View source for 944 Hidalgo

{{Short description|Centaur}}
{{Use dmy dates|date=November 2018}}
{{Infobox planet
 | minorplanet     = yes
 | name            = 944 Hidalgo
 | symbol          = [[file:Hidalgo symbol (bold).svg|24px]] (astrological)
 | background      = #C7FF8F
 | image           = Hidalgoanimation2003.gif
 | image_size      = 
 | caption         = Animation of 944 Hidalgo's movement over 5 minutes in 2003, taken by the [[Very Large Telescope]].
 | discovery_ref   = &thinsp;<ref name="MPC-object" />
 | discoverer      = [[Walter Baade|W. Baade]]
 | discovery_site  = [[Bergedorf Observatory|Bergedorf Obs.]]
 | discovered      = 31 October 1920
 | mpc_name        = (944) Hidalgo
 | alt_names       = 1920 HZ{{·}}A920 UB
 | pronounced      = {{IPAc-en|h|ᵻ|ˈ|d|æ|l|ɡ|oʊ}}<ref>{{OED|hidalgo}}</ref>
 | 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 />[[Unusual minor planet|unusual]]&thinsp;<ref name="MPC-Other-Unusual" /><ref name="johnstonsarchive-TNO-list" />
 | orbit_ref       = &thinsp;<ref name="jpldata" />
 | epoch           = 27 April 2019 ([[Julian day|JD]] 2458600.5)
 | uncertainty     = 0
 | observation_arc = 97.97 [[Julian year (astronomy)|yr]] (35,784 d)
 | aphelion        = 9.5345 [[Astronomical unit|AU]]
 | perihelion      = 1.9474 AU
 | semimajor       = 5.7410 AU
 | eccentricity    = 0.6608
 | period          = 13.76 yr (5,024 d)
 | mean_anomaly    = 13.078[[Degree (angle)|°]]
 | mean_motion     = {{Deg2DMS|0.0717|sup=ms}} / day
 | inclination     = 42.521°
 | asc_node        = 21.420°
 | arg_peri        = 56.651°
 | jupiter_moid    = 0.3285 AU
 | tisserand       = 2.0690
 | mean_diameter   = {{val|52.45|3.60|u=km}}<ref name="AKARI" /><ref name="johnstonsarchive-TNO-list" /><br />{{val|61.4|12.7|u=km}}<ref name="Licandro-2016a" />
 | mass            =
 | 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="Ferret" />
 | albedo          = {{val|0.028}}<ref name="Licandro-2016a" /><br />{{val|0.042}}<ref name="AKARI" />
 | abs_magnitude   = 10.77<ref name="MPC-object" /><ref name="jpldata" />
}}

'''944 Hidalgo''' {{IPAc-en|h|ᵻ|ˈ|d|æ|l|ɡ|oʊ}} 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|52|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 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 [[Solar eclipse of September 10, 1923|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]]

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" />

With a semi-major axis between that of [[Jupiter]] (5.2&nbsp;AU) and [[Neptune]] (30.1&nbsp;AU), Hidalgo is a member of the dynamically unstable population of [[Centaur (minor planet)|centaur]]s, located between the classical [[asteroid]]s and the [[trans-Neptunian object]]s.<ref name="jpldata" /> The [[Minor Planet Center]] classifies it both as [[main-belt asteroid]] and [[unusual minor planet|unusual object]] due to an [[orbital eccentricity]] higher than 0.5.<ref name="MPC-object" /><ref name="MPC-Other-Unusual" /><ref name="johnstonsarchive-TNO-list" /> 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. Alternatively, cis-Neptunian object and [[Distant minor planet|distant object]] are more generic terms that also includes objects further out the Solar System.

Hidalgo{{'s}} orbit takes it to the inner edge of the asteroid belt and as far out as to 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" />

It is unlikely there are any large satellites orbiting Hidalgo larger than about 15 kilometers across. Observations from the [[Very Large Telescope]] in 2003 ruled out any secondary objects brighter than V=19.5 further than 200 kilometers from the asteroid. However, smaller moons have not been ruled out.

== Physical characteristics ==

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

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" /> The ''Collaborative Asteroid Lightcurve Link'' assumes a standard albedo for a [[C-type asteroid|carbonaceous asteroid]] of 0.057 and derives a diameter of 44.6&nbsp;km based on an [[absolute magnitude]] of 10.48,<ref name="lcdb" /> while Johnston's archive adopts Akari's diameter of 52&nbsp;km with an albedo of 0.042.<ref name="johnstonsarchive-TNO-list" />

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" />

== 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]] (Bob 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/generateOneAsteroidInfo.php?AstInfo=944%7CHidalgo LCDB].}}

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

== References ==
{{Reflist|refs=

<ref name="jpldata">{{cite web
  |type       = 2018-10-21 last obs.
  |title      = JPL Small-Body Database Browser: 944 Hidalgo (A920 UB)
  |url        = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2000944
  |publisher  = [[Jet Propulsion Laboratory]]
  |access-date = 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        = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=944;cad=1#cad
  |publisher  = Jet Propulsion Laboratory
  |access-date = 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       = 978-0816515059
  |access-date = 27 November 2018}}</ref>

<ref name="springer">{{cite book
  |title      = Dictionary of Minor Planet Names – (944) Hidalgo
  |last       = Schmadel | first = Lutz D.
  |publisher  = [[Springer Berlin Heidelberg]]
  |page       = 83
  |date       = 2007
  |isbn       = 978-3-540-00238-3
  |doi       = 10.1007/978-3-540-29925-7_945 |chapter       = (944) Hidalgo }}</ref>

