Probing Europa's subsurface ocean composition from surface salt minerals using in-situ techniques

Abstract

The composition of Europa's subsurface ocean is of great interest for understanding the internal geochemistry and potential habitability of this icy body. However, current constraints on the ocean composition need to rely largely on its expression on the surface. In this work, we combine chemical divide modeling with cryogenic Raman and X-ray diffraction experiments to examine freezing of a simple putative brine system containing Na+, Mg2+, Cl−, and SO42− across a range of ionic concentrations and freezing rates to assess the feasibility of inferring the ocean's chemical composition via in-situ techniques. The results suggest that multiple hydrated salts not predicted by chemical models are frequently encountered in the final solid phase, making accurate quantification of the subsurface liquid composition via surface observables rather challenging. In addition, flash freezing of diluted brines often produces water ice together with vitreous Mg-bearing salt hydrates, which may significantly hinder their detection. These findings can help inform both analytical protocols for a Raman spectrometer onboard a Europa surface lander as well as potential locations for exploration, in order to best provide meaningful constraints on emplacement mechanisms and the composition of frozen salt minerals on the surface.