pages = 2330–2335 | doi = 10.1126/science.288.5475.2330 | pmid = 10875910 | bibcode = 2000Sci...288.2330M }}</ref> They are believed to be relatively young because they have few, if any craters.
On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers believed that the processes carving the gullies involve liquid water. However, this remains a topic of active research. {{Main|Martian gullies}},
On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers believed that the processes carving the gullies involve liquid water. However, this remains a topic of active research.


{{Main|Gullies on Mars}}
{{wide image|ESP 039621 1315gullies.jpg|600px|align-cap=center|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program. Location is [[Phaethontis quadrangle]].}}|


{{wide image|ESP 039621 1315gullies.jpg|600px|align-cap=center|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program. Location is [[Phaethontis quadrangle]].}}
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ESP 039621 1315aprons.jpg|Close-up of gully aprons showing they are free of craters; hence very young. Location is [[Phaethontis quadrangle]]. Picture was taken by HiRISE under HiWish program.
ESP 039621 1315aprons.jpg|Close-up of gully aprons showing they are free of craters; hence very young. Location is [[Phaethontis quadrangle]]. Picture was taken by HiRISE under HiWish program.
ESP 037506 2285gullychannels.jpg|Gullies on wall of crater, as seen by HiRISE under HiWish program. Location is the [[Mare Acidalium quadrangle]].

ESP 037506 2285gullychannels.jpg|Gullies on wall of crater, as seen by HiRISE under HiWish program Location is the [[Mare Acidalium quadrangle]].
ESP 037506 2285gullychannelsclose.jpg|Close-up of gully channels, as seen by HiRISE under HiWish program. This image shows many streamlined forms and some benches along a channel. These features suggest formation by running water. Benches are usually formed when the water level goes down a bit and stays at that level for a time. Picture was taken with HiRISE under HiWish program. Location is the [[Mare Acidalium quadrangle]]. Note this is an enlargement of a previous image.
ESP 037506 2285gullychannelsclose.jpg|Close-up of gully channels, as seen by HiRISE under HiWish program. This image shows many streamlined forms and some benches along a channel. These features suggest formation by running water. Benches are usually formed when the water level goes down a bit and stays at that level for a time. Picture was taken with HiRISE under HiWish program. Location is the [[Mare Acidalium quadrangle]]. Note this is an enlargement of a previous image.

ESP 039753 1385gulliespits.jpg|Gullies in crater in [[Phaethontis quadrangle]], as seen by HiRISE under HiWish program
ESP 039753 1385gulliespits.jpg|Gullies in crater in [[Phaethontis quadrangle]], as seen by HiRISE under HiWish program

ESP 044707 2285gullies.jpg|Gullies along mesa wall in North [[Tempe Terra]], as seen by HiRISE under HiWish program
ESP 044707 2285gullies.jpg|Gullies along mesa wall in North [[Tempe Terra]], as seen by HiRISE under HiWish program
44707 2285apron.jpg|Close view of gully apron, as seen by HiRISE under HiWish program Note this is an enlargement of the previous image.
44707 2285apron.jpg|Close view of gully apron, as seen by HiRISE under HiWish program. Note this is an enlargement of the previous image.
44707 2285alcove.jpg|Close view of gully alcove, as seen by HiRISE under HiWish program Note this is an enlargement of a previous image.
44707 2285alcove.jpg|Close view of gully alcove, as seen by HiRISE under HiWish program. Note this is an enlargement of a previous image.
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47395 1415gullycurvedchannels.jpg|Close view of gullies from previous image The channels are quite curved. Because channels of gullies often form curves, it was thought that they were made by flowing water. Today, it is thought that they could be produced with chunks of dry ice. The image is from HiRISE under HiWish program.
47395 1415gullycurvedchannels.jpg|Close view of gullies from previous image The channels are quite curved. Because channels of gullies often form curves, it was thought that they were made by flowing water. Today, it is thought that they could be produced with chunks of dry ice. The image is from HiRISE under HiWish program.

File:ESP 084896 1355 small gullies 02.jpg|Gullies, as seen by HiRISE. The gullies range from very samll to large, as such they may represent different stages in the formation of gullies. The colored strip is about 1 km wide.
File:ESP 084896 1355 small gullies 03.jpg|Small gully This gully may be in its initial state of formation.
File:ESP 084896 1355 small gullies 04.jpg|Gully, as seen by HiRISE

File:ESP 084659 1355 gullies cropped 01.jpg|Wide view of gullies
File:ESP 084659 1355 gullies cropped 02.jpg|Close view of gully alcoves Picture is about 1 km across.
File:ESP 084659 1355 gullies cropped 03.jpg|Close view of gully alcoves Picture is about 1 km across.
File:ESP 084659 1355 gullies cropped 04.jpg|Close view of gully channels Picture is about 1 km across.
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==Latitude dependent mantle==
==Latitude dependent mantle==
{{Main|Latitude dependent mantle}}
Much of the Martian surface is covered with a thick ice-rich, mantle layer that has fallen from the sky a number of times in the past.<ref name="Hecht, M 2002">{{cite journal | last1 = Hecht | first1 = M | year = 2002 | title = Metastability of water on Mars | journal = Icarus | volume = 156 | issue = 2 | pages = 373–386 | doi = 10.1006/icar.2001.6794 | bibcode = 2002Icar..156..373H }}</ref><ref name="Mustard, J. 2001">{{cite journal | last1 = Mustard | first1 = J. | display-authors = etal | year = 2001 | title = Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice | journal = Nature | volume = 412 | issue = 6845| pages = 411–414 | doi = 10.1038/35086515 | pmid = 11473309 | bibcode = 2001Natur.412..411M | s2cid = 4409161 }}</ref><ref>{{cite journal | last1 = Pollack | first1 = J. | last2 = Colburn | first2 = D. | last3 = Flaser | first3 = F. | last4 = Kahn | first4 = R. | last5 = Carson | first5 = C. | last6 = Pidek | first6 = D. | year = 1979 | title = Properties and effects of dust suspended in the martian atmosphere | journal = J. Geophys. Res. | volume = 84 | pages = 2929–2945 | doi = 10.1029/jb084ib06p02929 | bibcode = 1979JGR....84.2929P }}</ref> In some places a number of layers are visible in the mantle.<ref>{{cite web|url=http://www.uahirise.org/ESP_048897_2125|title=HiRISE - Layered Mantling Deposits in the Northern Mid-Latitudes (ESP_048897_2125)|website=www.uahirise.org|access-date=20 November 2018}}</ref>


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{{see also|Latitude dependent mantle}}
Much of the Martian surface is covered with a thick ice-rich, mantle layer that has fallen from the sky a number of times in the past.<ref name="Hecht, M 2002">{{cite journal | last1 = Hecht | first1 = M | year = 2002 | title = Metastability of water on Mars | journal = Icarus | volume = 156 | issue = 2 | pages = 373–386 | doi = 10.1006/icar.2001.6794 | bibcode = 2002Icar..156..373H }}</ref><ref name="Mustard, J. 2001">{{cite journal | last1 = Mustard | first1 = J. | display-authors = etal | year = 2001 | title = Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice | journal = Nature | volume = 412 | issue = 6845| pages = 411–414 | doi = 10.1038/35086515 | pmid = 11473309 | bibcode = 2001Natur.412..411M | s2cid = 4409161 }}</ref><ref>{{cite journal | last1 = Pollack | first1 = J. | last2 = Colburn | first2 = D. | last3 = Flaser | first3 = F. | last4 = Kahn | first4 = R. | last5 = Carson | first5 = C. | last6 = Pidek | first6 = D. | year = 1979 | title = Properties and effects of dust suspended in the martian atmosphere | journal = J. Geophys. Res. | volume = 84 | pages = 2929–2945 | doi = 10.1029/jb084ib06p02929 | bibcode = 1979JGR....84.2929P }}</ref> In some places a number of layers are visible in the mantle.<ref>{{cite web|url=http://www.uahirise.org/ESP_048897_2125|title=HiRISE - Layered Mantling Deposits in the Northern Mid-Latitudes (ESP_048897_2125)|website=www.uahirise.org|access-date=20 November 2018}}</ref>

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Esp 037167 1445mantle.jpg|Surface showing appearance with and without mantle covering, as seen by HiRISE, under the HiWish program. Location is [[Terra Sirenum]] in Phaethontis quadrangle.
Esp 037167 1445mantle.jpg|Surface showing appearance with and without mantle covering, as seen by HiRISE, under the HiWish program. Location is [[Terra Sirenum]] in Phaethontis quadrangle.
Image:2509mantlelayers.jpg|Mantle layers, as seen by HiRISE under HiWish program. Location is [[Eridania quadrangle]]
Image:2509mantlelayers.jpg|Mantle layers, as seen by HiRISE under HiWish program. Location is [[Eridania quadrangle]]
Image:24589mantle.jpg|Close up view of mantle, as seen by HiRISE under the HiWish program. Mantle may be composed of ice and dust that fell from the sky during past climatic conditions. Location is [[Cebrenia quadrangle]].
Image:24589mantle.jpg|Close up view of mantle, as seen by HiRISE under the HiWish program. Mantle may be composed of ice and dust that fell from the sky during past climatic conditions. Location is [[Cebrenia quadrangle]].
45085 2205mantlethickness.jpg|Close view of mantle, as seen by HiRISE under HiWish program Arrows show craters along edge which highlight the thickness of mantle. Location is [[Ismenius Lacus quadrangle]].
45085 2205mantlethickness.jpg|Close view of mantle, as seen by HiRISE under HiWish program. Arrows show craters along edge which highlight the thickness of mantle. Location is [[Ismenius Lacus quadrangle]].
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program. Location is Ismenius Lacus quadrangle.

45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program Location is Ismenius Lacus quadrangle.
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ESP 050456 2250mantle.jpg|Wide view of surface with spots displaying mantle, as seen by HiRISE under HiWish program Location is the [[Arcadia quadrangle]].
ESP 050456 2250mantle.jpg|Wide view of surface with spots displaying mantle, as seen by HiRISE under HiWish program. Location is the [[Arcadia quadrangle]].

50456 2250mantle2.jpg|Close view of mantle, as seen by HiRISE under HiWish program
50456 2250mantle2.jpg|Close view of mantle, as seen by HiRISE under HiWish program

50456 2250mantle3.jpg|Close view of mantle, as seen by HiRISE under HiWish program
50456 2250mantle3.jpg|Close view of mantle, as seen by HiRISE under HiWish program
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It fell as snow and ice-coated dust. There is good evidence that this mantle is ice-rich. The shapes of the polygons common on many surfaces suggest ice-rich soil. High levels of hydrogen (probably from water) have been found with [[Mars Odyssey]].<ref>{{cite journal | last1 = Boynton | first1 = W. | display-authors = etal | year = 2002 | title = Distribution of hydrogen in the nearsurface of Mars: Evidence for sub-surface ice deposits | journal = Science | volume = 297 | issue = 5578 | pages = 81–85 | doi = 10.1126/science.1073722 | pmid = 12040090 | bibcode = 2002Sci...297...81B | s2cid = 16788398 | doi-access = free }}</ref><ref>{{cite journal | last1 = Kuzmin | first1 = R | display-authors = etal | year = 2004 | title = Regions of potential existence of free water (ice) in the near-surface martian ground: Results from the Mars Odyssey High-Energy Neutron Detector (HEND) | journal = Solar System Research | volume = 38 | issue = 1| pages = 1–11 | doi = 10.1023/b:sols.0000015150.61420.5b | bibcode = 2004SoSyR..38....1K | s2cid = 122295205 }}</ref><ref>Mitrofanov, I. et al. 2007a. Burial depth of water ice in Mars permafrost subsurface. In: LPSC 38, Abstract #3108. Houston, TX.</ref><ref>{{cite journal | last1 = Mitrofanov | first1 = I. | display-authors = etal | year = 2007b | title = Water ice permafrost on Mars: Layering structure and subsurface distribution according to HEND/Odyssey and MOLA/MGS data | journal = Geophys. Res. Lett. | volume = 34 | issue = 18 | page = 18 | doi = 10.1029/2007GL030030 | bibcode = 2007GeoRL..3418102M | s2cid = 45615143 | doi-access = free }}</ref><ref>{{cite journal | last1 = Mangold | first1 = N. | display-authors = etal | year = 2004 | title = Spatial relationships between patterned ground and ground ice detected by the neutron spectrometer on Mars | journal = J. Geophys. Res. | volume = 109 | issue = E8 | page = E8 | doi = 10.1029/2004JE002235 | bibcode = 2004JGRE..109.8001M | url = https://hal.archives-ouvertes.fr/hal-00380066/file/2004JE002235.pdf }}</ref> Thermal measurements from orbit suggest ice.<ref>{{cite journal | last1 = Feldman | first1 = W. | display-authors = etal | year = 2002 | title = Global distribution of neutrons from Mars: Results from Mars Odyssey | journal = Science | volume = 297 | issue = 5578 | pages = 75–78 | doi = 10.1126/science.1073541 | pmid = 12040088 | bibcode = 2002Sci...297...75F | s2cid = 11829477 | doi-access = free }}</ref><ref>{{cite journal | last1 = Feldman | first1 = W. | display-authors = etal | year = 2008 | title = North to south asymmetries in the water-equivalent hydrogen distribution at high latitudes on Mars | journal = J. Geophys. Res. | volume = 113| issue = E8 | doi = 10.1029/2007JE003020 | bibcode = 2008JGRE..113.8006F | hdl = 2027.42/95381 | hdl-access = free }}</ref> The [[Phoenix (spacecraft)]] discovered water ice with made direct observations since it landed in a field of polygons.<ref name=Press>[http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080619.html Bright Chunks at ''Phoenix'' Lander's Mars Site Must Have Been Ice] – Official NASA press release (19.06.2008)</ref><ref>{{cite web|url=http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080620.html |title=Confirmation of Water on Mars |publisher=Nasa.gov |date=2008-06-20 |access-date=2012-07-13}}</ref> In fact, its landing rockets exposed pure ice. Theory had predicted that ice would be found under a few cm of soil. This mantle layer is called "latitude dependent mantle" because its occurrence is related to the latitude. It is this mantle that cracks and then forms polygonal ground. This cracking of ice-rich ground is predicted based on physical processes.<ref>Mutch, T.A., and 24 colleagues, 1976. The surface of Mars: The view from the Viking2 lander ''Science'' 194 (4271), 1277–1283.</ref><ref>{{cite journal | last1 = Mutch | first1 = T. | display-authors = etal | year = 1977 | title = The geology of the Viking Lander 2 site | journal = J. Geophys. Res. | volume = 82 | issue = 28 | pages = 4452–4467 | doi = 10.1029/js082i028p04452 | bibcode = 1977JGR....82.4452M }}</ref>
It fell as snow and ice-coated dust. There is good evidence that this mantle is ice-rich. The shapes of the polygons common on many surfaces suggest ice-rich soil. High levels of hydrogen (probably from water) have been found with [[Mars Odyssey]].<ref>{{cite journal | last1 = Boynton | first1 = W. | display-authors = etal | year = 2002 | title = Distribution of hydrogen in the nearsurface of Mars: Evidence for sub-surface ice deposits | journal = Science | volume = 297 | issue = 5578 | pages = 81–85 | doi = 10.1126/science.1073722 | pmid = 12040090 | bibcode = 2002Sci...297...81B | s2cid = 16788398 | doi-access = free }}</ref><ref>{{cite journal | last1 = Kuzmin | first1 = R | display-authors = etal | year = 2004 | title = Regions of potential existence of free water (ice) in the near-surface martian ground: Results from the Mars Odyssey High-Energy Neutron Detector (HEND) | journal = Solar System Research | volume = 38 | issue = 1| pages = 1–11 | doi = 10.1023/b:sols.0000015150.61420.5b | bibcode = 2004SoSyR..38....1K | s2cid = 122295205 }}</ref><ref>Mitrofanov, I. et al. 2007a. Burial depth of water ice in Mars permafrost subsurface. In: LPSC 38, Abstract #3108. Houston, TX.</ref><ref>{{cite journal | last1 = Mitrofanov | first1 = I. | display-authors = etal | year = 2007b | title = Water ice permafrost on Mars: Layering structure and subsurface distribution according to HEND/Odyssey and MOLA/MGS data | journal = Geophys. Res. Lett. | volume = 34 | issue = 18 | page = 18 | doi = 10.1029/2007GL030030 | bibcode = 2007GeoRL..3418102M | s2cid = 45615143 | doi-access = free }}</ref><ref>{{cite journal | last1 = Mangold | first1 = N. | display-authors = etal | year = 2004 | title = Spatial relationships between patterned ground and ground ice detected by the neutron spectrometer on Mars | journal = J. Geophys. Res. | volume = 109 | issue = E8 | page = E8 | doi = 10.1029/2004JE002235 | bibcode = 2004JGRE..109.8001M | url = https://hal.archives-ouvertes.fr/hal-00380066/file/2004JE002235.pdf }}</ref> Thermal measurements from orbit suggest ice.<ref>{{cite journal | last1 = Feldman | first1 = W. | display-authors = etal | year = 2002 | title = Global distribution of neutrons from Mars: Results from Mars Odyssey | journal = Science | volume = 297 | issue = 5578 | pages = 75–78 | doi = 10.1126/science.1073541 | pmid = 12040088 | bibcode = 2002Sci...297...75F | s2cid = 11829477 | doi-access = free }}</ref><ref>{{cite journal | last1 = Feldman | first1 = W. | display-authors = etal | year = 2008 | title = North to south asymmetries in the water-equivalent hydrogen distribution at high latitudes on Mars | journal = J. Geophys. Res. | volume = 113| issue = E8 | doi = 10.1029/2007JE003020 | bibcode = 2008JGRE..113.8006F | hdl = 2027.42/95381 | hdl-access = free }}</ref> The [[Phoenix (spacecraft)]] discovered water ice with made direct observations since it landed in a field of polygons.<ref name=Press>[http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080619.html Bright Chunks at ''Phoenix'' Lander's Mars Site Must Have Been Ice] {{Webarchive|url=https://web.archive.org/web/20160304075627/http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080619.html |date=2016-03-04 }} – Official NASA press release (19.06.2008)</ref><ref>{{cite web |url=http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080620.html |title=Confirmation of Water on Mars |publisher=Nasa.gov |date=2008-06-20 |access-date=2012-07-13 |archive-date=2008-07-01 |archive-url=https://web.archive.org/web/20080701104400/http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080620.html |url-status=dead }}</ref> In fact, its landing rockets exposed pure ice. Theory had predicted that ice would be found under a few cm of soil. This mantle layer is called "latitude dependent mantle" because its occurrence is related to the latitude. It is this mantle that cracks and then forms polygonal ground. This cracking of ice-rich ground is predicted based on physical processes.<ref>Mutch, T.A., and 24 colleagues, 1976. The surface of Mars: The view from the Viking2 lander ''Science'' 194 (4271), 1277–1283.</ref><ref>{{cite journal | last1 = Mutch | first1 = T. | display-authors = etal | year = 1977 | title = The geology of the Viking Lander 2 site | journal = J. Geophys. Res. | volume = 82 | issue = 28 | pages = 4452–4467 | doi = 10.1029/js082i028p04452 | bibcode = 1977JGR....82.4452M }}</ref><ref>{{cite journal | last1 = Levy | first1 = J. | display-authors = etal | year = 2009 | title = Thermal contraction crack polygons on Mars: Classification, distribution, and climate implications from HiRISE observations | journal = J. Geophys. Res. | volume = 114| issue = E1 | doi = 10.1029/2008JE003273 | bibcode = 2009JGRE..114.1007L | doi-access = free }}</ref><ref>Washburn, A. 1973. Periglacial Processes and Environments. St. Martin's Press,
<ref>{{cite journal | last1 = Levy | first1 = J. | display-authors = etal | year = 2009 | title = Thermal contraction crack polygons on Mars: Classification, distribution, and climate implications from HiRISE observations | journal = J. Geophys. Res. | volume = 114| issue = E1 | doi = 10.1029/2008JE003273 | bibcode = 2009JGRE..114.1007L | doi-access = free }}</ref><ref>Washburn, A. 1973. Periglacial Processes and Environments. St. Martin's Press,
New York, pp. 1–2, 100–147.</ref><ref>Mellon, M. 1997. Small-scale polygonal features on Mars: Seasonal thermal contraction cracks in permafrost ''J. Geophys. Res.'' 102, 25,617-25,628.</ref><ref name="High latitude patterned grounds on">{{cite journal | last1 = Mangold | first1 = N | year = 2005 | title = High latitude patterned grounds on Mars: Classification, distribution and climatic control | journal = Icarus | volume = 174 | issue = 2 | pages = 336–359 | doi = 10.1016/j.icarus.2004.07.030 | bibcode = 2005Icar..174..336M }}</ref><ref>{{cite journal | last1 = Marchant | first1 = D. | last2 = Head | first2 = J. | year = 2007 | title = Antarctic dry valleys: Microclimate zonation, variable geomorphic processes, and implications for assessing climate change on Mars | journal = Icarus | volume = 192 | issue = 1 | pages = 187–222 | doi = 10.1016/j.icarus.2007.06.018 | bibcode = 2007Icar..192..187M }}</ref>
New York, pp. 1–2, 100–147.</ref><ref>Mellon, M. 1997. Small-scale polygonal features on Mars: Seasonal thermal contraction cracks in permafrost ''J. Geophys. Res.'' 102, 25,617-25,628.</ref><ref name="High latitude patterned grounds on">{{cite journal | last1 = Mangold | first1 = N | year = 2005 | title = High latitude patterned grounds on Mars: Classification, distribution and climatic control | journal = Icarus | volume = 174 | issue = 2 | pages = 336–359 | doi = 10.1016/j.icarus.2004.07.030 | bibcode = 2005Icar..174..336M }}</ref><ref>{{cite journal | last1 = Marchant | first1 = D. | last2 = Head | first2 = J. | year = 2007 | title = Antarctic dry valleys: Microclimate zonation, variable geomorphic processes, and implications for assessing climate change on Mars | journal = Icarus | volume = 192 | issue = 1 | pages = 187–222 | doi = 10.1016/j.icarus.2007.06.018 | bibcode = 2007Icar..192..187M }}</ref>

