Fermentation Heterotrophy Can Reproduce Enceladus’s H2 And CH4 Under Limited Serpentinization

[astro-ph.EP] Saturn’s icy moon Enceladus is a prime target in the search for life beyond Earth. Abundant H₂ and CH₄ in Enceladus’s south-polar plume have been shown to be consistent with hydrogenotrophic methanogens feeding on products of long-lived serpentinization.

However, thermo-permeability models make sustained core-wide H₂ production by serpentinization uncertain. We therefore explore whether an alternative metabolism based on fermentation-driven heterotrophy could reproduce Cassini H₂ and CH₄ escape fluxes under limited serpentinization.

We develop a coupled ecosystem model of fermentation and methanogenesis in a hydrothermal-ocean-plume framework, using glycine as a proxy for amino-acid-like fermentable organics. With effectively no abiotic H₂ and CH₄ input, purely heterotrophic communities with fermenters and methanogens can reproduce both Cassini-derived flux intervals given sufficient hydrothermal glycine-equivalent supply, while the estimated organic stock could sustain the required H₂ production on gigayear timescales if fully available.

We then test a scenario with input ranges for fermentable organic matter, H₂, and CH₄ informed by asteroid-sample measurements and geochemical estimates of limited serpentinization. Simulations within both Cassini-derived flux intervals are concentrated in communities with acetoclastic methanogens; Bayesian model comparison favors the same communities.

This holds even allowing for greater abiotic H₂ and CH₄ inputs that reduce the fermentable-organic supply required to reproduce the plume. We therefore identify fermentation heterotrophy as a testable alternative to purely hydrogenotrophic, serpentinization-dominated biotic interpretations and motivate future plume searches for co-exported fermentation products, including acetate and ammonium, together with measurements of methane carbon isotopes.

Sam Nasreldine, Antonin Affholder, Laura Molares Moncayo, Régis Ferrière, François Guyot

Comments: 53 pages, 4 Main Figures, 6 SI Figures, 3 SI Tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2610.13434 [astro-ph.EP] (or arXiv:2610.13434v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2610.13434
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Submission history
From: Antonin Affholder
[v1] Fri, 9 Oct 2026 11:34:44 UTC (3,619 KB)
https://arxiv.org/abs/2610.13434

Astrobiology, Astrogeology, Astrochemistry,