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Harvard ADS: Europa's H₂O₂: Temperature Insensitivity and a Correlation with CO₂

Paper abstract: H₂O₂ is part of Europa's water-ice radiolytic cycle and a potential source of oxidants to Europa's subsurface ocean. However, factors controlling the concentration of this critical surface species remain unclear. Though laboratory experiments suggest that Europa's H₂O₂ should be concentrated in the coldest, most ice-rich regions toward the poles, Keck adaptive optics observations have shown the strongest H₂O₂ signatures in comparatively warm, salt-bearing terrain at low latitudes. As a result, it was suggested that the local non-ice composition of these terrains—particularly hypothesized enrichments of CO₂—may be a more dominant control on H₂O₂ than temperature or water-ice abundance. Here we use observations of Europa from the NASA Infrared Telescope Facility, Keck Observatory, and JWST to disentangle the potential effects of temperature and composition. In order to isolate the effect of temperature on Europa's H₂O₂, we use the ground-based observations to assess its response to temperature changes over timescales associated with Europa's daily eclipse and diurnal cycle. We use JWST Cycle 1 data to look for any geographic correlation between Europa's H₂O₂ and CO₂. Changes in Europa's 3.5 µm H₂O₂ absorption band both from pre- to post-eclipse and across a local day suggest minimal effects of the local temperature on these timescales. In contrast, the JWST observations show a strong positive correlation between Europa's H₂O₂ and CO₂ bands, supporting the previously suggested possibility that the presence of CO₂ in the ice may enhance H₂O₂ concentrations via electron scavenging.