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{{short description|Confirmed super-Earth extrasolar planet}}
{{short description|Super-Earth orbiting Kepler-69}}


{{Infobox planet
{{Infobox planet
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| discoverer = ''[[Kepler (spacecraft)|Kepler]]'' spacecraft
| discoverer = ''[[Kepler (spacecraft)|Kepler]]'' spacecraft
| discovered = 18 April 2013
| discovered = 18 April 2013
| discovery_method = [[Methods of detecting extrasolar planets#Transit method|Transit]] ([[Kepler Mission#Objectives and methods|Kepler Mission Method]])
| discovery_method = [[Methods of detecting extrasolar planets#Transit photometry|Transit]] ([[Kepler Mission#Objectives and methods|''Kepler'' Mission Method]])
<!-- DESIGNATIONS -->
<!-- DESIGNATIONS -->
<!-- ORBITAL -->
<!-- ORBITAL -->
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| mean_radius = {{val|1.71|0.34|0.23}}<ref name="arXiv-20130417" /> {{Earth radius|link=y}}
| mean_radius = {{val|1.71|0.34|0.23}}<ref name="arXiv-20130417" /> {{Earth radius|link=y}}
| mass = 2.14 {{Earth mass|link=y}}<ref name="supervenus"/>
| mass = 2.14 {{Earth mass|link=y}}<ref name="supervenus"/>
| density = 2.36 [[grams|g]] [[cubic centimeter|cm<sup>–3</sup>]]<ref name="supervenus"/>
| density = 2.36 [[Gram|g]] [[cubic centimeter|cm<sup>–3</sup>]]<ref name="supervenus"/>
| surface_grav = 0.73 [[g-force|g]]<ref name="supervenus"/>
| surface_grav = 0.73 [[g-force|g]]<ref name="supervenus"/>
| single_temperature = {{convert|548|K|C F}}<ref group="note">Based on improved models of Kepler-69c after it was found to be uninhabitable.</ref>
| single_temperature = [[Planetary equilibrium temperature|''T''<sub>eq</sub>]]: {{convert|325|K|C F}}<br />''Surface'': {{convert|548|K|C F}}<ref group="nb">Based on improved models of Kepler-69c after it was found to be uninhabitable.</ref>
<!-- ATMOSPHERE -->
<!-- ATMOSPHERE -->
<!-- NOTES -->
<!-- NOTES -->
}}
}}
'''Kepler-69c'''<ref name="arXiv-20130417">{{cite journal |last=Barclay|first=Thomas |display-authors=etal |year=2013 |title=A super-Earth-sized planet orbiting in or near the habitable zone around Sun-like star |journal=The Astrophysical Journal |volume=768 |issue=2 |pages=101 |arxiv=1304.4941 |doi=10.1088/0004-637X/768/2/101 |bibcode=2013ApJ...768..101B}}</ref><ref name="NASA-20130418">{{cite web |last1=Johnson |first1=Michele|last2=Harrington |first2=J.D. |title=NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date|url=http://www.nasa.gov/mission_pages/kepler/news/kepler-62-kepler-69.html |date=18 April 2013 |work=[[NASA]]|access-date=18 April 2013 }}</ref><ref name="NYT-20130418">{{cite news |last=Overbye |first=Dennis |title=2 Good Places to Live, 1,200 Light-Years Away|url=https://www.nytimes.com/2013/04/19/science/space/2-new-planets-are-most-earth-like-yet-scientists-say.html|date=18 April 2013 |newspaper=[[New York Times]] |access-date=18 April 2013 }}</ref> (also known by its [[Kepler Object of Interest]] designation ''KOI-172.02'')<ref name="Caltech-KOI-172.02" /><ref name="Johnston-20111002" /> is a confirmed [[super-Earth]] [[extrasolar planet]], likely rocky, orbiting the [[Sun]]-like star [[Kepler-69]], the outermore of two such planets discovered by [[NASA]]'s ''[[Kepler (spacecraft)|Kepler]]'' spacecraft. It is located about 2,430 [[light-year]]s (746 [[parsec]]s) from [[Earth]].
'''Kepler-69c'''<ref name="arXiv-20130417">{{cite journal |last=Barclay|first=Thomas |display-authors=etal |year=2013 |title=A super-Earth-sized planet orbiting in or near the habitable zone around Sun-like star |journal=The Astrophysical Journal |volume=768 |issue=2 |page=101 |arxiv=1304.4941 |doi=10.1088/0004-637X/768/2/101 |bibcode=2013ApJ...768..101B|s2cid=51490784 }}</ref><ref name="NASA-20130418">{{cite web |last1=Johnson |first1=Michele|last2=Harrington |first2=J.D. |title=NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date|url=http://www.nasa.gov/mission_pages/kepler/news/kepler-62-kepler-69.html |date=18 April 2013 |work=[[NASA]]|access-date=18 April 2013 }}</ref><ref name="NYT-20130418">{{cite news |last=Overbye |first=Dennis |title=2 Good Places to Live, 1,200 Light-Years Away|url=https://www.nytimes.com/2013/04/19/science/space/2-new-planets-are-most-earth-like-yet-scientists-say.html|date=18 April 2013 |newspaper=[[New York Times]] |access-date=18 April 2013 }}</ref> (also known by its [[Kepler Object of Interest]] designation ''KOI-172.02'')<ref name="Caltech-KOI-172.02" /><ref name="Johnston-20111002" /> is a confirmed [[super-Earth]] [[exoplanet]], likely rocky, orbiting the [[Sun]]-like star [[Kepler-69]], the outermore of two such planets discovered by [[NASA]]'s ''[[Kepler (spacecraft)|Kepler]]'' spacecraft. It is located about 2,430 [[light-year]]s (746 [[parsec]]s) from [[Earth]].

