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R. A. Fevig, U. Fink (LPL, University of Arizona)
We report the results of our visible to near-infrared observations from 0.55 to 1.00 microns of near-Earth asteroids (NEAs) in our ongoing survey. All observations were made with the University of Arizona Steward Observatory Catalina Site 154 cm telescope using the Lunar and Planetary Laboratory Spectrograph designed by Uwe Fink. These 40 moderate-resolution spectra, along with 14 previously published spectra from this survey (Hicks, M. D., U. Fink and W. M. Grundy 1998. Icarus 133, 69-78), show that there are a number of NEAs with spectral signatures consistent with the most common type of meteorite fall, the ordinary chondrites (OCs), with a slight trend toward increasing numbers of such objects with diminishing size in our sample. We also see evidence for orbit dependent trends in our data. The majority of objects with OC-like spectra are in highly eccentric orbits which encounter asteroids (meteoroids) in the main belt and experience multiple terrestrial planet crossings during each of their dynamically unstable orbits. S-type NEAs reside primarily in more dynamically stable orbits which cross only Mars and either never encounter main-belt objects or do so at relatively low energies due to low eccentricity orbits. While these findings should be considered preliminary since our current sample size is relatively small, they might help to explain how the surfaces of asteroids composed of OC material are modified to exhibit S-type spectra.
This research has been funded in part by NASA Planetary Astronomy Grant NAG 53937 and NASA Training Grant NGT 550243.