Surface composition of Hyperion
Sotin, C.; Brown, R. H.; Baines, K. H.; Buratti, B. J.; Clark, R. N.; Nicholson, P. D.; Bibring, J. -P.; Langevin, Y.; Bellucci, G.; Jaumann, R.; Stephan, K.; Hansen, C. J.; Hendrix, A. R.; Drossart, P.; Mennella, V.; Capaccioni, F.; McCord, T. B.; Cruikshank, D. P.; Dalton, J. B.; Sicardy, B.; Cerroni, P.; Coradini, A.; Formisano, V.; Matson, D. L.; Nelson, R. M.; Filacchione, G.; Tosi, F.; Combes, M.; Dalle Ore, C. M.; Bauer, J.; Meyer, A. W.
United States, Germany, Italy, France
Abstract
Hyperion, Saturn's eighth largest icy satellite, is a body of irregular shape in a state of chaotic rotation. The surface is segregated into two distinct units. A spatially dominant high-albedo unit having the strong signature of H2O ice contrasts with a unit that is about a factor of four lower in albedo and is found mostly in the bottoms of cup-like craters. Here we report observations of Hyperion's surface in the ultraviolet and near-infrared spectral regions with two optical remote sensing instruments on the Cassini spacecraft at closest approach during a fly-by on 25-26 September 2005. The close fly-by afforded us the opportunity to obtain separate reflectance spectra of the high- and low-albedo surface components. The low-albedo material has spectral similarities and compositional signatures that link it with the surface of Phoebe and a hemisphere-wide superficial coating on Iapetus.