Investigating the Thermodynamics and Seismic Profile of the Europan Hydrosphere through Pure-Water Modeling and Saltwater Experiments

We explore the properties of the hydrosphere on Europa involving both a modeling technique and experimental methods. We perform a computational analysis of the thermodynamic properties for an ideal, pure-water Europan ice shell using a Python programming framework called SeaFreeze. We create four models assuming surface temperatures of either 50 K or 140 K and ice shell thicknesses of either 3 km or 30 km. We observe mostly linear trends for the density and seismic wave velocities with respect to depth, and find that surface temperatures have the greatest effect on the models. Simultaneously, we experimentally investigate the phase diagram of different saltwater concentrations in an attempt to further constrain the ice shell properties. We determine the freezing-melting points of 5%, 10%, and 20% by-weight NaCl-water solutions under constant pressures from 0 MPa to 70 MPa. We find that increasing the salt concentration, the pressure, or both decreases the freezing point temperature with a freezing point temperature depression of about -20 °C from that of pure water at zero pressure. Based on our experimental results, we expect that adding NaCl to the pure-water computational models would cause them to have lower temperatures at the ice-water boundary, assuming saltwater has similar density and seismic wave velocity trends as pure-water. Areas of future development include continuing to explore the phase diagrams of different saltwater concentrations, including MgSO₄, KCl, and varying combinations of all three salts, extending the pure-water SeaFreeze models to analyze Europa’s subsurface ocean layer, implementing various new techniques to make our experiments more precise, and finally applying our results to the other icy moons, such as Ganymede or Callisto.