Radiolysis induced by solar radiation and magnetospheric charged particles alters the surface composition of Europa, which largely consists of water ice, as well as minor amounts of sulfur species (SO2, H2S, Sx, etc.), and hydrated salts. While the radiolytic reactions of sulfur species have been extensively studied in the laboratory over several decades (Moore 1984; Carlson et al. 1999; Strazzulla et al. 2007; Moore et al. 2007; Kanuchová et al. 2017), the thermal reactivity of sulfur species has received significantly less attention due to the cold surface temperatures (80–130 K) (Spencer et al. 1999). However, recent studies have shown that solid phase SO2 reacts readily with oxidants, such as O3, when they are mixed in H2O at temperatures as low as 80 K (Loeffler and Hudson 2016). These studies suggest that compositional models and observational surveys may need to consider low temperature solid-state reactions to fully describe the composition of Europa. Moreover, characterization of these potential thermal reactions will be required to interpret data acquired by NASA’s Europa Clipper Mission and ESA’s JUICE Mission. Here, we present spectral and kinetic data for the thermal oxidation reaction of H2S within H2S:H2O:O3 ice mixtures at temperatures relevant to Europa. Our results will inform future studies examining the composition of Europa’s surface.
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