![Surface temperature of the 22 exoplanets in an aquaplanet configuration. Obliquity and eccentricity are set to zero, and all are tidally locked with Earth-like atmospheric chemistry and pressure. Level lines correspond to the temperatures of 223.15, 273.15, and 323.15 K. White lines indicate the terminator, that is, the boundary between the illuminated and the dark sides of a planet. Black dots indicate the prevalence of sea ice (ice fraction larger than 0.5). -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/08/Assessing-1.png?fit=1200%2C673&ssl=1)
[astro-ph.EP] Tidally locked exoplanets orbiting M dwarf stars are prime targets in the search for habitable worlds, yet their complex climate dynamics challenge conventional models of habitability.
We homogeneously estimated the liquid-water habitability of exoplanets with the highest up-to-date Earth-similarity index. We modified the climate model PLASIM to apply it to tidally locked exoplanets across a range of parameters.
We systematically classified and compared potentially habitable exoplanets and selected among the ones featuring the highest Earth-similarity index in the conservative sample of the Habitable Worlds Catalog, both relative to each other and as a function of atmospheric pressure.
Our analysis revealed three main climate regimes: Snowball, Hot, and Eyeball planets-the latter having a warm and habitable substellar region with T > 273 K and a localized hydrological cycle. Although surface temperature generally increases with pressure, Eyeball planet climates remain stable in a wide pressure range.
Complex atmospheric dynamics govern the behavior of the climate, highlighting the need for detailed climate simulations to guide future observations.
Classification of exoplanets into the three climate regimes identified in Figure 2 and discussed in the main text. In both panels, the lower abscissa is Te (A = 0.3), the emission temperature assuming a terrestrial albedo (ABond = 0.30). Upper panel: difference between substellar and antistellar point temperatures (∆Tsa, Eq. 5) versus Te (A = 0.3); upper abscissa reports the instellation. Lower panel: surface average temperature calculated by PLASIM versus Te (A = 0.3); the color map indicates the ∆Tsa values. The horizontal dashed lines demarcate the transitions between the identified three regimes: Ts PLASIM > 270 K; 180 K < Ts PLASIM < 270 K; Ts PLASIM < 180 K. The diagonal line represents the condition Ts PLASIM = Te (A = 0.3). The semi-transparent ellipses refer to the Transitional outliers. — [astro-ph.EP]
Erica Bisesi, Giuseppe Murante, Jost von Hardenberg, José A. Caballero, Michele Maris, Daniela Billi, Nicoletta La Rocca, Laura Silva
Comments: Accepted manuscript. 34 pages, 1 table, 9 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
MSC classes: 85-08
Cite as: arXiv:2608.25451 [astro-ph.EP] (or arXiv:2608.25451v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.25451
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Journal reference: Astrobiology. 2026;0(0)
Related DOI:
https://doi.org/10.1177/15311074261479167
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Submission history
From: Erica Bisesi Dr
[v1] Wed, 26 Aug 2026 07:15:36 UTC (12,305 KB)
https://arxiv.org/abs/2608.25451
Astrobiology, exoplanet,
