1. NASA Ames Research Center, MS 245-6
2. USRA/SOFIA, NASA Ames Research Center, MS 211-3, Moffett Field, California 94035, USA
3. SETI Institute, 515 N. Whisman Road, Mountain View, California 94043, USA
4. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA
5. DLR, Institute for Planetary Exploration, Rutherfordstrasse 2, D-12489 Berlin, Germany
6. INAF-IASF Istituto di Astrofisica Spaziale e Fisica Cosmica,
7. INAF-IASF Istituto dello Spazio Interplanetario, Via del Fosso del Cavaliere, 100, 00133 Roma, Italy
8. USGS, Mail Stop 964, Box 25046, Denver Federal Center, Denver, Colorado 80225, USA
9. Lunar and Planetary Laboratory and Steward Observatory, University of Arizona, Tucson, Arizona 85721, USA
10. Space Science Institute NW, 22 Fiddler's Road, Winthrop, Washington 98862-0667, USA
11. Cornell University, 418 Space Sciences Building, Ithaca, New York 14853, USA
12. University of Nantes, BP 92208, 2 rue de la Houssinière, 44072 Nantes Cedex 3, France
13. Observatoire de Paris-Meudon, Département Recherche Spatial, 5 Place Jules Jannsen, 95129 Meudon Cedex, France
14. Université de Paris Sud-Orsay, Institut d'Astrophysique Spatial, Batiment 120, 91405 Orsay Cedex, France
15. INAF-OAC Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli, Italy

Correspondence to: D. P. Cruikshank¹ Correspondence and requests for materials should be addressed to D.P.C. (Email: Dale.P.Cruikshank@nasa.gov).

Hyperion, Saturn's eighth largest icy satellite, is a body of irregular shape in a state of chaotic rotation^{1, 2}. 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.

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