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B.E. Clark (Ithaca College), A.S. Rivkin (M.I.T.), S.J. Bus (University of Hawaii)
We have initiated a program of infrared observations of the X-type asteroids, a mysterious class of objects with ambiguous taxonomic and mineralogic interpretations. Infrared spectroscopy is critical to resolving the composition of the X-types because these asteroids have visible spectra that are degenerate with the E, M, and P-type asteroids (Tholen 1984). The results of this project will be a full characterization of the X-types, including spectral, albedo and size properties. The observations have begun and are being conducted at the NASA Infrared Telescope Facility (IRTF) in a series of 3 phases. The motivating questions we ask are: What are the X-types made of? How would knowledge of their composition change our picture of the geological structure of the asteroid regions?
X-type asteroids are important in the main belt, yet we do not understand their composition or meteorite linkage. This is an outstanding problem in asteroid-meteorite studies, because (a) X-types are a significant fraction of the known asteroid population, comprising 20% of the inner main belt (Tholen 1984; Bus 1999), and (b) models of the geological structure of the asteroid belt depend partly on the composition of the X-types (Bell et al. 1989; Gaffey et al. 1989). Our research plan for observations of X-type asteroids will allow us to constrain their compositions and meteorite linkages. This information will shed new light on the geological structure of the main asteroid belt.
We will present preliminary results of our X-type asteroid exploration. Specifically, results from the first two near-infrared spectroscopy surveys are ready for analysis. These data were obtained with the SpeX instrument at the IRTF, from 0.8 to 2.5 microns. These initial observations are useful for a first-cut classification of the X-types into component sub-types: E, M, P, and core-X, based on subtle spectral features and continuum slope ranges.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.