We are conducting an experimental program designed to establish the extent to which chemical compositions of icy world surfaces are indicative of subsurface ocean chemistry/composition. Europa and other icy worlds containing vast global oceans beneath crusts of ice are key targets for understanding the impact of an extensive rock-water interface on a body’s habitability. This Investigation is shedding light on the evolution of ocean materials expressed on the surface of airless icy bodies and exposed to surface temperatures, vacuum, photolysis and radiolysis. Our work illuminates the connection between observables on the surface to the habitability of these past and present aqueous environments. This Investigation will provide the means to interpret the data acquired by flyby, orbital, or in situ missions to icy worlds, and assess the potential habitability of these environments.
To date, comprehensive geochemical modeling efforts attempting to link putative ocean compositions with observed surface materials have been limited. Typical geochemical approaches do not account for out-of-equilibrium conditions encountered during rapid freezing at icy world surfaces. Even in the absence of radiative alteration, the details of how icy world ocean fluids would freeze out in the ice shell (and thus generate observable surface chemistry) are not well understood. This important aspect of the evolution of icy satellites is crucial to assess the nature of the chemical compounds that may reach the surface and act as tracers (possibly detectable from orbit or in situ) of chemical disequilibria at depth.
We are experimentally determining the evolution of candidate ocean compositions as they are subjected to freezing, dehydration and radiolysis/photolysis using Raman and infrared spectroscopies. Our goal is to fill a gap in our understanding of these processes and shed light on chemical changes induced by these processes when fluid from a subsurface ocean is expressed on the surface of an icy body. Further, by understanding these processes over a range of likely and/or predicted ocean compositions, we will enable constraints to be placed on the composition of a subsurface ocean based on the observed surface chemistry. In doing so, we will also enable constraints to be placed on the habitability of the subsurface ocean.
Vu, T. H., R. Hodyss, M. Choukroun and P. V. Johnson (2016) Chemistry of Frozen Sodium-Magnesium-Sulfate-Chloride Brines: Implications for Surface Expression of Europa's Ocean Composition The Astrophysical Journal Letters 816(2): L26.
The composition of Europa's subsurface ocean is a critical determinant of its habitability.