Europa

Laboratory Investigation Of CO2-Driven Enhancement Of Radiolytic H2O2 On Europa And Other Icy Moons

By Keith Cowing

Status Report

astro-ph.EP

June 23, 2025

Filed under astro-ph.EP, Charon, Europa, Ganymede, geochemistry, icy world, peroxide

Laboratory Investigation Of CO2-Driven Enhancement Of Radiolytic H2O2 On Europa And Other Icy Moons — A: Schematic of the ultra-high vacuum chamber used for electron irradiation experiments of Europan ice analogs. B: Shift in the resonant frequency of the QCM during co-deposition of H2O and CO2 ice from dedicated gas dosers. We first condense CO2 [1] from a doser at a constant rate of (0.25 ± 0.01) Hz/s (zoomed in the inset). We then admit water vapor [2] through a second doser which increases the deposition rate to (4.8 ± 0.2) Hz/s. When the film approaches the desired thickness (2.8 µm, which corresponds to a frequency shift of ∼ 21, 000 Hz), we terminate H2O gas deposition first [3] and continue with CO2 condensation briefly to ensure the terminal CO2 rate did not drift significantly from the initial value (< 10%). The CO2 doser is shut off at [4]. This co-deposition scheme using multiple gas dosers with QCM gravimetry allows for producing mixed ices with precisely tailored composition. This film has CO2 intimately mixed with water ice at (2.5 ± 0.1)% (by number) concentration. -- astro-ph.EP

Observations of Europa’s leading hemisphere reveal elevated H₂O₂ in the warmer, low latitude chaos terrains compared to the colder, polar regions.

This distribution disagrees with prior laboratory radiolysis studies of pure water ice, which show higher H₂O₂ yields at colder temperatures. The regions with higher peroxide abundance, Tara and Powys Regiones, also present increased amounts of CO₂, possibly sourced from Europa’s interior.

To investigate whether CO₂ influences radiolysis of water ice to boost H₂O₂ production, we irradiated water ice doped with varying amounts of CO₂ with 10 keV electrons at 70 and 100 K. Our results indicate that CO₂, even in trace amounts (< 3%), significantly enhances H₂O₂ yields at temperatures relevant to Europa.

We discuss the mechanisms by which CO₂ boosts peroxide synthesis and quantify H₂O₂ creation and destruction cross sections and G-values across different CO₂ concentrations.

These findings provide a plausible explanation for the perplexing H₂O₂ distribution on Europa and has implications for understanding peroxide on other icy bodies such as Ganymede and Charon, where it has been detected alongside CO₂.

Bereket D. Mamo, Ujjwal Raut, Ben D. Teolis, Trevor P. Erwin, Richard J. Cartwright, Silvia Protopapa, Kurt D. Retherford, Tom A. Nordheim

Comments: 17 pages, 8 figures, accepted to AAS Planetary Science Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2506.15819 [astro-ph.EP] (or arXiv:2506.15819v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2506.15819
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Related DOI:
https://doi.org/10.3847/PSJ/ade3d8
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Submission history
From: Bereket Mamo
[v1] Wed, 18 Jun 2025 19:04:25 UTC (1,314 KB)
https://arxiv.org/abs/2506.15819

Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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