Surface composition of Iapetus

Iapetus surface composition (Credit: NASA/JPL/University of Arizona) 12 January 2005 This colour composite image of Saturn's moon Iapetus from NASA/ESA/ASI Cassini spacecraft was obtained on 31 December 2004, an hour and a half before the New Year. It was taken with Cassini's Visual and Infrared Mapping Spectrometer (VIMS) at a distance of 121 000 kilometres, with a spatial resolution of about 60 kilometres. The three colours used in the mosaic correspond to 1.01, 3.21, and 3.80 microns. The different colours represent vastly different surface compositions. The upper bright blue region is rich in water ice, while the lower, dark brown region is composed mainly of a substance rich in organic material. The yellow region consists of a mixture of ice and organics, suggesting a gradual change in composition on the surface. This pattern suggests Iapetus swept up the dark material, which may have come from debris created from meteoritic impacts onto the small, outer satellites of Saturn.   The Cassini-Huygens mission is a co-operative project of NASA, ESA and ASI, the Italian space agency.