Crystallization Kinetics of Vitreous Magnesium Sulfate Hydrate and Implications for Europa’s Surface

Abstract

Brines consistent with that expected for Europa’s global subsurface ocean have been shown to form vitreous salt hydrates when frozen. We report experiments examining the crystallization kinetics of vitreous MgSO _4 hydrate in order to better understand the stability of such materials on the surface of Europa. Vitreous MgSO _4 hydrates formed from a 2 M parent solution were found to crystallize into MgSO _4 ·11H _2 O (meridianiite) upon annealing at 195–225 K. Raman spectroscopy was used to monitor the crystallization and reaction rates were determined from the growth of the crystalline fraction as a function of time. Arrhenius analysis yielded an activation energy of 60 ± 9 kJ mol ^−1 for the vitreous to crystalline transition, implying that such transformation does not occur spontaneously at Europa’s surface temperatures. If emplacement processes favor the formation of vitreous salt hydrates, they are likely to still be stable and could be an important non-ice component on Europa at present day.

Keywords

• Europa
• Surface ices
• Chemical kinetics
• Ice spectroscopy