EFFECT OF CHANGING THE INTERIOR AND SEAWATER COMPOSITIONS OF ENCELADUS ON SERPENTINIZATION-DRIVEN HABITABILITY

Enceladus’ South Pole plumes show promising geological activity and these plumes have compositionally included salts, aqueous silica, organic molecules, and molecular hydrogen (Postberg et al., 2011; Hsu et al., 2015; Watie et al., 2017). Recent laboratory work (Taubner et al., 2018) shows the potential of methanogenesis tied to low-temperature serpentinization under Enceladus conditions. To more effectively assess the habitability of serpentinization reactions that are plausible on Enceladus, we model the potential bioenergetic pathways that would be thermodynamically favorable at the water-rock boundary resulting from different serpentinization reaction stages. Previous geochemical models of Enceladus (Glein et al., 2015; Neveu et al., 2017; Hart and Cardace, 2017; Taubner et al., 2018), and bioenergetic modeling (as in Amend and Shock, 2001; Cardace et al., 2015; Hart and Cardace, 2017), anchored the modeling approach plausible at the subsurface ocean-interior interface of Enceladus. Interior compositions were based on mean values of ordinary chondrites, carbonaceous chondrites, and achondrites reacting with Na-Cl, Mg-Cl, and Ca-Cl seawater major ion chemistries. Simulations were completed using a modified thermodynamic database of Geochemist’s Workbench REACT. We utilized Gibbs Free Energy to evaluate the thermodynamic feasibility of CO₂-CH₄-H₂ driven microbial habitability. Methanogenesis and methanotrophy, as modeled, both have negative Gibbs Free Energy values, thus proceed spontaneously in the modeled system at 273.15 K and using the free energy values as a habitability proxy, are habitable for both ordinary chondrites and carbonaceous chondrites reacting with all modeled oceans.

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