On 11 June 2004, Cassini-Huygens sees probable evidence on Phoebe of an ice-rich body overlain with a thin layer of dark material.
The sharply-defined crater at above centre exhibits two or more layers of alternating bright and dark material.
Imaging scientists on the Cassini-Huygens mission have hypothesised that the layering might occur during the crater formation, when ejecta thrown out from the crater buries the pre-existing surface that was itself covered by a relatively thin, dark deposit over an icy mantle.
The lower thin dark layer on the crater wall appears to define the base of the ejecta blanket. The ejecta blanket itself appears to be mantled by a more recent dark surface 'lag'.
The Cassini-Huygens mission is a co-operative project of NASA, ESA and the Italian Space Agency.
Credits: NASA/JPL/Space Science Institute