A Framework For Evaluating Biosignature Potential Against The Abiotic Baseline On Ocean Worlds

Ocean worlds are considered as targets for life detection missions because they meet several key requirements for habitability. However, identifying potential life on other worlds requires observing clear and unambiguous biosignature signals above the existing abiotic baseline.

Consequently, this necessitates evaluating uncertainty and variability in the abiotic baseline, including processes that can overlap, attenuate, or obfuscate biosignatures before they are observed. This article develops a quantitative framework for holistically evaluating abiotic baselines on ocean worlds to guide life detection strategies.

Using Enceladus as an example, we assess the potential of using: i) CH₄ isotopes and their relationship with CO₂, and ii) amino acid chirality as biosignatures, demonstrating that uncertainties in abiotic processes currently prevent hypothetical future δ13CCO₂ and δ13CCH₄ measurements from definitively inferring a biosphere on Enceladus.

Additionally, our results quantitatively show that neglecting the abiotic baseline risks false negative life detection claims for both isotopic and chiral biosignatures. Interpreting these and other alternative biosignatures on Enceladus, Europa, Titan, and similar planetary bodies therefore requires complimentary geophysical observations such as constraining internal temperatures to within ∼10-100∘C, and improving characterisation of the target’s rheology, lithology, initial abiotic organic inventory and ocean transport timescales.

Schematic of carbon isotope cycling processes on Enceladus. Each black box represents a module that monitors key processes affecting influxes and outfluxes of chemical species, and their interactions therein (both bulk chemical and isotopic). For each module, the process-based isotope enrichment factor and/or the model predicted net isotope difference is noted. — astro-ph.EP

Peter M. Higgins, Weibin Chen, Oliver Warr, Lucas M. Fifer, Wanying Kang, Charles S. Cockell, Barbara Sherwood Lollar

Comments: Preprint. Journal reference and DOI will be added when available. 60 pages, 11 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2605.15337 [astro-ph.EP] (or arXiv:2605.15337v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2605.15337
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Submission history
From: Peter M. Higgins
[v1] Thu, 14 May 2026 19:00:57 UTC (4,034 KB)
https://arxiv.org/abs/2605.15337
Astrobiology,