{{Main|Latitude dependent mantle}},

==Polygonal patterned ground==
==Polygonal patterned ground==


{{see also|Polygonal patterned ground}}
{{Main|Polygonal patterned ground}}
Polygonal, patterned ground is quite common in some regions of Mars.<ref>{{cite web|url=http://www.diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000003198/16_ColdClimateLandforms-13-utopia.pdf?hosts=|title=Refubium - Suche|website=www.diss.fu-berlin.de|access-date=20 November 2018}}</ref><ref>{{cite journal | last1 = Kostama | first1 = V.-P. | last2 = Kreslavsky | first2 = Head | year = 2006 | title = Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement | journal = Geophys. Res. Lett. | volume = 33 | issue = 11 | page = L11201 | doi = 10.1029/2006GL025946 | bibcode = 2006GeoRL..3311201K | s2cid = 17229252 | doi-access = free }}</ref><ref>{{cite journal | last1 = Malin | first1 = M. | last2 = Edgett | first2 = K. | year = 2001 | title = Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission | journal = J. Geophys. Res. | volume = 106 | issue = E10| pages = 23429–23540 | doi = 10.1029/2000je001455 | bibcode = 2001JGR...10623429M | doi-access = free }}</ref><ref>{{cite journal | last1 = Milliken | first1 = R. | display-authors = etal | year = 2003 | title = Viscous flow features on the surface of Mars: Observations from high-resolution Mars Orbiter Camera (MOC) images | journal = J. Geophys. Res. | volume = 108 | issue = E6 | page = E6 | doi = 10.1029/2002JE002005 | bibcode = 2003JGRE..108.5057M }}</ref><ref name="High latitude patterned grounds on"/><ref>{{cite journal | last1 = Kreslavsky | first1 = M. | last2 = Head | first2 = J. | year = 2000 | title = Kilometer-scale roughness on Mars: Results from MOLA data analysis | journal = J. Geophys. Res. | volume = 105 | issue = E11| pages = 26695–26712 | doi = 10.1029/2000je001259 | bibcode = 2000JGR...10526695K | doi-access = free }}</ref><ref>{{cite journal | last1 = Seibert | first1 = N. | last2 = Kargel | first2 = J. | year = 2001 | title = Small-scale martian polygonal terrain: Implications for liquid surface water | journal = Geophys. Res. Lett. | volume = 28 | issue = 5| pages = 899–902 | doi = 10.1029/2000gl012093 | bibcode = 2001GeoRL..28..899S | s2cid = 129590052 }}</ref> It is commonly believed to be caused by the sublimation of ice from the ground. [[Sublimation (phase transition)|Sublimation]] is the direct change of solid ice to a gas. This is similar to what happens to [[dry ice]] on the Earth. Places on Mars that display polygonal ground may indicate where future colonists can find water ice. Patterned ground forms in a mantle layer, called [[latitude dependent mantle]], that fell from the sky when the climate was different.<ref name="Hecht, M 2002"/><ref name="Mustard, J. 2001"/><ref>Kreslavsky, M.A., Head, J.W., 2002. High-latitude Recent Surface Mantle on Mars: New Results from MOLA and MOC. European Geophysical Society XXVII, Nice.</ref><ref>{{cite journal | last1 = Head | first1 = J.W. | last2 = Mustard | first2 = J.F. | last3 = Kreslavsky | first3 = M.A. | last4 = Milliken | first4 = R.E. | last5 = Marchant | first5 = D.R. | year = 2003 | title = Recent ice ages on Mars | journal = Nature | volume = 426 | issue = 6968| pages = 797–802 | doi = 10.1038/nature02114 | pmid = 14685228 | bibcode = 2003Natur.426..797H | s2cid = 2355534 }}</ref>


Polygonal, patterned ground is quite common in some regions of Mars.<ref>{{cite web|url=http://www.diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000003198/16_ColdClimateLandforms-13-utopia.pdf?hosts=|title=Refubium - Suche|website=www.diss.fu-berlin.de|access-date=20 November 2018}}</ref><ref>{{cite journal | last1 = Kostama | first1 = V.-P. | last2 = Kreslavsky | first2 = Head | year = 2006 | title = Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement | journal = Geophys. Res. Lett. | volume = 33 | issue = 11 | page = L11201 | doi = 10.1029/2006GL025946 | bibcode = 2006GeoRL..3311201K | s2cid = 17229252 | doi-access = free }}</ref><ref>{{cite journal | last1 = Malin | first1 = M. | last2 = Edgett | first2 = K. | year = 2001 | title = Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission | journal = J. Geophys. Res. | volume = 106 | issue = E10| pages = 23429–23540 | doi = 10.1029/2000je001455 | bibcode = 2001JGR...10623429M | doi-access = free }}</ref><ref>{{cite journal | last1 = Milliken | first1 = R. | display-authors = etal | year = 2003 | title = Viscous flow features on the surface of Mars: Observations from high-resolution Mars Orbiter Camera (MOC) images | journal = J. Geophys. Res. | volume = 108 | issue = E6 | page = E6 | doi = 10.1029/2002JE002005 | bibcode = 2003JGRE..108.5057M }}</ref><ref name="High latitude patterned grounds on" /><ref>{{cite journal | last1 = Kreslavsky | first1 = M. | last2 = Head | first2 = J. | year = 2000 | title = Kilometer-scale roughness on Mars: Results from MOLA data analysis | journal = J. Geophys. Res. | volume = 105 | issue = E11| pages = 26695–26712 | doi = 10.1029/2000je001259 | bibcode = 2000JGR...10526695K | doi-access = free }}</ref><ref>{{cite journal | last1 = Seibert | first1 = N. | last2 = Kargel | first2 = J. | year = 2001 | title = Small-scale martian polygonal terrain: Implications for liquid surface water | journal = Geophys. Res. Lett. | volume = 28 | issue = 5| pages = 899–902 | doi = 10.1029/2000gl012093 | bibcode = 2001GeoRL..28..899S | s2cid = 129590052 }}</ref> It is commonly believed to be caused by the sublimation of ice from the ground. [[Sublimation (phase transition)|Sublimation]] is the direct change of solid ice to a gas. This is similar to what happens to [[dry ice]] on the Earth. Places on Mars that display polygonal ground may indicate where future colonists can find water ice. Patterned ground forms in a mantle layer, called [[latitude dependent mantle]], that fell from the sky when the climate was different.<ref name="Hecht, M 2002" /><ref name="Mustard, J. 2001" /><ref>Kreslavsky, M.A., Head, J.W., 2002. High-latitude Recent Surface Mantle on Mars: New Results from MOLA and MOC. European Geophysical Society XXVII, Nice.</ref><ref>{{cite journal | last1 = Head | first1 = J.W. | last2 = Mustard | first2 = J.F. | last3 = Kreslavsky | first3 = M.A. | last4 = Milliken | first4 = R.E. | last5 = Marchant | first5 = D.R. | year = 2003 | title = Recent ice ages on Mars | journal = Nature | volume = 426 | issue = 6968| pages = 797–802 | doi = 10.1038/nature02114 | pmid = 14685228 | bibcode = 2003Natur.426..797H | s2cid = 2355534 }}</ref>
{{Main|Polygonal patterned ground}},


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
File:56148 1145polygonswide.jpg|Wide view of crater containing polygons with frost in the low parts, as seen by HiRISE under the HiWish program
File:56148 1145polygonswide.jpg|Wide view of crater containing polygons with frost in the low parts, as seen by HiRISE under the HiWish program
File:56148 1145polygonsclose.jpg|Closer view of polygons with frost in the low parts, as seen by HiRISE under the HiWish program
File:56148 1145polygonsclose.jpg|Closer view of polygons with frost in the low parts, as seen by HiRISE under the HiWish program
File:56148 1145polygonsveryclose.jpg|Still closer view of polygons, as seen by HiRISE under the HiWish program
File:56148 1145polygonsveryclose.jpg|Still closer view of polygons, as seen by HiRISE under the HiWish program
File:56148 1145polygonsveryclosecircles.jpg|Close view of polygons with frost in the low parts, as seen by HiRISE under the HiWish program Circular shapes are also visible.
File:56148 1145polygonsveryclosecircles.jpg|Close view of polygons with frost in the low parts, as seen by HiRISE under the HiWish program. Circular shapes are also visible.

</gallery>
</gallery>
<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">

44042 2240highcenterpolygons.jpg|High center polygons, shown with arrows, as seen by HiRISE under HiWish program. Location is [[Casius quadrangle]]. Image enlarged with HiView.
44042 2240highcenterpolygons.jpg|High center polygons, shown with arrows, as seen by HiRISE under HiWish program. Location is [[Casius quadrangle]]. Image enlarged with HiView.
44042 2240scallops.jpg|Scalloped terrain labeled with both low center polygons and high center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
44042 2240scallops.jpg|Scalloped terrain labeled with both low center polygons and high center polygons, as seen by HiRISE under HiWish program. Location is [[Casius quadrangle]]. Image enlarged with HiView.
44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program. Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program. Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView. Location is [[Casius quadrangle]].
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program. Location is [[Casius quadrangle]]. Image enlarged with HiView. Location is [[Casius quadrangle]].
45070 1440glacialsnout.jpg|Close view of snout of glacier, as seen by HiRISE under the HiWish program. High center polygons are visible. Box shows size of football field.

45070 1440glacialsnout.jpg|Close view of snout of glacier, as seen by HiRISE under the HiWish program High center polygons are visible. Box shows size of football field.
45070 1440polygonscloseshadows.jpg|Close view of high center polygons near glacier, as seen by HiRISE under the HiWish program. Box shows size of football field.
45070 1440polygonscloseshadows.jpg|Close view of high center polygons near glacier, as seen by HiRISE under the HiWish program Box shows size of football field.
45070 1440polygonshadows.jpg|Close view of high center polygons near glacier, as seen by HiRISE under the HiWish program
45070 1440polygonshadows.jpg|Close view of high center polygons near glacier, as seen by HiRISE under the HiWish program
</gallery>
</gallery>


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 045299 1545channelswide.jpg|Wide view of a group of channels, as seen by HiRISE under HiWish project Some parts of the surface show patterned ground when enlarged.
ESP 045299 1545channelswide.jpg|Wide view of a group of channels, as seen by HiRISE under HiWish project Some parts of the surface show patterned ground when enlarged.
45299 1545patternedground.jpg|Patterned ground, as seen by HiRISE under HiWish program This is a close up from previous image.
45299 1545patternedground.jpg|Patterned ground, as seen by HiRISE under HiWish program. This is a close up from previous image.
45299 1545ridges.jpg|Ridges, as seen by HiRISE under HiWish program. This is a close up from a previous image.

45299 1545ridges.jpg|Ridges, as seen by HiRISE under HiWish program This is a close up from a previous image.

ESP 045299 1545mediumclose.jpg|Color view of surface in a previous image, as seen by HiRISE under HiWish program
ESP 045299 1545mediumclose.jpg|Color view of surface in a previous image, as seen by HiRISE under HiWish program

ESP 045299 1545coloredclose.jpg|Color image of patterned ground, enlarged from a previous image, as seen by HiRISE under HiWish program
ESP 045299 1545coloredclose.jpg|Color image of patterned ground, enlarged from a previous image, as seen by HiRISE under HiWish program
</gallery>
</gallery>
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==Complex polygonal patterned ground==
==Complex polygonal patterned ground==


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 049660 1200polygons.jpg|Wide view of polygons, as seen by HiRISE under HiWish program Parts of this image are enlarged in following images. The location is the [[Noachis quadrangle]]
ESP 049660 1200polygons.jpg|Wide view of polygons, as seen by HiRISE under HiWish program. Parts of this image are enlarged in following images. The location is the [[Noachis quadrangle]].

49660 1200polygonswide.jpg|Polygons, as seen by HiRISE under HiWish program
49660 1200polygonswide.jpg|Polygons, as seen by HiRISE under HiWish program
49660 1200polygonsrockscraters.jpg|Close view of polygons, as seen by HiRISE under HiWish program. Arrow point to boulders that sit inside of small craters.

49660 1200polygonsrockscraters.jpg|Close view of polygons, as seen by HiRISE under HiWish program Arrow point to boulders that sit inside of small craters.

49660 1200polygonspits.jpg|Close view of polygons, as seen by HiRISE under HiWish program
49660 1200polygonspits.jpg|Close view of polygons, as seen by HiRISE under HiWish program

49660 1200polygonsrockscratersclose.jpg|Close view of polygons, as seen by HiRISE under HiWish program
49660 1200polygonsrockscratersclose.jpg|Close view of polygons, as seen by HiRISE under HiWish program
</gallery>
</gallery>


==Exposed Ice Sheets==
==Exposed ice sheets==


HiRISE images taken under the HiWish program found triangular shaped depressions in [[Milankovič (Martian crater)|Milankovic Crater]] that researchers found contain vast amounts of ice that are found under only 1–2 meters of soil.
HiRISE images taken under the HiWish program found triangular shaped depressions in [[Milankovič (Martian crater)|Milankovic Crater]] that researchers found contain vast amounts of ice that are found under only 1–2 meters of soil.
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The following images are ones referred to in this study of subsurface ice sheets.<ref name="ReferenceA">Supplementary Materials Exposed subsurface ice sheets in the Martian mid-latitudes Colin M. Dundas, Ali M. Bramson, Lujendra Ojha, James J. Wray, Michael T. Mellon, Shane Byrne, Alfred S. McEwen, Nathaniel E. Putzig, Donna Viola, Sarah Sutton, Erin Clark, John W. Holt</ref>
The following images are ones referred to in this study of subsurface ice sheets.<ref name="ReferenceA">Supplementary Materials Exposed subsurface ice sheets in the Martian mid-latitudes Colin M. Dundas, Ali M. Bramson, Lujendra Ojha, James J. Wray, Michael T. Mellon, Shane Byrne, Alfred S. McEwen, Nathaniel E. Putzig, Donna Viola, Sarah Sutton, Erin Clark, John W. Holt</ref>


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 045290 2350icelayers.jpg|Wide view of part of [[Milankovič (Martian crater)|Milankovic Crater]], as seen by HiRISE under HiWish program Many depressions here contain ice in their walls.
ESP 045290 2350icelayers.jpg|Wide view of part of [[Milankovič (Martian crater)|Milankovic Crater]], as seen by HiRISE under HiWish program. Many depressions here contain ice in their walls.
ESP 045290 2350icelayersscale.jpg|Close view from a previous image, as seen by HiRISE under HiWish program. The triangular shape of some depressions are noted. The area in the box is enlarged in following images.

