Implications of high-pressure oxygen hydrates on radiolytic oxygen in Jovian icy moons

• Published in: Communications chemistry Vol. 8; no. 1; pp. 128 - 7
• Main Authors: Frost, Mungo, Kuzovnikov, Mikhail A., Dalladay-Simpson, Philip, Howie, Ross T., Loveday, John S., Ranieri, Umbertoluca, Gregoryanz, Eugene
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 29.04.2025; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/119; 639/638/169/894; 639/638/298; Atmospheres; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Clathrates; Europa; High pressure oxygen; Icy satellites; Jupiter; Jupiter satellites; Low pressure; Methane hydrates; Moons; Penetration depth; Radiolysis; Saturn
• ISSN: 2399-3669; 2399-3669
• DOI: 10.1038/s42004-025-01509-y

Various icy moons, such as Europa and Ganymede, have thin oxygen atmospheres and exhibit spectral features attributed to oxygen held in their surface ices. The oxygen forms from the radiolysis of water. The interiors of these bodies are subject to high pressures and it is not known how deep into icy moons oxygen-bearing ices can penetrate, or the structures formed by the oxygen–water system at high pressure. Here, we show that oxygen hydrates are stable to 2.6 GPa, allowing them to penetrate deep into icy moons, both above and below proposed sub-surface liquid-water oceans. Similarities between oxygen and hydrogen hydrates indicate potentially enhanced recombination rates, transforming them back into water and offering a resolution to the discrepancy between predicted and measured radiolysis rates. In addition to the low-pressure CS-II clathrate, our results find three high-pressure phases in the oxygen–water system: an ST clathrate, a C 0 hydrate, and a filled ice isomorphous with methane hydrate III. This shows a vast storage potential for molecular oxygen in icy moons and indicates that Europa could still be absorbing oxygen into its crustal ice. Icy moons exhibit thin oxygen atmospheres, but the penetration depth of oxygen-bearing ices and their structures remain unclear. Here, the authors show that oxygen hydrates are able to penetrate deep into icy moons despite the high-pressure interior and identify four phases in the oxygen–water system under icy moon conditions.