Kepler-69c orbits its star at a distance of {{convert |0.64|AU|abbr=on}} from its host star with an orbital period of roughly 242.46 [[days]], has a mass at least 2.14 times that of Earth, and has a radius of around 1.7 times that of Earth. Initial findings found that it could possibly be habitable, however updated analysis shows that Kepler-69c resides outside of the inner edge of the habitable zone, and thus is highly likely to resemble the planet [[Venus]] with temperatures and conditions far too hot to sustain any life, making it uninhabitable.<ref name="supervenus"/>

The [[Discovery (observation)|discovery]] of the exoplanet was announced in April 2013 by [[NASA]] as part of the ''Kepler'' spacecraft data release.<ref name="arXiv-20130417"/> The exoplanet was found by using the [[transit method]], in which the dimming effect that a planet causes as it crosses in front of its star is measured.


== Physical characteristics ==
== Physical characteristics ==
=== Mass, radius and temperature ===
=== Mass, radius and temperature ===
Kepler-69c is a [[super-Earth]], an exoplanet that has a radius and mass larger than Earth, but smaller than that of the ice giants [[Uranus]] and [[Neptune]]. It has a surface temperature of {{convert|548|K|C F}}. It has an estimated mass of around 6 {{Earth mass}} and a radius of 1.71 {{Earth radius}}. These characteristics make it an analog to [[Venus]], but more massive, so it is called a "[[super-Venus]]".
Kepler-69c is a [[super-Earth]], an exoplanet that has a radius and mass larger than Earth, but smaller than that of the ice giants [[Uranus]] and [[Neptune]]. It has an estimated equilibrium temperature of {{convert|325|K|C F}}, but likely has a far hotter surface temperature of {{convert|548|K|C F}}. It has an estimated mass of around 2.14 {{Earth mass}} and a radius of 1.71 {{Earth radius}}.<ref name="supervenus"/><ref name="arXiv-20130417"/> These characteristics make it an analog to the planet [[Venus]], but more massive, so it is called a "[[super-Venus]]".<ref name="supervenus"/>