ESP 045290 2350icelayersscale.jpg|Close view from a previous image, as seen by HiRISE under HiWish program The triangular shape of some depressions are noted. The area in the box is enlarged in following images.
45290 2350icelayerscloseer.jpg|Close view of depression, as seen by HiRISE under HiWish program. Arrows indicate where there is a very thin, 1–2 meter covering on what is believed to be ice.

45290 2350icelayerscloseer.jpg|Close view of depression, as seen by HiRISE under HiWish program Arrows indicate where there is a very thin, 1-2 meter covering on what is believed to be ice.
</gallery>
</gallery>


These triangular depressions are similar to those in scalloped terrain. However scalloped terrain, displays a gentle equator-facing slope and is rounded. Scarps discussed here have a steep pole-facing side and have been found between 55 and 59 degrees north and south latitude<ref name="ReferenceA"/> [[Scalloped topography]] is common in the [[mid-latitudes]] of Mars, between 45° and 60° north and south.
These triangular depressions are similar to those in scalloped terrain. However scalloped terrain, displays a gentle equator-facing slope and is rounded. Scarps discussed here have a steep pole-facing side and have been found between 55 and 59 degrees north and south latitude<ref name="ReferenceA"/> [[Scalloped topography]] is common in the [[mid-latitudes]] of Mars, between 45° and 60° north and south.


==Scalloped topography==
==Scalloped topography==


{{Main|Scalloped topography}}
[[Scalloped topography]] is common in the [[mid-latitudes]] of Mars, between 45° and 60° north and south. It is particularly prominent in the region of [[Utopia Planitia]]<ref name=ref1>{{cite journal | last1=Lefort | first1=A. | last2=Russell | first2=P. S. | last3=Thomas | first3=N. | last4=McEwen | first4=A. S. | last5=Dundas | first5=C. M. | last6=Kirk | first6=R. L. | title=Observations of periglacial landforms in Utopia Planitia with the High Resolution Imaging Science Experiment (HiRISE) | journal=Journal of Geophysical Research | volume=114 | issue=E4 | pages=E04005 | year=2009 | doi=10.1029/2008JE003264 | bibcode=2009JGRE..114.4005L| s2cid=129442086 | url=https://boris.unibe.ch/36929/ | doi-access=free }}</ref><ref>{{cite journal|last1=Morgenstern |first1=A |last2=Hauber |first2=E |last3=Reiss |first3=D |last4=van Gasselt |first4=S |last5=Grosse |first5=G |last6=Schirrmeister |first6=L |year=2007 |title=Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars |url=http://epic.awi.de/Publications/Mor2007e.pdf |journal=Journal of Geophysical Research: Planets |volume=112 |issue=E6 |page=E06010 |doi=10.1029/2006JE002869 |bibcode=2007JGRE..112.6010M |url-status=dead |archive-url=https://web.archive.org/web/20111004001248/http://epic.awi.de/Publications/Mor2007e.pdf |archive-date=2011-10-04 }}</ref> in the northern hemisphere and in the region of [[Peneus]] and Amphitrites Patera<ref>{{cite journal | last1=Lefort | first1=A. | last2=Russell | first2=P.S. | last3=Thomas | first3=N. | title=Scalloped terrains in the Peneus and Amphitrites Paterae region of Mars as observed by HiRISE | journal=Icarus | volume=205 | issue=1 | page=259 | year=2010 | doi=10.1016/j.icarus.2009.06.005 | bibcode = 2010Icar..205..259L }}</ref><ref>{{cite journal | last1=Zanetti |first1= M. |last2= Hiesinger |first2=H. |last3= Reiss |first3= D. |last4= Hauber |first4= E. |last5= Neukum |first5= G. |year=2009 |url=http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2178.pdf | title=Scalloped Depression Development on Malea Planum and the Southern Wall of the Hellas Basin, Mars | volume=40| journal= Lunar and Planetary Science |at= p. 2178, abstract 2178 | bibcode = 2009LPI....40.2178Z }}</ref> in the southern hemisphere. Such topography consists of shallow, rimless depressions with scalloped edges, commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. A typical scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp. This topographic asymmetry is probably due to differences in [[insolation]]. Scalloped depressions are believed to form from the removal of subsurface material, possibly interstitial ice, by [[Sublimation (phase transition)|sublimation]]. This process may still be happening at present.<ref>http://hiroc.lpl.arizona.edu/images/PSP?diafotizo.php?ID=PSP_002296_1215{{dead link|date=April 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

[[Scalloped topography]] is common in the [[mid-latitudes]] of Mars, between 45° and 60° north and south. It is particularly prominent in the region of [[Utopia Planitia]]<ref name="ref1">{{cite journal | last1=Lefort | first1=A. | last2=Russell | first2=P. S. | last3=Thomas | first3=N. | last4=McEwen | first4=A. S. | last5=Dundas | first5=C. M. | last6=Kirk | first6=R. L. | title=Observations of periglacial landforms in Utopia Planitia with the High Resolution Imaging Science Experiment (HiRISE) | journal=Journal of Geophysical Research | volume=114 | issue=E4 | pages=E04005 | year=2009 | doi=10.1029/2008JE003264 | bibcode=2009JGRE..114.4005L| s2cid=129442086 | url=https://boris.unibe.ch/36929/ | doi-access=free }}</ref><ref>{{cite journal|last1=Morgenstern |first1=A |last2=Hauber |first2=E |last3=Reiss |first3=D |last4=van Gasselt |first4=S |last5=Grosse |first5=G |last6=Schirrmeister |first6=L |year=2007 |title=Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars |url=http://epic.awi.de/Publications/Mor2007e.pdf |journal=Journal of Geophysical Research: Planets |volume=112 |issue=E6 |page=E06010 |doi=10.1029/2006JE002869 |bibcode=2007JGRE..112.6010M |url-status=dead |archive-url=https://web.archive.org/web/20111004001248/http://epic.awi.de/Publications/Mor2007e.pdf |archive-date=2011-10-04 }}</ref> in the northern hemisphere and in the region of [[Peneus]] and Amphitrites Patera<ref>{{cite journal | last1=Lefort | first1=A. | last2=Russell | first2=P.S. | last3=Thomas | first3=N. | title=Scalloped terrains in the Peneus and Amphitrites Paterae region of Mars as observed by HiRISE | journal=Icarus | volume=205 | issue=1 | page=259 | year=2010 | doi=10.1016/j.icarus.2009.06.005 | bibcode = 2010Icar..205..259L }}</ref><ref>{{cite journal | last1=Zanetti |first1= M. |last2= Hiesinger |first2=H. |last3= Reiss |first3= D. |last4= Hauber |first4= E. |last5= Neukum |first5= G. |year=2009 |url=http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2178.pdf | title=Scalloped Depression Development on Malea Planum and the Southern Wall of the Hellas Basin, Mars | volume=40| journal= Lunar and Planetary Science |at= p. 2178, abstract 2178 | bibcode = 2009LPI....40.2178Z }}</ref> in the southern hemisphere. Such topography consists of shallow, rimless depressions with scalloped edges, commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. A typical scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp. This topographic asymmetry is probably due to differences in [[insolation]]. Scalloped depressions are believed to form from the removal of subsurface material, possibly interstitial ice, by [[Sublimation (phase transition)|sublimation]]. This process may still be happening at present.<ref>http://hiroc.lpl.arizona.edu/images/PSP?diafotizo.php?ID=PSP_002296_1215{{dead link|date=April 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>


On November 22, 2016, NASA reported finding a large amount of [[Water on Mars|underground ice]] in the Utopia Planitia region of Mars.<ref>{{cite web|url=http://www.space.com/34811-mars-ice-more-water-than-lake-superior.html|title=Huge Underground Ice Deposit on Mars Is Bigger Than New Mexico|website=[[Space.com]]|date=22 November 2016|access-date=20 November 2018}}</ref> The volume of water detected has been estimated to be equivalent to the volume of water in [[Lake Superior]].<ref name="NASA-20161122">{{cite web |author=Staff |title=Scalloped Terrain Led to Finding of Buried Ice on Mars |url=http://photojournal.jpl.nasa.gov/catalog/PIA21136 |date=November 22, 2016 |work=[[NASA]] |access-date=November 23, 2016 }}</ref><ref name="Register-2016">{{cite web|url=https://www.theregister.co.uk/2016/11/22/nasa_finds_ice_under_martian_surface/ |title=Lake of frozen water the size of New Mexico found on Mars – NASA |website=The Register|date=November 22, 2016 |access-date=November 23, 2016}}</ref>
On November 22, 2016, NASA reported finding a large amount of [[Water on Mars|underground ice]] in the Utopia Planitia region of Mars.<ref>{{cite web|url=http://www.space.com/34811-mars-ice-more-water-than-lake-superior.html|title=Huge Underground Ice Deposit on Mars Is Bigger Than New Mexico|website=[[Space.com]]|date=22 November 2016|access-date=20 November 2018}}</ref> The volume of water detected has been estimated to be equivalent to the volume of water in [[Lake Superior]].<ref name="NASA-20161122">{{cite web |author=Staff |title=Scalloped Terrain Led to Finding of Buried Ice on Mars |url=http://photojournal.jpl.nasa.gov/catalog/PIA21136 |date=November 22, 2016 |work=[[NASA]] |access-date=November 23, 2016 }}</ref><ref name="Register-2016">{{cite web|url=https://www.theregister.co.uk/2016/11/22/nasa_finds_ice_under_martian_surface/ |title=Lake of frozen water the size of New Mexico found on Mars – NASA |website=The Register|date=November 22, 2016 |access-date=November 23, 2016}}</ref>
The volume of water ice in the region were based on measurements from the ground-penetrating radar instrument on [[Mars Reconnaissance Orbiter]], called [[SHARAD]]. From the data obtained from SHARAD, "[[dielectric permittivity]]", or the dielectric constant was determined. The dielectric constant value was consistent with a large concentration of water ice.<ref>Bramson, A, et al. 2015. Widespread excess ice in Arcadia Planitia, Mars. Geophysical Research Letters: 42, 6566-6574</ref><ref>{{Cite web |url=https://planetarycassie.com/2016/11/04/widespread-thick-water-ice-found-in-utopia-planitia-mars/ |title=Widespread, Thick Water Ice found in Utopia Planitia, Mars &#124; Cassie Stuurman |access-date=2016-11-29 |archive-url=https://web.archive.org/web/20161130042608/https://planetarycassie.com/2016/11/04/widespread-thick-water-ice-found-in-utopia-planitia-mars/ |archive-date=2016-11-30 |url-status=dead }}</ref><ref>Stuurman, C., et al. 2016. SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters: 43, 9484_9491.</ref>
The volume of water ice in the region were based on measurements from the ground-penetrating radar instrument on [[Mars Reconnaissance Orbiter]], called [[SHARAD]]. From the data obtained from SHARAD, "[[dielectric permittivity]]", or the dielectric constant was determined. The dielectric constant value was consistent with a large concentration of water ice.<ref>Bramson, A, et al. 2015. Widespread excess ice in Arcadia Planitia, Mars. Geophysical Research Letters: 42, 6566-6574</ref><ref>{{Cite web |url=https://planetarycassie.com/2016/11/04/widespread-thick-water-ice-found-in-utopia-planitia-mars/ |title=Widespread, Thick Water Ice found in Utopia Planitia, Mars &#124; Cassie Stuurman |access-date=2016-11-29 |archive-url=https://web.archive.org/web/20161130042608/https://planetarycassie.com/2016/11/04/widespread-thick-water-ice-found-in-utopia-planitia-mars/ |archive-date=2016-11-30 |url-status=dead }}</ref><ref>Stuurman, C., et al. 2016. SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters: 43, 9484_9491.</ref>


<gallery class="center" widths="380px" heights="360px">
{{Main|Scalloped topography}},
ESP 037461 2255scallopstop.jpg|Scalloped ground, as seen by HiRISE under HiWish program

<gallery class="center" widths="380px" heights="360px">
ESP 037461 2255scallopstop.jpg|Scalloped ground, as seen by HiRISE under HiWish program.

ESP 037461 2255scallopground.jpg|Close-up of scalloped ground, as seen by HiRISE under HiWish program. Surface is divided into polygons; these forms are common where ground freezes and thaws. Note: this is an enlargement of a previous image.
ESP 037461 2255scallopground.jpg|Close-up of scalloped ground, as seen by HiRISE under HiWish program. Surface is divided into polygons; these forms are common where ground freezes and thaws. Note: this is an enlargement of a previous image.
ESP 037461 2255scallopsbottom.jpg|Scalloped ground, as seen by HiRISE under HiWish program.
ESP 037461 2255scallopsbottom.jpg|Scalloped ground, as seen by HiRISE under HiWish program
ESP 037461 2255scallopsclose.jpg|Close-up of scalloped ground, as seen by HiRISE under HiWish program. Surface is divided into polygons; these forms are common where ground freezes and thaws. Note: this is an enlargement of a previous image.
ESP 037461 2255scallopsclose.jpg|Close-up of scalloped ground, as seen by HiRISE under HiWish program. Surface is divided into polygons; these forms are common where ground freezes and thaws. Note: this is an enlargement of a previous image.
44042 2240lowcenterpolygons.jpg|Low center polygons, shown with arrows, as seen by HiRISE under HiWish program. Image was enlarged with HiView.
46916 2270scallopsclose.jpg|Scalloped terrain, as seen by HiRISE under HiWish program. The location is the [[Casius quadrangle]].
46916 2270scallopsmerging.jpg|Scalloped terrain, as seen by HiRISE under HiWish program. The location is the Casius quadrangle.
</gallery>

==Images of variety of craters==


<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenterpolygons.jpg|Low center polygons, shown with arrows, as seen by HiRISE under HiWish program Image was enlarged with HiView.
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.


46916 2270scallopsclose.jpg|Scalloped terrain, as seen by HiRISE under HiWish program The location is the [[Casius quadrangle]].
46916 2270scallopsmerging.jpg|Scalloped terrain, as seen by HiRISE under HiWish program The location is the Casius quadrangle.
</gallery>
</gallery>


==Pedestal Craters==
==Pedestal craters==
{{Main|Pedestal crater}}
A '''pedestal crater''' is a [[impact crater|crater]] with its ejecta sitting above the surrounding terrain and thereby forming a raised platform (like a [[pedestal]]). They form when an impact crater ejects material which forms an erosion-resistant layer, thus causing the immediate area to erode more slowly than the rest of the region. Some pedestals have been accurately measured to be hundreds of meters above the surrounding area. This means that hundreds of meters of material were eroded away. The result is that both the crater and its ejecta blanket stand above the surroundings. Pedestal craters were first observed during the [[Mariner program|Mariner]] missions.<ref>http://hirise.lpl.eduPSP_008508_1870{{dead link|date=April 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref><ref>{{cite web|url=http://themis.asu.edu/feature_utopiacraters |title=Mars Odyssey Mission THEMIS: Feature Image: Pedestal Craters in Utopia |access-date=2010-03-26 |url-status=dead |archive-url=https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters |archive-date=2010-01-18 }}</ref><ref>{{cite journal | last1 = McCauley | first1 = J. F. | date = 1973 | title = Mariner 9 evidence for wind erosion in the equatorial and mid-latitude regions of Mars | journal = Journal of Geophysical Research | volume = 78 | issue = 20| pages = 4123–4137 | bibcode = 1973JGR....78.4123M | doi = 10.1029/JB078i020p04123 }}</ref>
A '''pedestal crater''' is a [[impact crater|crater]] with its ejecta sitting above the surrounding terrain and thereby forming a raised platform (like a [[pedestal]]). They form when an impact crater ejects material which forms an erosion-resistant layer, thus causing the immediate area to erode more slowly than the rest of the region. Some pedestals have been accurately measured to be hundreds of meters above the surrounding area. This means that hundreds of meters of material were eroded away. The result is that both the crater and its ejecta blanket stand above the surroundings. Pedestal craters were first observed during the [[Mariner program|Mariner]] missions.<ref>http://hirise.lpl.eduPSP_008508_1870{{dead link|date=April 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref><ref>{{cite web|url=http://themis.asu.edu/feature_utopiacraters |title=Mars Odyssey Mission THEMIS: Feature Image: Pedestal Craters in Utopia |access-date=2010-03-26 |url-status=dead |archive-url=https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters |archive-date=2010-01-18 }}</ref><ref>{{cite journal | last1 = McCauley | first1 = J. F. | date = 1973 | title = Mariner 9 evidence for wind erosion in the equatorial and mid-latitude regions of Mars | journal = Journal of Geophysical Research | volume = 78 | issue = 20| pages = 4123–4137 | bibcode = 1973JGR....78.4123M | doi = 10.1029/JB078i020p04123 }}</ref>


<gallery class="center" widths="380px" heights="360px">
{{Main|Pedestal crater}}

<gallery class="center" widths="380px" heights="360px">
ESP 037528 2350pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program. Top layer has protected the lower material from being eroded. The location is [[Casius quadrangle]].
ESP 037528 2350pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program. Top layer has protected the lower material from being eroded. The location is [[Casius quadrangle]].
ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program. Location is [[Hellas quadrangle]].

ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Location is [[Hellas quadrangle]].
ESP 046487 2345pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program. Location is [[Casius quadrangle]].
ESP 046487 2345pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]].
ESP 047772 2210pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program. Location is [[Cebrenia quadrangle]].
ESP 047772 2210pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Location is [[Cebrenia quadrangle]].
</gallery>
</gallery>


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Ring mold craters are believed to be formed from asteroid impacts into ground that has an underlying layer of ice. The impact produces an rebound of the ice layer to form a "ring-mold" shape.
Ring mold craters are believed to be formed from asteroid impacts into ground that has an underlying layer of ice. The impact produces an rebound of the ice layer to form a "ring-mold" shape.


