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M.D. Hicks, B.J. Buratti (JPL), D.L. Rabinowitz (Yale University)
Centaurs, Extinct Comet Candidates (ECCs) and Near-Earth Asteroids (NEAs) are three distinct yet interrelated classes of primitive solar system bodies and may represent the most accessible and pristine remnants of early solar system formation. The cataloged numbers of each population is greatly increasing, with the enhanced discovery rates provided by the automated NEA discovery programs.
Since 1998 we have been collecting low-resolution CCD spectra of these bodies with the 200-inch Hale telescope and facility CCD spectrometer. We present our preliminary results which includes 6 ECCs, 3 Centaurs, and 18 NEAs.
Our spectral studies confirm the results obtained with our ongoing broadband NEA photometric program (Rabinowitz, Icarus 134, 1998; Rabinowitz and Hicks, DPS #30 1998), namely that there are strong size and orbit dependent trends in the reflectance colors of Earth-approaching asteroids. We find that our ECC spectra exhibit featureless flat to modestly red slopes spanning the range from C to D-type asteroids, comparable with the spectral diversity measured for cometary nuclei (Luu, Icarus 104, 1993). One of our Centaurs, 1999 UG5, manifests an extremely red slope similar to that of 5145 Pholus and 7066 Nessus, supporting the theory that the apparent bimodal distribution in spectral slopes of Kuiper Belt Objects (Tegler and Romanishin, Nature 392, 1998) may exist in the Centaurs as well (Davies et al, Icarus 134, 1998).
This work is supported by NASA.