The presence of MgSO4 on Mars is thought to have arisen from reactions of basaltic material with sulphuric acid of volcanic origin, and subsequent evaporation. The Imaging Spectrometer aboard the Mars Reconnaissance Orbiter has found evidence for the presence of slope lineae, finger-like features suggestive of running liquid. Where the lineae are most pronounced there is evidence for hydrated salts. The presence of these lineae, along with hydrated salts which can depress the freezing point of water by up to 80 K, strongly support the premise that the lineae arise due to the presence of water on Mars. Of the possible hydrous sulphates, chemical models predict Meridianiite (MgSO4 ∙11H2O, MS11) to be the most abundant phase, and it is thought therefore to be the most likely source of liquid water on the present day surface.

We use synchrotron X-ray powder diffraction (SXRPD) and in situ Raman spectroscopy to observe the change in structure of epsomite (MgSO4 ∙7H2O, MS7) as it is cycled through a range of temperatures replicating diurnal and seasonal changes on the Martian surface. We find no evidence thus far to support a low temperature phase of epsomite which would be the more prevalent form on colder surfaces. We have also investigated the kinetics and thermodynamics of MS11; we found that kinetic effects are more pronounced at lower concentrations and/or when forming in the presence of ice; this has implications for the interpretation for both hydrous mineralisation processes and dynamical constraints on environmental conditions on Mars, Europa and Ganymede.