Another, later idea, for their formation suggests that the impacting body goes through layers of different densities. Later, erosion could have helped shape them. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>
Another, later idea, for their formation suggests that the impacting body goes through layers of different densities. Later, erosion could have helped shape them. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>{{cite journal | url=https://www.sciencedirect.com/science/article/pii/S0019103518301532 | doi=10.1016/j.icarus.2018.09.009 | title=Probing supraglacial debris on Mars 2: Crater morphology | date=2019 | last1=Baker | first1=David M.H. | last2=Carter | first2=Lynn M. | journal=Icarus | volume=319 | pages=264–280 | bibcode=2019Icar..319..264B | s2cid=126156734 }}</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>


<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 037622 2200ringmoldfield.jpg|Ring mold craters of various sizes on floor of a crater, as seen by HiRISE under HiWish program Location is [[Ismenius Lacus quadrangle]].
ESP 037622 2200ringmoldfield.jpg|Ring mold craters of various sizes on floor of a crater, as seen by HiRISE under HiWish program. Location is [[Ismenius Lacus quadrangle]].
26055cratermesaswide.jpg|Wide view of a field of ring mold craters, as seen by HiRISE under HiWish program
26055cratermesaswide.jpg|Wide view of a field of ring mold craters, as seen by HiRISE under HiWish program
26055ringmoldcrater.jpg|Close view of ring mold crater, as seen by HiRISE under HiWish program Note: this is an enlargement of the previous image of a field of ring mold craters.
26055ringmoldcrater.jpg|Close view of ring mold crater, as seen by HiRISE under HiWish program. Note: this is an enlargement of the previous image of a field of ring mold craters.
</gallery>
</gallery>
<gallery class="center" widths="380px" heights="360px">
<gallery class="center" widths="380px" heights="360px">
ESP 052260 2165ringmold.jpg|Wide view of ring-mold craters on floor of larger crater, as seen by HiRISE under HiWish program
ESP 052260 2165ringmold.jpg|Wide view of ring-mold craters on floor of larger crater, as seen by HiRISE under HiWish program
52260 2165ringmold.jpg|Ring-mold craters, as seen by HiRISE under HiWish program
52260 2165ringmold.jpg|Ring-mold craters, as seen by HiRISE under HiWish program
52260 2165ringmoldclose.jpg|Close view of Ring-mold craters and brain terrain, as seen by HiRISE under HiWish program
52260 2165ringmoldclose.jpg|Close view of ring-mold craters and brain terrain, as seen by HiRISE under HiWish program
</gallery>
</gallery>


==Halo Craters==
==Halo craters==
<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
ESP_044939 2390pedestalhalocrater.jpg|Pedestal crater with boulders along rim. Such craters are called "halo craters."<ref>Levy, J. et al. 2008. Origin and arrangement of boulders on the martian northern plains: Assessment of emplacement and modification environments> In 39th Lunar and Planetary Science Conference, Abstract #1172. League City, TX</ref> Picture taken with HiRISE under HiWish program.
ESP_044939 2390pedestalhalocrater.jpg|Pedestal crater with boulders along rim. Such craters are called "halo craters".<ref>Levy, J. et al. 2008. Origin and arrangement of boulders on the martian northern plains: Assessment of emplacement and modification environments> In 39th Lunar and Planetary Science Conference, Abstract #1172. League City, TX</ref> Picture taken with HiRISE under HiWish program.

44939 2390bouldersleft.jpg|Close view of boulders on lower left of crater rim Box is the size of a football field, so boulders are roughly the size of cars or small houses. Picture taken with HiRISE under HiWish program.
44939 2390bouldersleft.jpg|Close view of boulders on lower left of crater rim Box is the size of a football field, so boulders are roughly the size of cars or small houses. Picture taken with HiRISE under HiWish program.
44939 2390boulders.jpg|Close view of boulders along crater rim Boulders are roughly the size of cars or small houses. Picture taken with HiRISE under HiWish program.
44939 2390boulders.jpg|Close view of boulders along crater rim Boulders are roughly the size of cars or small houses. Picture taken with HiRISE under HiWish program.
Line 443: Line 395:


==Boulders==
==Boulders==
<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
ESP 045415 2220boulders.jpg|Boulders, as seen by HiRISE under HiWish program Location is [[Ismenius Lacus quadrangle]].
ESP 045415 2220boulders.jpg|Boulders, as seen by HiRISE under HiWish program. Location is [[Ismenius Lacus quadrangle]].
45575 2535duneboulders.jpg|Boulder and boulder tracks, as seen by HiRISE under HiWish program The arrow shows a boulder that has made a track in the sand as it rolled down dune. Location is [[Mare Boreum quadrangle]].
45575 2535duneboulders.jpg|Boulder and boulder tracks, as seen by HiRISE under HiWish program. The arrow shows a boulder that has made a track in the sand as it rolled down dune. Location is [[Mare Boreum quadrangle]].
45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune. Location is [[Mare Boreum quadrangle]].
45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program. The arrows show a boulders that have produced a track by rolling down dune. Location is [[Mare Boreum quadrangle]].
47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope, as seen by HiRISE under HiWish program. Arrows show two boulders at the end of their tracks. Location is [[Arabia quadrangle]].

47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope, as seen by HiRISE under HiWish program Arrows show two boulders at the end of their tracks. Location is [[Arabia quadrangle]].
</gallery>
</gallery>


Line 456: Line 407:
Dust devil tracks can be very pretty. They are caused by giant dust devils removing bright colored dust from the Martian surface; thereby exposing a dark layer. Dust devils on Mars have been photographed both from the ground and high overhead from orbit. They have even blown dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>[http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit]. Marsrovers.jpl.nasa.gov. Retrieved on 7 August 2011.</ref> The pattern of the tracks has been shown to change every few months.<ref>{{cite web|url=http://hirise.lpl.arizona.edu/PSP_005383_1255|title=HiRISE - Dust Devils Dancing on Dunes (PSP_005383_1255)|website=hirise.lpl.arizona.edu|access-date=20 November 2018}}</ref> A study that combined data from the [[High Resolution Stereo Camera]] (HRSC) and the [[Mars Orbiter Camera]] (MOC) found that some large dust devils on Mars have a diameter of {{convert|700|m}} and last at least 26 minutes.<ref>{{cite journal | last1 = Reiss | first1 = D. | display-authors = etal | year = 2011 | title = Multitemporal observations of identical active dust devils on Mars with High Resolution Stereo Camera (HRSC) and Mars Orbiter Camera (MOC) | journal = Icarus | volume = 215 | issue = 1 | pages = 358–369 | doi = 10.1016/j.icarus.2011.06.011 | bibcode = 2011Icar..215..358R }}</ref>
Dust devil tracks can be very pretty. They are caused by giant dust devils removing bright colored dust from the Martian surface; thereby exposing a dark layer. Dust devils on Mars have been photographed both from the ground and high overhead from orbit. They have even blown dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>[http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit]. Marsrovers.jpl.nasa.gov. Retrieved on 7 August 2011.</ref> The pattern of the tracks has been shown to change every few months.<ref>{{cite web|url=http://hirise.lpl.arizona.edu/PSP_005383_1255|title=HiRISE - Dust Devils Dancing on Dunes (PSP_005383_1255)|website=hirise.lpl.arizona.edu|access-date=20 November 2018}}</ref> A study that combined data from the [[High Resolution Stereo Camera]] (HRSC) and the [[Mars Orbiter Camera]] (MOC) found that some large dust devils on Mars have a diameter of {{convert|700|m}} and last at least 26 minutes.<ref>{{cite journal | last1 = Reiss | first1 = D. | display-authors = etal | year = 2011 | title = Multitemporal observations of identical active dust devils on Mars with High Resolution Stereo Camera (HRSC) and Mars Orbiter Camera (MOC) | journal = Icarus | volume = 215 | issue = 1 | pages = 358–369 | doi = 10.1016/j.icarus.2011.06.011 | bibcode = 2011Icar..215..358R }}</ref>


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
WikiESP 036324 2325devils.jpg|Dust devil tracks, as seen by HiRISE under HiWish program.
WikiESP 036324 2325devils.jpg|Dust devil tracks, as seen by HiRISE under HiWish program
ESP 036297 2370devils.jpg|[[Dust devil tracks]], as seen by HiRISE under HiWish program
ESP 036297 2370devils.jpg|[[Dust devil tracks]], as seen by HiRISE under HiWish program
44507 1880devils.jpg|Layers in [[Danielson Crater]] with dust devil tracks at the top of the picture, as seen by HiRISE under HiWish program Location is [[Oxia Palus quadrangle]].
44507 1880devils.jpg|Layers in [[Danielson Crater]] with dust devil tracks at the top of the picture, as seen by HiRISE under HiWish program. Location is [[Oxia Palus quadrangle]].
File:ESP 057581 1340devils.jpg|Wide view of dust devil tracks, as seen by HiRISE under HiWish program Location is the [[Phaethontis quadrangle]].
File:ESP 057581 1340devils.jpg|Wide view of dust devil tracks, as seen by HiRISE under HiWish program. Location is the [[Phaethontis quadrangle]].
</gallery>
</gallery>


==Yardangs==
==Yardangs==


{{Main|Yardangs on Mars}}
'''Yardangs''' are common in some regions on Mars, especially in what's called the "[[Medusae Fossae Formation]]." This formation is found in the [[Amazonis quadrangle]] and near the equator.<ref>{{cite journal|title=Yardangs on Mars: Evidence of recent wind erosion|first=A. Wesley|last=Ward|date=20 November 1979|journal=Journal of Geophysical Research|volume=84|issue=B14|pages=8147–8166|doi=10.1029/JB084iB14p08147|bibcode = 1979JGR....84.8147W}}</ref> They are formed by the action of wind on sand sized particles; hence they often point in the direction that the winds were blowing when they were formed.<ref>{{cite web|url=http://www.esa.int/Our_Activities/Space_Science/Mars_Express/Yardangs_on_Mars|title='Yardangs' on Mars|last=esa|access-date=20 November 2018}}</ref> Because they exhibit very few impact craters they are believed to be relatively young.<ref>{{cite web|url=http://themis.asu.edu/zoom-20020416a|title=Medusae Fossae Formation - Mars Odyssey Mission THEMIS|website=themis.asu.edu|access-date=20 November 2018}}</ref>


'''Yardangs''' are common in some regions on Mars, especially in what is called the "[[Medusae Fossae Formation]]". This formation is found in the [[Amazonis quadrangle]] and near the equator.<ref>{{cite journal|title=Yardangs on Mars: Evidence of recent wind erosion|first=A. Wesley|last=Ward|date=20 November 1979|journal=Journal of Geophysical Research|volume=84|issue=B14|pages=8147–8166|doi=10.1029/JB084iB14p08147|bibcode = 1979JGR....84.8147W}}</ref> They are formed by the action of wind on sand sized particles; hence they often point in the direction that the winds were blowing when they were formed.<ref>{{cite web|url=http://www.esa.int/Our_Activities/Space_Science/Mars_Express/Yardangs_on_Mars|title='Yardangs' on Mars|last=esa|access-date=20 November 2018}}</ref> Because they exhibit very few impact craters they are believed to be relatively young.<ref>{{cite web|url=http://themis.asu.edu/zoom-20020416a|title=Medusae Fossae Formation - Mars Odyssey Mission THEMIS|website=themis.asu.edu|access-date=20 November 2018}}</ref>
{{Main|Yardangs on Mars}},


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
WikiESP 035558 1830yardang.jpg|Yardangs, as seen by HiRISE under HiWish program Location is near Gordii Dorsum in the [[Amazonis quadrangle]]. These yardangs are in the upper member of the Medusae Fossae Formation.
WikiESP 035558 1830yardang.jpg|Yardangs, as seen by HiRISE under HiWish program. Location is near Gordii Dorsum in the [[Amazonis quadrangle]]. These yardangs are in the upper member of the Medusae Fossae Formation.
35558 1830yardangs.jpg|Yardangs, as seen by HiRISE under HiWish program Location is near Gordii Dorsum in the [[Amazonis quadrangle]]. Note: this is an enlargement of previous image.
35558 1830yardangs.jpg|Yardangs, as seen by HiRISE under HiWish program. Location is near Gordii Dorsum in the [[Amazonis quadrangle]]. Note: this is an enlargement of previous image.
35558 1830yardangsclose.jpg|Yardangs, as seen by HiRISE under HiWish program Location is near Gordii Dorsum in the [[Amazonis quadrangle]]. Note: this is an enlargement of previous image.
35558 1830yardangsclose.jpg|Yardangs, as seen by HiRISE under HiWish program. Location is near Gordii Dorsum in the [[Amazonis quadrangle]]. Note: this is an enlargement of previous image.
</gallery>
</gallery>

<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
WikiESP 039563 1730yardangs.jpg|Yardangs formed in light-toned material and surrounded by dark, volcanic basalt sand, as seen by HiRISE under HiWish program. Loacation is [[Margaritifer Sinus quadrangle]].
WikiESP 039563 1730yardangs.jpg|Yardangs formed in light-toned material and surrounded by dark, volcanic basalt sand, as seen by HiRISE under HiWish program. Loacation is [[Margaritifer Sinus quadrangle]].
WikiESP 039563 1730yardangsclose.jpg|Close-up image of yardangs, as seen by HiRISE under HiWish program. Arrows point to transverse aeolian ridges, TAR's, a type of dune. Note this is an enlargement of the previous image from HiRISE.
WikiESP 039563 1730yardangsclose.jpg|Close-up image of yardangs, as seen by HiRISE under HiWish program. Arrows point to transverse aeolian ridges (TARs), a type of dune. Note this is an enlargement of the previous image from HiRISE.
</gallery>
</gallery>


==Plumes and spiders==
==Plumes and spiders==
At certain times in the Martian, dark eruptions of gas and dust occur. Wind often blows the material into a fan or a tail-like shape. During the winter, much frost accumulates. It freezes out directly onto the surface of the permanent polar cap, which is made of water ice covered with layers of dust and sand. The deposit begins as a layer of dusty {{CO2}} frost. Over the winter, it recrystallizes and becomes denser. The dust and sand particles caught in the frost slowly sink. By the time temperatures rise in the spring, the frost layer has become a slab of semi-transparent ice about 3 feet thick, lying on a substrate of dark sand and dust. This dark material absorbs light and causes the ice to sublimate (turn directly into a gas). Eventually much gas accumulates and becomes pressurized. When it finds a weak spot, the gas escapes and blows out the dust. Speeds can reach 100 miles per hour.<ref name="themis.asu.edu">{{cite web|url=http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap|title=Gas jets spawn dark 'spiders' and spots on Mars icecap - Mars Odyssey Mission THEMIS|website=themis.asu.edu|access-date=20 November 2018}}</ref> Calculations show that the plumes are 20–80 meters high.<ref>Thomas, N., G. Portyankina, C.J. Hansen, A. Pommerol. 2011. HiRISE observations of gas sublimation-driven activity in Mars' southern polar regions: IV. Fluid dynamics models of {{CO2}} jets
At certain times in the Martian, dark eruptions of gas and dust occur. Wind often blows the material into a fan or a tail-like shape. During the winter, much frost accumulates. It freezes out directly onto the surface of the permanent polar cap, which is made of water ice covered with layers of dust and sand. The deposit begins as a layer of dusty {{CO2}} frost. Over the winter, it recrystallizes and becomes denser. The dust and sand particles caught in the frost slowly sink. By the time temperatures rise in the spring, the frost layer has become a slab of semi-transparent ice about 3 feet thick, lying on a substrate of dark sand and dust. This dark material absorbs light and causes the ice to sublimate (turn directly into a gas). Eventually much gas accumulates and becomes pressurized. When it finds a weak spot, the gas escapes and blows out the dust. Speeds can reach 100 miles per hour.<ref name="themis.asu.edu">{{cite web|url=http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap|title=Gas jets spawn dark 'spiders' and spots on Mars icecap - Mars Odyssey Mission THEMIS|website=themis.asu.edu|access-date=20 November 2018}}</ref> Calculations show that the plumes are 20–80 meters high.<ref>Thomas, N., G. Portyankina, C.J. Hansen, A. Pommerol. 2011. HiRISE observations of gas sublimation-driven activity in Mars' southern polar regions: IV. Fluid dynamics models of {{CO2}} jets
Icarus: 212, pp. 66–85</ref><ref>Buhler, Peter, Andrew Ingersoll, Bethany Ehlmann, Cale Fassett, James Head. 2017. How the martian residual south polar cap develops quasi-circular and heart-shaped pits, troughs, and moats. Icarus: 286, 69–93</ref> Dark channels can sometimes be seen; they are called "spiders."<ref>Benson, M. 2012. Planetfall: New Solar System Visions</ref><ref>{{cite web |title=Spiders invade Mars |url=http://www.astrobio.net/topic/solar-system/mars/spiders-invade-mars/ |website=Astrobiology Magazine |access-date=20 November 2018 |date=17 August 2006}}</ref><ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. {{CO2}} jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> The surface appears covered with dark spots when this process is occurring.<ref name="themis.asu.edu"/><ref>{{cite web|url=http://www.jpl.nasa.gov/news/news.php?release=2013-034|title=Thawing 'Dry Ice' Drives Groovy Action on Mars|website=NASA/JPL|access-date=20 November 2018}}</ref>
Icarus: 212, pp. 66–85</ref><ref>Buhler, Peter, Andrew Ingersoll, Bethany Ehlmann, Cale Fassett, James Head. 2017. How the martian residual south polar cap develops quasi-circular and heart-shaped pits, troughs, and moats. Icarus: 286, 69–93</ref> Dark channels can sometimes be seen; they are called "spiders".<ref>Benson, M. 2012. Planetfall: New Solar System Visions</ref><ref>{{cite web |title=Spiders invade Mars |url=http://www.astrobio.net/topic/solar-system/mars/spiders-invade-mars/ |website=Astrobiology Magazine |access-date=20 November 2018 |date=17 August 2006}}</ref><ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. {{CO2}} jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> The surface appears covered with dark spots when this process is occurring.<ref name="themis.asu.edu"/><ref>{{cite web|url=http://www.jpl.nasa.gov/news/news.php?release=2013-034|title=Thawing 'Dry Ice' Drives Groovy Action on Mars|website=NASA/JPL|access-date=20 November 2018}}</ref>