=== Host star ===
=== Host star ===
{{main|Kepler-69}}
{{main|Kepler-69}}
The planet orbits a ([[Stellar classification#Class G|G-type]]) star named [[Kepler-69]], orbited by a total of two planets. The star has a mass of 0.81 {{Solar mass}} and a radius of 0.93 {{Solar radius}}. It has a surface temperatures of 5638 [[Kelvin|K]] and has an estimated age of around 400 million years, meaning it has probably finished planet formation. In comparison, the Sun is about 4.6 billion years old<ref>{{cite web |url=http://www.universetoday.com/18237/how-old-is-the-sun/ |title=How Old is the Sun? |author=Fraser Cain |date=16 September 2008 |publisher=[[Universe Today]] |access-date=19 February 2011}}</ref> and has a surface temperature of 5778 K.<ref>{{cite web |url=http://www.universetoday.com/18092/temperature-of-the-sun/ |title=Temperature of the Sun |author=Fraser Cain |date=September 15, 2008 |publisher=Universe Today |access-date=19 February 2011}}</ref>
The planet orbits a ([[Stellar classification#Class G|G-type]]) star named [[Kepler-69]], orbited by a total of two planets. The star has a mass of 0.81 {{Solar mass}} and a radius of 0.93 {{Solar radius}}.<ref name="arXiv-20130417" /> It has a surface temperature of 5638 [[Kelvin|K]] and has an estimated age of around 9.8 billion years,<ref name="arXiv-20130417" /> meaning it is probably nearing the end of its lifetime. In comparison, the Sun is about 4.6 billion years old<ref>{{cite web |url=http://www.universetoday.com/18237/how-old-is-the-sun/ |title=How Old is the Sun? |author=Fraser Cain |date=16 September 2008 |publisher=[[Universe Today]] |access-date=19 February 2011}}</ref> and has a surface temperature of 5778 K.<ref>{{cite web |url=http://www.universetoday.com/18092/temperature-of-the-sun/ |title=Temperature of the Sun |author=Fraser Cain |date=September 15, 2008 |publisher=Universe Today |access-date=19 February 2011}}</ref>


The star's [[apparent magnitude]], or how bright it appears from Earth's perspective, is 13.7.<ref name="arXiv-20130417" /> Therefore, Kepler-69 is too dim to be seen with the naked eye.
The star's [[apparent magnitude]], or how bright it appears from Earth's perspective, is 13.7.<ref name="arXiv-20130417" /> Therefore, Kepler-69 is too dim to be seen with the naked eye.
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=== Orbit ===
=== Orbit ===


Kepler-69c orbits its host star with about 80% of the Sun's luminosity every 242 days at a distance of 0.64 times that of Earth. This is very similar to that of [[Venus]]'s orbital period and distance in the [[Solar System]].
Kepler-69c orbits its host star every 242 days at a distance of 0.64 times that of Earth.<ref name="arXiv-20130417" /> This is very similar to that of [[Venus]]'s orbital period and distance in the [[Solar System]].


==Proposed habitability==
==Proposed habitability==
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The exoplanet, along with the exoplanets [[Kepler-62e]] and [[Kepler-62f]], were announced in the media as being located within the star's "[[habitable zone]]", a region where [[liquid water]] could exist on the surface of the [[planet]]. It was described as being one of the most [[Earth analog|Earth-like planets]], in terms of size and [[Habitable zone|temperature]] yet found and, according to the scientists, a "prime candidate to host [[extraterrestrial life|alien life]]".<ref name="Space-20130109" />
The exoplanet, along with the exoplanets [[Kepler-62e]] and [[Kepler-62f]], were announced in the media as being located within the star's "[[habitable zone]]", a region where [[liquid water]] could exist on the surface of the [[planet]]. It was described as being one of the most [[Earth analog|Earth-like planets]], in terms of size and [[Habitable zone|temperature]] yet found and, according to the scientists, a "prime candidate to host [[extraterrestrial life|alien life]]".<ref name="Space-20130109" />