<ref name="MPC-object">{{cite web
  |title      = 944 Hidalgo (A920 UB)
  |work       = Minor Planet Center
  |url        = https://www.minorplanetcenter.net/db_search/show_object?object_id=944
  |access-date = 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
  |access-date = 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
  |access-date = 2008-05-27| archive-url= https://web.archive.org/web/20080531083221/http://ssd.jpl.nasa.gov/sbdb_query.cgi
  |archive-date= 31 May 2008 
  |url-status    = live}} (characteristic:[[Semi-major axis|a]]>5.7)</ref>

<ref name="johnstonsarchive-TNO-list">{{cite web
  |title      = List of Known Trans-Neptunian Objects
  |work       = Johnston's Archive
  |date       = 7 October 2018
  |last       = Johnston |first= Wm. Robert
  |url        = http://www.johnstonsarchive.net/astro/tnoslist.html
  |access-date = 27 November 2018}}</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
  |access-date = 27 November 2018}}</ref>

<ref name="lcdb">{{cite web
  |title      = LCDB Data for (944) Hidalgo
  |publisher  = Asteroid Lightcurve Database (LCDB)
  |url        = http://www.minorplanet.info/PHP/generateOneAsteroidInfo.php?AstInfo=944%7CHidalgo
  |access-date = 12 October 2017}}</ref>

<ref name="Licandro-2016a">{{Cite journal
  |first1     = J. |last1 = Licandro
  |first2     = V. |last2 = Alí-Lagoa
  |first3     = G. |last3 = Tancredi
  |first4     = Y. |last4 = Fernández
  |date       = January 2016
  |title      = Size and albedo distributions of asteroids in cometary orbits using WISE data
  |journal    = Astronomy and Astrophysics
  |volume     = 585
  |page       = 12
  |bibcode    = 2016A&A...585A...9L
  |doi        = 10.1051/0004-6361/201526866
  |arxiv      = 1510.02282
  |s2cid = 119218056
 }}</ref>

<ref name="AKARI">{{cite journal
  |display-authors = 6
  |first1     = Fumihiko |last1 = Usui
  |first2     = Daisuke |last2 = Kuroda
  |first3     = Thomas G. |last3 = Müller
  |first4     = Sunao |last4 = Hasegawa
  |first5     = Masateru |last5 = Ishiguro
  |first6     = Takafumi |last6 = Ootsubo
  |first7     = Daisuke |last7 = Ishihara
  |first8     = Hirokazu |last8 = Kataza
  |first9     = Satoshi |last9 = Takita
  |first10    = Shinki |last10 = Oyabu
  |first11    = Munetaka |last11 = Ueno
  |first12    = Hideo |last12 = Matsuhara
  |first13    = Takashi |last13 = Onaka
  |date       = October 2011
  |title      = Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey
  |journal    = Publications of the Astronomical Society of Japan
  |volume     = 63
  |issue      = 5
  |pages      = 1117–1138
  |bibcode    = 2011PASJ...63.1117U
  |doi        = 10.1093/pasj/63.5.1117
  |doi-access= 
  }} ([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>

<ref name="Durech-2007">{{Cite journal
  |display-authors = 6
  |first1     = J. |last1 = Durech
  |first2     = M. |last2 = Kaasalainen
  |first3     = A. |last3 = Marciniak
  |first4     = W. H. |last4 = Allen
  |first5     = R. |last5 = Behrend
  |first6     = C. |last6 = Bembrick
  |first7     = T. |last7 = Bennett
  |first8     = L. |last8 = Bernasconi
  |first9     = J. |last9 = Berthier
  |first10    = G. |last10 = Bolt
  |first11    = S. |last11 = Boroumand
  |first12    = L. |last12 = Crespo da Silva
  |first13    = R. |last13 = Crippa
  |first14    = M. |last14 = Crow
  |first15    = R. |last15 = Durkee
  |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
  |journal    = Astronomy and Astrophysics
  |volume     = 465
  |issue      = 1
  |pages      = 331–337
  |bibcode    = 2007A&A...465..331D
  |doi        = 10.1051/0004-6361:20066347
  |doi-access= free
  }}</ref>

}} <!-- end of reflist -->

== External links ==
* [https://web.archive.org/web/20160303173103/http://www.antelopehillsobservatory.org/Lightcurves/944.gif Lightcurve plot of (944) Hidalgo], Antelope Hills Observatory
* [http://www.minorplanet.info/PHP/lcdbsummaryquery.php Asteroid Lightcurve Database (LCDB)], query form ([http://www.minorplanet.info/lightcurvedatabase.html info] {{Webarchive|url=https://web.archive.org/web/20171216050541/http://www.minorplanet.info/lightcurvedatabase.html |date=16 December 2017 }})
* [https://books.google.com/books?id=aeAg1X7afOoC&pg Dictionary of Minor Planet Names], Google books
* [https://www.minorplanetcenter.net/iau/lists/NumberedMPs000001.html Discovery Circumstances: Numbered Minor Planets (1)–(5000)] – Minor Planet Center
* {{AstDys|944}}
* {{JPL small body}}

{{Minor planets navigator |943 Begonia |number=944 |945 Barcelona}}
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{{DEFAULTSORT:Hidalgo}}
[[Category:Centaurs (small Solar System bodies)]]
[[Category:Unusual minor planets|000944]]
[[Category:Discoveries by Walter Baade]]
[[Category:Named minor planets]]
[[Category:D-type asteroids (Tholen)|000944]]
[[Category:Astronomical objects discovered in 1920|19201031]]