Many ideas have been advanced to explain these features.<ref name=Kieffer2000 >{{Cite journal|first=H. H. | last=Kieffer |title=Mars Polar Science 2000 - Annual Punctuated CO<sub>2</sub> Slab-ice and Jets on Mars.| date=2000| url=http://www.lpi.usra.edu/meetings/polar2000/pdf/4095.pdf| access-date=6 September 2009 }}</ref><ref name=Kieffer2003 >{{Cite journal| first=Hugh H. |last=Kieffer |title=Third Mars Polar Science Conference (2003)- Behavior of Solid CO | date=2003 |url=http://www.lpi.usra.edu/meetings/polar2003/pdf/8083.pdf| access-date=6 September 2009 }}</ref><ref name=Portyankina >{{Cite journal|title=Fourth Mars Polar Science Conference - Simulations of Geyser-Type Eruptions in Cryptic Region of Martian South| editor-first=G. |editor-last=Portyankina| date=2006| url=http://www.lpi.usra.edu/meetings/polar2006/pdf/8040.pdf| access-date=11 August 2009 }}</ref><ref name=clathrate >{{Cite journal |title=Lunar and Planetary Science XXXV (2004) - Stratigraphy of Special Layers – Transient Ones on Permeable Ones: Examples|editor=Sz. Bérczi |display-editors=etal | date=2004| url=http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1317.pdf| access-date=12 August 2009}}</ref><ref name=2006-100 >{{cite news | title=NASA Findings Suggest Jets Bursting From Martian Ice Cap | date=16 August 2006 | publisher=NASA | url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100 | work=Jet Propulsion Laboratory | access-date=11 August 2009 | archive-date=25 February 2021 | archive-url=https://web.archive.org/web/20210225080149/https://www.jpl.nasa.gov/news/news.cfm?release=2006-100 | url-status=dead }}</ref><ref>{{cite journal | doi = 10.1016/j.icarus.2009.07.021 | title = HiRISE observations of gas sublimation-driven activity in Mars' southern polar regions: I. Erosion of the surface | journal=Icarus | date = 2010 |author=C.J. Hansen |author2=N. Thomas |author3=G. Portyankina |author4=A. McEwen |author5=T. Becker |author6=S. Byrne |author7=K. Herkenhoff |author8=H. Kieffer |author9=M. Mellon |display-authors=3 | volume = 205 | issue = 1 | pages = 283–295| url = http://www.lpl.arizona.edu/~shane/publications/hansen_etal_icarus_2010.pdf | access-date =26 July 2010 | bibcode = 2010Icar..205..283H }}</ref> These features can be seen in some of the pictures below.
Many ideas have been advanced to explain these features.<ref name=Kieffer2000 >{{Cite journal|first=H. H. | last=Kieffer |title=Mars Polar Science 2000 - Annual Punctuated CO<sub>2</sub> Slab-ice and Jets on Mars.| date=2000| url=http://www.lpi.usra.edu/meetings/polar2000/pdf/4095.pdf| access-date=6 September 2009 }}</ref><ref name=Kieffer2003 >{{Cite journal| first=Hugh H. |last=Kieffer |title=Third Mars Polar Science Conference (2003)- Behavior of Solid CO | date=2003 |url=http://www.lpi.usra.edu/meetings/polar2003/pdf/8083.pdf| access-date=6 September 2009 }}</ref><ref name=Portyankina >{{Cite journal|title=Fourth Mars Polar Science Conference - Simulations of Geyser-Type Eruptions in Cryptic Region of Martian South| editor-first=G. |editor-last=Portyankina| date=2006| url=http://www.lpi.usra.edu/meetings/polar2006/pdf/8040.pdf| access-date=11 August 2009 }}</ref><ref name=clathrate >{{Cite journal |title=Lunar and Planetary Science XXXV (2004) - Stratigraphy of Special Layers – Transient Ones on Permeable Ones: Examples|editor=Sz. Bérczi |display-editors=etal | date=2004| url=http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1317.pdf| access-date=12 August 2009}}</ref><ref name=2006-100 >{{cite news | title=NASA Findings Suggest Jets Bursting From Martian Ice Cap | date=16 August 2006 | publisher=NASA | url=http://www.jpl.nasa.gov/news/news.cfm?release=2006-100 | work=Jet Propulsion Laboratory | access-date=11 August 2009 | archive-date=25 February 2021 | archive-url=https://web.archive.org/web/20210225080149/https://www.jpl.nasa.gov/news/news.cfm?release=2006-100 | url-status=dead }}</ref><ref>{{cite journal | doi = 10.1016/j.icarus.2009.07.021 | title = HiRISE observations of gas sublimation-driven activity in Mars' southern polar regions: I. Erosion of the surface | journal=Icarus | date = 2010 |author=C.J. Hansen |author2=N. Thomas |author3=G. Portyankina |author4=A. McEwen |author5=T. Becker |author6=S. Byrne |author7=K. Herkenhoff |author8=H. Kieffer |author9=M. Mellon |display-authors=3 | volume = 205 | issue = 1 | pages = 283–295| url = http://www.lpl.arizona.edu/~shane/publications/hansen_etal_icarus_2010.pdf | access-date =26 July 2010 | bibcode = 2010Icar..205..283H }}</ref> <ref>{{cite web | url=https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief | title='Spiders on Mars' fully awakened on Earth for 1st time — and scientists are shrieking with joy | website=[[Live Science]] | date=16 September 2024 }}</ref> These features can be seen in some of the pictures below.

<gallery class="center" widths="190px" heights="180px" >
ESP 047609 0985spiders.jpg|Wide view of plumes, as seen by HiRISE under HiWish program Many of the plumes show spiders when enlarged.
47609 0985plumes.jpg|Plumes, as seen by HiRISE under HiWish program Arrow shows a double plume. This may have been because of shifting winds.


<gallery class="center" widths="380px" heights="360px">
ESP 047609 0985spiders.jpg|Wide view of plumes, as seen by HiRISE under HiWish program. Many of the plumes show spiders when enlarged.
47609 0985plumes.jpg|Plumes, as seen by HiRISE under HiWish program. Arrow shows a double plume. This may have been because of shifting winds.
47609 0985spiderlong.jpg|Long plume, as seen by HiRISE under HiWish program
47609 0985spiderlong.jpg|Long plume, as seen by HiRISE under HiWish program
47609 0985spiderlongclose.jpg|Spiders, as seen by HiRISE under HiWish program
47609 0985spiderlongclose.jpg|Spiders, as seen by HiRISE under HiWish program

47609 0985spiders.jpg|Plumes and spiders, as seen by HiRISE under HiWish program
47609 0985spiders.jpg|Plumes and spiders, as seen by HiRISE under HiWish program

47609 0985spidersclose.jpg|Plumes and spiders, as seen by HiRISE under HiWish program
47609 0985spidersclose.jpg|Plumes and spiders, as seen by HiRISE under HiWish program

47609 0985spidersdark.jpg|Plumes and spiders, as seen by HiRISE under HiWish program
47609 0985spidersdark.jpg|Plumes and spiders, as seen by HiRISE under HiWish program

47609 0985spiderswide.jpg|Wide view of plumes and spiders, as seen by HiRISE under HiWish program
47609 0985spiderswide.jpg|Wide view of plumes and spiders, as seen by HiRISE under HiWish program

47609 0985spidersdarkclose.jpg|Plumes and spiders, as seen by HiRISE under HiWish program
47609 0985spidersdarkclose.jpg|Plumes and spiders, as seen by HiRISE under HiWish program
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</gallery>


==Upper Plains Unit==
==Upper plains unit==


{{see also|Upper Plains Unit}}
{{Main|Upper plains unit}}
Remnants of a 50-100 meter thick mantling, called the upper plains unit, has been discovered in the mid-latitudes of Mars. First investigated in the [[Deuteronilus Mensae]] ([[Ismenius Lacus quadrangle]]) region, but it occurs in other places as well. The remnants consist of sets of dipping layers in craters and along mesas.<ref>Carr, M. 2001.</ref> Sets of dipping layers may be of various sizes and shapes—some look like Aztec pyramids from Central America


Remnants of a 50–100 meter thick mantling, called the upper plains unit, has been discovered in the mid-latitudes of Mars. First investigated in the [[Deuteronilus Mensae]] ([[Ismenius Lacus quadrangle]]) region, but it occurs in other places as well. The remnants consist of sets of dipping layers in craters and along mesas.<ref>Carr, M. 2001.</ref> Sets of dipping layers may be of various sizes and shapes—some look like Aztec pyramids from Central America. Dipping layers are common in some regions of Mars. They may be the remains of mantle layers. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>
<gallery class="center" widths="190px" heights="180px" >

<gallery class="center" widths="380px" heights="360px">
ESP 019778 1385pyramid.jpg|Layered structure in crater that is probably what is left of a layered unit that once covered a much larger area. Material for this unit fell from the sky as ice-coated dust. The picture was taken by HiRISE, under the HiWish program. Picture is from [[Hellas quadrangle]].
ESP 019778 1385pyramid.jpg|Layered structure in crater that is probably what is left of a layered unit that once covered a much larger area. Material for this unit fell from the sky as ice-coated dust. The picture was taken by HiRISE, under the HiWish program. Picture is from [[Hellas quadrangle]].
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</gallery>


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
ESP 050793 1365pyramids.jpg|Tilted layers, as seen by HiRISE under HiWish program. Location is [[Hellas quadrangle]].

ESP 050793 1365pyramids.jpg|Tilted layers, as seen by HiRISE under HiWish program Location is [[Hellas quadrangle]].
50793 1365layers.jpg|Tilted layers, as seen by HiRISE under HiWish program. Location is [[Hellas quadrangle]].
50793 1365layers.jpg|Tilted layers, as seen by HiRISE under HiWish program Location is [[Hellas quadrangle]].
50793 1365layers2.jpg|Tilted layers, as seen by HiRISE under HiWish program. Location is [[Hellas quadrangle]].

50793 1365layers2.jpg|Tilted layers, as seen by HiRISE under HiWish program Location is [[Hellas quadrangle]].
</gallery>
</gallery>


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
ESP 035684 2160pyramidsbrains.jpg|Dipping layers, as seen by HiRISE under HiWish program
ESP 035684 2160pyramidsbrains.jpg|Dipping layers, as seen by HiRISE under HiWish program

ESP 037146 2195pyramidismenius.jpg|Layered features in crater, as seen by HiRISE under HiWish program
ESP 037146 2195pyramidismenius.jpg|Layered features in crater, as seen by HiRISE under HiWish program

ESP 035801 2210pyramidsismenius.jpg|Layered structures, as seen by HiRISE under HiWish program
ESP 035801 2210pyramidsismenius.jpg|Layered structures, as seen by HiRISE under HiWish program
45613 2230pyramids.jpg|Close view of dipping layers along a mesa wall, as seen by HiRISE under HiWish program. Location is [[Ismenius Lacus quadrangle]].

45613 2230pyramids.jpg|Close view of dipping layers along a mesa wall, as seen by HiRISE under HiWish program Location is [[Ismenius Lacus quadrangle]].

45917 2220pyramids.jpg|Close view of dipping layers in [[Ismenius Lacus quadrangle]], as seen by HiRISE under HiWish program
45917 2220pyramids.jpg|Close view of dipping layers in [[Ismenius Lacus quadrangle]], as seen by HiRISE under HiWish program
ESP 045917 2220gulliespyramids.jpg|Wide view of dipping layers in Ismenius Lacus quadrangle, as seen by HiRISE under HiWish program Gullies are also visible at the bottom of the image.
ESP 045917 2220gulliespyramids.jpg|Wide view of dipping layers in Ismenius Lacus quadrangle, as seen by HiRISE under HiWish program. Gullies are also visible at the bottom of the image.
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</gallery>


This unit also degrades into [[brain terrain]]. Brain terrain is a region of maze-like ridges 3–5 meters high. Some ridges may consist of an ice core, so they may be sources of water for future colonists.
This unit also degrades into [[brain terrain]]. Brain terrain is a region of maze-like ridges 3–5 meters high. Some ridges may consist of an ice core, so they may be sources of water for future colonists.


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
45507 2200brains.jpg|Brain terrain, as seen by HiRISE under HiWish program Location is [[Ismenius Lacus quadrangle]].
45507 2200brains.jpg|Brain terrain, as seen by HiRISE under HiWish program. Location is [[Ismenius Lacus quadrangle]].
ESP 028273 2240pyramidbrain.jpg|Layered features and brain terrain, as seen by HiRISE under HiWish program. The upper plains unit often changes into brain terrain.
44229 2235brainsforming.jpg|Brain terrain is forming from the breakdown of upper plains unit, as seen by HiRISE under HiWish program. Arrow points to a place where fractures are forming that will turn into brain terrain.
44229 2235brainsupper.jpg|Brain terrain is forming from the breakdown of upper plains unit, as seen by HiRISE under HiWish program. Arrow points to a place where fractures are forming that will turn into brain terrain.
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<gallery class="center" widths="380px" heights="360px">
ESP 028273 2240pyramidbrain.jpg|Layered features and brain terrain, as seen by HiRISE under HiWish program The upper plains unit often changes into brain terrain.
44229 2235brainsforming.jpg|Brain terrain is forming from the breakdown of upper plains unit, as seen by HiRISE under HiWish program Arrow points to a place where fractures are forming that will turn into brain terrain.
44229 2235brainsupper.jpg|Brain terrain is forming from the breakdown of upper plains unit, as seen by HiRISE under HiWish program Arrow points to a place where fractures are forming that will turn into brain terrain.
</gallery>
<gallery class="center" widths="190px" heights="180px" >
ESP 045349 2235brains.jpg|Wide view of brain terrain being formed, as seen by HiRISE under HiWish program
ESP 045349 2235brains.jpg|Wide view of brain terrain being formed, as seen by HiRISE under HiWish program
45349 2235brainsforming2.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program. Note: this is an enlargement of the previous image using HiView. Arrows indicate spots where brain terrain is beginning to form.

45349 2235brainsforming2.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program Note: this is an enlargement of the previous image using HiView. Arrows indicate spots where brain terrain is beginning to form.
45349 2235brainsforming.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program. Note: this is an enlargement of a previous image using HiView. Arrows indicate spots where brain terrain is beginning to form.
45349 2235brainsforming.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program Note: this is an enlargement of a previous image using HiView. Arrows indicate spots where brain terrain is beginning to form.
45349 2235brainsforming3.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program. Note: this is an enlargement of a previous image using HiView.
45349 2235brainsforming3.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program Note: this is an enlargement of a previous image using HiView.
45349 2235brainschanging.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program. Note: this is an enlargement of a previous image using HiView.
45349 2235brainschanging.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program Note: this is an enlargement of a previous image using HiView.
45917 2220brainsopenclosed.jpg|Open and closed brain terrain with labels, as seen by HiRISE under HiWish program. Location is Ismenius Lacus quadrangle.
45917 2220brainsforming.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program. Location is Ismenius Lacus quadrangle.

45917 2220brainsopenclosed.jpg|Open and closed brain terrain with labels, as seen by HiRISE under HiWish program Location is Ismenius Lacus quadrangle.

45917 2220brainsforming.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program Location is Ismenius Lacus quadrangle.
</gallery>
</gallery>


<gallery class="center" widths="190px" heights="180px">
<gallery class="center" widths="380px" heights="360px">
ESP 045363 2190brain.jpg|Wide view of brain terrain being formed, as seen by HiRISE under HiWish program
ESP 045363 2190brain.jpg|Wide view of brain terrain being formed, as seen by HiRISE under HiWish program
45363 2190brainsforming.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program Note: this is an enlargement of the previous image using HiView.
45363 2190brainsforming.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program. Note: this is an enlargement of the previous image using HiView.
45363 2190brainsforming2.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program Note: this is an enlargement of a previous image using HiView.
45363 2190brainsforming2.jpg|Brain terrain being formed, as seen by HiRISE under HiWish program. Note: this is an enlargement of a previous image using HiView.
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</gallery>


Some regions of the upper plains unit display large fractures and troughs with raised rims; such regions are called ribbed upper plains. Fractures are believed to have started with small cracks from stresses. Stress is suggested to initiate the fracture process since ribbed upper plains are common when debris aprons come together or near the edge of debris aprons—such sites would generate compressional stresses. Cracks exposed more surfaces, and consequently more ice in the material sublimates into the planet's thin atmosphere. Eventually, small cracks become large canyons or troughs.
Some regions of the upper plains unit display large fractures and troughs with raised rims; such regions are called ribbed upper plains. Fractures are believed to have started with small cracks from stresses. Stress is suggested to initiate the fracture process since ribbed upper plains are common when debris aprons come together or near the edge of debris aprons—such sites would generate compressional stresses. Cracks exposed more surfaces, and consequently more ice in the material sublimates into the planet's thin atmosphere. Eventually, small cracks become large canyons or troughs.


<gallery class="center" widths="190px" heights="180px">
<gallery class="center" widths="380px" heights="360px">
ESP 028339 2245headarticle.jpg|Well developed ribbed upper plains material. These start with small cracks that expand as ice sublimates from the surfaces of the crack. Picture was taken with HiRISE under HiWish program
ESP 028339 2245headarticle.jpg|Well developed ribbed upper plains material. These start with small cracks that expand as ice sublimates from the surfaces of the crack. Picture was taken with HiRISE under HiWish program.
ESP 035011 2240pyramidshead.jpg|Dipping layers, as seen by HiRISE under HiWish program. Also, Ribbed Upper plains material is visible in the upper right of the picture. It is forming from the upper plains unit, and in turn is being eroded into brain terrain.

