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R.A. Baragiola, D.A. Bahr (University of Virginia), J Schou (Risoe National Lab., Denmark), M Shi (University of Virginia), R.A. Vidal (INTEC-CONICET, Argentina)
Past studies of sputtering of water ice, related to the question of magnetospheric effects on icy satellites, have concluded that desorption of intact water molecules dominates at low temperatures (below ~ 100 K) and that emission of H2, and O2 become important at higher temperatures. The temperature dependence of sputtering was predicted to change with the magnitude of the energy deposition at the surface. However, our new results show that the temperature dependence of the total sputtering yields for ions and Lyman-alpha photons scales with energy deposition over five orders of magnitude, against predictions. With new, absolute measurements of the sputtered ejecta produced by 100 keV protons, we have discovered that O and OH are primary species, even at low temperatures. This surprising finding will require revision of models for sputter generation of atmospheres. The presence of radicals imply strongly oxidizing atmospheres, which in turn has implications on the state of the surface of the satellites: formation of hydrogen peroxide from ice and oxidation of non-ice components.
Work supported by NASA-Office of Space Research and Cassini mission, and by NSF-Astronomy Div.