A metamorphic origin for Europa's ocean

Europa likely contains an iron-rich core. In order for it to have formed, temperatures within Europa reached ≳ 1250 K. At that temperature, accreted chondritic minerals---e.g., carbonates and phyllosilicates---would partially devolatilize. Here, we compute the amounts and compositions of exsolved volatiles. We find that volatiles released from the interior would have carried solutes (including redox-sensitive species), and generated the entirety of Europa's ocean and likely an early CO2 atmosphere. No late delivery of cometary water was necessary. Contrasting with prior work, we find CO2 could be the most abundant solute in the ocean, followed by Ca^2+, SO4^2-, and HCO3^-. However, gypsum precipitation from the seafloor to the ice shell decreases the dissolved S/Cl ratio, such that Cl > S at the shallowest depths, consistent with the recent inference of endogenous chlorides at Europa's surface. Gypsum would form a 3--10 km thick sedimentary layer at the seafloor. The Europa Clipper mission will be able to test these predictions.