Fermentation heterotrophy can reproduce Enceladus's plume H2 and CH4 under limited serpentinization
Abstract
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.
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BibTeX
@misc{nasreldine2026fermentation,
title = {{Fermentation heterotrophy can reproduce Enceladus's plume H2 and CH4 under limited serpentinization}},
author = {Sam Nasreldine and Antonin Affholder and Laura Molares Moncayo and Régis Ferrière and François Guyot},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.13434},
eprint = {2610.13434},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.13434},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Fermentation heterotrophy can reproduce Enceladus's plume H2 and CH4 under limited serpentinization
AU - Sam Nasreldine
AU - Antonin Affholder
AU - Laura Molares Moncayo
AU - Régis Ferrière
AU - François Guyot
PY - 2026
DA - 2026/10/12
PB - arXiv
DO - 10.48550/arxiv.2610.13434
UR - https://arxiv.org/abs/2610.13434
AB - 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.
ER -