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The Effect of a Biosphere on the Habitable Timespan of Stagnant-lid Planets and Implications for the Atmospheric Spectrum

By Keith Cowing

Status Report

astro-ph.EP

December 18, 2024

Filed under astro-ph.EP, atmosphere, biological productivity, biosignature, biosphere, carbonate-silicate cycle, climate, Earth-like Planet, exoplanet, habitability, Habitable Zone, JWST, Runaway Greenhouse, stagnant-lid planet

The Effect of a Biosphere on the Habitable Timespan of Stagnant-lid Planets and Implications for the Atmospheric Spectrum — Transmission spectra for the biotic scenarios. We show the JWST/NIRSpec range between 3 – 5 micron with a continuous grey cloud deck at the p = 0.01 bar (solid lines) and the dry biotic scenarios 1 & 2 with a lower cloud deck at the p = 0.1 bar (dashed line). The inlay for the 3.2 – 3.35 micron range highlights the O3 (grey box) and CH4 feature (magenta box). We further simulated JWST observations with PANDEXO for the dry biotic scenarios 1 & 2 with the lower cloud deck, simulating 100 transit observations of TRAPPIST-1e (black error bars). We chose the G395M grism setting and combined 10 pixels in one bin. — astro-ph.EP

Temperature-dependent biological productivity controls silicate weathering and thereby extends the potential habitable timespan of Earth.

Models and theoretical considerations indicate that the runaway greenhouse on Earth-like exoplanets is generally accompanied by a dramatic increase in atmospheric H₂O and CO₂, which might be observed with the upcoming generation of space telescopes. If an active biosphere extends the habitable timespan of exoplanets similarly to Earth, observing the atmospheric spectra of exoplanets near the inner edge of the habitable zone could then give insights into whether the planet is inhabited.

Here, we explore this idea for Earth-like stagnant-lid planets. We find that while for a reduced mantle, a surface biosphere extends the habitable timespan of the planet by about 1 Gyr, for more oxidising conditions, the biologically enhanced rate of weathering becomes increasingly compensated for by an increased supply rate of CO₂ to the atmosphere.

Observationally, the resulting difference in atmospheric CO₂ near the inner edge of the habitable zone is clearly distinguishable between biotic planets with active weathering and abiotic planets that have experienced a runaway greenhouse. For an efficient hydrological cycle, the increased bioproductivity also leads to a CH₄ biosignature observable with JWST.

As the planet becomes uninhabitable, the H₂O infrared absorption bands dominate, but the 4.3-micron CO₂ band remains a clear window into the CO₂ abundances. In summary, while the effect of life on the carbonate-silicate cycle leaves a record in the atmospheric spectrum of Earth-like stagnant-lid planets, future work is needed especially to determine the tectonic state and composition of exoplanets and to push forward the development of the next generation of space telescopes.

Dennis Höning, Ludmila Carone, Philipp Baumeister, Kathy L. Chubb, John Lee Grenfell, Kaustubh Hakim, Nicolas Iro, Benjamin Taysum, Nicola Tosi

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2412.11537 [astro-ph.EP] (or arXiv:2412.11537v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2412.11537
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Related DOI:
https://doi.org/10.1051/0004-6361/202451940
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Submission history
From: Dennis Höning
[v1] Mon, 16 Dec 2024 08:14:33 UTC (3,300 KB)
https://arxiv.org/abs/2412.11537
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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