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| image_size =
| image_size =
| caption =
| caption =
| discovery_ref = &thinsp;<ref name="jpldata" />
| discovery_ref = &thinsp;<ref name="MPC-object" />
| discoverer = [[Walter Baade|W. Baade]]
| discoverer = [[Walter Baade|W. Baade]]
| discovery_site = [[Bergedorf Observatory|Bergedorf Obs.]]
| discovery_site = [[Bergedorf Observatory|Bergedorf Obs.]]
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| pronounced = {{IPAc-en|h|ᵻ|ˈ|d|æ|l|ɡ|oʊ}} {{Respell|hi|DAL|goh}}
| pronounced = {{IPAc-en|h|ᵻ|ˈ|d|æ|l|ɡ|oʊ}} {{Respell|hi|DAL|goh}}
| named_after = {{nowrap|[[Miguel Hidalgo y Costilla]]}}<br />{{small|(Mexican revolutionary)}}<ref name="springer" />
| named_after = {{nowrap|[[Miguel Hidalgo y Costilla]]}}<br />{{small|(Mexican revolutionary)}}<ref name="springer" />
|mp_category = [[Centaur (minor planet)|centaur]]&nbsp;<ref name="jpldata" />{{·}}[[main-belt]]&thinsp;<ref name="MPC-object" /><br />[[Distant minor planet|distant]]<br />[[Jupiter-crosser]]<br />[[Saturn-crosser]]
|mp_category = [[Centaur (minor planet)|centaur]]&nbsp;<ref name="jpldata" />{{·}}[[main-belt]]&thinsp;<ref name="MPC-object" /><br />[[Unusual minor planet|unusual]]&thinsp;<ref name="MPC-Other-Unusual" />
| orbit_ref = &thinsp;<ref name="jpldata" />
| orbit_ref = &thinsp;<ref name="jpldata" />
| epoch = 4 September 2017 ([[Julian day|JD]] 2458000.5)
| epoch = 27 April 2019 ([[Julian day|JD]] 2458600.5)
| uncertainty = 0
| uncertainty = 0
| observation_arc = 96.59 yr (35,278 days)
| observation_arc = 97.97 [[Julian year (astronomy)|yr]] (35,784 d)
| aphelion = 9.5366 [[Astronomical unit|AU]]
| aphelion = 9.5345 [[Astronomical unit|AU]]
| perihelion = 1.9470 AU
| perihelion = 1.9474 AU
| semimajor = 5.7418 AU
| semimajor = 5.7410 AU
| eccentricity = 0.6609
| eccentricity = 0.6608
| period = 13.76 [[Julian year (astronomy)|yr]] (5,025 days)
| period = 13.76 yr (5,024 d)
| mean_anomaly = 330.09[[Degree (angle)|°]]
| mean_anomaly = 13.078[[Degree (angle)|°]]
| mean_motion = {{Deg2DMS|0.0716|sup=ms}} / day
| mean_motion = {{Deg2DMS|0.0717|sup=ms}} / day
| inclination = 42.524°
| inclination = 42.521°
| asc_node = 21.422°
| asc_node = 21.420°
| arg_peri = 56.682°
| arg_peri = 56.651°
| jupiter_moid = 0.3286 AU
| jupiter_moid = 0.3285 AU
| tisserand = 2.0690
| dimensions = 38 km {{small|(Gehrels)}}<ref name="jpldata" /><br />44.62 km {{small|(derived)}}<ref name="lcdb" /><br />{{val|52.45|3.60}} km<ref name="AKARI" /><br />{{val|61.4|12.7}} km<ref name="Licandro-2016a" />
| mean_diameter = {{val|38|ul=km}} {{small|(Gehrels)}}<ref name="jpldata" /><br />{{val|52.45|3.60|u=km}}<ref name="AKARI" /><br />{{val|61.4|12.7|u=km}}<ref name="Licandro-2016a" />
| mass =
| mass =
| rotation = {{val|10.063|0.0003}} [[Hour|h]]<ref name="lcdb" />
| rotation = {{val|10.063|0.0003|ul=h}}<ref name="lcdb" />{{efn|name=lightcurve-plot-Koff-2011}}
| spectral_type = [[Tholen classification|Tholen]] {{=}} [[D-type asteroid|D]]&thinsp;<ref name="jpldata" /><ref name="lcdb" />
| spectral_type = [[Tholen classification|Tholen]] {{=}} [[D-type asteroid|D]]&thinsp;<ref name="jpldata" /><ref name="Ferret" />
| albedo = 0.057 {{small|(estimate)}}<ref name="lcdb" /><br />0.06 {{small|(unverified)}}<ref name="jpldata" />
| albedo = {{val|0.028}}<ref name="Licandro-2016a" /><br />{{val|0.042}}<ref name="AKARI" /><br />0.06 {{small|(unverified)}}<ref name="jpldata" />
| abs_magnitude = 10.48<ref name="lcdb" />{{·}}10.77<ref name="jpldata" />
| abs_magnitude = 10.77<ref name="MPC-object" /><ref name="jpldata" />
}}
}}


