Issue |
A&A
Volume 693, January 2025
|
|
---|---|---|
Article Number | A205 | |
Number of page(s) | 17 | |
Section | Planets, planetary systems, and small bodies | |
DOI | https://doi.org/10.1051/0004-6361/202451940 | |
Published online | 17 January 2025 |
The effect of a biosphere on the habitable timespan of stagnant-lid planets and implications for the atmospheric spectrum
1
Potsdam-Institute for Climate Impact Research,
Potsdam,
Germany
2
Space Research Institute, Austrian Academy of Sciences,
Schmiedlstr. 6,
8042
Graz,
Austria
3
Institute of Planetary Research, German Aerospace Center (DLR),
Berlin,
Germany
4
Center for Exoplanet Science, University of St Andrews,
North Haugh,
St Andrews,
UK
5
Royal Observatory of Belgium,
Ringlaan 3,
1180
Brussels,
Belgium
6
Institute of Astronomy, KU Leuven,
Celestijnenlaan 200D,
3001
Leuven,
Belgium
★★ Corresponding author; dennis.hoening@gmail.com
Received:
20
August
2024
Accepted:
2
December
2024
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-µm 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.
Key words: Earth / planets and satellites: atmospheres / planets and satellites: interiors / planets and satellites: physical evolution / planets and satellites: terrestrial planets
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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