Iapetus surface composition

This colour composite image of Saturn's moon Iapetus from Cassini's Visual and Infrared Mapping Spectrometer (VIMS) was obtained on 31 December 2004, 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 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.