'''Hidalgo''' ({{IPAc-en|h|ᵻ|ˈ|d|æ|l|ɡ|oʊ}} {{Respell|hi|DAL|goh}}; [[minor planet designation]]: '''944 Hidalgo''') is a dark and eccentric [[minor planet]] from the [[outer Solar System]], approximately 50 kilometers in diameter. Discovered by German astronomer [[Walter Baade]] in 1920, it is the first member of the [[centaur (minor planet)|centaur]]s – a dynamical population with [[semi-major axis]] between those of [[Jupiter]] and [[Saturn]] – ever to be discovered. It was named after Mexican revolutionary [[Miguel Hidalgo y Costilla]].<ref name="springer" />
'''944 Hidalgo''' ({{IPAc-en|h|ᵻ|ˈ|d|æ|l|ɡ|oʊ}} {{Respell|hi|DAL|goh}}), provisional designation {{mp|1920 HZ}}, is a [[centaur (minor planet)|centaur]] and [[Unusual minor planet|unusual object]] on an eccentric, [[comet]]ary-like orbit between the [[asteroid belt]] and the [[outer Solar System]], approximately {{convert|60|km|mi|abbr=off|sigfig=2|sp=us}} in diameter. Discovered by German astronomer [[Walter Baade]] in 1920, it is the first member of the dynamical class of [[centaur (minor planet)|centaur]]s ever to be discovered. The dark [[D-type asteroid|D-type object]] has a [[rotation period]] of 10.1 hours and likely an elongated shape.<ref name="lcdb" /> It was named after Mexican revolutionary [[Miguel Hidalgo y Costilla]].<ref name="springer" />


== Discovery and subsequent studies ==
== Discovery and naming ==

''Hidalgo'' was [[discovery (observation)|discovered]] by German astronomer [[Walter Baade]] on 31 October 1920 at [[Bergedorf Observatory]] in Hamburg, Germany.<ref name="MPC-object" /> It is named for [[Miguel Hidalgo y Costilla]] (1753–1811), who was responsible for declaring Mexico's independence in 1810 and the ensuing [[Mexican War of Independence]]. German astronomers who were in [[Mexico]] to observe a total [[solar eclipse|eclipse]] on 10 September 1923 had an audience with [[president of Mexico|President]] [[Álvaro Obregón]]. During this meeting, they asked his permission to name the asteroid after Hidalgo ({{small|[[Astronomische Nachrichten|AN 221, 159]] from 1924}}).<ref name="springer" />

== Orbit and classification ==
[[File:944Hidalgo-position.png|thumb|left|Orbital diagram of ''Hidalgo'']]
[[File:944Hidalgo-position.png|thumb|left|Orbital diagram of ''Hidalgo'']]


