CASSINI VIMS: ONE YEAR OF COMPOSITIONAL MAPPING OF SURFACES IN THE SATURN SYSTEM AND THE ROLE OF WATER, CYANIDE COMPOUNDS AND CARBON DIOXIDE

The Cassini Visual and Infrared Mapping Spectrometer (VIMS) has completed one year of mapping in Saturn orbit and has provided a wealth of compositional information on the satellite surfaces and rings. While water ice is abundant in the Saturn system, carbon dioxide, cyanide compounds, and organic materials are also detected. The 2.42-micron absorption first observed on Phoebe (Clark et al., Nature, v435, 66-69, 2005), is reported here for the first time on Iapetus, Dione, and the F-ring. Trapped CO2 has also been discovered in the darker regions on Dione and Hyperion. Possible trace amounts of CO2 are seen on Mimas, Tethys, and Rhea, although near the calibration noise limit of VIMS and no CO2 is detected on Enceladus or the F-ring. No 2.42-micron feature has yet been detected in spectra of Hyperion, but VIMS has yet to adequately spatially resolve the darker regions. Following Clark et al., 2005, the 2.42-micron band is due to cyanide compounds, and while the exact cyanide composition is still under study, complex CN molecules are ruled out by observed spectral structure favoring simple molecules such as KCN or HCN. Ultraviolet photolysis experiments conducted on cyanide compounds, nitriles, and organic compounds show that the origin of the trapped CO2 on the satellites of both Jupiter and Saturn can be explained by photolysis of cyanide compounds. The UV photolysis of laboratory samples shows the growth of CO2 with a corresponding decrease in CN, and the production of a brown color, commonly observed in the creation of tholins. The oxygen most likely comes from water in the systems. The cyanide photolysis appears to occur in the Saturn and Jupiter systems and probably in comets explaining a common link in chemistry, photochemical processing, and the commonly observed spectral properties.