High-pressure polymorphism of magnesium-chloride hydrates at ice-moon conditions

The 2030s will be the decade of the ice moons with both NASA and ESA space crafts scheduled to arrive at Jupiter. To be able to interpret their future measurements, lab-based studies are now urgently required. The ultimate aim is to develop full structural and dynamic models of Europa, Ganymede and Calisto, with a particular focus on the ice layers and subsurface oceans. Understanding the effects of salts on the various icy materials is key in this respect. Building on previous work at ISIS investigating the effects of the ammonium fluoride salt on water’s phase diagram, we now aim to investigate ice-moon relevant salts. Using in-situ volume-change measurements at UCL, which precisely detect phase transitions and give in-situ density values, we plan to build a large dataset using a high-throughput approach to explore the effects of pressure, temperature, pH as well as salt concentration and type. To be able to fully interpret our large dataset with respect to which phases exist at certain conditions, we require in-situ neutron diffraction measurements. In a sense, these will form the cornerstones of our interpretations and will “unlock” our entire large dataset. Some of the high-pressure salt hydrates to be encountered are expected to be new discoveries. As a first step, we request 2 days of beamtime on the PEARL instrument to investigate particularly interesting pressure-temperature conditions for 1 M magnesium-chloride samples.