Ocean-sourced CO2 inflates radiolytic H2O2 at Europa’s Chaos

JWST observations of Europa's leading hemisphere show excess CO₂ over chaos terrains [1, 2] where the subsurface ocean is likely to have breached the ice shell. Analysis of the 3.5-µm hydrogen peroxide (H₂O₂) absorption band reveals elevated amounts of H₂O₂ in these chaos regions. Peroxide abundance scales with CO₂ abundance, presenting a strong pixel-level linear correlation, particularly with the υ₃ CO₂ feature at 4.27 mm (Figure 1).

New laboratory experiments [3] motivated by these observations show that trace inclusions of CO₂ can substantially inflate the radiolytic peroxide yield, more so than in pure water ice. We considered various mechanisms by which CO₂ boosts H₂O₂ synthesis and developed an analytical model to quantify the dependence of peroxide enhancement on CO₂ abundance [3]. These experiments support the hypothesis that endogenic CO₂ may amplify H₂O₂ synthesis in the Tara and Powys Regiones when processed by Jupiter's magnetospheric particles. We combine the CO₂-enhanced H₂O₂ yields with the energy dose delivered by the magnetospheric particles onto the leading hemisphere [4, 5] to generate a peroxide distribution map to compare with the observed distribution. Our results highlight the intricate interplay of Europa’s interior ocean, geologic activity, and precipitating radiation in shaping surface chemistry, boosting the synthesis of molecules vital for habitability.

Figure 1: Exploring correlations between Europa’s peroxide and CO₂ absorption. Integrated H₂O₂ band area against each of the three CO₂ band areas. Grey data points are individual pixel values, while red points are binned data. The red lines are linear fits to these binned datasets. The strongest linear correlation, quantified by Pearson’s correlation coefficient, occurs between the peroxide and the 4.27 µm CO₂ absorptions.

The rapid transport of peroxide to the subsurface ocean via brine-percolated conduits [6] has strong implications for Europa's habitability. The mixing of these oxidants with reduced seawater, derived from geochemical cycling through the porous seafloor, could generate ‘redox potential’, supplying chemical energy that putative life forms may utilize to sustain metabolism, cellular maintenance, and reproduction [7]. These JWST observations combined with laboratory measurements set the stage for detailed mapping of CO₂ (via its 2.7 and ~ 4.2 - 4.3 µm absorptions), H₂O₂ (via its 3.5 µm absorption) and possibly CHO organics with MISE (Europa Clipper) and MAJIS (Juice) at finer spatial scales to advance our understanding of Europa’s surface and subsurface composition and chemistry.

References:

[1] Villanueva, G. L., et al. 2023, Science, 381, 1305. [2] Trumbo, S. K., & Brown, M. E., 2023, Science, 381, 1308. [3] Mamo, B. et al., 2025, Planetary Science Journal, submitted. [4] Nordheim, T. A., et al., 2022, Planetary Science Journal, 3, 5. [5] Nordheim, T. A., 2018, Nat. Astro., 2, 673-679. [6] Hesse, M.A., et al., 2022, Geophysical Research Letters, 49, 5. [7] Hand, K., et al., 2007, Astrobiology, 7, 1006-1022.