37th DPS Meeting, 4-9 September 2005
Session 7 Asteroids II
Oral, Monday, September 5, 2005, 2:00-3:50pm, Law LG19

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[7.07] A Long-Term Radar Survey of M-Class Asteroids

M.K. Shepard (Bloomsburg University), B.E. Clark (Ithaca College), L.A.M. Benner, J.D. Giorgini (Jet Propulsion Laboratory), E.S. Howell (Arecibo Observatory, NAIC), C. Magri (University of Maine, Farmington), M.C. Nolan (Arecibo Observatory, NAIC), S.J. Ostro (Jet Propulsion Laboratory)

We have begun a long-term radar survey of M-class asteroids. Because metals are denser and more radar reflective than silicates, an asteroid's radar cross-section can provide unambiguous information on its composition and near surface porosity [1]. Until August 2004, only eight M-class asteroids had been observed with radar: 16 Psyche [2,3], 21 Lutetia [3], 22 Kalliope [3], 83 Beatrix (unpublished), 97 Klotho [3], 216 Kleopatra [4], 796 Sarita [3], and 6178 (1986 DA) [1]. Of these, only two, 216 Kleopatra and 6178 (1986 DA), are unambiguously metallic [1,4]. Radar observations of 16 Psyche are consistent with a metal composition if the surface porosity is similar to the Moon (porosity of 30%-50%) [2]. A recent analysis of infrared spectra determined that Psyche and Kleopatra formed under reducing conditions and is also consistent with a metallic interpretation [5].

In the past year, we observed the M-class asteroids 129 Antigone, 135 Hertha, 224 Oceana, 325 Heidelberga, and 785 Zwetana using the Arecibo S-band radar. Our goal is to increase the number of radar observed M-class targets to ~40 within the next five years.

Acknowledgements. This work is partially supported by a grant from Bloomsburg University to MKS. The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is operated by Cornell University under a cooperative agreement with the National Science Foundation and with support from the National Aeronautics and Space Administration.

Refs. [1] Ostro et al. Science 252, 1399-1404, 1991. [2] Ostro et al. Science 229,442-446, 1985. [3] Magri et al. Icarus 140, 379-407, 1999. [4] Ostro et al. Science 288, 836-839, 2000. [5] Hardersen et al. Icarus 175, 141-158, 2005.

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