5261 Eureka

Infobox Planet | discovery=yes | physical_characteristics = yes | bgcolour=#FFFFC0
name=5261 Eureka
discoverer=David H. Levy
discovered=June 20, 1990
alt_names=1990 MB
mp_category=Mars-crosser asteroid
epoch=July 14, 2004 (JD 2453200.5)
semimajor=227.908 Gm (1.523 AU)
perihelion=213.132 Gm (1.425 AU)
aphelion=242.684 Gm (1.622 AU)
eccentricity=0.065
period=686.829 d (1.88 a)
inclination=20.280°
asc_node=245.108°
arg_peri=95.361°
mean_anomaly=104.086°
avg_speed=24.11 km/s
dimensions=~2-4 km
mass=? kg
density=? g/cm³
surface_grav=? m/s²
escape_velocity=? km/s
rotation=? d
spectral_type=?
abs_magnitude=16.1
albedo=?
single_temperature=~225 K

5261 Eureka (pronEng|jʊˈriːkə) was discovered at Mt Palomar on June 20, 1990 and turned out to be the first known Mars Trojan asteroid. 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 the 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: mpl|1999 UJ|7 at the L₄ point, mpl|1998 VF|31 at the L₅ point, [http://cfa-www.harvard.edu/iau/lists/MarsTrojans.html] and mpl|2007 NS|2, also at the L₅ point. [http://www.cfa.harvard.edu/mpec/K07/K07O09.html] At least six other asteroids have been discovered which are in near 1:1 resonances with Mars, but fail to exhibit trojan behavior. They are mpl|2001 FR|127, mpl|2001 FG|24, mpl|2001 DH|47, mpl|1999 ND|43, mpl|1998 QH|56 and mpl|1998 SD|4. [http://www.orbitsimulator.com/gravity/articles/eureka.html] [http://www.orbitsimulator.com/cgi-bin/yabb/YaBB.pl?num=1178159570]

The infrared spectrum for 5261 Eureka is typical of an A-class 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.

References

* [http://cfa-www.harvard.edu/iauc/05000/05045.html#Item1 IAUC 5045]
* [http://cfa-www.harvard.edu/iauc/05000/05047.html#Item3 IAUC 5047]
* [http://cfa-www.harvard.edu/iauc/05000/05067.html#Item1 IAUC 5067]
* [http://cfa-www.harvard.edu/iauc/05000/05075.html#Item2 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

* [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