Due to uncertainties in the stellar parameters, the error bars on the value of the incident flux on this planet are quite large, at 1.91{{±|0.43|0.56}} times the level of Earth. Using the nominal parameters, the planet is too close to the star to be habitable, though the uncertainties allow for the possibility that it may actually lie in the innermost region of the habitable zone and be a desert planet,<ref>{{cite arXiv|author1=L. Kaltenegger |author-link1=Lisa Kaltenegger |author2=D. Sasselov |author3=S. Rugheimer |author-link3=Sarah Rugheimer|title=Water Planets in the Habitable Zone: Atmospheric Chemistry, Observable Features, and the case of Kepler-62e and -62f|eprint=1304.5058v1|class=astro-ph.EP|date=2013}}</ref> however even with the lowest error bar measurement, a stellar flux of 1.35 ''S''<sub>⊕</sub> would still be high enough to boil away any oceans. A more recent analysis has shown that the planet is likely more analogous to Venus, which is known to be one of the most inhospitable places to life in the Solar System, and thus highly unlikely to be habitable to such organisms.<ref name="supervenus" />
Due to uncertainties in the stellar parameters, the error bars on the value of the incident flux on this planet are quite large, at 1.91{{±|0.43|0.56}} times the level of Earth. Using the nominal parameters, the planet is too close to the star to be habitable, though the uncertainties allow for the possibility that it may actually lie in the innermost region of the habitable zone and be a desert planet,<ref>{{cite arXiv|author1=L. Kaltenegger |author-link1=Lisa Kaltenegger |author2=D. Sasselov |author3=S. Rugheimer |author-link3=Sarah Rugheimer|title=Water Planets in the Habitable Zone: Atmospheric Chemistry, Observable Features, and the case of Kepler-62e and -62f|eprint=1304.5058v1|class=astro-ph.EP|date=2013}}</ref> however even with the lowest error bar measurement, a stellar flux of 1.35 ''S''<sub>🜨</sub> would still be high enough to boil away any oceans. A more recent analysis has shown that the planet is likely more analogous to Venus, which is known to be one of the most inhospitable places to life in the Solar System, and thus highly unlikely to be habitable to such organisms.<ref name="supervenus" />

⚫
[[File:Kepler-69c-_Super-Venus.jpg|thumb|right|250px|Artist’s impression of Kepler-69c as a “super-Venus” exoplanet.]]


⚫
[[File:Kepler-69c-_Super-Venus.jpg|thumb|right|250px|Artist's impression of Kepler-69c as a "super-Venus" exoplanet.]]
The planet would be inhospitable because of a [[runaway greenhouse effect]] on its surface. Any oceans on its surface would've boiled away due to the high stellar flux, and as this occurred, the temperature would've risen to around {{convert|322|K|C F}}. The [[water vapor]] would've accumulated in the atmosphere to the point where the surface temperature would rise to around {{convert|500|K|C F}} as the planet would've been overwhelmed by water vapor (it is a powerful greenhouse gas).<ref>http://csep10.phys.utk.edu/astr161/lect/venus/greenhouse.html</ref> Little amounts of [[carbon dioxide]] would've been present, as Kepler-69c was probably an [[ocean planet]] (with little to no landmasses) very shortly after its star was born into the [[main sequence]], before the stellar flux increased to its estimated present value. The surface pressure would've also increased to around 100 times Earth's surface pressure (100 [[kilopascal]]s, 100 [[atmospheric pressure|atm.]]) because of the amount of water vapor in the atmosphere.


==Discovery==
==Discovery==
In 2009, [[NASA]]'s [[Kepler (spacecraft)|Kepler]] spacecraft was observing stars with its [[photometer]], an instrument it uses to detect [[transit method|transit]] events, in which a planet crosses in front of and dims its host star for a brief and roughly regular period of time. In this last test, Kepler observed {{val|50,000}} stars in the [[Kepler Input Catalog]], including Kepler-69; the preliminary light curves were sent to the Kepler science team for analysis, who chose obvious planetary companions from the bunch for follow-up at observatories. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. After observing the respective transits, which for Kepler-69c occurred roughly every 242 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic 242-day transits. The discovery, along with the planetary system of the star [[Kepler-62]] were announced on April 18, 2013.<ref name="arXiv-20130417"/>
In 2009, [[NASA]]'s [[Kepler (spacecraft)|Kepler]] spacecraft was observing stars with its [[photometer]], an instrument it uses to detect [[transit method|transit]] events, in which a planet crosses in front of and dims its host star for a brief and roughly regular period of time. In this last test, Kepler observed {{val|50,000}} stars in the [[Kepler Input Catalog]], including Kepler-69; the preliminary light curves were sent to the Kepler science team for analysis, who chose obvious planetary companions from the bunch for follow-up at observatories. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. After observing the respective transits, which for Kepler-69c occurred roughly every 242 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic 242-day transits. The discovery, along with the planetary system of the star [[Kepler-62]] were announced on April 18, 2013.<ref name="arXiv-20130417"/>