With a [[semi-major axis]] between that of [[Jupiter]] and [[Neptune]], ''Hidalgo'' is a member of the dynamically unstable population of [[Centaur (minor planet)|centaur]], located between the classical [[asteroid]] and the [[trans-Neptunian object]]s.<ref name="jpldata" /> The [[Minor Planet Center]] classifies it as an [[main-belt asteroid]] and as an [[unusual minor planet|unusual object]] due to an [[orbital eccentricity]] higher than 0.5.<ref name="MPC-object" /><ref name="MPC-Other-Unusual" /> ''Hidalgo'' has traditionally been considered an asteroid because centaurs were not recognized as a distinct class until the discovery of [[2060&nbsp;Chiron]] in 1977. The term [[cis-Neptunian object]] and [[Distant minor planet|distant object]], a more generic term that also includes objects further out the Solar System such as [[trans-Neptunian objects]] – are also used.
''Hidalgo'' was [[discovery (observation)|discovered]] by German astronomer [[Walter Baade]] on 31 October 1920 at [[Bergedorf Observatory]] in [[Hamburg]], Germany.<ref name="MPC-object" /> It is named for [[Miguel Hidalgo y Costilla]], who was responsible for declaring Mexico's independence in 1810 and the ensuing [[Mexican War of Independence]]. German astronomers who were in [[Mexico]] to observe a total [[solar eclipse|eclipse]] on 10 September 1923 had an audience with [[president of Mexico|President]] [[Álvaro Obregón]]. During this meeting, they asked his permission to name the asteroid after Hidalgo.<ref name="springer" />


''Hidalgo'' orbits the Sun at a distance of 1.9–9.5&nbsp;[[Astronomical unit|AU]] once every 13 years and 9 months (5,024 days; [[semi-major axis]] of 5.74&nbsp;AU). Its orbit has a high eccentricity of 0.66 and an [[orbital inclination|inclination]] of 43[[Degree (angle)|°]] with respect to the [[ecliptic]].<ref name="jpldata" /> The body's [[observation arc]] begins with its official discovery observation on 31 October 1920.<ref name="MPC-object" />
It was one of five [[minor planets]] included in the 1993 study, [[Transition Comets—UV Search for OH Emissions in Asteroids]], which was research involving amateur astronomers who were permitted to make use of the Hubble Space Telescope.{{Citation needed|date=March 2008}}


This takes it to the inner edge of the asteroid belt and as far out as the orbit of [[Saturn]] (9.0–10.1&nbsp;AU), a characteristic normally associated with Saturn's family of [[comet]]s. Some astronomers therefore suspect that it was once a [[comet]]. It is a [[Jupiter-crosser|Jupiter-]] and [[Saturn-crosser]]. Strictly speaking, ''Hidalgo'' is a Saturn-grazer rather than a crosser as its aphelion does not clear Saturn's. The object's severe orbital inclination is suspected to be the result of a close encounter with Jupiter. Even as recently as 1922, ''Hidalgo'' passed within 0.89&nbsp;AU of Jupiter.<ref name="jpl-close" /> Its orbit has a Jupiter [[minimum orbit intersection distance]] of only {{convert|0.33|AU|km mi|abbr=on|lk=off}}.<ref name="jpldata" />
In the late 1990s, a network of astronomers worldwide gathered [[light curve]] data that was ultimately used to derive the spin states and shape models of 10 new asteroids, including ''Hidalgo''. The authors describe the shape model as having 'very large flat areas and a "rectangular" pole-on silhouette, which are strong indications of a highly nonconvex shape'. Some of the light curves show sharp minima, which indicates the object shape may have two lobes.<ref name="Durech2007" /> Lightcurve data has also been recorded by observers at the Antelope Hills Observatory, which has been designated as an official observatory by the [[Minor Planet Center]].<ref>http://www.antelopehillsobservatory.org/Lightcurves/944.gif</ref>


== Physical characteristics ==
When [[Pluto]] was discovered Hidalgo was the furthest known minor planet from the Sun.<ref name=searchengine>{{cite web
|title=JPL Small-Body Database Search Engine
|publisher=[[JPL Solar System Dynamics]]
|url=http://ssd.jpl.nasa.gov/sbdb_query.cgi
|accessdate=2008-05-27| archiveurl= https://web.archive.org/web/20080531083221/http://ssd.jpl.nasa.gov/sbdb_query.cgi| archivedate= 31 May 2008 <!--DASHBot-->| deadurl= no}} (characteristic:[[Semi-major axis|a]]>5.7)</ref>


