Oxygenated False Positive Biosignatures in Mars-like Exoplanet Atmospheres

Oxygen is a well-studied biosignature. Studying potential abiotic pathways for O2 build-up in exoplanet atmospheres is essential for evaluating whether the detection of O₂ would constitute a biosignature detection on other worlds.

Previous modeling efforts in the literature demonstrated that detectable abiotic O₂ and O₃ can be produced through CO₂ photolysis for rocky planets around M dwarf stars. Building on modeling approaches from previous studies, we use photochemical simulations to reassess the conditions under which O₂2 and O₃ may accumulate through similar photochemical mechanisms.

Using a Mars-like atmospheric composition and planetary parameters, we vary the hydrogen mole fraction to assess how changes in HOx chemistry can affect the resulting accumulation of abiotic O₂ and O₃. Across the range of hydrogen mole fractions explored, we obtain a maximum O₂ abundance of ~2.7% for H = 0.0065 ppm, about an order of magnitude lower than reported in the literature.

This reduction is consistent with the elevated water vapor abundance adopted in our simulations, which enhances HOx-driven recycling of CO and O and thereby suppresses the accumulation of O₂ and O₃. Our improved understanding of how this cycle results in atmospheric false positive biosignatures in crucial towards developing future exoplanet characterization strategies.

Mixing ratio profiles for CO, O₂, O₃, H, H₂, H₂O, OH, HO₂, and H₂O₂ for cases 1 (red), 2 (orange), 3 (yellow), 4 (green), 5 (blue), and 6 (purple) as functions of altitude z. Note the different x-axis values for each column. The curves for cases 2, 3, 4, 5, and 6 overlap each other for most species. — astro-ph.EP

Margaret Turcotte Seavey, Shawn Domagal-Goldman, Amber Young, Jaime Crouse, Jacob Lustig-Yaeger, Giada Arney

Comments: 8 pages, 3 figures, 2 tables. Submitted to The Astrophysical Journal Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2603.11017 [astro-ph.EP](or arXiv:2603.11017v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2603.11017
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Submission history
From: Margaret Turcotte Seavey
[v1] Wed, 11 Mar 2026 17:45:53 UTC (602 KB)
https://arxiv.org/abs/2603.11017

Astrobiology, Exoplanet,