On 9 May 2013, a congressional hearing by two [[U.S. House of Representatives]] [[United States congressional committee|subcommittees]] discussed "Exoplanet Discoveries: Have We Found Other Earths?," prompted by the discovery of [[exoplanet]] ''Kepler-69c'', along with [[Kepler-62e]] and [[Kepler-62f]]. A related special issue of the journal [[Science (journal)|''Science'']], published earlier, described the discovery of the exoplanets.<ref name="SCI-20130503">{{cite web |authors=Staff |title=Special Issue: Exoplanets |url=http://www.sciencemag.org/site/special/exoplanets/ |date=3 May 2013 |work=[[Science (journal)|Science]] |access-date=18 May 2013 }}</ref>
On 9 May 2013, a congressional hearing by two [[U.S. House of Representatives]] [[United States congressional committee|subcommittees]] discussed "Exoplanet Discoveries: Have We Found Other Earths?," prompted by the discovery of [[exoplanet]] ''Kepler-69c'', along with [[Kepler-62e]] and [[Kepler-62f]]. A related special issue of the journal [[Science (journal)|''Science'']], published earlier, described the discovery of the exoplanets.<ref name="SCI-20130503">{{cite journal |title=Special Issue: Exoplanets |url=https://www.science.org/toc/science/340/6132 |date=3 May 2013 |journal=[[Science (journal)|Science]] |volume=340 |issue=6132 |access-date=18 May 2013}}</ref>


{| class="wikitable" style="margin:0.5em auto; width:600px;"
{| class="wikitable" style="margin:0.5em auto; width:600px;"
! colspan=2 | [[Exoplanet|Notable Exoplanets]] – [[Kepler (spacecraft)|Kepler Space Telescope]]
! colspan=2 | [[Exoplanet|Notable Exoplanets]] – [[Kepler (spacecraft)|Kepler Space Telescope]]
|- valign=top style="font-size:88%; text-align:center;"
|- valign=top style="font-size:88%; text-align:center;"
| [[File:Relative sizes of all of the habitable-zone planets discovered to date alongside Earth.jpg|301px]] Comparison of the sizes of planets Kepler-69c, [[Kepler-62e]], [[Kepler-62f]], and the [[Earth]].<br>Exoplanets are artists' impressions.
| [[File:Relative sizes of all of the habitable-zone planets discovered to date alongside Earth.jpg|301px]] Comparison of the sizes of planets Kepler-69c, [[Kepler-62e]], [[Kepler-62f]], and the [[Earth]].<br />Exoplanets are artists' impressions.
| [[File:LombergA1024.jpg|299px]] The ''[[Kepler (spacecraft)|Kepler Space Telescope]]'' search volume, in the context of the [[Milky Way Galaxy]].
| [[File:LombergA1024.jpg|299px]] The ''[[Kepler (spacecraft)|Kepler Space Telescope]]'' search volume, in the context of the [[Milky Way Galaxy]].
|}
|}
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==See also==
==See also==
* [[List of potentially habitable exoplanets]]
* [[List of potentially habitable exoplanets]]
*[[Desert planet]]
*[[Venus]]


