Modeling Late-State Serpentinization on Enceladus and Implications for Methane-Utilizing Microbial Metabolisms
Abstract
Modeling investigations of Enceladus and other icy-satellites have included physicochemical properties (Sohl et al., 2010; Glein et al., 2015; Neveu et al., 2015), geophysical prospects of serpentinization (Malamud and Prialnik, 2016; Vance et al., 2016), and aqueous geochemistry across different antifreeze fluid-rock scenarios (Neveu et al., 2017). To more effectively evaluate the habitability of Enceladus, in the context of recent observations (Waite et al., 2017), we model the potential bioenergetic pathways that would be thermodynamically favorable at the interface of hydrothermal water-rock reactions resulting from late stage serpentinization (>90% serpentinized), hypothesized on Enceladus. Building on previous geochemical model outputs of Enceladus (Neveu et al., 2017), and bioenergetic modeling (as in Amend and Shock, 2001; Cardace et al., 2015), we present a model of late stage serpentinization possible at the water-rock interface of Enceladus, and report changing activities of chemical species related to methane utilization by microbes over the course of serpentinization using the Geochemist's Workbench REACT code [modified Extended Debye-Hückel (Helgeson, 1969) using the thermodynamic database of SUPCRT92 (Johnson et al., 1992)]. Using a model protolith speculated to exist at Enceladus's water-rock boundary, constrained by extraterrestrial analog analytical data for subsurface serpentinites of the Coast Range Ophiolite (Lower Lake, CA, USA) mélange rocks, we deduce evolving habitability conditions as the model protolith reacts with feasible, though hypothetical, planetary ocean chemistries (from Glien et al., 2015, and Neveu et al., 2017). Major components of modeled oceans, Na-Cl, Mg-Cl, and Ca-Cl, show shifts in the feasibility of CO2-CH4-H2 driven microbial habitability, occurring early in the reaction progress, with methanogenesis being bioenergetically favored. Methanotrophy was favored late in the reaction progress of some Na-Cl systems and in the Mg-Cl systems, with shifts in Gibbs Energy values for Mg-Cl systems progressing in the middle of the reaction process. In sum, we show that the bioenergetic yield of fundamental methanogenetic and methanotrophic reactions changes as late stage serpentinization progresses under different Enceladus seawater conditions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.P43B2885H
- Keywords:
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- 4850 Marine organic chemistry;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL;
- 5215 Origin of life;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 6282 Enceladus;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 8450 Planetary volcanism;
- VOLCANOLOGY