5261 Eureka

S/2011 (5261) 1
Discovery
Discovery date	28 November 2011
Designations
Designation	(5261) Eureka
Orbital characteristics
	Epoch9 December 2014
Semi-major axis	2.1 km
Orbital period (sidereal)	0.7054 ± 0.0004 d
Physical characteristics
Dimensions	0.46 km

5261 Eureka
Discovery
Discovered by	David H. Levyand Henry Holt
Discovery date	20 June 1990
Designations
Pronunciation	/jʊˈriːkə/yuurr-EE-kə
Named after	Eureka
Alternative designations	1990 MB
Minor planet category	Martian L5
Orbital characteristics
	Epoch13 January 2016 (JD2457400.5)
	Uncertainty parameter0
Observation arc	13267 days (36.32 yr)
Aphelion	1.6222AU(242.68Gm)
Perihelion	1.4249 AU (213.16 Gm)
Semi-major axis	1.5236 AU (227.93 Gm)
Eccentricity	0.064766
Orbital period (sidereal)	1.88yr(686.89d)
Averageorbital speed	24.11 km/s
Mean anomaly	145.29°
Mean motion	0° 31m26.76s/ day
Inclination	20.280°
Longitude of ascending node	245.057°
Argument of perihelion	95.456°
Knownsatellites	1
EarthMOID	0.497052 AU (74.3579 Gm)
JupiterMOID	3.52162 AU (526.827 Gm)
TJupiter	4.428
Physical characteristics
Dimensions	1.3km; ~2–4 kmH
Synodic rotation period	2.6902h(0.11209d)
Geometric albedo	0.39
Temperature	~250K
Spectral type	S(I)(Gaffey)
Absolute magnitude(H)	16.0,16.1

5261 Eurekais the firstMars trojandiscovered.^[5]It was discovered byDavid H. Levyand Henry Holt atPalomar Observatoryon 20 June 1990.^[1]It trailsMars(at theL₅point) at a distance varying by only 0.3AUduring each revolution (with asecular trendsuperimposed, changing the distance from 1.5–1.8 AU around 1850 to 1.3–1.6 AU around 2400). Minimum distances fromEarth,Venus,andJupiter,are 0.5, 0.8, and 3.5 AU, respectively.

Long-termnumerical integrationshows that the orbit is stable.Kimmo A. InnanenandSeppo Mikkolanote that "contrary to intuition, there is clearempirical evidencefor the stability of motion around theL₄andL₅points of all the terrestrial planets over a timeframe of several million years ".

Since the discovery of 5261 Eureka, theMinor Planet Centerhas recognized three other asteroids as Martian trojans:1999 UJ7at theL₄point,1998 VF31at theL₅point,^[5]and2007 NS2,also at theL₅point.^[6]At least five other asteroids in near-1:1resonanceswith Mars have been discovered, but they do not exhibit trojan behavior. They are2001 FR127,2001 FG24,(36017) 1999 ND₄₃,1998 QH56and(152704) 1998 SD₄.Due to close orbital similarities, most of the other, smaller, members of the L₅group are hypothesized to be fragments of 5261 Eureka that were detached after it was spun up by theYORP effect(consistent with its rotational period of 2.69 h).^[7]

Theinfraredspectrum for 5261 Eureka is typical for anA-type asteroid,but the visual spectrum is consistent with an evolved form ofachondritecalled anangrite.A-class asteroids are tinted red in hue, with a moderatealbedo.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 theSolar System.^{[citation needed]}

Satellite[edit]

On 28 November 2011, anatural satelliteof 5261 Eureka was found. It has yet to be named, and its provisional designation isS/2011 (5261) 1.The moon is about 0.46 km in diameter and orbits 2.1 km from Eureka. The satellite's existence was announced in September 2014.^[8]

References[edit]

^^a ^bSchmadel, Lutz D. (2003),Dictionary of minor planet names,Physics and astronomy online library (5th ed.), Springer, p. 452,ISBN 3-540-00238-3
^"Eureka".Oxford English Dictionary(Online ed.).Oxford University Press.(Subscription orparticipating institution membershiprequired.)
^^a ^bYeomans, Donald K.,"5261 Eureka (1990 MB)",JPL Small-Body Database Browser,NASA,retrieved13 April2016.
^^a ^b ^c ^d ^eRivkin, Andrew S.; Trilling, David E.; Thomas, Cristina A.; DeMeo, Francesca; Spahr, Timothy B.; Binzel, Richard P. (December 2007), "Composition of the L5 Mars Trojans: Neighbors, not siblings",Icarus,192(2): 434–441,arXiv:0709.1925,Bibcode:2007Icar..192..434R,doi:10.1016/j.icarus.2007.06.026,S2CID 15118710.
^^a ^b"List of Martian Trojans".Retrieved26 February2011.
^MPEC 2007-O09: 2007 NS2
^Lovett, R. (20 October 2017). "Sun's light touch explains asteroids flying in formation behind Mars".Science.doi:10.1126/science.aar2794.
^Johnston, Robert (16 November 2014)."(5261) Eureka".Johnston's Archive.Retrieved6 September2015.

Further reading

IAUC 5045
IAUC 5047
IAUC 5067
IAUC 5075
A. S. Rivkin,R. P. Binzel,S. J. Bus,andJ. A. Grier,"Spectroscopy and Classification of Mars Trojan Asteroids",Bulletin of the American Astronomical Society34, 2002, p. 840.
S. Tabachnikand N. W. Evans, "Cartography for Martian Trojans",The Astrophysical Journal517, 1999, pp. L63–L66.

External links[edit]

The co-orbital asteroids of MarsA simulation and animation showing Mars's co-orbital and near co-orbital asteroids
Asteroids with Satellites,Robert Johnston, johnstonsarchive.net
5261 EurekaatAstDyS-2, Asteroids—Dynamic Site
- Ephemeris·Observation prediction·Orbital info·Proper elements·Observational info
5261 Eurekaat theJPL Small-Body Database
- Close approach·Discovery·Ephemeris·Orbit diagram·Orbital elements·Physical parameters

[schmadel2003-1] Schmadel, Lutz D. (2003),Dictionary of minor planet names,Physics and astronomy online library (5th ed.), Springer, p. 452,ISBN 3-540-00238-3

[2] "Eureka".Oxford English Dictionary(Online ed.).Oxford University Press.(Subscription orparticipating institution membershiprequired.)

[JPLSBDB-3] Yeomans, Donald K.,"5261 Eureka (1990 MB)",JPL Small-Body Database Browser,NASA,retrieved13 April2016.

[Rivkin2007-4] Rivkin, Andrew S.; Trilling, David E.; Thomas, Cristina A.; DeMeo, Francesca; Spahr, Timothy B.; Binzel, Richard P. (December 2007), "Composition of the L5 Mars Trojans: Neighbors, not siblings",Icarus,192(2): 434–441,arXiv:0709.1925,Bibcode:2007Icar..192..434R,doi:10.1016/j.icarus.2007.06.026,S2CID 15118710.

[mtrojans-5] "List of Martian Trojans".Retrieved26 February2011.

[6] MPEC 2007-O09: 2007 NS2

[Lovett2017-7] Lovett, R. (20 October 2017). "Sun's light touch explains asteroids flying in formation behind Mars".Science.doi:10.1126/science.aar2794.

[8] Johnston, Robert (16 November 2014)."(5261) Eureka".Johnston's Archive.Retrieved6 September2015.

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