==References==
==References==
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<ref name="Space-20130109">{{cite web |last=Moskowitz|first=Clara |title=Most Earth-Like Alien Planet Possibly Found|url=http://www.space.com/19201-most-earth-like-alien-planet.html |date=January 9, 2013 |work=[[Space.com]]|access-date=January 9, 2013 }}</ref>
<ref name="Space-20130109">{{cite web |last=Moskowitz|first=Clara |title=Most Earth-Like Alien Planet Possibly Found|url=http://www.space.com/19201-most-earth-like-alien-planet.html |date=January 9, 2013 |work=[[Space.com]]|access-date=January 9, 2013 }}</ref>


<ref name="supervenus">{{cite journal |last=Kane |first=Stephen |display-authors=etal |title=A Potential Super-Venus in the Kepler-69 System |journal=The Astrophysical Journal Letters |volume=770 |issue=2 |page=L20 |arxiv=1305.2933 |doi= 10.1088/2041-8205/770/2/L20 |bibcode=2013ApJ...770L..20K|year=2013 }}</ref>
<ref name="supervenus">{{cite journal |last=Kane |first=Stephen |display-authors=etal |title=A Potential Super-Venus in the Kepler-69 System |journal=The Astrophysical Journal Letters |volume=770 |issue=2 |page=L20 |arxiv=1305.2933 |doi= 10.1088/2041-8205/770/2/L20 |bibcode=2013ApJ...770L..20K|year=2013 |s2cid=9808447 }}</ref>


}}
}}


==Notes==
==Notes==
{{reflist|group=note}}
{{reflist|group=nb}}


==External links==
==External links==
* [https://www.nasa.gov/mission_pages/kepler/overview/index.html NASA – Mission overview].
* [https://www.nasa.gov/mission_pages/kepler/overview/index.html NASA – Mission overview].
* [http://kepler.nasa.gov/Mission/discoveries/ Kepler – Discoveries – Summary Table] – [[NASA]].
* [https://web.archive.org/web/20100527104316/http://kepler.nasa.gov/Mission/discoveries/ Kepler – Discoveries – Summary Table] – [[NASA]].
* [http://hzgallery.org The Habitable Zone Gallery]
* [https://web.archive.org/web/20110925025908/http://www.hzgallery.org/ The Habitable Zone Gallery]
* [http://www.nasa.gov/mission_pages/kepler/news/kepler-62-kepler-69.html Kepler – Discovery of New Planetary Systems (2013)].
* [http://www.nasa.gov/mission_pages/kepler/news/kepler-62-kepler-69.html Kepler – Discovery of New Planetary Systems (2013)].
* [https://www.nytimes.com/interactive/science/space/keplers-tally-of-planets.html Kepler – Tally of Planets/interactive (2013)] – [[NYT]].
* [https://www.nytimes.com/interactive/science/space/keplers-tally-of-planets.html Kepler – Tally of Planets/interactive (2013)] – [[NYT]].
* [https://www.youtube.com/watch?v=P8PJt-R5NxI Video (02:27) – NASA Finds Three New Planets in "Habitable Zone" (04/18/2013).]
* [https://www.youtube.com/watch?v=P8PJt-R5NxI Video (02:27) – NASA Finds Three New Planets in "Habitable Zone" (04/18/2013).]
* [http://archive.stsci.edu/kepler/koi/search.php Kepler KOI Data Search].
* [http://archive.stsci.edu/kepler/koi/search.php Kepler KOI Data Search].
* [http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=KOI-172 KOI-172.02 Data at Exoplanet Archive/[[Caltech]]]
* [http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=KOI-172 KOI-172.02 Data at Exoplanet Archive] [[Caltech]]
* [https://web.archive.org/web/20131102182321/http://www.cthreepo.com/stars/viewK.php?KIC=8692861 KOI-172 Star on Star Finder/KPGraham]
* [https://web.archive.org/web/20131102182321/http://www.cthreepo.com/stars/viewK.php?KIC=8692861 KOI-172 Star on Star Finder/KPGraham]
* [http://www.johnstonsarchive.net/astro/extrasolarplanets.html Extrasolar Planets&nbsp;– Data/JohnstonArchive]
* [http://www.johnstonsarchive.net/astro/extrasolarplanets.html Extrasolar Planets&nbsp;– Data/JohnstonArchive]
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[[Category:Exoplanets discovered by the Kepler space telescope|69c]]
[[Category:Exoplanets discovered by the Kepler space telescope|69c]]
[[Category:Transiting exoplanets]]
[[Category:Transiting exoplanets]]
[[Category:Super-Earths]]

