Spectral Reflectance Properties of Mars-Crossing Asteroids

S. J. Bus, R. P. Binzel, T. H. Burbine (MIT)

Spectral reflectance properties have been measured for approximately 100 Mars-crossing asteroids as part of the Small Main-belt Asteroid Spectroscopic Survey (SMASS). These observations were obtained using a CCD spectrograph on the 2.4m Hiltner telescope of the Michigan-Dartmouth-MIT Observatory on Kitt Peak, and cover the wavelength interval from 4400-9200Å.

In this study, an asteroid is defined as Mars-crossing if its current osculating perihelion distance is greater than 1.3 AU, and if, as a result of gravitational perturbations, its orbit will eventually intersect that of Mars as estimated using the secular perturbation theory of Williams (J. G. Williams, Ph.D. thesis, 1969). Knowing the distribution of taxonomic types among these asteroids is critical for achieving a bias-corrected estimate for the population of Mars-crossers. In addition, a comparison of these spectra with those of the near-Earth asteroids can be used to assess the contribution Mars-crossers may make to the resupply of NEAs. Our data indicate that a majority of the Mars-crossing asteroids can be classified as S-types, and that the diversity seen among their spectra is smaller than that seen in the NEA population, suggesting that Mars-crossers may be more closely associated with inner main-belt asteroids than with the NEAs. We will examine these Mars-crossing asteroid spectra for trends with respect to asteroid diameter, and orbital elements, including the Mars-crossing depth and collisional probability. This research is supported by NASA Grant NAGW-1450 and The Planetary Society.