View source for 5261 Eureka

{{Short description|Trojan asteroid of Mars}}
{{Use dmy dates|date=October 2019}}
{{Infobox planet
| minorplanet = yes
| background = #FA8072
| name = 5261 Eureka
| discovery_ref = <ref name="schmadel2003"/>
| discoverer = [[David H. Levy]] and Henry Holt
| discovered = 20 June 1990
| alt_names = 1990 MB
| named_after = [[Eureka (word)|Eureka]]
| pronounced = {{IPAc-en|j|ʊ|ˈ|r|iː|k|ə}} {{respell|yuurr|EE|kə}}<ref>{{OED|Eureka}}</ref>
| mp_category = {{mpcat|Martian L5|125}}
| orbit_ref = <ref name="JPLSBDB"/>
| epoch = 13 January 2016 ([[Julian day|JD]] 2457400.5)
| aphelion = {{Convert|1.6222|AU|Gm|abbr=on|lk=on}}
| perihelion = {{Convert|1.4249|AU|Gm|abbr=on}}
| semimajor = {{Convert|1.5236|AU|Gm|abbr=on}}
| eccentricity = 0.064766
| period = 1.88 [[Julian year (astronomy)|yr]] (686.89 [[Julian year (astronomy)|d]])
| inclination = 20.280°
| asc_node = 245.057°
| arg_peri = 95.456°
| mean_anomaly = 145.29[[Degree (angle)|°]]
| avg_speed = 24.11 km/[[second|s]]
| satellites = 1
| dimensions = 1.3<ref name="Rivkin2007"/>&nbsp;km<br />~2–4&nbsp;km<sup>[https://web.archive.org/web/20010302182040/http://neo.jpl.nasa.gov/glossary/h.html H]</sup>
| abs_magnitude = 16.0,<ref name="Rivkin2007"/> 16.1<ref name="JPLSBDB"/>
| single_temperature = ~250<ref name="Rivkin2007"/>&nbsp;[[kelvin|K]]
| spectral_type = [[S-type asteroid|S(I)]]<ref name="Rivkin2007"/> (Gaffey)
| albedo = 0.39<ref name="Rivkin2007"/>
| mean_motion = {{Deg2DMS|0.52410|sup=ms}} / day
| rotation = {{Convert|2.6902|h|d|abbr=on|lk=on}}
| observation_arc = 13267 days (36.32 yr)
| uncertainty = 0
| moid = {{Convert|0.497052|AU|Gm|abbr=on}}
| jupiter_moid = {{Convert|3.52162|AU|Gm|abbr=on}}
| tisserand = 4.428
}}

'''5261 Eureka''' is the first [[Mars trojan]] discovered.<ref name=mtrojans>{{Cite web|title=List of Martian Trojans|access-date=2011-02-26|url=https://www.minorplanetcenter.net/iau/lists/MarsTrojans.html}}</ref> It was discovered by [[David H. Levy]] and Henry Holt at [[Palomar Observatory]] on 20 June 1990.<ref name="schmadel2003"/> It trails [[Mars]] (at the {{L5|pt=yes}}) at a distance varying by only 0.3 [[Astronomical unit|AU]] during each revolution (with a [[secular variation|secular trend]] superimposed, changing the distance from 1.5–1.8 AU around 1850 to 1.3–1.6 AU around 2400). Minimum distances from [[Earth]], [[Venus]], and [[Jupiter]], are 0.5, 0.8, and 3.5 AU, respectively.

Long-term [[numerical integration]] shows that the orbit is stable. [[Kimmo Innanen|Kimmo A. Innanen]] and [[Seppo Mikkola]] note that "contrary to intuition, there is clear [[empirical evidence]] for the stability of motion around the {{L4}} and {{L5}} points of all the terrestrial planets over a timeframe of several million years".

Since the discovery of 5261 Eureka, the [[Minor Planet Center]] has recognized three other asteroids as Martian trojans: {{mpl|(121514) 1999 UJ|7}} at the {{L4}} point, {{mpl|(101429) 1998 VF|31}} at the {{L5}} point,<ref name=mtrojans/> and {{mpl|(311999) 2007 NS|2}}, also at the {{L5}} point.<ref>[https://www.minorplanetcenter.net/mpec/K07/K07O09.html MPEC 2007-O09 : 2007 NS2]</ref> At least five other asteroids in near-1:1 [[orbital resonance|resonances]] with Mars have been discovered, but they do not exhibit trojan behavior. They are {{mpl|2001 FR|127}}, {{mpl|2001 FG|24}}, [[(36017) 1999 ND43|(36017) 1999 ND<sub>43</sub>]], {{mpl|1998 QH|56}} and [[(152704) 1998 SD4|(152704) 1998 SD<sub>4</sub>]]. Due to close orbital similarities, most of the other, smaller, members of the L<sub>5</sub> group are hypothesized to be fragments of 5261 Eureka that were detached after it was spun up by the [[YORP effect]] (consistent with its rotational period of 2.69 h).<ref name="Lovett2017">{{cite journal|last1= Lovett|first1= R.|title= Sun's light touch explains asteroids flying in formation behind Mars|journal= Science|date= 2017-10-20|doi= 10.1126/science.aar2794}}</ref>

The [[infrared]] spectrum for 5261 Eureka is typical for an [[A-type asteroid]], but the visual spectrum is consistent with an evolved form of [[achondrite]] called an [[angrite]]. A-class asteroids are tinted red in hue, with a moderate [[albedo]]. The asteroid is located deep within a stable Lagrangian zone of Mars, which is considered indicative of a primordial origin—meaning the asteroid has most likely been in this orbit for much of the history of the [[Solar System]].{{citation needed|date=December 2020}}

