  The ubiquity of sulfur ions within the Jovian magnetosphere has led to
suggestions that the implantation of these ions into the surface of Europa may
lead to the formation of SO2. However, previous studies on the implantation of
sulfur ions into H2O ice (the dominant species on the Europan surface) have
failed to detect SO2 formation. Other studies concerned with similar
implantations into CO2 ice, which is also known to exist on Europa, have
offered seemingly conflicting results. In this letter, we describe the results
of a study on the implantation of 290 keV S+ ions into condensed CO2 at 20 and
70 K. Our results demonstrate that SO2 is observed after implantation at 20 K,
but not at the Europa-relevant temperature of 70 K. We conclude that this
process is likely not a reasonable mechanism for SO2 formation on Europa, and
that other mechanisms should be explored instead.
