Comparisons of meteorite and asteroid spectral reflectivities

Abstract

Laboratory spectral reflectivities have been measured for 41 meteorites, including 22 ordinary chondrites of all chemical and petrologic types. They are compared with available spectral reflectivities for 36 asteroids. We find that absorption band depths, center positions, and breadths are diagnostic of the various types of ordinary chondrites, and that other meteorite types may also be distinguished by reflectivity characteristics. Asteroid spectral reflectivities approximately resemble those for meteorites (especially unequilibrated types), and the range of differences among asteroids is similar to that for meteorites. However, detailed comparisons show that few meteorites exactly match observed asteroids in spectral properties. Impact vitrification and shock can modify the spectral reflectance of materials, but vitrification, at least, is an unimportant process on asteroidal regoliths. Assuming the comparisons can be taken at face value, we conclude that ordinary chondrites either do not come from the main asteroid belt or they come from a few unusual asteroids. Some asteroidal/meteorite matches have been found for enstatite chondrites, a basaltic achondrite, an optically unusual L6 chondrite, and possibly a carbonaceous chondrite. Only 1685 Toro, an Earth-crossing asteroid, resembles typical ordinary chondrites.