Detectability Of Biosignatures In Warm, Water-rich Atmospheres

Warm rocky exoplanets within the habitable zone of Sun-like stars are favoured targets for current and future missions. Theory indicates these planets could be wet at formation and remain habitable long enough for life to develop.

In this work we test the climate-chemistry response, maintenance, and detectability of biosignatures in warm, water-rich atmospheres with Earth biomass fluxes within the framework of the planned LIFE mission. We used the coupled climate-chemistry column model 1D-TERRA to simulate the composition of planetary atmospheres at different distances from the Sun, assuming Earth’s planetary parameters and evolution.

We increased the incoming instellation by up to 50 percent in steps of 10 percent, corresponding to orbits of 1.00 to 0.82 AU. Simulations were performed with and without modern Earth’s biomass fluxes. Emission spectra of all simulations were produced using the GARLIC radiative transfer model.

LIFEsim was then used to add noise to and simulate observations of these spectra to assess how biotic and abiotic atmospheres of Earth-like planets can be distinguished. Increasing instellation leads to surface water vapour pressures rising from 0.01 bar (1.13%) to 0.61 bar (34.72%).

In the biotic scenarios, the ozone layer survives because hydrogen oxide reactions with nitrogen oxides prevent the net ozone chemical sink from increasing. Synthetic observations with LIFEsim, assuming a 2.0 m aperture and resolving power of R = 50, show that O₃ signatures at 9.6 micron reliably point to Earth-like biosphere surface fluxes of O₂ only for systems within 10 parsecs.

Increasing the aperture to 3.5 m increases this range to 22.5 pc. The differences in atmospheric temperature due to differing H₂O profiles also enables observations at 15.0 micron to reliably identify planets with a CH₄ surface flux equal to that of Earth’s biosphere.

Benjamin Taysum, Iris van Zelst, John Lee Grenfell, Franz Schreier, Juan Cabrera, Heike Rauer

Comments: To be published in Astronomy and Astrophysics; 14 pages, 12 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2412.01266 [astro-ph.EP] (or arXiv:2412.01266v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2412.01266
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Submission history
From: Benjamin Taysum
[v1] Mon, 2 Dec 2024 08:32:05 UTC (10,423 KB)
https://arxiv.org/abs/2412.01266
Astrobiology