36th DPS Meeting, 8-12 November 2004
Session 32 Asteroids
Poster II, Thursday, November 11, 2004, 4:15-7:00pm, Exhibition Hall 1A

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[32.11] Orbital Distribution of Main-belt S-type Asteroids

S. J. Bus (IfA, UH), R. P. Binzel (MIT), E. L. Volquardsen (IfA, UH), J. L. Berghuis (UH-Hilo)

We present preliminary results from an ongoing near-infrared spectroscopic survey of silicate-rich asteroids. The goals of this survey are to sample the full range of silicate mineralogies present in the main belt for asteroids with diameters larger than 5 km, and to map the distributions of these mineralogies as functions of orbital elements. Results from this work will help place constraints on conditions in the inner solar system during proto-planetary formation, and on the degree of heating/differentiation that occurred in the asteroid belt.

The largest class of silicate-rich asteroids is the S-types. Members of this class have spectra containing diagnostic absorption bands centered near 1- and 2-microns. Variations in these bands are indicative of a wide range in pyroxene/olivine compositions (i.e. Gaffey et al. 1993, Icarus 106, 573). Our study of the S-type asteroids combines visible-wavelength spectra from the SMASSII survey (Bus and Binzel 2002, Icarus 158, 106) with high S/N near-IR (0.8 - 2.5 micron) spectra that are being obtained with SpeX (Rayner et al. 2003, PASP 115, 362) at the NASA Infrared Telescope Facility. The analysis presented here uses both band-parameter measurements (Cloutis et al. 1986, JGR 91, 11641) and principal component analysis (PCA) to group the S-type asteroids into sub-classes based on their spectral properties and inferred compositions. Based on our present sample of over 150 asteroids, we examine the distributions of these groupings as functions of orbital semi-major axis, eccentricity and inclination. Our goal is to determine the amount of spectral variation present among members of several dynamical families, and to look for larger-scale trends in olivine/pyroxene composition with heliocentric distance that may provide clues about heating across the early asteroid belt.

This work was supported by NSF grant AST-0307688.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.