ESP 035011 2240pyramidshead.jpg|Dipping layers, as seen by HiRISE under HiWish program Also, Ribbed Upper plains material is visible in the upper right of the picture. It is forming from the upper plains unit, and in turn is being eroded into brain terrain.
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<gallery class="center" widths="190px" heights="180px">
<gallery class="center" widths="380px" heights="360px">
ESP 045402 2230dipping.jpg|Wide view showing ribbed terrain and brain terrain, as seen by HiRISE under HiWish program
ESP 045402 2230dipping.jpg|Wide view showing ribbed terrain and brain terrain, as seen by HiRISE under HiWish program
45402 2230cracksmesas.jpg|Ribbed terrain being formed from upper plains unit, as seen by HiRISE under HiWish program Formation begins with cracks that enhance sublimation. Bok shows the size of football field.
45402 2230cracksmesas.jpg|Ribbed terrain being formed from upper plains unit, as seen by HiRISE under HiWish program. Formation begins with cracks that enhance sublimation. Box shows the size of football field.

File:ESP 057494 2230upperplains 01.jpg|Wide view of upper plains with many hollows
File:ESP 057494 2230 upperplains 02.jpg|Close view of upper plains unit showing hollows--where ice left the ground. Picture is about 1 Km across. This is part of an image named HiRISE picture of the day for October 21, 2024.
File:ESP 057494 2230 upperplains with hollows 03.jpg|Close view of upper plains unit showing hollows--where ice left the ground. Picture is about 1 Km across. This is part of an image named HiRISE picture of the day for October 21, 2024.
File:ESP 057494 2230 upperplains with many hollows 04.jpg|Close view of upper plains unit showing hollows--where ice left the ground. Picture is about 1 Km across. This is part of an image named HiRISE picture of the day for October 21, 2024.
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Small cracks often contain small pits and chains of pits; these are thought to be from [[sublimation (phase transition)]] of ice in the ground.<ref>Morgenstern, A., et al. 2007</ref><ref name="Baker, D. 2015">{{cite journal | last1 = Baker | first1 = D. | last2 = Head | first2 = J. | year = 2015 | title = Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation | journal = Icarus | volume = 260 | pages = 269–288 | doi = 10.1016/j.icarus.2015.06.036 | bibcode = 2015Icar..260..269B }}</ref>
Small cracks often contain small pits and chains of pits; these are thought to be from [[sublimation (phase transition)|sublimation]] of ice in the ground.<ref>Morgenstern, A., et al. 2007</ref><ref name="Baker, D. 2015">{{cite journal | last1 = Baker | first1 = D. | last2 = Head | first2 = J. | year = 2015 | title = Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation | journal = Icarus | volume = 260 | pages = 269–288 | doi = 10.1016/j.icarus.2015.06.036 | bibcode = 2015Icar..260..269B }}</ref>
Large areas of the Martian surface are loaded with ice that is protected by a meters thick layer of dust and other material. However, if cracks appear, a fresh surface will expose ice to the thin atmosphere.<ref>{{cite journal | last1 = Mangold | first1 = N | year = 2003 | title = Geomorphic analysis of lobate debris aprons on Mars at Mars Orbiter Camera scale: Evidence for ice sublimation initiated by fractures | journal = J. Geophys. Res. | volume = 108 | issue = E4 | page = 8021 | doi = 10.1029/2002je001885 | bibcode = 2003JGRE..108.8021M | doi-access = free }}</ref><ref>Levy, J. et al. 2009. Concentric</ref> In a short time, the ice will disappear into the cold, thin atmosphere in a process called [[sublimation (phase transition)]]. Dry ice behaves in a similar fashion on the Earth. On Mars sublimation has been observed when the [[Phoenix lander]] uncovered chunks of ice that disappeared in a few days.<ref name="Press"/><ref name="nasa.gov">{{cite web|url=http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080619.html|title=NASA - Bright Chunks at Phoenix Lander's Mars Site Must Have Been Ice|website=www.nasa.gov|access-date=20 November 2018}}</ref> In addition, HiRISE has seen fresh craters with ice at the bottom. After a time, HiRISE saw the ice deposit disappear.<ref>{{cite journal | last1 = Byrne | first1 = S. | display-authors = etal | year = 2009 | title = Distribution of Mid-Latitude Ground Ice on Mars from New Impact Craters | journal = Science | volume = 325 | issue = 5948 | pages = 1674–1676 | doi = 10.1126/science.1175307 | pmid = 19779195 | bibcode = 2009Sci...325.1674B | s2cid = 10657508 }}</ref>
Large areas of the Martian surface are loaded with ice that is protected by a meters thick layer of dust and other material. However, if cracks appear, a fresh surface will expose ice to the thin atmosphere.<ref>{{cite journal | last1 = Mangold | first1 = N | year = 2003 | title = Geomorphic analysis of lobate debris aprons on Mars at Mars Orbiter Camera scale: Evidence for ice sublimation initiated by fractures | journal = J. Geophys. Res. | volume = 108 | issue = E4 | page = 8021 | doi = 10.1029/2002je001885 | bibcode = 2003JGRE..108.8021M | doi-access = free }}</ref><ref>Levy, J. et al. 2009. Concentric</ref> In a short time, the ice will disappear into the cold, thin atmosphere in a process called sublimation. Dry ice behaves in a similar fashion on the Earth. On Mars sublimation has been observed when the [[Phoenix lander]] uncovered chunks of ice that disappeared in a few days.<ref name="Press"/><ref name="nasa.gov">{{cite web|url=http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080619.html|title=NASA - Bright Chunks at Phoenix Lander's Mars Site Must Have Been Ice|website=www.nasa.gov|access-date=20 November 2018|archive-date=4 March 2016|archive-url=https://web.archive.org/web/20160304075627/http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080619.html|url-status=dead}}</ref> In addition, HiRISE has seen fresh craters with ice at the bottom. After a time, HiRISE saw the ice deposit disappear.<ref>{{cite journal | last1 = Byrne | first1 = S. | display-authors = etal | year = 2009 | title = Distribution of Mid-Latitude Ground Ice on Mars from New Impact Craters | journal = Science | volume = 325 | issue = 5948 | pages = 1674–1676 | doi = 10.1126/science.1175307 | pmid = 19779195 | bibcode = 2009Sci...325.1674B | s2cid = 10657508 }}</ref>


The upper plains unit is thought to have fallen from the sky. It drapes various surfaces, as if it fell evenly. As is the case for other mantle deposits, the upper plains unit has layers, is fine-grained, and is ice-rich. It is widespread; it does not seem to have a point source. The surface appearance of some regions of Mars is due to how this unit has degraded. It is a major cause of the surface appearance of [[lobate debris apron]]s.<ref name="Baker, D. 2015"/>
The upper plains unit is thought to have fallen from the sky. It drapes various surfaces, as if it fell evenly. As is the case for other mantle deposits, the upper plains unit has layers, is fine-grained, and is ice-rich. It is widespread; it does not seem to have a point source. The surface appearance of some regions of Mars is due to how this unit has degraded. It is a major cause of the surface appearance of [[lobate debris apron]]s.<ref name="Baker, D. 2015"/>
The layering of the upper plains mantling unit and other mantling units are believed to be caused by major changes in the planet's climate. Models predict that the obliquity or tilt of the rotational axis has varied from its present 25 degrees to maybe over 80 degrees over geological time. Periods of high tilt will cause the ice in the polar caps to be redistributed and change the amount of dust in the atmosphere.<ref>Head, J. et al. 2003.</ref><ref>Madeleine, et al. 2014.</ref><ref>{{cite journal | last1 = Schon | display-authors = etal | year = 2009 | title = A recent ice age on Mars: Evidence for climate oscillations from regional layering in mid-latitude mantling deposits | journal = Geophys. Res. Lett. | volume = 36 | issue = 15 | page = L15202 | doi = 10.1029/2009GL038554 | bibcode = 2009GeoRL..3615202S | s2cid = 18570952 | doi-access = free }}</ref>
The layering of the upper plains mantling unit and other mantling units are believed to be caused by major changes in the planet's climate. Models predict that the obliquity or tilt of the rotational axis has varied from its present 25 degrees to maybe over 80 degrees over geological time. Periods of high tilt will cause the ice in the polar caps to be redistributed and change the amount of dust in the atmosphere.<ref>Head, J. et al. 2003.</ref><ref>Madeleine, et al. 2014.</ref><ref>{{cite journal | last1 = Schon | display-authors = etal | year = 2009 | title = A recent ice age on Mars: Evidence for climate oscillations from regional layering in mid-latitude mantling deposits | journal = Geophys. Res. Lett. | volume = 36 | issue = 15 | page = L15202 | doi = 10.1029/2009GL038554 | bibcode = 2009GeoRL..3615202S | s2cid = 18570952 | doi-access = free }}</ref>


==Linear Ridge Networks==
==Linear ridge networks==


[[Linear ridge networks]] are found in various places on Mars in and around craters.<ref>{{cite journal | last1 = Head | first1 = J. | last2 = Mustard | first2 = J. | year = 2006 | title = Breccia dikes and crater-related faults in impact craters on Mars: Erosion and exposure on the floor of a crater 75 km in diameter at the dichotomy boundary | journal = Meteorit. Planet Science | volume = 41 | issue = 10 | pages = 1675–1690 | doi = 10.1111/j.1945-5100.2006.tb00444.x | bibcode = 2006M&PS...41.1675H | s2cid = 12036114 }}</ref> Ridges often appear as mostly straight segments that intersect in a lattice-like manner. They are hundreds of meters long, tens of meters high, and several meters wide. It is thought that impacts created fractures in the surface, these fractures later acted as channels for fluids. Fluids cemented the structures. With the passage of time, surrounding material was eroded away, thereby leaving hard ridges behind.
[[Linear ridge networks]] are found in various places on Mars in and around craters.<ref>{{cite journal | last1 = Head | first1 = J. | last2 = Mustard | first2 = J. | year = 2006 | title = Breccia dikes and crater-related faults in impact craters on Mars: Erosion and exposure on the floor of a crater 75 km in diameter at the dichotomy boundary | journal = Meteorit. Planet Science | volume = 41 | issue = 10 | pages = 1675–1690 | doi = 10.1111/j.1945-5100.2006.tb00444.x | bibcode = 2006M&PS...41.1675H | s2cid = 12036114 }}</ref> Ridges often appear as mostly straight segments that intersect in a lattice-like manner. They are hundreds of meters long, tens of meters high, and several meters wide. It is thought that impacts created fractures in the surface, these fractures later acted as channels for fluids. Fluids cemented the structures. With the passage of time, surrounding material was eroded away, thereby leaving hard ridges behind.
Since the ridges occur in locations with clay, these formations could serve as a marker for clay which requires water for its formation. Water here could have supported life.<ref>{{cite journal | last1 = Mangold | display-authors = etal | year = 2007 | title = Mineralogy of the Nili Fossae region with OMEGA/Mars Express data: 2. Aqueous alteration of the crust | journal = J. Geophys. Res. | volume = 112| issue = E8 | doi = 10.1029/2006JE002835 | bibcode = 2007JGRE..112.8S04M | s2cid = 15188454 | url = https://hal.archives-ouvertes.fr/hal-00376813 | doi-access = free }}</ref><ref>{{cite journal | last1 = Mustard | display-authors = etal | year = 2007 | title = Mineralogy of the Nili Fossae region with OMEGA/Mars Express data: 1. Ancient impact melt in the Isidis Basin and implications for the transition from the Noachian to Hesperian | journal = J. Geophys. Res. | volume = 112 | issue = E8 | doi = 10.1029/2006JE002834 | bibcode = 2007JGRE..112.8S03M | url = https://hal.archives-ouvertes.fr/hal-00376823 }}</ref><ref>{{cite journal | last1 = Mustard | display-authors = etal | year = 2009 | title = Composition, Morphology, and Stratigraphy of Noachian Crust around the Isidis Basin | journal = J. Geophys. Res. | volume = 114| issue = 7 | doi = 10.1029/2009JE003349 | bibcode = 2009JGRE..114.0D12M | url = https://hal.archives-ouvertes.fr/hal-00489726/file/2009JE003349.pdf }}</ref>
Since the ridges occur in locations with clay, these formations could serve as a marker for clay which requires water for its formation. Water here could have supported life.<ref>{{cite journal | last1 = Mangold | display-authors = etal | year = 2007 | title = Mineralogy of the Nili Fossae region with OMEGA/Mars Express data: 2. Aqueous alteration of the crust | journal = J. Geophys. Res. | volume = 112| issue = E8 | doi = 10.1029/2006JE002835 | bibcode = 2007JGRE..112.8S04M | s2cid = 15188454 | url = https://hal.archives-ouvertes.fr/hal-00376813 | doi-access = free }}</ref><ref>{{cite journal | last1 = Mustard | display-authors = etal | year = 2007 | title = Mineralogy of the Nili Fossae region with OMEGA/Mars Express data: 1. Ancient impact melt in the Isidis Basin and implications for the transition from the Noachian to Hesperian | journal = J. Geophys. Res. | volume = 112 | issue = E8 | doi = 10.1029/2006JE002834 | bibcode = 2007JGRE..112.8S03M | url = https://hal.archives-ouvertes.fr/hal-00376823 }}</ref><ref>{{cite journal | last1 = Mustard | display-authors = etal | year = 2009 | title = Composition, Morphology, and Stratigraphy of Noachian Crust around the Isidis Basin | journal = J. Geophys. Res. | volume = 114| issue = 7 | doi = 10.1029/2009JE003349 | bibcode = 2009JGRE..114.0D12M | url = https://hal.archives-ouvertes.fr/hal-00489726/file/2009JE003349.pdf }}</ref>


<gallery class="center" widths="190px" heights="180px">
<gallery class="center" widths="380px" heights="360px">
ESP 043845 2130ridges.jpg|Network of ridges, as seen by HiRISE under HiWish program Ridges may be formed in various ways.
ESP 043845 2130ridges.jpg|Network of ridges, as seen by HiRISE under HiWish program. Ridges may be formed in various ways.
ESP 043845 2130ridgesclose.jpg|Color, close-up of ridges seen in previous image, as seen by HiRISE under HiWish program
ESP 043845 2130ridgesclose.jpg|Color, close-up of ridges seen in previous image, as seen by HiRISE under HiWish program

ESP 036869 2105ridgesclose.jpg|Close-up and color image of linear ridge network, as seen by HiRISE under HiWish program
ESP 036869 2105ridgesclose.jpg|Close-up and color image of linear ridge network, as seen by HiRISE under HiWish program

ESP 036869 2105ridgesbottom.jpg|More linear ridge networks from same location as previous image, as seen by HiRISE under HiWish program
ESP 036869 2105ridgesbottom.jpg|More linear ridge networks from same location as previous image, as seen by HiRISE under HiWish program
ESP 036745 1905top.jpg|Linear ridge networks, as seen by HiRISE under HiWish program. Location is [[Amazonis quadrangle]].

ESP 036745 1905top.jpg|Linear ridge networks, as seen by HiRISE under HiWish program Location is [[Amazonis quadrangle]].
ESP 036893 1765ridgesnepenthestop.jpg|Linear ridge network, as seen by HiRISE under HiWish program. Location is [[Mare Tyrrhenum quadrangle]].
ESP 036869 2105ridgeswide.jpg|Linear ridge network, as seen by HiRISE under HiWish program. Location is [[Casius quadrangle]].

ESP 036893 1765ridgesnepenthestop.jpg|Linear ridge network, as seen by HiRISE under HiWish program Location is [[Mare Tyrrhenum quadrangle]].
ESP 047054 2160ridges.jpg|Wide view of ridge network, as seen by HiRISE under HiWish program. Location is [[Arcadia quadrangle]].
ESP 036869 2105ridgeswide.jpg|Linear ridge network, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]].
47054 2160largeridges.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program. Arrow points to small, straight ridge. Location is [[Arcadia quadrangle]].

ESP 047054 2160ridges.jpg|Wide view of ridge network, as seen by HiRISE under HiWish program Location is [[Arcadia quadrangle]].
47054 2160largeridges.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Arrow points to small, straight ridge. Location is [[Arcadia quadrangle]].
</gallery>
</gallery>
<gallery class="center" widths="190px" heights="180px" >
ESP 048236 2105ridgeswide.jpg|Wide view of network of ridges, as seen by HiRISE under HiWish program Portions of this image are enlarged in following images.


<gallery class="center" widths="380px" heights="360px">
48236 2105ridges3.jpg|Close view of network of ridges, as seen by HiRISE under HiWish program This is an enlargement of a previous image.
ESP 048236 2105ridgeswide.jpg|Wide view of network of ridges, as seen by HiRISE under HiWish program. Portions of this image are enlarged in following images.

48236 2105ridges2.jpg|Close view of network of ridges, as seen by HiRISE under HiWish program This is an enlargement of a previous image. Box shows the size of a football field.
48236 2105ridges3.jpg|Close view of network of ridges, as seen by HiRISE under HiWish program. This is an enlargement of a previous image.
48236 2105ridges2.jpg|Close view of network of ridges, as seen by HiRISE under HiWish program. This is an enlargement of a previous image. Box shows the size of a football field.

48236 2105ridges.jpg|Close view of network of ridges, as seen by HiRISE under HiWish program This is an enlargement of a previous image.
48236 2105ridges.jpg|Close view of network of ridges, as seen by HiRISE under HiWish program. This is an enlargement of a previous image.
48236 2105ridgesmesa.jpg|Close view of ridges, as seen by HiRISE under HiWish program. This is an enlargement of a previous image. A small mesa in the image displays layers.

48236 2105ridgesmesa.jpg|Close view of ridges, as seen by HiRISE under HiWish program This is an enlargement of a previous image. A small mesa in the image displays layers.
ESP 048236 2105ridgesclosecolor.jpg|Close, color view of network of ridges, as seen by HiRISE under HiWish program. This is an enlargement of a previous image.

ESP 048236 2105ridgesclosecolor.jpg|Close, color view of network of ridges, as seen by HiRISE under HiWish program This is an enlargement of a previous image.
</gallery>
</gallery>


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
File:ESP 054850 1900ridges.jpg|Wide view of large ridge network, as seen by HiRISE under HiWish program
File:ESP 054850 1900ridges.jpg|Wide view of large ridge network, as seen by HiRISE under HiWish program
File:54850 1900ridges.jpg|Close view of ridge network, as seen by HiRISE under HiWish program. Box shows size of football field.