In the [[Tholen classification|Tholen]] and [[Bus–DeMeo classification]], ''Hidalgo'' is a dark, carbonaceous [[D-type asteroid]].<ref name="jpldata" /><ref name="Ferret" />
== Orbit ==


According to the surveys carried out by the Japanese [[Akari (satellite)|Akari satellite]] and the [[NEOWISE]] mission of NASA's [[Wide-field Infrared Survey Explorer]], ''Hidalgo'' measures 52.45 and 61.4 kilometers in diameter and its surface has a low [[astronomical albedo|albedo]] of 0.042 and 0.028, respectively.<ref name="AKARI" /><ref name="Licandro-2016a" /> The prominent [[JPL Small-Body Database]] currently gives a diameter of 38 kilometers taken from the publication ''Hazards due to Comets and Asteroids'' ([[Tom Gehrels]], 1994).<ref name="jpldata" /><ref name="Gehrels-1994" />
''Hidalgo'' is a [[Centaur (minor planet)|centaur]] because it has a [[semi-major axis]] between [[Jupiter]]'s and [[Neptune]]'s,<ref name="jpldata" /> while the [[Minor Planet Center]] simply classifies it as an [[asteroid]] of the [[main belt]].<ref name="MPC-object" /> ''Hidalgo'' has traditionally been considered an [[asteroid]] because centaurs were not recognized as a distinct class until the discovery of [[2060&nbsp;Chiron]] in 1977. The term [[cis-Neptunian object]] and [[Distant minor planet|distant object]], a more generic term that also includes objects further out the Solar System such as [[trans-Neptunian objects]] – are also used.


In the late 1990s, a network of astronomers worldwide gathered [[lightcurve]] data that was ultimately used to derive the spin states and shape models of 10 new asteroids, including ''Hidalgo''. The authors describe the shape model as having 'very large flat areas and a "rectangular" pole-on silhouette, which are strong indications of a highly nonconvex shape'. Some of the light curves show sharp minima, which indicates the object shape may have two lobes.<ref name="Durech-2007" /> Lightcurve data has also been recorded by observers at the Antelope Hills Observatory {{Obscode|H09}} in Colorado, United States.{{efn|name=lightcurve-plot-Koff-2011}} When [[Pluto]] was discovered ''Hidalgo'' was the furthest known minor planet from the Sun.<ref name="searchengine" />
With a high [[eccentricity (orbit)|eccentricity]] of 0.66, its [[perihelion]] of 1.95 [[astronomical unit|AU]] takes it to the inner edge of the asteroid belt, whereas its [[aphelion]] of 9.54 AU takes it out to [[Saturn]]'s orbit, a characteristic normally associated with Saturn's family of comets. Some astronomers therefore suspect that it was once a [[comet]]. Strictly speaking, Hidalgo is a Saturn-grazer rather than a [[Saturn-crosser asteroid|Saturn-crosser]] as its aphelion does not clear Saturn's. Hidalgo's severe orbital inclination of 43° is suspected to be the result of a close encounter with Jupiter. Even as recently as 1922, Hidalgo passed within 0.89 AU of Jupiter.<ref name=jpl-close>{{cite web |type=2008-06-10 last obs |title=JPL Close-Approach Data: 944 Hidalgo (1920 HZ) |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=944;cad=1#cad |accessdate=2009-05-05}}</ref> The orbit of Hidalgo has a Jupiter [[Minimum orbit intersection distance]] (MOID) of only {{convert|0.33|AU|km mi|abbr=on|lk=off}}.<ref name="jpldata" />

== Notes ==
{{notelist|refs=

{{efn|name=lightcurve-plot-Koff-2011|1=[http://www.antelopehillsobservatory.org/Lightcurves/944.gif Lightcurve plot of (944) Hidalgo] by Robert A. Koff (William Koff) at the Antelope Hills Observatory, Colorado {{Obscode|H09}}; Rotation period {{val|10.06}} hours with a brightness amplitude of {{val|0.31}} mag. Quality code is 3. Summary figures at the [http://www.minorplanet.info/PHP/GenerateALCDEFPage_Local.php?AstInfo=944%7CHidalgo LCDB].}}

