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Radar observations of E-class Asteroids 44 Nysa and 434 Hungaria |
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| Authors: | Michael K Shepard Karelyn M Kressler Maureen E Ockert-Bell Ellen S Howell Jon D Giorgini Steven J Ostro |
| Institution: | a Department of Geography and Geosciences, Bloomsburg University, 400 E. Second St., Bloomsburg, PA 17815, USA b Department of Physics and Astronomy, Earlham College, Richmond, IN 47374, USA c Department of Physics, Ithaca College, 267 Center for Natural Science, Ithaca, NY 14850, USA d Arecibo Observatory, National Astronomy and Ionosphere Center, HC03 Box 53995, Arecibo, PR 00612, USA e University of Maine at Farmington, 173 High Street-Preble Hall, Farmington, ME 04938, USA f 301-150, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USA g 300-233, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USA |
| Abstract: | We observed the E-class main-belt Asteroids (MBAs) 44 Nysa and 434 Hungaria with Arecibo Observatory's S-band (12.6 cm) radar. Both asteroids exhibit polarization ratios higher than those measured for any other MBA: Nysa, μc=0.50±0.02 and Hungaria, μc=0.8±0.1. This is consistent with the high polarization ratios measured for every E-class near-Earth asteroid (NEA) observed by Benner et al. Benner, L.A.M., and 10 collegues, 2008. Icarus, submitted for publication] and suggests a common cause. Our estimates of radar albedo are 0.19±0.06 for Nysa and 0.22±0.06 for Hungaria. These values are higher than those of most MBAs and, when combined with their high polarization ratios, suggest that the surface bulk density of both asteroids is high. We model Nysa as an ellipsoid of dimension 113×67×65 km (±15%) giving an effective diameter Deff=79±10 km, consistent with previous estimates. The echo waveforms are not consistent with a contact binary as suggested by Kaasalainen et al. Kaasalainen, M., Torppa, J., Piironen, J., 2002. Astron. Astrophys. 383, L19-L22]. We place a constraint on Hungaria's maximum diameter, Dmax?11 km consistent with previous size estimates. |
| Keywords: | Asteroids Asteroids composition Asteroids surfaces Radar observations |
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