Latest revision as of 03:44, 20 October 2024

Kepler-69c
Artist's impression of the Kepler-69 system (sizes to scale) compared to the planets of the inner Solar System with their respective habitable zones.
Discovery
Discovered byKepler spacecraft
Discovery date18 April 2013
Transit (Kepler Mission Method)
Orbital characteristics
0.64+0.15
−0.11[1][2] AU
Eccentricity0.14+0.18
−0.1[1][2]
242.4613 ± 0.006[1][3][2] d
Inclination89.85+0.03
−0.08[1][2]
StarKepler-69
Physical characteristics
1.71+0.34
−0.23[3] R🜨
Mass2.14 ME[4]
Mean density
2.36 g cm–3[4]
0.73 g[4]
TemperatureTeq: 325 K (52 °C; 125 °F)
Surface: 548 K (275 °C; 527 °F)[nb 1]

Kepler-69c[3][5][6] (also known by its Kepler Object of Interest designation KOI-172.02)[2][7] is a confirmed super-Earth exoplanet, likely rocky, orbiting the Sun-like star Kepler-69, the outermore of two such planets discovered by NASA's Kepler spacecraft. It is located about 2,430 light-years (746 parsecs) from Earth.

Kepler-69c orbits its star at a distance of 0.64 AU (96,000,000 km; 59,000,000 mi) from its host star with an orbital period of roughly 242.46 days, has a mass at least 2.14 times that of Earth, and has a radius of around 1.7 times that of Earth. Initial findings found that it could possibly be habitable, however updated analysis shows that Kepler-69c resides outside of the inner edge of the habitable zone, and thus is highly likely to resemble the planet Venus with temperatures and conditions far too hot to sustain any life, making it uninhabitable.[4]

The discovery of the exoplanet was announced in April 2013 by NASA as part of the Kepler spacecraft data release.[3] The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured.

Physical characteristics

[edit]

Mass, radius and temperature

[edit]

Kepler-69c is a super-Earth, an exoplanet that has a radius and mass larger than Earth, but smaller than that of the ice giants Uranus and Neptune. It has an estimated equilibrium temperature of 325 K (52 °C; 125 °F), but likely has a far hotter surface temperature of 548 K (275 °C; 527 °F). It has an estimated mass of around 2.14 ME and a radius of 1.71 R🜨.[4][3] These characteristics make it an analog to the planet Venus, but more massive, so it is called a "super-Venus".[4]

Host star

[edit]
Main article: Kepler-69

The planet orbits a (G-type) star named Kepler-69, orbited by a total of two planets. The star has a mass of 0.81 M☉ and a radius of 0.93 R☉.[3] It has a surface temperature of 5638 K and has an estimated age of around 9.8 billion years,[3] meaning it is probably nearing the end of its lifetime. In comparison, the Sun is about 4.6 billion years old[8] and has a surface temperature of 5778 K.[9]

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 13.7.[3] Therefore, Kepler-69 is too dim to be seen with the naked eye.

Orbit

[edit]

Kepler-69c orbits its host star every 242 days at a distance of 0.64 times that of Earth.[3] This is very similar to that of Venus's orbital period and distance in the Solar System.

Proposed habitability

[edit]
Artist's conception of a comparison between a Venus-like and Earth-like planet. Based on recent research, Kepler-69c is more likely a super-Venus, analogous to Venus but more massive, and completely uninhabitable.

