Radiation sputtering of hydrocarbon ices at Europa-relevant temperatures

Abstract

The surfaces of some icy moons, such as Jupiter's moon Europa, are heavily bombarded by energetic particles that can alter the surface materials and affect the composition of its exosphere. Detection of CO₂ on Europa's surface indicate that Europa's interior may be transporting freshly exposed carbon-containing material to the surface. It is unknown whether this CO₂ is a product of radiation of carbon-containing precursors or whether it is present in the initial deposits. Regardless, further radiolysis by high-energy electrons or ions can sputter CO₂ (and organic fragments if present) into Europa's exosphere. In this study, we investigate the radiation sputtering of CO₂ and organic fragments from hydrocarbon water ice mixtures at different Europa-relevant surface temperatures to identify how its sputtering products evolve over time. This study shows that the sputtering of hydrocarbon water ice leads to the production of mostly CO₂, CO, and fragmented hydrocarbons. The onset of sputtered hydrocarbons is immediate, and quickly reaches a steady state, whereas CO₂ and CO are formed more gradually. It is found that higher temperatures cause more sputtering, and that there are some notable differences in the distribution of species that are sputtered at different temperatures, indicating local heterogeneity of sputtering yields depending on the surface temperature.