![Map of surface mass balance in the star-centered frame, averaged over the final synodic day of the simulation, for the 1-year synodic day, 500 m GEL case. Left: Nightside. Right: Dayside. The yellow star represents the substellar point. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/11/The-Fate-of-Ice.png?fit=1200%2C676&ssl=1)
[astro-ph.EP] Rocky exoplanets orbiting M dwarf stars are often assumed to be synchronously rotating, such that water-trapping in ice sheets on the permanent nightside may pose a threat to habitability.
However, in compact M dwarf systems, gravitational interactions between planets may cause the substellar point to librate or circulate on millennial timescales and sporadically change direction or speed. Here, we use a 3D global climate model to quantify, for the first time, the water-trapping capabilities of these “near”-synchronously rotating exoplanets, with TRAPPIST-1e as our test case.
Across a range of synodic day lengths, we find that there is a permanent polar ice reservoir and an increasingly large build-up of lower-latitude transient nightside ice for longer days. A persistent ice-free region develops on the dayside where surface conditions can sustain liquid water.
However, this steady-state ice distribution may never be realized since the accumulation timescale may be slower than changes in the spin regime. Additionally, we revise the nightside ice build-up on a synchronously rotating exoplanet using a coupled atmosphere+ice numerical model that accounts for atmospheric lapse rate and isostatic adjustment feedbacks.
We find that accounting for this ice-elevation feedback reduces the predicted ice accumulation by a factor of ~3. Taken together, our study suggests that water-trapping in ice sheets is less severe than previously thought for land planets orbiting M dwarf stars.
Sarah Silverman, Thomas Navarro, Martin Turbet, Nicolas B. Cowan, Natalya Gomez, Siddharth Bhatnagar, Emeline Bolmont
Comments: Submitted to ApJ on October 20, 2026
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2610.33884 [astro-ph.EP](or arXiv:2610.33884v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2610.33884
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Submission history
From: Sarah Silverman
[v1] Sat, 24 Oct 2026 19:51:12 UTC (5,542 KB)
https://arxiv.org/abs/2610.33884
Astrobiology,