}} <!-- end of notelist -->


== References ==
== References ==
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<ref name="jpldata">{{cite web
<ref name="jpldata">{{cite web
|type = 2017-06-02 last obs.
|type = 2018-10-21 last obs.
|title = JPL Small-Body Database Browser: 944 Hidalgo (1920 HZ)
|title = JPL Small-Body Database Browser: 944 Hidalgo (A920 UB)
|url = http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2000944
|url = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2000944
|publisher = [[Jet Propulsion Laboratory]]
|publisher = [[Jet Propulsion Laboratory]]
|accessdate = 12 October 2017}}</ref>
|accessdate = 27 November 2018}}</ref>

<ref name="jpl-close">{{cite web
|type = 2018-10-21 last obs.
|title = JPL Close-Approach Data: 944 Hidalgo (1920 HZ)
|url = http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=944;cad=1#cad
|publisher = Jet Propulsion Laboratory
|accessdate = 27 November 2018}}</ref>

<ref name="Gehrels-1994">{{cite book
|title = Hazards due to Comets and Asteroids
|author = Tom Gehrels
|date = 1994
|pages = 540–543
|url = https://uapress.arizona.edu/book/hazards-due-to-comets-and-asteroids
|publisher = University of Arizona Press
|ISBN = 0816515050
|accessdate = 27 November 2018}}</ref>


<ref name="springer">{{cite book
<ref name="springer">{{cite book
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|page = 83
|page = 83
|date = 2007
|date = 2007
|url = https://link.springer.com/referenceworkentry/10.1007/978-3-540-29925-7_945
|isbn = 978-3-540-00238-3
|isbn = 978-3-540-00238-3
|accessdate = 27 November 2018}}</ref>
|doi = 10.1007/978-3-540-29925-7_945 |chapter = (944) Hidalgo }}</ref>


<ref name="MPC-object">{{cite web
<ref name="MPC-object">{{cite web
|title = 944 Hidalgo (1920 HZ)
|title = 944 Hidalgo (A920 UB)
|work = Minor Planet Center
|work = Minor Planet Center
|url = http://www.minorplanetcenter.net/db_search/show_object?object_id=944
|url = https://www.minorplanetcenter.net/db_search/show_object?object_id=944
|accessdate = 12 October 2017}}</ref>
|accessdate = 27 November 2018}}</ref>

<ref name="MPC-Other-Unusual">{{cite web
|title = List Of Other Unusual Objects
|work = Minor Planet Center
|url = https://www.minorplanetcenter.net/iau/lists/t_others.html
|accessdate = 27 November 2018}}</ref>

<ref name="searchengine">{{cite web
|title = JPL Small-Body Database Search Engine
|publisher = JPL Solar System Dynamics
|url = http://ssd.jpl.nasa.gov/sbdb_query.cgi
|accessdate = 2008-05-27| archiveurl= https://web.archive.org/web/20080531083221/http://ssd.jpl.nasa.gov/sbdb_query.cgi
|archivedate= 31 May 2008 <!--DASHBot-->
|deadurl = no}} (characteristic:[[Semi-major axis|a]]>5.7)</ref>

<ref name="Ferret">{{cite web
|title = Asteroid 944 Hidalgo
|work = Small Bodies Data Ferret
|url = https://sbntools.psi.edu/ferret/SimpleSearch/results.action?targetName=944+Hidalgo
|accessdate = 27 November 2018}}</ref>


<ref name="lcdb">{{cite web
<ref name="lcdb">{{cite web
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|date = January 2016
|date = January 2016
|title = Size and albedo distributions of asteroids in cometary orbits using WISE data
|title = Size and albedo distributions of asteroids in cometary orbits using WISE data
|url = http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=2016A&A...585A...9L
|url = https://arxiv.org/pdf/1510.02282.pdf
|journal = Astronomy and Astrophysics
|journal = Astronomy and Astrophysics
|volume = 585
|volume = 585
Line 105: Line 151:
|bibcode = 2016A&A...585A...9L
|bibcode = 2016A&A...585A...9L
|doi = 10.1051/0004-6361/201526866
|doi = 10.1051/0004-6361/201526866
|access-date= 12 October 2017|arxiv= 1510.02282}}</ref>
|arxiv = 1510.02282
|access-date= 27 November 2018}}</ref>


