Date: April 13th  

Time: 2pm ET 

Defense Location: Ford ES&T L1114

Title: The Habitable Ocean World Box (HOWBOX) Model: Coupling Europa’s Thermal and Chemical Evolution  

Advisor: Dr. Britney Schmidt

Committee: James Wray, Annalisa Bracco, Christopher Reinhard, Sanjoy Som

Abstract:  Europa, a moon of Jupiter, has evidence for a liquid water ocean in contact with a rocky mantle beneath its icy surface. Due to the presence of this ocean, Europa has been a primary target for investigations of habitability within our solar system. Europa’s ocean has remained liquid, in part, due to tidal heating in the interior. However, this interior tidal heat production has likely varied and potentially even been oscillatory over Europa’s history due to evolving orbital eccentricity. Such thermal oscillations will affect Europa’s interior geochemistry, defining changes to chemical and energy inventories for putative biology. Therefore, Europa’s long-term habitability depends on both geochemical pathways and thermodynamics—modulated by tidal evolution—that define chemical and energy inventories. Here, we demonstrate how thermally-modulated volumetric changes to Europa’s ice shell, ocean, and fluid-accessible rocky mantle affect oceanic composition in Europa’s interior due to variation in salinity, reduced volatile flux from the seafloor, and oxidized material delivery from the ice shell. We find that Europa may have undergone major oxidation events in its past during periods of increased orbital eccentricity, with oxidant flux increasing by up to 10 orders of magnitude, affecting the composition of the ocean. We also find that stable hydrogen flux into the ocean from serpentinization is tied to the water activity of the ocean and pore fluids, which also vary with heat production. Periods of fluctuating heat production, driven by orbital dynamics, can result in substantial oscillations to hydrogen flux ranging from 100 -1013 moles of H2 per year, with the degree of variability controlled by the dissolved ion composition and concentration. These results suggest new ways that water activity and salinity of the ocean are important to stability of habitable conditions in ocean worlds. By demonstrating that Europa’s ocean composition will be sensitive to its orbital dynamics and the degree to which it undergoes oscillatory tidal heat production, we reinforce that Europa’s long-term habitability is directly tied to its thermal-orbital history.