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The Curious Case of H₂O₂ on Europa

Presentation #220.08 in the session Laboratory Investigations (Poster)

Published onOct 23, 2023
The Curious Case of H₂O₂ on Europa

Hydrogen peroxide (H2O2) is an important constituent of Europa’s surface formed by the radiolytic processing of the H2O-ice rich surface: continuous surface bombardment by energetic particles within the Jovian magnetosphere dissociates water molecules producing OH radicals, which recombine to form H2O2 (Carlson et al. 2009). Laboratory investigations of this process conducted through electron and ion irradiation of H2O ice have established an inverse relation between ice temperature and equilibrium H2O2 abundances (Loeffler et al. 2006; Hand & Carlson 2011). Recent spatially-resolved infrared observations of Europa, however, reveal the opposite: the 3.5 µm H2O2 absorption feature is strongest in the warmer, low-latitude regions of the leading/anti-Jovian hemisphere, correlated with the chaos terrain, while the colder, polar latitudes show relative depletions (Trumbo et al. 2019). This apparent discrepancy has been linked to the presence of electron accepting contaminants such as CO2, whose addition has been shown to increase H2O2 yields (Moore & Hudson 2000) by ‘scavenging’ otherwise destructive electrons produced by incident radiation. The spatial correlation between H2O2 and CO2 noted from leading-side Galileo NIMS spectra (Carlson et al. 2004) is consistent with the purported electron scavenging role of CO2. We examine the influence of CO2 inclusion on H2O2 synthesis by electron irradiation of H2O ice films containing varying amounts of CO2. Infrared spectra of pristine and 10 keV electron irradiated H2O + CO2 films are obtained to test the validity of the electron scavenging hypothesis against alternative explanations such as the contribution to the ~3.5 µm absorption feature by other C-bearing species such as methanol (CH3OH) or carbonic acid (H2CO3) (Zheng & Kaiser 2007; Hodyss et al. 2009), expected to have synthesized from radiolysis of H2O-CO2 icy mixtures.

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