Iapetus is historically the most intriguing satellite of Saturn because of its color dichotomy. A major advance in the understanding of the origin of the dichotomy has come recently from two fundamental pieces of information. The first was the discovery by Verbiscer et al. (2009) of a ring of dark material that originates in the Phoebe’s neighborhood and spirals down to Iapetus collecting on its leading side. The second fundamental piece of information comes from thermal modeling of Iapetus’ surface. This has demonstrated that the darkening of the leading side results in a temperature rise of a few degrees on that hemisphere of Iapetus. Consequently, the higher temperature causes the H2O ice to sublimate and effectively migrate to cooler regions of the surface making them brighter and colder.
A variation in the color of the dark material in different regions of the surface of Iapetus has also been reported, suggesting differing properties possibly related to the nature and origin of the material. Dr. Dalle Ore used a statistical tool to explore a mosaic of 30 spectral image cubes of a portion of the surface of Iapetus observed in 2007 with the Cassini Visible-Infrared Mapping Spectrometer (VIMS). She has identified the spectroscopic signature of the dark materials and she will compare it to the spectra of dark materials detected on the surface of other satellites in the Saturn system to trace their theoretically predicted origin.