Salt hydrate mineralogy at the conditions of icy moon interiors and surfaces

The icy moons of Jupiter and Saturn, such as Europa, Ganymede, Callisto, and Enceladus, are expected to host saltwater oceans beneath their icy crusts, raising the intriguing possibility of habitability in these water-rich environments. The distribution and compositions of salts, both dissolved in the oceans and present in solid form as hydrates, are key factors in shaping the internal structures and evolutionary pathways of these icy worlds. Constraining the compositions of salts and salt hydrates detected on icy moon surfaces provides critical insights into the geochemistry of the subsurface oceans and interior processes.¹ Salt-water interactions under the high-pressure, low-temperature conditions characteristic of icy moon interiors give rise to a diverse range of hydrated salt structures that are not always accessible through temperature variations alone.² However, relatively few experimental studies have investigated the combined effects of pressure and temperature on these systems.

Here we characterise the binary salt-water systems of NaCl,² KCl, MgCl₂, and CaCl₂ under high-pressure, low-temperature conditions (0–2 GPa; 300–150 K) using in situ single-crystal synchrotron X-ray diffraction experiments to constrain the mineralogy of the chloride salts in icy moon interiors. This structural work, along with planned spectroscopic measurements, will help establish a foundation for identifying high-pressure salt hydrates that have been transported from the internal hydrosphere to the surface.

 

1. Dalton, J. B. et al. Chemical Composition of Icy Satellite Surfaces. Space Sci Rev 153, 113–154 (2010).

2. Journaux, B. et al. On the identification of hyperhydrated sodium chloride hydrates, stable at icy moon conditions. PNAS 120, e2217125120 (2023).