Ion irradiation of H2O ice on top of sulfurous solid residues and its relevance to the Galilean satellites

Abstract In this paper we present the results of new experiments of ion irradiation of water ice deposited on top of a solid sulfurous residue to study the potential formation of SO 2 at the interface ice/refractory material and discuss the possibility that this mechanism accounts for the sulfur dioxide ice detected on the surfaces of the Galilean satellites. In situ infrared spectroscopy was the used experimental technique. We have irradiated a thin film of H 2 O frost on a sulfurous layer with 200 keV of He + at 80 K. The used sulfurous residue was obtained by irradiation of frozen SO 2 at 16 K and it is used as a template of sulfur bearing solid materials. We have not found evidences of the efficient formation of SO 2 after irradiation of H 2 O ice on top of the sulfurous residue. An upper limit to the production yield of SO 2 , Y ⩽ 6.3 × 10 −7 molecules cm −2 of interface area for each 100 eV of energy absorbed in 1 cm 3 of ice-covered residue, has been estimated. These results have relevance in the context of the surfaces of the icy Galilean satellites in which SO 2 was detected. Our results show that radiolysis of mixtures of water ice and refractory sulfurous materials is not the primary formation mechanism responsible for the SO 2 present on the surfaces of the Galilean satellites.