Spectral properties of near-earth objects: Palomar and IRTF results for 48 objects including spacecraft targets (9969) Braille and (10302) 1989 ML

We present results of visible wavelength spectroscopic measurements for 48 near-Earth objects (NEOs) obtained with the 5-m telescope at Palomar Mountain Observatory during 1998, 1999, and early 2000. The compositional interpretations for 15 of these objects have been enhanced by the addition of near-infrared spectra obtained with the NASA Infrared Telescope Facility, One-third of our sampled objects fall in the Sq and Q classes and resemble ordinary chondrite meteorites. Overall our sample shows a cleat transition between S-type and Q-type compositional classes over visible and near-infrared wavelengths. Taken together these results point toward an abundance of near-Earth asteroids capable of providing sources for ordinary chondrite meteorites. Our sampling strategy favors targeting the smallest observable objects and we report results for the 15-m diameter object 1998 BT13, the smallest spectroscopically measured NEO to date. NEOs show a greater spectral diversity than main-belt asteroids, and our small sample includes objects falling in the rare categories of K, L, O, and V classes. The K-class object 1999 JD6 is found to match CV chondrite meteorites. Potential spacecraft targets received top priority for observation, with the ordinary chondrite-like composition of (9969) Braille being reported prior to the Deep Space-1 encounter. The relatively accessible asteroid (10302) 1989 ML displays a neutral spectrum that may be interpreted as a shock-darkened ordinary chondrite. (C) 2001 Academic Press.