File:54850 1900ridges.jpg|Close view of ridge network, as seen by HiRISE under HiWish program Box shows size of football field.

File:54850 1900ridgesclosecolor.jpg|Close, color view of ridges, as seen by HiRISE under HiWish program
File:54850 1900ridgesclosecolor.jpg|Close, color view of ridges, as seen by HiRISE under HiWish program

</gallery>
</gallery>


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Some places on Mars break up with large fractures that created a terrain with mesas and valleys. Some of these can be quite pretty.
Some places on Mars break up with large fractures that created a terrain with mesas and valleys. Some of these can be quite pretty.


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
ESP 048878 2095fractures.jpg|Wide view of fractured ground, as seen by HiRISE under HiWish program
ESP 048878 2095fractures.jpg|Wide view of fractured ground, as seen by HiRISE under HiWish program

48878 2095fractures.jpg|Close view of fractured ground, as seen by HiRISE under HiWish program
48878 2095fractures.jpg|Close view of fractured ground, as seen by HiRISE under HiWish program
48878 2095fracturesboulders.jpg|Close view of fractured ground, as seen by HiRISE under HiWish program. Box shows size of football field. The boulders are the size of houses.

48878 2095fracturesboulders.jpg|Close view of fractured ground, as seen by HiRISE under HiWish program Box shows size of football field. The boulders are the size of houses.

ESP 048878 2095fracturesclosecolor.jpg|Close, color view of fractured ground, as seen by HiRISE under HiWish program
ESP 048878 2095fracturesclosecolor.jpg|Close, color view of fractured ground, as seen by HiRISE under HiWish program
</gallery>
</gallery>
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==Mesas==
==Mesas==


<gallery class="center" widths="260px" heights="230px" >
<gallery class="center" widths="380px" heights="360px">
46050 1775race.jpg|Mesa, as seen by HiRISE under HiWish program This may make for a good race around a mesa someday in the far future.
46050 1775race.jpg|Mesa, as seen by HiRISE under HiWish program. This may make for a good race around a mesa someday in the far future.
</gallery>
</gallery>


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
ESP 047080 2120layered mesa.jpg|Mesa with layers, as seen by HiRISE under HiWish program Location is [[Mare Acidalium quadrangle]].
ESP 047080 2120layered mesa.jpg|Mesa with layers, as seen by HiRISE under HiWish program. Location is [[Mare Acidalium quadrangle]].
47080 2120layersclose.jpg|Close view of layers in mesa, as seen by HiRISE under HiWish program
47080 2120layersclose.jpg|Close view of layers in mesa, as seen by HiRISE under HiWish program
</gallery>
</gallery>


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
ESP 047441 1800layerstreaks.jpg|Wide view of layered buttes and small mesas, as seen by HiRISE under HiWish program Some [[dark slope streaks]] are visible. Location is [[Aeolis quadrangle]]. Parts of this image are enlarged in next three pictures.
ESP 047441 1800layerstreaks.jpg|Wide view of layered buttes and small mesas, as seen by HiRISE under HiWish program. Some [[dark slope streaks]] are visible. Location is [[Aeolis quadrangle]]. Parts of this image are enlarged in next three pictures.
47441 1800moundsstreaks.jpg|Layered mesa and mounds with dark slope streaks, as seen by HiRISE under HiWish program
47441 1800mesaclose.jpg|Close view of layered small mesa with dark slope streak, as seen by HiRISE under HiWish program. Box shows the size of a football field.
47441 1800pyramidrock.jpg|Very close view of individual blocks breaking off layer in a butte, as seen by HiRISE under HiWish program. Blocks have angular shapes. Box shows size of football field.


47441 1800moundsstreaks.jpg|Layered mesa and mounds with dark slope streaks, as seen by HiRISE under HiWish program
File:82500 1845 layered mesas rgb.jpg|Layered mesa, as seen by HiRISE under HiWish program
47441 1800mesaclose.jpg|Close view of layered small mesa with dark slope streak, as seen by HiRISE under HiWish program Box shows the size of a football field.
File:82500 1845 layered mesas with scale.jpg|Layered mesa, as seen by HiRISE under HiWish program Box is the size of a football field.
47441 1800pyramidrock.jpg|Very close view of individual blocks breaking off layer in a butte, as seen by HiRISE under HiWish program Blocks have angular shapes. Box shows size of football field.
</gallery>
</gallery>


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<gallery class="center" widths="190px" heights="180px">
<gallery class="center" widths="190px" heights="180px">
ESP 043201 2160blocks.jpg|Group of mesas, as seen by HiRISE under HiWish program Oval box contains mesas that may have moved apart.
ESP 043201 2160blocks.jpg|Group of mesas, as seen by HiRISE under HiWish program. Oval box contains mesas that may have moved apart.
43201 2160blocks.jpg|Enlarged view of a group of mesas, as seen by HiRISE under HiWish program One surface is forming square shapes.
43201 2160blocks.jpg|Enlarged view of a group of mesas, as seen by HiRISE under HiWish program. One surface is forming square shapes.
43201 2160blocksbreakup.jpg|Mesas breaking up forming straight edges, as seen by HiRISE under HiWish program
43201 2160blocksbreakup.jpg|Mesas breaking up forming straight edges, as seen by HiRISE under HiWish program
</gallery>
</gallery>
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There is evidence that volcanoes sometimes erupt under ice, as they do on Earth at times. What seems to happen it that much ice melts, the water escapes, and then the surface cracks and collapses. These exhibit concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water, hence they may be fruitful places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>
There is evidence that volcanoes sometimes erupt under ice, as they do on Earth at times. What seems to happen it that much ice melts, the water escapes, and then the surface cracks and collapses. These exhibit concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water, hence they may be fruitful places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>


<gallery class="center" widths="190px" heights="180px">
<gallery class="center" widths="380px" heights="360px">
Image:25755concentriccracks.jpg|Large group of concentric cracks, as seen by HiRISE, under HiWish program Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.<ref name="Levy, J. 2017"/>
Image:25755concentriccracks.jpg|Large group of concentric cracks, as seen by HiRISE, under HiWish program. Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.<ref name="Levy, J. 2017"/>

25755 2200collapse.jpg|Tilted layers formed when ground collapsed, as seen by HiRISE, under HiWish program
25755 2200collapse.jpg|Tilted layers formed when ground collapsed, as seen by HiRISE, under HiWish program
25755 2200tiltedlayers.jpg|Tilted layers formed from ground collapse, as seen by HiRISE, under HiWish program.
25755 2200tiltedlayers.jpg|Tilted layers formed from ground collapse, as seen by HiRISE, under HiWish program
25755 2200blocksforming.jpg|Mesas breaking up into blocks, as seen by HiRISE, under HiWish program.
25755 2200blocksforming.jpg|Mesas breaking up into blocks, as seen by HiRISE, under HiWish program
</gallery>
</gallery>


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In places large fractures break up surfaces. Sometimes straight edges are formed and large cubes are created by the fractures.
In places large fractures break up surfaces. Sometimes straight edges are formed and large cubes are created by the fractures.


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
44757 2185wide.jpg|Wide view of mesas that are forming fractures, as seen by HiRISE under HiWish program.
44757 2185wide.jpg|Wide view of mesas that are forming fractures, as seen by HiRISE under HiWish program
44757 2185zoom.jpg|Enlarged view of a part of previous image, as seen by HiRISE under HiWish program. The rectangle represents the size of a football field.
44757 2185zoom.jpg|Enlarged view of a part of previous image, as seen by HiRISE under HiWish program. The rectangle represents the size of a football field.
44757 2185closeleft.jpg|Close-up of blocks being formed, as seen by HiRISE under HiWish program as seen by HiRISE under HiWish program.
44757 2185closeleft.jpg|Close-up of blocks being formed, as seen by HiRISE under HiWish program
44757 2185blocks.jpg|Close-up of blocks being formed, as seen by HiRISE under HiWish program The rectangle represents the size of a football field, so blocks are the size of buildings.
44757 2185blocks.jpg|Close-up of blocks being formed, as seen by HiRISE under HiWish program. The rectangle represents the size of a football field, so blocks are the size of buildings.
44757 2185cosefractures.jpg|Close-up of blocks being formed, as seen by HiRISE under HiWish program as seen by HiRISE under HiWish program. Many long fractures are visible on the surface.
44757 2185cosefractures.jpg|Close-up of blocks being formed, as seen by HiRISE under HiWish program. Many long fractures are visible on the surface.
44757 2185edgebrains.jpg|Surface breaking up, as seen by HiRISE under HiWish program as seen by HiRISE under HiWish program. Near the top the surface is eroding into brain terrain.
44757 2185edgebrains.jpg|Surface breaking up, as seen by HiRISE under HiWish program. Near the top the surface is eroding into brain terrain.
ESP 045377 2170odd.jpg|Wide view showing light-toned feature that is breaking into blocks, as seen by HiRISE under HiWish program
ESP 045377 2170odd.jpg|Wide view showing light-toned feature that is breaking into blocks, as seen by HiRISE under HiWish program
45377 2170blocks.jpg|Close view showing blocks being formed, as seen by HiRISE under HiWish program Note: this is an enlargement of the previous image. Box represents size of football field.
45377 2170blocks.jpg|Close view showing blocks being formed, as seen by HiRISE under HiWish program. Note: this is an enlargement of the previous image. Box represents size of football field.
</gallery>
</gallery>


==Lava flows==
==Lava flows==
<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
WikiESP 035095 1975lavalobestharsis.jpg|Lava flow in Tharsis quadrangle, as seen by HiRISE under HiWish program
WikiESP 035095 1975lavalobestharsis.jpg|Lava flow in Tharsis quadrangle, as seen by HiRISE under HiWish program
WikiESP 035095 1975lavalobestharsiswide.jpg|Close-up of lava flow with labels, as seen by HiRISE under HiWish program Note: this is an enlargement of the previous image of lava flows.
WikiESP 035095 1975lavalobestharsiswide.jpg|Close-up of lava flow with labels, as seen by HiRISE under HiWish program. Note: this is an enlargement of the previous image of lava flows.
44828 2030lavaflow.jpg|Lava flows with older and younger flows labeled, as seen by HiRISE under HiWish program
44828 2030lavaflow.jpg|Lava flows with older and younger flows labeled, as seen by HiRISE under HiWish program
ESP 044840 1620lavaflow.jpg|Edge of lava flow, as seen by HiRISE under HiWish program Location is [[Solis Planum]] in [[Phoenicis Lacus quadrangle]].
ESP 044840 1620lavaflow.jpg|Edge of lava flow, as seen by HiRISE under HiWish program. Location is [[Solis Planum]] in [[Phoenicis Lacus quadrangle]].

ESP 045133 1970lava.jpg|Wide view of streamlined shape and rafts of lava, as seen by HiRISE under HiWish program
ESP 045133 1970lava.jpg|Wide view of streamlined shape and rafts of lava, as seen by HiRISE under HiWish program

45133 1970lvarafts.jpg|Close view of lava rafts from previous image, as seen by HiRISE under HiWish program
45133 1970lvarafts.jpg|Close view of lava rafts from previous image, as seen by HiRISE under HiWish program
</gallery>
</gallery>


==Rootless Cones==
==Rootless cones==
So-called "Rootless cones" are caused by explosions of lava with ground ice under the flow.<ref name="psrd.hawaii.edu">{{cite web|url=http://www.psrd.hawaii.edu/June01/lavaIceMars.html|title=PSR Discoveries: Rootless cones on Mars|website=www.psrd.hawaii.edu|access-date=20 November 2018}}</ref><ref>Lanagan, P., A. McEwen, L. Keszthelyi, and T. Thordarson. 2001. Rootless cones on Mars indicating the presence of shallow equatorial ground ice in recent times, Geophysical Research Letters: 28, 2365-2368.</ref> The ice melts and turns into a vapor that expands in an explosion that produces a cone or ring. Featureslike these are found in Iceland, when lavas cover water-saturated substrates.<ref>S. Fagents1, a., P. Lanagan, R. Greeley. 2002. Rootless cones on Mars: a consequence of lava-ground ice interaction. Geological Society, Londo. Special Publications: 202, 295-317.</ref><ref name="psrd.hawaii.edu"/><ref>Jaeger, W., L. Keszthelyi, A. McEwen, C. Dundas, P. Russell, and the HiRISE team. 2007. EARLY HiRISE OBSERVATIONS OF RING/MOUND LANDFORMS IN ATHABASCA VALLES, MARS. Lunar and Planetary Science XXXVIII 1955.pdf.</ref>
So-called "rootless cones" are caused by explosions of lava with ground ice under the flow.<ref name="psrd.hawaii.edu">{{cite web|url=http://www.psrd.hawaii.edu/June01/lavaIceMars.html|title=PSR Discoveries: Rootless cones on Mars|website=www.psrd.hawaii.edu|access-date=20 November 2018}}</ref><ref>Lanagan, P., A. McEwen, L. Keszthelyi, and T. Thordarson. 2001. Rootless cones on Mars indicating the presence of shallow equatorial ground ice in recent times, Geophysical Research Letters: 28, 2365-2368.</ref> The ice melts and turns into a vapor that expands in an explosion that produces a cone or ring. Featureslike these are found in Iceland, when lavas cover water-saturated substrates.<ref>S. Fagents1, a., P. Lanagan, R. Greeley. 2002. Rootless cones on Mars: a consequence of lava-ground ice interaction. Geological Society, Londo. Special Publications: 202, 295-317.</ref><ref name="psrd.hawaii.edu"/><ref>Jaeger, W., L. Keszthelyi, A. McEwen, C. Dundas, P. Russell, and the HiRISE team. 2007. EARLY HiRISE OBSERVATIONS OF RING/MOUND LANDFORMS IN ATHABASCA VALLES, MARS. Lunar and Planetary Science XXXVIII 1955.pdf.</ref>


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
ESP 045384 2065lavaice.jpg|Wide view of field of rootless cones, as seen by HiRISE under HiWish program Location is [[Elysium quadrangle]].
ESP 045384 2065lavaice.jpg|Wide view of field of rootless cones, as seen by HiRISE under HiWish program. Location is [[Elysium quadrangle]].
45384 2065cones.jpg|Close view of rootless cones with tails that suggest lava was moving toward the Southwest over ice-rich ground, as seen by HiRISE under HiWish program
45384 2065cones.jpg|Close view of rootless cones with tails that suggest lava was moving toward the Southwest over ice-rich ground, as seen by HiRISE under HiWish program
45384 2065conesclose.jpg|Close view of cones with the size of a football field shown, as seen by HiRISE under HiWish program
45384 2065conesclose.jpg|Close view of cones with the size of a football field shown, as seen by HiRISE under HiWish program
45885 2070cones.jpg|Close view of cones, as seen by HiRISE under HiWish program These cones probably formed when hot lava flowed over ice-rich ground. The location is the [[Elysium quadrangle]].
45885 2070cones.jpg|Close view of cones, as seen by HiRISE under HiWish program. These cones probably formed when hot lava flowed over ice-rich ground. The location is the [[Elysium quadrangle]].

Wikiesp37643 2060coneslong.jpg|Rootless Cones, as seen by HiRISE under HiWish program. These group of rings or cones are believed to be caused by lava flowing over water ice or ground containing water ice. The ice quickly changes to steam which blows out a ring or cone. Here the kink in the chain may have been caused by the lava changing direction. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. The location is the [[Elysium quadrangle]].
Wikiesp37643 2060coneslong.jpg|Rootless Cones, as seen by HiRISE under HiWish program. These group of rings or cones are believed to be caused by lava flowing over water ice or ground containing water ice. The ice quickly changes to steam which blows out a ring or cone. Here the kink in the chain may have been caused by the lava changing direction. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. The location is the [[Elysium quadrangle]].
</gallery>
</gallery>
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Some features look like volcanoes. Some of them may be [[mud volcano]]es where pressurized mud is forced upward forming cones. These features may be places to look for life as they bring to the surface possible life that has been protected from radiation.
Some features look like volcanoes. Some of them may be [[mud volcano]]es where pressurized mud is forced upward forming cones. These features may be places to look for life as they bring to the surface possible life that has been protected from radiation.


<gallery class="center" widths="190px" heights="180px">
<gallery class="center" widths="380px" heights="360px">
Image:ESP 040775 2235cones.jpg|Large field of cones that may be mud volcanoes, as seen by HiRISE under HiWish program Location is [[Mare Acidalium quadrangle]].
Image:ESP 040775 2235cones.jpg|Large field of cones that may be mud volcanoes, as seen by HiRISE under HiWish program. Location is [[Mare Acidalium quadrangle]].
Image:040775 2235conesclose.jpg|Close-up of possible mud volcanoes, as seen by HiRISE under HiWish program Note: this is an enlargement of the previous image.
Image:040775 2235conesclose.jpg|Close-up of possible mud volcanoes, as seen by HiRISE under HiWish program. Note: this is an enlargement of the previous image.
</gallery>
</gallery>


<gallery class="center" widths="190px" heights="180px">
<gallery class="center" widths="380px" heights="360px">
ESP 046617 2210mudvolcanoes.jpg|Mud volcanoes, as seen by HiRISE under HiWish program The location is [[Mare Acidalium quadrangle]]. There are many mud volcanoes in Mare Acidalium quadrangle.
ESP 046617 2210mudvolcanoes.jpg|Mud volcanoes, as seen by HiRISE under HiWish program. The location is [[Mare Acidalium quadrangle]]. There are many mud volcanoes in Mare Acidalium quadrangle.
ESP 044665 2240cone.jpg|Possible mud volcano, as seen by HiRISE under HiWish program The location is Mare Acidalium quadrangle.
ESP 044665 2240cone.jpg|Possible mud volcano, as seen by HiRISE under HiWish program. The location is Mare Acidalium quadrangle.
</gallery>
</gallery>


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
ESP 052050 2200mudvolcanoes.jpg|Wide view of field of mud volcanoes, as seen by HiRISE under HiWish program
ESP 052050 2200mudvolcanoes.jpg|Wide view of field of mud volcanoes, as seen by HiRISE under HiWish program
52050 2200mudvolcanoes.jpg|Close view of mud volcanoes, as seen by HiRISE under HiWish program
52050 2200mudvolcanoes.jpg|Close view of mud volcanoes, as seen by HiRISE under HiWish program
52050 2200mudvolcanoesboulders.jpg|Close view of mud volcanoes and boulders, as seen by HiRISE under HiWish program
52050 2200mudvolcanoesboulders.jpg|Close view of mud volcanoes and boulders, as seen by HiRISE under HiWish program

File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for remains of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>
</gallery>


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Strange terrain was discovered on parts of the floor of Hellas Planitia. Scientists are not sure of how it formed.
Strange terrain was discovered on parts of the floor of Hellas Planitia. Scientists are not sure of how it formed.


