Iapetus: Unique Surface Properties and a Global Color Dichotomy from Cassini Imaging

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Science  10 Dec 2009:
DOI: 10.1126/science.1177088


Since 2004, Saturn's moon Iapetus has been observed repeatedly with the ISS camera of the Cassini spacecraft. The images show numerous impact craters down to the resolution limit of ~10 m/pixel. Small bright craters within the dark hemisphere indicate a dark blanket thickness on the order of meters or less. Dark equator-facing and bright poleward-facing crater walls suggest temperature-driven water-ice sublimation as the process responsible for local albedo patterns. Imaging data also reveal a global color dichotomy, wherein both dark and bright materials on the leading side have a substantially redder color than the respective trailing-side materials. This global pattern indicates an exogenic origin for the redder leading-side parts, and suggests that the global color dichotomy initiated the thermal formation of the global albedo dichotomy.