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TY - JOUR AU - Thomas, P. C. AU - Armstrong, J. W. AU - Asmar, S. W. AU - Burns, J. A. AU - Denk, T. AU - Giese, B. AU - Helfenstein, P. AU - Iess, L. AU - Johnson, T. V. AU - McEwen, A. AU - Nicolaisen, L. AU - Porco, C. AU - Rappaport, N. AU - Richardson, J. AU - Somenzi, L. AU - Tortora, P. AU - Turtle, E. P. AU - Veverka, J. PY - 2007 DA - 2007/07/01 TI - Hyperion's sponge-like appearance JO - Nature SP - 50 EP - 53 VL - 448 IS - 7149 AB - Saturn's moon Hyperion, an irregular shaped object in a tumbling orbit, looks odd: the Cassini flyby of September 2005 revealed a unique spongy surface. Two papers this week present the initial Cassini results. First, imaging and radio data suggest that the spongy appearance is caused by impact cratering on a porous body. And second, near-infrared and ultraviolet spectroscopy reveal details of the surface composition of the highly reflective areas that cover much of the surface, and also of the darker areas, mostly at the bottom of craters. The spectra are consistent with the presence of water ice contaminated with an organic solid. The low-albedo (dark) material is spectroscopically similar to that found on two other saturnian moons, Iapetus and Phoebe, containing a mixture of water ice, complex organics, carbon dioxide and nitriles. This cocktail of materials resembles those seen in comets and probably in Kuiper Belt objects. SN - 1476-4687 UR - https://doi.org/10.1038/nature05779 DO - 10.1038/nature05779 ID - Thomas2007 ER -