Theoretical Considerations on the Characteristic Timescales of Hydrogen Generation by Serpentinization Reactions on Enceladus

The Cassini spacecraft demonstrated that Saturn's small moon Enceladus may harbor hydrothermal activity. In particular, molecular hydrogen production could result from water-rock interactions in a tidally heated, water-filled porous rocky core. lifetime of such reactions is key to assess the habitability potential and constrain plausible durations active stage context where evolution debated. Although it has recently been suggested serpentinization timescale does not exceed few hundred million years, this estimation was based on assumptions regarding silicate dissolution kinetics are prone overestimate actual reactivity primary silicates. Here, we investigated rate-limiting mechanisms governing fluid-rock delay completion Enceladus' core serpentinization. considered impact (a) various secondary mineral assemblages Gibbs free energy Fe-bearing associated rates; (b) rate-laws alternative transition state theory; (c) diffusion nanoporous assemblages; (d) slow water supply. Overall, our results confirm timescales never 500 Myr, indicate fluid flow ultimately sets tempo for Only unreasonable grain sizes (>1 m) or unexpectedly low diffusivity coatings covering silicates would be consistent with several billion years. We thus suggest either activity developed Enceladus, processes (pyrolysis insoluble organic matter, microbial activity) must tested explain observed H2 flux plume.