5261 Eureka

5261 Eureka is the first Mars trojan discovered.^[5] It was discovered by David H. Levy and Henry Holt at Palomar Observatory on 20 June 1990.^[1] 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,^[5] and 2007 NS2, also at the L₅ point.^[6] 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).^[7]

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]}

Satellite

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.^[8]

See also

• (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

References

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.

External links

• 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
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 5261 Eureka at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters