[astro-ph.EP] Given their abundance and observational advantages, M stars will arguably be the best candidates for characterizing and searching for biosignatures on terrestrial exoplanets in the near future.
However, photochemistry that can suppress or enhance key biosignature molecules in planetary atmospheres is primarily driven by UV flux from the host M star, which is influenced by stellar activity that decreases with age.
Here, we simulate Pre-Industrial Earth-like and Archean Earth-like atmospheres around M4 and M8 stars from 650 Myr to 5 Gyr old. We find that our Pre-Industrial Earth atmospheres around 5 Gyr M stars have up to ten times more CH4 than those around 650 Myr M stars, producing 68% stronger methane bands in NIR transit spectroscopy.
Additionally, photochemical shielding from O2 in our Pre-Industrial Earth atmospheres reduces the impact UV-driven photochemistry on composition, while the Archean Earth exhibits larger compositional changes due to weaker shielding from CO2.
Lastly, enhanced CO2 photolysis, driven by the strong net UV flux and high Far/Near-UV ratios of 650 Myr and 1 Gyr M stars, cause our Archean Earth-like planets to produce up to 5.4 dex more O3 than when around 5 Gyr M stars. The excess O3 causes the Archean Earth to become half as reflective in the 0.2-0.3 μm Hartley band feature in ultraviolet reflectance spectroscopy, which the Habitable Worlds Observatory may be sensitive to.
Without the context of the star’s real-time, age-dependent UV radiation, this O3 feature could be misinterpreted as a proxy for low, biogenic O2.
C. Evan Davis, Victoria S. Meadows, Evgenya L. Shkolnik, Andrew P. Lincowski, Sarah Peacock, R. O. Parke Loyd, Adam C. Schneider, Travis Barman
Comments: 25 pages, 7 figures, 2 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2608.19328 [astro-ph.EP] (or arXiv:2608.19328v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.19328
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Related DOI:
https://doi.org/10.3847/1538-4357/ae994a
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Submission history
From: Christopher Evan Davis
[v1] Wed, 19 Aug 2026 18:00:07 UTC (1,146 KB)
https://arxiv.org/abs/2608.19328
Astrobiology, Astrochemistry,
