Surface composition of Hyperion

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Hyperion, Saturn’s eighth largest icy satellite, is a body of irregular shape in a state of chaotic rotation1,2. 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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Figure 1: Image and spectra from Cassini’s UVIS.
Figure 2: Spectra and models from Cassini’s VIMS.
Figure 3: Compositional map of a region of Hyperion.


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We thank the many people in the Cassini Project whose skills and diligence have made the mission to Saturn a success. The Cassini Project is managed by the Jet Propulsion Laboratory.

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Correspondence to D. P. Cruikshank.

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