<ref name="AKARI">{{cite journal
<ref name="AKARI">{{cite journal
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|bibcode = 2011PASJ...63.1117U
|bibcode = 2011PASJ...63.1117U
|doi = 10.1093/pasj/63.5.1117
|doi = 10.1093/pasj/63.5.1117
|access-date= 27 November 2018}} ([http://vizier.cfa.harvard.edu/viz-bin/VizieR-5?-source=J/PASJ/63/1117/acua_v1&Num=944 online], [https://core.ac.uk/download/pdf/43545172.pdf AcuA catalog p. 153])</ref>
|access-date= 12 October 2017}}</ref>


<ref name="Durech2007">{{Citation
<ref name="Durech-2007">{{Cite journal
|display-authors = 6
| last1 = Durech
| first1 = J.
|first1 = J. |last1 = Durech
| last2 = Kaasalainen
|first2 = M. |last2 = Kaasalainen
| first2 = M.
|first3 = A. |last3 = Marciniak
|first4 = W. H. |last4 = Allen
| last3 = Marciniak
| first3 = A.
|first5 = R. |last5 = Behrend
|first6 = C. |last6 = Bembrick
| display-authors = 1
|first7 = T. |last7 = Bennett
| title = Physical models of ten asteroids from an observers' collaboration network
|first8 = L. |last8 = Bernasconi
| journal = Astronomy and Astrophysics
|first9 = J. |last9 = Berthier
| volume = 465
| issue = 1
|first10 = G. |last10 = Bolt
| pages = 331–337
|first11 = S. |last11 = Boroumand
|first12 = L. |last12 = Crespo da Silva
|date=April 2007
|first13 = R. |last13 = Crippa
| doi = 10.1051/0004-6361:20066347
|first14 = M. |last14 = Crow
| bibcode = 2007A&A...465..331D
|first15 = R. |last15 = Durkee
| postscript= .}}</ref>
|first16 = R. |last16 = Dymock
|first17 = M. |last17 = Fagas
|first18 = M. |last18 = Fauerbach
|first19 = S. |last19 = Fauvaud
|first20 = M. |last20 = Frey
|first21 = R. |last21 = Gonçalves
|first22 = R. |last22 = Hirsch
|first23 = D. |last23 = Jardine
|first24 = K. |last24 = Kaminski
|first25 = R. |last25 = Koff
|first26 = T. |last26 = Kwiatkowski
|first27 = A. |last27 = López
|first28 = F. |last28 = Manzini
|first29 = T. |last29 = Michalowski
|first30 = R. |last30 = Pacheco
|first31 = M. |last31 = Pan
|first32 = F. |last32 = Pilcher
|first33 = R. |last33 = Poncy
|first34 = D. |last34 = Pray
|first35 = W. |last35 = Pych
|first36 = R. |last36 = Roy
|first37 = G. |last37 = Santacana
|first38 = S. |last38 = Slivan
|first39 = S. |last39 = Sposetti
|first40 = R. |last40 = Stephens
|first41 = B. |last41 = Warner
|first42 = M. |last42 = Wolf
|date = April 2007
|title = Physical models of ten asteroids from an observers' collaboration network
|url = http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=2007A&A...465..331D
|journal = Astronomy and Astrophysics
|volume = 465
|issue = 1
|pages = 331–337
|bibcode = 2007A&A...465..331D
|doi = 10.1051/0004-6361:20066347
|access-date= 27 November 2018}}</ref>


}} <!-- end of reflist -->
}} <!-- end of reflist -->
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* [https://books.google.com/books?id=aeAg1X7afOoC&pg Dictionary of Minor Planet Names], Google books
* [https://books.google.com/books?id=aeAg1X7afOoC&pg Dictionary of Minor Planet Names], Google books
* [http://www.minorplanetcenter.net/iau/lists/NumberedMPs000001.html Discovery Circumstances: Numbered Minor Planets (1)-(5000)] – Minor Planet Center
* [http://www.minorplanetcenter.net/iau/lists/NumberedMPs000001.html Discovery Circumstances: Numbered Minor Planets (1)-(5000)] – Minor Planet Center
* {{AstDys|944}}
* {{JPL small body}}
* {{JPL small body}}