The exoplanet, along with the exoplanets Kepler-62e and Kepler-62f, were announced in the media as being located within the star's "habitable zone", a region where liquid water could exist on the surface of the planet. It was described as being one of the most Earth-like planets, in terms of size and temperature yet found and, according to the scientists, a "prime candidate to host alien life".[10]

Due to uncertainties in the stellar parameters, the error bars on the value of the incident flux on this planet are quite large, at 1.91+0.43
−0.56 times the level of Earth. Using the nominal parameters, the planet is too close to the star to be habitable, though the uncertainties allow for the possibility that it may actually lie in the innermost region of the habitable zone and be a desert planet,[11] however even with the lowest error bar measurement, a stellar flux of 1.35 S🜨 would still be high enough to boil away any oceans. A more recent analysis has shown that the planet is likely more analogous to Venus, which is known to be one of the most inhospitable places to life in the Solar System, and thus highly unlikely to be habitable to such organisms.[4]

Artist's impression of Kepler-69c as a "super-Venus" exoplanet.

Discovery

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In 2009, NASA's Kepler spacecraft was observing stars with its photometer, an instrument it uses to detect transit events, in which a planet crosses in front of and dims its host star for a brief and roughly regular period of time. In this last test, Kepler observed 50000 stars in the Kepler Input Catalog, including Kepler-69; the preliminary light curves were sent to the Kepler science team for analysis, who chose obvious planetary companions from the bunch for follow-up at observatories. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. After observing the respective transits, which for Kepler-69c occurred roughly every 242 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic 242-day transits. The discovery, along with the planetary system of the star Kepler-62 were announced on April 18, 2013.[3]

On 9 May 2013, a congressional hearing by two U.S. House of Representatives subcommittees discussed "Exoplanet Discoveries: Have We Found Other Earths?," prompted by the discovery of exoplanet Kepler-69c, along with Kepler-62e and Kepler-62f. A related special issue of the journal Science, published earlier, described the discovery of the exoplanets.[12]

Notable Exoplanets – Kepler Space Telescope
Comparison of the sizes of planets Kepler-69c, Kepler-62e, Kepler-62f, and the Earth.
Exoplanets are artists' impressions. 		The Kepler Space Telescope search volume, in the context of the Milky Way Galaxy.

See also

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References

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  1. ^ a b c d Staff (January 7, 2013). "Kepler KOI Search Results for KOI-172.02". Space Telescope Science Institute. Retrieved January 11, 2013.
  2. ^ a b c d e Staff. "NASA Exoplanet Archive -KOI-172.02". Caltech. Retrieved January 11, 2013.
  3. ^ a b c d e f g h i j Barclay, Thomas; et al. (2013). "A super-Earth-sized planet orbiting in or near the habitable zone around Sun-like star". The Astrophysical Journal. 768 (2): 101. arXiv:1304.4941. Bibcode:2013ApJ...768..101B. doi:10.1088/0004-637X/768/2/101. S2CID 51490784.
  4. ^ a b c d e f g Kane, Stephen; et al. (2013). "A Potential Super-Venus in the Kepler-69 System". The Astrophysical Journal Letters. 770 (2): L20. arXiv:1305.2933. Bibcode:2013ApJ...770L..20K. doi:10.1088/2041-8205/770/2/L20. S2CID 9808447.
  5. ^ Johnson, Michele; Harrington, J.D. (18 April 2013). "NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date". NASA. Retrieved 18 April 2013.
  6. ^ Overbye, Dennis (18 April 2013). "2 Good Places to Live, 1,200 Light-Years Away". New York Times. Retrieved 18 April 2013.
  7. ^ Johnston, Wm. Robert (October 2, 2011). "List of Extrasolar Planets". JohnstonArchive.com. Retrieved January 11, 2013.
  8. ^ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
  9. ^ Fraser Cain (September 15, 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
  10. ^ Moskowitz, Clara (January 9, 2013). "Most Earth-Like Alien Planet Possibly Found". Space.com. Retrieved January 9, 2013.
  11. ^ L. Kaltenegger; D. Sasselov; S. Rugheimer (2013). "Water Planets in the Habitable Zone: Atmospheric Chemistry, Observable Features, and the case of Kepler-62e and -62f". arXiv:1304.5058v1 [astro-ph.EP].
  12. ^ "Special Issue: Exoplanets". Science. 340 (6132). 3 May 2013. Retrieved 18 May 2013.

Notes

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  1. ^ Based on improved models of Kepler-69c after it was found to be uninhabitable.
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