|Discovered by||David H. Levy and Henry Holt|
|Discovery date||20 June 1990|
|Orbital characteristics |
|Epoch 13 January 2016 ( JD 2457400.5)|
|Uncertainty parameter 0|
|Observation arc||13267 days (36.32 yr)|
|Aphelion||1.6222 AU (242.68 Gm)|
|Perihelion||1.4249 AU (213.16 Gm)|
|1.5236 AU (227.93 Gm)|
|1.88 yr (686.89 d)|
Average orbital speed
|24.11 km/ s|
|0° 31m 26.76s / day|
|Earth MOID||0.497052 AU (74.3579 Gm)|
|Jupiter MOID||3.52162 AU (526.827 Gm)|
~2–4 km H
|2.6902 h (0.11209 d)|
|Temperature||~250  K|
|S(I)  (Gaffey)|
|16.0,  16.1 |
5261 Eureka is the first Mars trojan discovered.  It was discovered by David H. Levy and Henry Holt at Palomar Observatory on 20 June 1990.  It trails Mars (at the L5 point) at a distance varying by only 0.3 AU during each revolution (with a 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 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: 1999 UJ7 at the L4 point, 1998 VF31 at the L5 point,  and 2007 NS2, also at the L5 point.  At least five other asteroids in near-1:1 resonances with Mars have been discovered, but they do not exhibit trojan behavior. They are 2001 FR127, 2001 FG24, (36017) 1999 ND43, 1998 QH56 and (152704) 1998 SD4. Due to close orbital similarities, most of the other, smaller, members of the L5 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). 
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]
|Discovery date||28 November 2011|
|Epoch 9 December 2014|
|0.7054 ± 0.0004 d|
On 28 November 2011, a natural satellite of 5261 Eureka was found. It has yet to be named, and its provisional designation is S/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. 
- (101429) 1998 VF31
- (121514) 1999 UJ7
- (311999) 2007 NS2
- (385250) 2001 DH47
- 2009 SE
- 2011 SC191
- 2011 SL25
- 2011 SP189
- 2011 UB256
- 2011 UN63
- 2016 CP31
- 2018 EC4
- 2018 FC4
- 2020 VT1
- Schmadel, 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 or participating institution membership required.)
- Yeomans, Donald K., "5261 Eureka (1990 MB)", JPL Small-Body Database Browser, NASA, retrieved 13 April 2016.
- 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.
- "List of Martian Trojans". Retrieved 26 February 2011.
- 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. Retrieved 6 September 2015.
- Further reading
- IAUC 5045
- IAUC 5047
- IAUC 5067
- IAUC 5075
- A. S. Rivkin, R. P. Binzel, S. J. Bus, and J. A. Grier, "Spectroscopy and Classification of Mars Trojan Asteroids", Bulletin of the American Astronomical Society 34, 2002, p. 840.
- S. Tabachnik and N. W. Evans, "Cartography for Martian Trojans", The Astrophysical Journal 517, 1999, pp. L63-L66.
- The co-orbital asteroids of Mars A simulation and animation showing Mars's co-orbital and near co-orbital asteroids
- Asteroids with Satellites, Robert Johnston, johnstonsarchive.net
- 5261 Eureka at AstDyS-2, Asteroids—Dynamic Site
- 5261 Eureka at the JPL Small-Body Database