The origin of sulfur-bearing species on the surfaces of icy satellites

Abstract: We present experimental results in order to understand the physico-chemical effects induced by fast ions irradiating sulfur bearing molecules. The experiments are relevant both to Solar System objects (icy satellites, comets, TNOs) and icy mantles on grains in the interstellar medium. Here we concentrate on the application to the Galilean moons that are exposed to high energetic particle fluxes in the jovian magnetosphere. In particular we show that: [–] Implantation of sulfur ions into water ice produces hydrated sulfuric acid with high efficiency providing an important contribution to the sulfur cycle on the surfaces of Europa and other jovian satellites. [–] Implantation of protons into sulfur dioxide produces mainly SO3, polymers, and O3 but not H–S bonds. The suggested hypothesis that H implantation could result in the formation of H2SO3 on Io is not confirmed by our experiments. [–] Irradiation of sulfur dioxide mainly produces SO3 and sulfur polymers. [–] Irradiation and subsequent warming of H2S induces the formation of a sulfurous residue that exhibits S–H bonds. [–] Water ice has been deposited on refractory sulfurous materials originating from SO2 or H2S irradiation. We looked to the formation of new species at the interface (ion mixing). We have not found evidence for the efficient synthesis of SO2. In the case of residues rich in species containing S–H bonds, H2S is re-formed. [Copyright &y& Elsevier]