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, constraints on the ocean composition currently need to rely on its expression on the surface. In this work, we combine chemical divide modeling with cryogenic Raman and X-ray diffraction (XRD) experiments to examine freezing of a simple putative brine system containing Na⁺, Mg²⁺, Cl^-, and SO₄^2- to assess the feasibility of inferring the ocean’s chemical composition via in-situ techniques. The results suggest that accurate quantification of the composition of subsurface liquids via their surface expression is rather challenging as the observed products are highly dependent on relative ionic concentrations and freezing rates. In addition, flash freezing of diluted brines often produces water ice together with amorphous hydrated Mg salts, significantly hindering their detection. These findings can help inform both analytical protocols for a Raman spectrometer onboard a Europa surface lander as well as potential areas for exploration, in order to best provide meaningful constraints on the emplacement mechanism and composition of frozen salt minerals on the surface.