{{Use dmy dates|date=November 2018}}
{{Minor planets navigator |943 Begonia |number=944 |945 Barcelona}}
{{Minor planets navigator |943 Begonia |number=944 |945 Barcelona}}
{{Small Solar System bodies}}
{{Small Solar System bodies}}

Revision as of 15:01, 27 November 2018

944 Hidalgo
Discovery [1]
Discovered byW. Baade
Discovery siteBergedorf Obs.
Discovery date31 October 1920
Designations
(944) Hidalgo
Pronunciation/hɪˈdælɡoʊ/ hi-DAL-goh
Named after
Miguel Hidalgo y Costilla
(Mexican revolutionary)[2]
1920 HZ
centaur [3] · main-belt [1]
unusual [4]
Orbital characteristics [3]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 0
Observation arc97.97 yr (35,784 d)
Aphelion9.5345 AU
Perihelion1.9474 AU
5.7410 AU
Eccentricity0.6608
13.76 yr (5,024 d)
13.078°
0° 4m 18.12s / day
Inclination42.521°
21.420°
56.651°
Jupiter MOID0.3285 AU
TJupiter2.0690
Physical characteristics
38 km (Gehrels)[3]
52.45±3.60 km[5]
61.4±12.7 km[6]
10.063±0.0003 h[7][a]
0.028[6]
0.042[5]
0.06 (unverified)[3]
Tholen = D [3][8]
10.77[1][3]

944 Hidalgo (/hɪˈdælɡoʊ/ hi-DAL-goh), provisional designation 1920 HZ, is a centaur and unusual object on an eccentric, cometary-like orbit between the asteroid belt and the outer Solar System, approximately 60 kilometers (37 miles) in diameter. Discovered by German astronomer Walter Baade in 1920, it is the first member of the dynamical class of centaurs ever to be discovered. The dark D-type object has a rotation period of 10.1 hours and likely an elongated shape.[7] It was named after Mexican revolutionary Miguel Hidalgo y Costilla.[2]

Discovery and naming

Hidalgo was discovered by German astronomer Walter Baade on 31 October 1920 at Bergedorf Observatory in Hamburg, Germany.[1] It is named for Miguel Hidalgo y Costilla (1753–1811), who was responsible for declaring Mexico's independence in 1810 and the ensuing Mexican War of Independence. German astronomers who were in Mexico to observe a total eclipse on 10 September 1923 had an audience with President Álvaro Obregón. During this meeting, they asked his permission to name the asteroid after Hidalgo (AN 221, 159 from 1924).[2]

Orbit and classification

Orbital diagram of Hidalgo

With a semi-major axis between that of Jupiter and Neptune, Hidalgo is a member of the dynamically unstable population of centaur, located between the classical asteroid and the trans-Neptunian objects.[3] The Minor Planet Center classifies it as an main-belt asteroid and as an unusual object due to an orbital eccentricity higher than 0.5.[1][4] Hidalgo has traditionally been considered an asteroid because centaurs were not recognized as a distinct class until the discovery of 2060 Chiron in 1977. The term cis-Neptunian object and distant object, a more generic term that also includes objects further out the Solar System such as trans-Neptunian objects – are also used.

Hidalgo orbits the Sun at a distance of 1.9–9.5 AU once every 13 years and 9 months (5,024 days; semi-major axis of 5.74 AU). Its orbit has a high eccentricity of 0.66 and an inclination of 43° with respect to the ecliptic.[3] The body's observation arc begins with its official discovery observation on 31 October 1920.[1]

This takes it to the inner edge of the asteroid belt and as far out as the orbit of Saturn (9.0–10.1 AU), a characteristic normally associated with Saturn's family of comets. Some astronomers therefore suspect that it was once a comet. It is a Jupiter- and Saturn-crosser. Strictly speaking, Hidalgo is a Saturn-grazer rather than a crosser as its aphelion does not clear Saturn's. The object's severe orbital inclination is suspected to be the result of a close encounter with Jupiter. Even as recently as 1922, Hidalgo passed within 0.89 AU of Jupiter.[9] Its orbit has a Jupiter minimum orbit intersection distance of only 0.33 AU (49,000,000 km; 31,000,000 mi).[3]

