Effects of Io ejecta on Europa

The effects of plasma ejected from Io on the nature and evolution of the surface of Europa and on the relative importance of the roles played by the two satellites in the Jupiter magnetosphere are examined. Observations of an ultraviolet absorption feature on the trailing side of Europa are interpreted as due to an equilibrium column density of SO2 in a steady-state model of the implantation of iogenic ions into the surface of Europa and their subsequent sputtering. The observed sulfur column density of 2 x 10 to the 16th/sq cm implies a slow loss of material from Europa, mainly water ice, and indicates that the spectrum of particles sputtered is soft. Considerations of the comparative roles of corotating and energetic heavy ions are shown to suggest that the implantation and sputtering is primarily the result of the proton and light ion component of the plasma. The weakness of Europa as a plasma source resulting from the soft sputtered particle spectrum thus leads to the dominance of Io in contributing to the magnetospheric plasma.