Radiation Synthesis of carbon dioxide in ice-coated grains

U. RAUT; M. J. LOEFFLER; B. D.TEOLIS; R.A. VIDAL; R.A. BARAGIOLA

Cambridge, Inglaterra

Workshop; 37th DPS (Division for Planetary Science) Meeting; 2005

American Astronomical Society

 We have investigated the synthesis of carbon dioxide in amorphous carbon grains coated with amorphous water ice ( 0.1 microns thick) as a result of irradiation with 100 keV protons at 16 K and 120 K. The quantitative studies report a saturation column density of CO2 of the order of 3 - 9 x 1014 molecules/cm2, with more CO2 produced at lower temperatures. We discuss radiation induced chemical processes involving reactions of radicals in water ice with the carbon surface, and identify this type of synthesis to contribute significantly to the condensed carbon dioxide observed in interstellar grains and the Jovian satellites. Of particular interest are the two Galilean satellites Callisto and Ganymede, where the relative CO2 abundance on its cratered surface as inferred from the Galileo NIMS reflectance spectra is on the same order as observed in our experiments.