<gallery class="center" widths="190px" heights="180px" >
<gallery class="center" widths="380px" heights="360px">
File:ESP 055080 1425twistedbands.jpg|Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program
File:ESP 055080 1425twistedbands.jpg|Twisted bands on the floor of Hellas Planitia, as seen by HiRISE under HiWish program


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==Exhumed craters==
==Exhumed craters==


Exhumed craters seem to be in the process of being uncovered.<ref>{{Cite web|url=https://archive.org/details/PLAN-PIA06808|title = Exhumed Craters near Kaiser}}</ref> It is believed that they formed, were covered over, and now are being exhumed as material is being eroded. When a crater forms, it will destroy what's under it. In the example below, only part of the crater is visible. if the crater came after the layered feature, it would have removed part of the feature and we would see the entire crater.
Exhumed craters seem to be in the process of being uncovered.<ref>{{Cite web|url=https://archive.org/details/PLAN-PIA06808|title = Exhumed Craters near Kaiser}}</ref> It is believed that they formed, were covered over, and now are being exhumed as material is being eroded. When a crater forms, it will destroy what is under it. In the example below, only part of the crater is visible. if the crater came after the layered feature, it would have removed part of the feature and we would see the entire crater.

<gallery class="center" widths="190px" heights="180px">


<gallery class="center" widths="380px" heights="360px">
File:ESP 057652 2215pyramidexhumed.jpg|Wide view of exhumed craters, as seen by HiRISE under HiWish program
File:ESP 057652 2215pyramidexhumed.jpg|Wide view of exhumed craters, as seen by HiRISE under HiWish program
File:57652 2215exhumed.jpg|Close view of exhumed crater, as seen by HiRISE under HiWish program. This crater is and was under a set of dipping layers.

File:57652 2215exhumed.jpg|Close view of exhumed crater, as seen by HiRISE under HiWish program This crater is and was under a set of dipping layers.
</gallery>
</gallery>


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* [https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]
* [https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]
* Stillman, D., et al. 2017. Characteristics of the numerous and widespread recurring slope lineae (RSL) in Valles Marineris, Mars. Icarus. Volume 285. Pages 195-210
* Stillman, D., et al. 2017. Characteristics of the numerous and widespread recurring slope lineae (RSL) in Valles Marineris, Mars. Icarus. Volume 285. Pages 195-210

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.
{{Mars Reconnaissance Orbiter}}
{{Mars Reconnaissance Orbiter}}
{{Mars}}
{{Mars}}

Latest revision as of 16:10, 12 November 2024

HiWish is a program created by NASA so that anyone can suggest a place for the HiRISE camera on the Mars Reconnaissance Orbiter to photograph.[1][2][3] It was started in January 2010. In the first few months of the program 3000 people signed up to use HiRISE.[4][5] The first images were released in April 2010.[6] Over 12,000 suggestions were made by the public; suggestions were made for targets in each of the 30 quadrangles of Mars. Selected images released were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.[7]

Glacial features

[edit]

Some landscapes look just like glaciers moving out of mountain valleys on Earth. Some have a hollowed-out appearance, looking like a glacier after almost all the ice has disappeared. What is left are the moraines—the dirt and debris carried by the glacier. The center is hollowed out because the ice is mostly gone.[8] These supposed alpine glaciers have been called glacier-like forms (GLF) or glacier-like flows (GLF).[9] Glacier-like forms are a later and maybe more accurate term because we cannot be sure the structure is currently moving.[10]

Martian glacier moving down a valley, as seen by HiRISE under HiWish program

Possible pingos

[edit]

The radial and concentric cracks visible here are common when forces penetrate a brittle layer, such as a rock thrown through a glass window. These particular fractures were probably created by something emerging from below the brittle Martian surface. Ice may have accumulated under the surface in a lens shape; thus making these cracked mounds. Ice being less dense than rock, pushed upwards on the surface and generated these spider web-like patterns. A similar process creates similar sized mounds in arctic tundra on Earth. Such features are called "pingos", an Inuit word.[11] Pingos would contain pure water ice; thus they could be sources of water for future colonists of Mars. Many features that look like the pingos on the Earth are found in Utopia Planitia (~35-50° N; ~80-115° E).[12]

Ancient rivers and streams

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There is great deal of evidence that water once flowed in river valleys on Mars. Pictures from orbit show winding valleys, branched valleys, and even meanders with oxbow lakes.[13] Some are visible in the pictures below.

Streamlined shapes

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Streamlined shapes represent more evidence of past flowing water on Mars. Water shaped features into streamlined shapes.

New crater

[edit]

Sand dunes

[edit]

Many locations on Mars have sand dunes. The dunes are covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. Many martian dunes strongly resemble terrestrial dunes but images acquired by the High-Resolution Imaging Science Experiment on the Mars Reconnaissance Orbiter have shown that martian dunes in the north polar region are subject to modification via grainflow triggered by seasonal CO2 sublimation, a process not seen on Earth. Many dunes are black because they are derived from the dark volcanic rock basalt. Extraterrestrial sand seas such as those found on Mars are referred to as "undae" from the Latin for waves.

Landing site

[edit]

Some of the targets suggested became possible sites for a Rover Mission in 2020. The targets were in Firsoff (crater) and Holden Crater. These locations were picked as two of 26 locations considered for a mission that will look for signs of life and gather samples for a later return to Earth.[14][15][16]

Landscape features

[edit]

Dark slope streaks

[edit]

Recurrent slope lineae

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Recurrent slope lineae are small dark streaks on slopes that elongate in warm seasons. They may be evidence of liquid water.[18][19][20] However, there remains debate about whether water or much water is needed.[21][22][23] [24]

Layers

[edit]

Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers.[26] Layers can be hardened by the action of groundwater.

This group of layers that are found in a crater all come from the Arabia quadrangle.

This next group of layered terrain comes from the Louros Valles in the Coprates quadrangle.

Layers in ice cap

[edit]

Gullies

[edit]

Martian gullies are small, incised networks of narrow channels and their associated downslope sediment deposits, found on the planet of Mars. They are named for their resemblance to terrestrial gullies. First discovered on images from Mars Global Surveyor, they occur on steep slopes, especially on the walls of craters. Usually, each gully has a dendritic alcove at its head, a fan-shaped apron at its base, and a single thread of incised channel linking the two, giving the whole gully an hourglass shape.[27] They are believed to be relatively young because they have few, if any craters. On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers believed that the processes carving the gullies involve liquid water. However, this remains a topic of active research.

Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program. Location is Phaethontis quadrangle.

Latitude dependent mantle

[edit]

Much of the Martian surface is covered with a thick ice-rich, mantle layer that has fallen from the sky a number of times in the past.[28][29][30] In some places a number of layers are visible in the mantle.[31]

It fell as snow and ice-coated dust. There is good evidence that this mantle is ice-rich. The shapes of the polygons common on many surfaces suggest ice-rich soil. High levels of hydrogen (probably from water) have been found with Mars Odyssey.[32][33][34][35][36] Thermal measurements from orbit suggest ice.[37][38] The Phoenix (spacecraft) discovered water ice with made direct observations since it landed in a field of polygons.[39][40] In fact, its landing rockets exposed pure ice. Theory had predicted that ice would be found under a few cm of soil. This mantle layer is called "latitude dependent mantle" because its occurrence is related to the latitude. It is this mantle that cracks and then forms polygonal ground. This cracking of ice-rich ground is predicted based on physical processes.[41][42][43][44][45][46][47]

Polygonal patterned ground

[edit]

Polygonal, patterned ground is quite common in some regions of Mars.[48][49][50][51][46][52][53] It is commonly believed to be caused by the sublimation of ice from the ground. Sublimation is the direct change of solid ice to a gas. This is similar to what happens to dry ice on the Earth. Places on Mars that display polygonal ground may indicate where future colonists can find water ice. Patterned ground forms in a mantle layer, called latitude dependent mantle, that fell from the sky when the climate was different.[28][29][54][55]

Complex polygonal patterned ground

[edit]

Exposed ice sheets

[edit]

HiRISE images taken under the HiWish program found triangular shaped depressions in Milankovic Crater that researchers found contain vast amounts of ice that are found under only 1–2 meters of soil. These depressions contain water ice in the straight wall that faces the pole, according to the study published in the journal Science. Eight sites were found with Milankovic Crater being the only one in the northern hemisphere. Research was conducted with instruments on board the Mars Reconnaissance Orbiter (MRO).[56][57][58][59][60]

The following images are ones referred to in this study of subsurface ice sheets.[61]

These triangular depressions are similar to those in scalloped terrain. However scalloped terrain, displays a gentle equator-facing slope and is rounded. Scarps discussed here have a steep pole-facing side and have been found between 55 and 59 degrees north and south latitude[61] Scalloped topography is common in the mid-latitudes of Mars, between 45° and 60° north and south.

Scalloped topography

[edit]

Scalloped topography is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is particularly prominent in the region of Utopia Planitia[62][63] in the northern hemisphere and in the region of Peneus and Amphitrites Patera[64][65] in the southern hemisphere. Such topography consists of shallow, rimless depressions with scalloped edges, commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. A typical scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp. This topographic asymmetry is probably due to differences in insolation. Scalloped depressions are believed to form from the removal of subsurface material, possibly interstitial ice, by sublimation. This process may still be happening at present.[66]

On November 22, 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars.[67] The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior.[68][69] The volume of water ice in the region were based on measurements from the ground-penetrating radar instrument on Mars Reconnaissance Orbiter, called SHARAD. From the data obtained from SHARAD, "dielectric permittivity", or the dielectric constant was determined. The dielectric constant value was consistent with a large concentration of water ice.[70][71][72]

Images of variety of craters

[edit]

Pedestal craters

[edit]

A pedestal crater is a crater with its ejecta sitting above the surrounding terrain and thereby forming a raised platform (like a pedestal). They form when an impact crater ejects material which forms an erosion-resistant layer, thus causing the immediate area to erode more slowly than the rest of the region. Some pedestals have been accurately measured to be hundreds of meters above the surrounding area. This means that hundreds of meters of material were eroded away. The result is that both the crater and its ejecta blanket stand above the surroundings. Pedestal craters were first observed during the Mariner missions.[73][74][75][76]

Ring mold craters

[edit]

Ring mold craters are believed to be formed from asteroid impacts into ground that has an underlying layer of ice. The impact produces an rebound of the ice layer to form a "ring-mold" shape.

Another, later idea, for their formation suggests that the impacting body goes through layers of different densities. Later, erosion could have helped shape them. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.[77] [78]

Halo craters

[edit]

Boulders

[edit]

Dust devil tracks

[edit]

Dust devil tracks can be very pretty. They are caused by giant dust devils removing bright colored dust from the Martian surface; thereby exposing a dark layer. Dust devils on Mars have been photographed both from the ground and high overhead from orbit. They have even blown dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.[80] The pattern of the tracks has been shown to change every few months.[81] A study that combined data from the High Resolution Stereo Camera (HRSC) and the Mars Orbiter Camera (MOC) found that some large dust devils on Mars have a diameter of 700 metres (2,300 ft) and last at least 26 minutes.[82]

Yardangs

[edit]

Yardangs are common in some regions on Mars, especially in what is called the "Medusae Fossae Formation". This formation is found in the Amazonis quadrangle and near the equator.[83] They are formed by the action of wind on sand sized particles; hence they often point in the direction that the winds were blowing when they were formed.[84] Because they exhibit very few impact craters they are believed to be relatively young.[85]

Plumes and spiders

[edit]

At certain times in the Martian, dark eruptions of gas and dust occur. Wind often blows the material into a fan or a tail-like shape. During the winter, much frost accumulates. It freezes out directly onto the surface of the permanent polar cap, which is made of water ice covered with layers of dust and sand. The deposit begins as a layer of dusty CO2 frost. Over the winter, it recrystallizes and becomes denser. The dust and sand particles caught in the frost slowly sink. By the time temperatures rise in the spring, the frost layer has become a slab of semi-transparent ice about 3 feet thick, lying on a substrate of dark sand and dust. This dark material absorbs light and causes the ice to sublimate (turn directly into a gas). Eventually much gas accumulates and becomes pressurized. When it finds a weak spot, the gas escapes and blows out the dust. Speeds can reach 100 miles per hour.[86] Calculations show that the plumes are 20–80 meters high.[87][88] Dark channels can sometimes be seen; they are called "spiders".[89][90][91] The surface appears covered with dark spots when this process is occurring.[86][92]

Many ideas have been advanced to explain these features.[93][94][95][96][97][98] [99] These features can be seen in some of the pictures below.

Upper plains unit

[edit]

Remnants of a 50–100 meter thick mantling, called the upper plains unit, has been discovered in the mid-latitudes of Mars. First investigated in the Deuteronilus Mensae (Ismenius Lacus quadrangle) region, but it occurs in other places as well. The remnants consist of sets of dipping layers in craters and along mesas.[100] Sets of dipping layers may be of various sizes and shapes—some look like Aztec pyramids from Central America. Dipping layers are common in some regions of Mars. They may be the remains of mantle layers. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.[101]

This unit also degrades into brain terrain. Brain terrain is a region of maze-like ridges 3–5 meters high. Some ridges may consist of an ice core, so they may be sources of water for future colonists.

Some regions of the upper plains unit display large fractures and troughs with raised rims; such regions are called ribbed upper plains. Fractures are believed to have started with small cracks from stresses. Stress is suggested to initiate the fracture process since ribbed upper plains are common when debris aprons come together or near the edge of debris aprons—such sites would generate compressional stresses. Cracks exposed more surfaces, and consequently more ice in the material sublimates into the planet's thin atmosphere. Eventually, small cracks become large canyons or troughs.

Small cracks often contain small pits and chains of pits; these are thought to be from sublimation of ice in the ground.[102][103] Large areas of the Martian surface are loaded with ice that is protected by a meters thick layer of dust and other material. However, if cracks appear, a fresh surface will expose ice to the thin atmosphere.[104][105] In a short time, the ice will disappear into the cold, thin atmosphere in a process called sublimation. Dry ice behaves in a similar fashion on the Earth. On Mars sublimation has been observed when the Phoenix lander uncovered chunks of ice that disappeared in a few days.[39][106] In addition, HiRISE has seen fresh craters with ice at the bottom. After a time, HiRISE saw the ice deposit disappear.[107]

The upper plains unit is thought to have fallen from the sky. It drapes various surfaces, as if it fell evenly. As is the case for other mantle deposits, the upper plains unit has layers, is fine-grained, and is ice-rich. It is widespread; it does not seem to have a point source. The surface appearance of some regions of Mars is due to how this unit has degraded. It is a major cause of the surface appearance of lobate debris aprons.[103] The layering of the upper plains mantling unit and other mantling units are believed to be caused by major changes in the planet's climate. Models predict that the obliquity or tilt of the rotational axis has varied from its present 25 degrees to maybe over 80 degrees over geological time. Periods of high tilt will cause the ice in the polar caps to be redistributed and change the amount of dust in the atmosphere.[108][109][110]

Linear ridge networks

[edit]

Linear ridge networks are found in various places on Mars in and around craters.[111] Ridges often appear as mostly straight segments that intersect in a lattice-like manner. They are hundreds of meters long, tens of meters high, and several meters wide. It is thought that impacts created fractures in the surface, these fractures later acted as channels for fluids. Fluids cemented the structures. With the passage of time, surrounding material was eroded away, thereby leaving hard ridges behind. Since the ridges occur in locations with clay, these formations could serve as a marker for clay which requires water for its formation. Water here could have supported life.[112][113][114]

Fractured ground

[edit]

Some places on Mars break up with large fractures that created a terrain with mesas and valleys. Some of these can be quite pretty.

Mesas

[edit]

Mesas formed by ground collapse

[edit]

Volcanoes under ice

[edit]

There is evidence that volcanoes sometimes erupt under ice, as they do on Earth at times. What seems to happen it that much ice melts, the water escapes, and then the surface cracks and collapses. These exhibit concentric fractures and large pieces of ground that seemed to have been pulled apart.[115] Sites like this may have recently had held liquid water, hence they may be fruitful places to search for evidence of life.[116][117]

Fractures forming blocks

[edit]

In places large fractures break up surfaces. Sometimes straight edges are formed and large cubes are created by the fractures.

Lava flows

[edit]

Rootless cones

[edit]

So-called "rootless cones" are caused by explosions of lava with ground ice under the flow.[118][119] The ice melts and turns into a vapor that expands in an explosion that produces a cone or ring. Featureslike these are found in Iceland, when lavas cover water-saturated substrates.[120][118][121]

Mud volcanoes

[edit]

Some features look like volcanoes. Some of them may be mud volcanoes where pressurized mud is forced upward forming cones. These features may be places to look for life as they bring to the surface possible life that has been protected from radiation.

Hellas floor features

[edit]

Strange terrain was discovered on parts of the floor of Hellas Planitia. Scientists are not sure of how it formed.

Exhumed craters

[edit]

Exhumed craters seem to be in the process of being uncovered.[122] It is believed that they formed, were covered over, and now are being exhumed as material is being eroded. When a crater forms, it will destroy what is under it. In the example below, only part of the crater is visible. if the crater came after the layered feature, it would have removed part of the feature and we would see the entire crater.

How to suggest image

[edit]

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick an exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

See also

[edit]

References

[edit]
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Further reading

[edit]
  • Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
  • Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.
  • Grotzinger, J. and R. Milliken (eds.). 2012. Sedimentary Geology of Mars. SEPM.
[edit]
  • McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.