Laboratory Investigation of CO2-Driven Enhancement of Radiolytic H2O2 on Europa and Other Icy Moons

TL;DR

This study demonstrates that trace amounts of CO2 significantly enhance hydrogen peroxide production in water ice under radiation, explaining the observed peroxide distribution on Europa and other icy moons.

Contribution

It provides experimental evidence that CO2 boosts radiolytic H2O2 yields in water ice, a novel insight into surface chemistry of icy moons.

Findings

CO2 increases H2O2 yields even in trace amounts

Enhanced peroxide production at Europa-like temperatures

Quantified H2O2 creation and destruction cross sections

Abstract

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.