Investigating the Effects of Temperature on Europa’s Hydrogen Peroxide

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. Contrary to the laboratory prediction that Europa’s H₂O₂ should be concentrated in the coldest, iciest regions, Keck adaptive optics (AO) observations have shown the exact opposite—the largest abundances in warm, salty terrain at equatorial latitudes. To help understand this discrepancy and disentangle the effect of temperature on Europa’s H₂O₂ from that of composition, we design a controlled temperature experiment using disk-integrated IRTF/SpeX spectra of Europa’s 3.5-μm H₂O₂ absorption before and after eclipse. When Europa undergoes eclipse, its surface temperature is expected to drop by ~20 K, which simple extrapolation from laboratory studies suggests may increase the band area of the H₂O₂ absorption by approximately a factor of 3. The surface then takes ~ 6 hours to recover back to its pre-eclipse temperature. We assess changes in Europa’s H₂O₂ absorption band immediately before and after eclipse and throughout this recovery period. While we find that the H₂O₂ absorption does appear to change following the eclipse, the magnitude and pattern do not match our predictions, implying more nuance to the degree and timescale of the temperature effect. We discuss possible interpretations and combine our IRTF results with spatially resolved Keck AO observations of specific regions at different times of the local day, which provides additional perspective.