Compositional Distribution of Near-Earth Asteroids:
New Results for 80 Objects

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

We report new spectroscopic observations for about 80 near-Earth asteroids. These observations allow the compositional distribution of near-Earth asteroids to be compared with the distributions measured for main-belt asteroids and meteorites. For all objects in our sample, we obtained visible wavelength spectra, typically covering 0.45- to 0.95-microns, by utilizing the 2.4m Hiltner telescope at Kitt Peak, AZ. For nearly 20 objects, we extended our spectral coverage to about 1.7-microns utilizing the new "Asteroid Grism" system and NSFCAM detector developed by one of us (RPB) for use at the IRTF at Mauna Kea. Our observations demonstrate the limiting magnitudes for our infrared and visible spectroscopy capabilities to be near V magnitudes 17.5 and 18.5, respectively.

Near-Earth asteroids display a spectral diversity as great, or greater, than main-belt asteroids. More importantly, we have identified at least six near-Earth asteroids (in addition to new observations of 1862 Apollo) which have spectra matching ordinary chondrite meteorites (Binzel et al. 1996, Science 273, 946). Overall the compositional distribution of near-Earth asteroids provides a much closer match to meteorites and appears to fill in the gap in spectral properties previously existing between main-belt asteroids and meteorites. This research is supported by NASA Grant NAGW-1450, NSF Grant AST-9530282, and The Planetary Society.