5261 Eureka

5261 Eureka 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, other Mars Trojans have been identified; namely at the L₄ point and , , , and at the L₅ point. The co-orbitals and will not remain as Trojans —they will be perturbed away by Mars within the next 500,000 years or so.

Note, however, that as of 2005 the Minor Planet Center does not officially recognize any asteroid as being a Mars Trojan "in light of some recent ill-informed speculations on an astronomy-related Yahoo group of which the MPC has been made aware, this [Martian Trojan list is being removed for the foreseeable future."

The infrared spectrum for this asteroid 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

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, 2002, Bulletin of the American Astronomical Society, 34, #3.
S. Tabachnik and N. W. Evans, Cartography for Martian Trojans, April 1999.

Mars Trojans | A-type asteroids

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References