The Diversity of Exoplanetary Environments and the Search for Signs of Life Beyond Earth

Thousands of exoplanets orbit nearby stars, showcasing a remarkable diversity in mass, size, and orbits.

With the James Webb Space Telescope now operational, we are observing exoplanet atmospheres and aiming to reach down to small, habitable-zone exoplanets in search of signs of habitability and possibly even biosignature gases.

Given the scarcity of targets, it is imperative to embrace the known diversity and consider the range of exoplanets that might host life. We review how Earth life interacts with various atmospheric gases, noting that bacteria can survive in high concentrations of gases such as H₂, He, CO₂, and CO.

Additionally, we consider the potential for life in alternative solvents and in cloud biospheres where rocky surfaces are excessively hot, as well as in hypothesized planetary global oceans. We highlight that life fundamentally requires metal ions for catalytic reactions, suggesting that environments without surface contact need meteoritic delivery to provide these essential elements.

Despite today’s observational limits, a suite of next-generation telescopes is being designed specifically for exoplanet studies, promising to expand our capabilities and understanding in the future.

The diversity of exoplanets. Exoplanets with measured masses (x axis) and radii (y axis) are shown as points colored by their equilibrium temperature. Colored points are those with uncertainties less than 30% and grey are planets with uncertainties between 30% and 50%. The curves are illustrative models representing planetary compositions; if a planet aligns with a curve, its interior may match that composition. Although only a subset of the thousands of detected exoplanets have measured masses and radii, those shown here illustrate the theme of exoplanet diversity as captured by wide range of masses, radii, and orbits (via their temperatures). Data from the Exoplanet Archive https://exoplanetarchive.ipac.caltech.edu/ (Akeson et al., 2013). Models from (Seager et al., 2007). Credit: L. Herrington and S. Seager.

Sara Seager, Janusz J. Petkowski, William Bains

Comments: This article is part of the theme issue ‘Chance and purpose in the evolution of biospheres’. Published in Philosophical Transactions of the Royal Society B (Philos. Trans. R. Soc. B)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2506.11690 [astro-ph.EP] (or arXiv:2506.11690v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2506.11690
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From: Janusz Petkowski
[v1] Fri, 13 Jun 2025 11:37:49 UTC (1,033 KB)
https://arxiv.org/abs/2506.11690

Astrobiology,