==Satellite==
{{Infobox planet
| name = Satellite
| symbol = 
| image = 
| caption = 
| apsis = astron
| discovered = 28 November 2011
| mpc_name = S/2011 (5261) 1
| mp_category = <!--(Minor planet category)-->
| alt_names = <!--(Alternative names)-->
| epoch = 9 December 2014
| aphelion = 
| perihelion = 
| semimajor = 2.1 km
| eccentricity = 
| period = 0.7054 ± 0.0004 d
| dimensions = 0.46 km
| abs_magnitude = <!--(Absolute magnitude)-->
}}

On 28 November 2011, a [[Minor-planet moon|natural satellite]] of 5261 Eureka was found. This unnamed moon is about 0.46&nbsp;km in diameter and orbits 2.1&nbsp;km from Eureka. The satellite's existence was announced in September 2014.<ref>{{cite web | url=http://www.johnstonsarchive.net/astro/astmoons/am-05261.html | title=(5261) Eureka | publisher=Johnston's Archive | date=16 November 2014 | access-date=6 September 2015 | author=Johnston, Robert}}</ref>

== See also ==
* {{mpl|(101429) 1998 VF|31}} 
* {{mpl|(121514) 1999 UJ|7}} 
* {{mpl|(311999) 2007 NS|2}} 
* {{mpl|(385250) 2001 DH|47}}
* {{mpl|(816688) 2011 SC|191}}
* {{mpl|2009 SE|}}
* {{mpl|2011 SL|25}}
* {{mpl|2011 SP|189}}
* {{mpl|2011 UB|256}}
* {{mpl|2011 UN|63}}
* {{mpl|2016 CP|31}}
* {{mpl|2018 EC|4}}
* {{mpl|2018 FC|4}}
* {{mpl|2020 VT|1}}

== References ==
{{Reflist|refs=

<ref name="schmadel2003">{{citation
 | first = Lutz D.
 | last = Schmadel
 | title = Dictionary of minor planet names
 | page = 452
 | series = Physics and astronomy online library
 | edition = 5th
 | publisher = Springer
 | year = 2003
 | isbn = 3-540-00238-3
 | url = https://books.google.com/books?id=VoJ5nUyIzCsC&pg=PA452}}</ref>

<ref name="JPLSBDB">{{citation
 | first1 = Donald K.
 | last1 = Yeomans
 | title = 5261 Eureka (1990 MB)
 | work = JPL Small-Body Database Browser
 | publisher = [[NASA]]
 | url = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=5261
 | access-date = 13 April 2016
 | postscript = .}}</ref>

<ref name="Rivkin2007">{{citation
 | last1 = Rivkin | first1 = Andrew S.
 | last2 = Trilling | first2 = David E.
 | last3 = Thomas | first3 = Cristina A.
 | last4 = DeMeo | first4 = Francesca
 | last5 = Spahr | first5 = Timothy B.
 | last6 = Binzel | first6 = Richard P.
 | title     = Composition of the L5 Mars Trojans: Neighbors, not siblings
 | journal   = Icarus
 | volume    = 192
 | issue     = 2
 | pages     = 434–441
 |date=December 2007
 | bibcode   = 2007Icar..192..434R
 | doi       = 10.1016/j.icarus.2007.06.026
 | arxiv     = 0709.1925
 | s2cid = 15118710
 | postscript = .}}</ref>

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

;Further reading
* [http://www.cbat.eps.harvard.edu/iauc/05000/05045.html#Item1 IAUC 5045]
* [http://www.cbat.eps.harvard.edu/iauc/05000/05047.html#Item3 IAUC 5047]
* [http://www.cbat.eps.harvard.edu/iauc/05000/05067.html#Item1 IAUC 5067]
* [http://www.cbat.eps.harvard.edu/iauc/05000/05075.html#Item2 IAUC 5075]
* [[Andrew S. Rivkin|A. S. Rivkin]], [[Richard P. Binzel|R. P. Binzel]], [[Schelte J. Bus|S. J. Bus]], and [[Jennifer A. Grier|J. A. Grier]], "Spectroscopy and Classification of Mars Trojan Asteroids", ''Bulletin of the American Astronomical Society'' 34, 2002, p.&nbsp;840.
* [[Serge Tabachnik|S. Tabachnik]] and N. W. Evans, "Cartography for Martian Trojans", ''The Astrophysical Journal'' 517, 1999, pp.&nbsp;L63–L66.

== External links ==
* [http://orbitsimulator.com/gravity/articles/eureka.html The co-orbital asteroids of Mars] A simulation and animation showing Mars's co-orbital and near co-orbital asteroids
* [http://www.johnstonsarchive.net/astro/asteroidmoons.html Asteroids with Satellites], Robert Johnston, johnstonsarchive.net
* {{AstDys|5261}}
* {{JPL small body}}

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{{DEFAULTSORT:005261}}
[[Category:Mars trojans]]
[[Category:Discoveries by David H. Levy|Eureka]]
[[Category:Discoveries by Henry E. Holt|Eureka]]
[[Category:Named minor planets|Eureka]]
[[Category:Binary asteroids]]
[[Category:Sr-type asteroids (SMASS)]]
[[Category:Astronomical objects discovered in 1990|19900620]]