Abstract EANA2026-16

Europa’s subsurface ocean is a leading candidate for habitable environments beyond Earth, yet its chemical composition remains uncertain, with competing hypotheses favouring either chloride- or sulphate-dominated oceans. This work-in-progress study explores the sulphate end-member scenario by applying the geochemical code PHREEQC, coupled with the core10.dat database, to model hydrothermal water–rock interactions at Europa’s seafloor. CM2 chondrite compositions (Rubin & Wasson, 1987) are used as a proxy for the rocky substrate. Two experimental series were conducted: (i) progressive rock addition at constant temperature, and (ii) temperature increments at constant rock:water ratio.

Preliminary results show that low water-to-rock ratios (1:1) drive extensive serpentinisation, producing strongly alkaline, reducing fluids enriched in H₂, stabilising serpentine ± magnetite, and favouring hydrogenotrophic metabolisms such as methanogenesis. At higher dilutions (1:10, 1:100), serpentinisation is weakened or suppressed, with ocean chemistry buffered by sulphate, maintaining oxidising conditions more consistent with sulphate-reducing pathways. Temperature-dependent runs indicate that increasing heat enhances H₂ generation and serpentine–brucite–magnetite stability, particularly above ~100 °C, suggesting that hydrothermal gradients could sustain diverse redox environments.

These results underline that Europa’s ocean, under the sulphate-rich assumption, may host spatially heterogeneous chemical niches. Ongoing work aims to refine these models and assess their implications for biosignature detection in future missions.