A Systematic North-South Asymmetry In The Steady-state Climate Of Rapidly-rotating Oblique Water Worlds

Planetary obliquity (axial tilt) plays an important role in regulating the climate evolution and habitability of water-covered planets.

Despite the suspicion of large obliquities in several exoplanetary systems, this phenomenon remains hard to observe directly. We aimed to study the effect of mass, obliquity, and rotation on the steady state climate of water-covered planets.

We simulated the climate evolution of such planets with varying obliquities, rotational speed, and mass using a general circulation model (GCM) of intermediate complexity, assuming aqua-planet configurations.

High obliquity supports an asymmetry between the equilibrium climatological conditions in the northern and southern hemispheres. The polar temperature ratio deviates further from unity with increasing obliquity and rotation rate. Cloud coverage patterns also shift with obliquity, displaying distinct latitudinal bands and increased cloudiness in the warmer hemisphere.

The climate of habitable-zone aqua-planets turns out to be sensitive to changes in obliquity and rotation rate, but are independent of planet mass. Our results highlight the importance of considering these factors when assessing the surface conditions of exoplanets. As a consequence, surface condition asymmetries in water-world exo-planets can be used to infer the planet’s obliquity and rotation rate.

Mass and radius for a number of potentially habitable ocean worlds. The bullet points show identified ocean worlds: listed from bottom to top: HD 11505b, WASP 35, TOI 157, TOI 1452b, KELT 10b, HD 80883b, HD 221585b, HIP 67537b, K2-18b, Kepler 1980b, HD 50499b, Kepler 1766b, HD 50499c. The green curve gives the mass-radius relation for planets with a water content of > ∼ 30 % (by mass) from [40]. The arrows (and black crosses [right-most one is white]) give the simulation atmosphere models. — astro-ph.EP

Y Wu, S. Portegies Zwart, H Dijkstra

Comments: Accepted for publication in New Astronomy
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2510.11904 [astro-ph.EP] (or arXiv:2510.11904v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2510.11904
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Submission history
From: Simon Portegies Zwart
[v1] Mon, 13 Oct 2025 20:13:43 UTC (1,026 KB)
https://arxiv.org/abs/2510.11904

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