Physical characteristics

In the Tholen and Bus–DeMeo classification, Hidalgo is a dark, carbonaceous D-type asteroid.[3][8]

According to the surveys carried out by the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Hidalgo measures 52.45 and 61.4 kilometers in diameter and its surface has a low albedo of 0.042 and 0.028, respectively.[5][6] The prominent JPL Small-Body Database currently gives a diameter of 38 kilometers taken from the publication Hazards due to Comets and Asteroids (Tom Gehrels, 1994).[3][10]

In the late 1990s, a network of astronomers worldwide gathered lightcurve data that was ultimately used to derive the spin states and shape models of 10 new asteroids, including Hidalgo. The authors describe the shape model as having 'very large flat areas and a "rectangular" pole-on silhouette, which are strong indications of a highly nonconvex shape'. Some of the light curves show sharp minima, which indicates the object shape may have two lobes.[11] Lightcurve data has also been recorded by observers at the Antelope Hills Observatory (H09) in Colorado, United States.[a] When Pluto was discovered Hidalgo was the furthest known minor planet from the Sun.[12]

Notes

  1. ^ a b Lightcurve plot of (944) Hidalgo by Robert A. Koff (William Koff) at the Antelope Hills Observatory, Colorado (H09); Rotation period 10.06 hours with a brightness amplitude of 0.31 mag. Quality code is 3. Summary figures at the LCDB.

References

  1. ^ a b c d e f "944 Hidalgo (A920 UB)". Minor Planet Center. Retrieved 27 November 2018.
  2. ^ a b c Schmadel, Lutz D. (2007). Dictionary of Minor Planet Names – (944) Hidalgo. Springer Berlin Heidelberg. p. 83. ISBN 978-3-540-00238-3. Retrieved 27 November 2018.
  3. ^ a b c d e f g h i j k "JPL Small-Body Database Browser: 944 Hidalgo (A920 UB)" (2018-10-21 last obs.). Jet Propulsion Laboratory. Retrieved 27 November 2018.
  4. ^ a b "List Of Other Unusual Objects". Minor Planet Center. Retrieved 27 November 2018.
  5. ^ a b c Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. Retrieved 27 November 2018. (online, AcuA catalog p. 153)
  6. ^ a b c Licandro, J.; Alí-Lagoa, V.; Tancredi, G.; Fernández, Y. (January 2016). "Size and albedo distributions of asteroids in cometary orbits using WISE data" (PDF). Astronomy and Astrophysics. 585: 12. arXiv:1510.02282. Bibcode:2016A&A...585A...9L. doi:10.1051/0004-6361/201526866. Retrieved 27 November 2018.
  7. ^ a b "LCDB Data for (944) Hidalgo". Asteroid Lightcurve Database (LCDB). Retrieved 12 October 2017.
  8. ^ a b "Asteroid 944 Hidalgo". Small Bodies Data Ferret. Retrieved 27 November 2018.
  9. ^ "JPL Close-Approach Data: 944 Hidalgo (1920 HZ)" (2018-10-21 last obs.). Jet Propulsion Laboratory. Retrieved 27 November 2018.
  10. ^ Tom Gehrels (1994). Hazards due to Comets and Asteroids. University of Arizona Press. pp. 540–543. ISBN 0816515050. Retrieved 27 November 2018.
  11. ^ Durech, J.; Kaasalainen, M.; Marciniak, A.; Allen, W. H.; Behrend, R.; Bembrick, C.; et al. (April 2007). "Physical models of ten asteroids from an observers' collaboration network". Astronomy and Astrophysics. 465 (1): 331–337. Bibcode:2007A&A...465..331D. doi:10.1051/0004-6361:20066347. Retrieved 27 November 2018.
  12. ^ "JPL Small-Body Database Search Engine". JPL Solar System Dynamics. Archived from the original on 31 May 2008. Retrieved 27 May 2008. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help) (characteristic:a>5.7)

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