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A. S. Rivkin, R. P. Binzel (MIT), E. S. Howell (Arecibo Observatory), S. J. Bus (IRTF), J. A. Grier (PSI)
Mars is the only planet other than Jupiter known to have co-orbiting ``Trojan" asteroids. We have obtained visible and near-IR reflectance spectra of three of these objects: 5261 Eureka and 1998 VF31 in the L5 region and 1999 UJ7 in the L4 region. We also obtained JHK spectrophotometry and some lightcurve data for 5261 Eureka. 5261 Eureka has a visible spectrum that is classified as Sr in the Bus taxonomy, and has infrared colors typical of the A-class asteroids. The data for 1998 VF31 have a restricted wavelength range, and are consistent with both the S and D classes, though we can rule out a C-class classification. 1999 UJ7 has an X-class spectrum, which is unlike that of the other two Mars Trojans. None of the asteroids have spectra like Mars, though 1999 UJ7 is consistent with a spectral unit on Phobos associated with Stickney crater.
Dynamical studies by Tabachnik and Evans (Ap. J. Lett., 1999) suggest that 5261 Eureka and 1998 VF31 are in dynamically stable orbits, leading them to suspect that they may be in primoridal orbits. The similarities in the spectra of these two bodies is consistent with this hypothesis. However, the spectrum of 1999 UJ7 is inconsistent with the other two. This is not what we would expect if all three of these bodies were still in their original formation regions. 1999 UJ7 appears to be near the edge of the L4 stability zone identified by Tabachnik and Evans, however a full dynamical model would be necessary to determine the long-term stability of its orbit.
This work was supported in part by the NASA PGG and Planetary Astronomy programs.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.