Salt Solution Freezing Point Depression at High Pressures, in Relation to Europa

Europa has an icy crust with the possibility of a liquid ocean beneath the solid layer, which holds promise as a potentially habitable environment. A growing interest around Europa is evidenced by upcoming missions, including NASA's Europa Clipper and ESA's JUpiter's ICy moon Explorer (JUICE). One objective of these missions is to understand more about the crust/ocean and its ability to sustain life. Previous missions have shown that the predominant salts on Europa may be NaCl and MgSO4, however the effect of pressure and salinity on the melting / freezing points of ice under relevant conditions is less well constrained. Having insight about the phase relationships of the salt solutions could provide important constraints in interpreting mission-based data. We have experimentally determined the freezing point of NaCl solutions at pressures up to 700 bars with concentrations ranging up to 20% salt in distilled water. Our results align closely to other published results from past experiments for the known data, and we have new data for previously unexplored conditions. Overall, an addition of 20% NaCl can depress the freezing point of water by close to 20„ƒ at pressures that would represent a 70km thick crust on Europa. These results can be used to place constraints on current models of crustal thickness on icy moons like Europa