Exploring TRAPPIST-1 Climate States With An Energy Balance Model

This paper presents a version of the HEXTOR energy balance model that has been configured for the study of habitable terrestrial planets orbiting low-mass stars. The model is validated for rapidly-rotating Earth-like planets using latitudinal coordinates, which shows expected patterns of bistability.

A tidally-locked coordinate transformation is then applied to the model, which is calibrated to match mean values of the minimum, average, and maximum surface temperatures from a general circulation model ensemble of TRAPPIST-1 e. This calibrated energy balance model is used to characterize the possible climate states of such a synchronously rotating planet across a parameter space of instellation and carbon dioxide partial pressure.

These calculations suggest a state of partial ice cover for TRAPPIST-1 e and complete ice cover for TRAPPIST-1 f, unless carbon dioxide partial pressure is ~1 bar or greater. This approach demonstrates the capability of a simplified one-dimensional model to study the climates of terrestrial planets in synchronous rotation, which can help guide more complex models and observations toward the most promising targets of interest.

Jacob Haqq-Misra
Comments: Submitted to The Open Journal of Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2605.06964 [astro-ph.EP] (or arXiv:2605.06964v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2605.06964
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Submission history
From: Jacob Haqq-Misra
[v1] Thu, 7 May 2026 21:33:36 UTC (94 KB)
https://arxiv.org/abs/2605.06964
Astrobiology, exoplanet,