Sulfur Ion Implantations Into Condensed CO2: Implications for Europa

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. Plain Language Summary SO2 ice is known to exist at the surface of one of Jupiter's moons; Europa. However, the method by which this ice forms is still uncertain. Due to the orbit of Europa being within the giant magnetosphere of Jupiter, it has been proposed that sulfur ions within the magnetosphere could implant into the cold surface ices on Europa and subsequently react to form SO2. However, laboratory experiments looking into the implantation of such ions into H2O ice (the dominant ice on Europa's surface) and CO2 ice have either failed to yield SO2 or have provided inconclusive results. We have therefore performed an experiment in which we have implanted high‐energy sulfur ions into CO2 ice at two temperatures. Our results indicate that such implantations are unlikely to be the mechanism by which the SO2 on Europa is formed, and that other chemical processes should be considered instead. Key Points Sulfur ions were implanted into CO2 ices at 20 and 70 K to simulate Jovian magnetospheric radiation chemistry at the surface of Europa SO2 was observed to be among the radiolytic products at 20 K, but not at the more Europa‐relevant temperature of 70 K Alternative explanations for the formation of SO2 on the surface of Europa should be considered