Radiation sputtering of hydrocarbon ices at Europa-relevant temperatures

TL;DR

This study investigates how energetic particle bombardment causes hydrocarbon ices on Europa to release CO2, CO, and hydrocarbons, revealing temperature-dependent sputtering yields and surface heterogeneity effects.

Contribution

It provides new insights into the temperature-dependent sputtering processes of hydrocarbon ices relevant to Europa's surface composition.

Findings

Sputtering produces CO2, CO, and hydrocarbons.

Higher temperatures increase sputtering yields.

Species distribution varies with temperature.

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.