![Normalized magnetospheric standoff distance rM/rpl as a function of the planetary magnetic field and the total stellar pressure for Modern Earth (left panel) and Early Earth (right panel) across the HZ of the host star. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/08/The-impact-of.png?fit=1200%2C673&ssl=1)
[astro-ph.EP] We investigate how tidal locking affects the planetary dynamo and the magnetospheres of Earth-like planets orbiting the habitable zones of M dwarfs.
We couple an empirical stellar wind model with two distinct planetary dynamo paradigms, direct rotational scaling and energy-flux scaling, using a Constant Time Lag (CTL) model to simulate continuous tidal spin-down until synchronization.
We model two hypothetical planets based on a highly dissipative Modern Earth and a less dissipative, rapidly rotating Early Earth representative of the Paleoarchean.
Our results show that tidal locking acts as a severe negative feedback on planetary magnetism across both paradigms, where the dipolar field frequently collapses before full tidal synchronization is reached.
Essentially, a shielded atmospheric environment around M dwarfs requires a host massive enough (≥0.32M⊙) to place the HZ at wider orbital distances, sparing the planet from the sub-Alfvénic environment, and the internal tidal dissipation of the planet must be sufficiently low to prevent rapid rotational decay.
For mid-to-late M dwarfs, the inevitable tidal locking and the extreme stellar wind pressures result in a total collapse of the magnetic shield, reducing the likelihood of atmospheric protection to essentially zero across the habitable zone.
J. P. Hidalgo, D. R. G Schleicher
Comments: 6 pages, 4 figures. Conference proceeding from Cool Stars 23, Tokyo, Japan
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2608.20949 [astro-ph.EP](or arXiv:2608.20949v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.20949
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Journal reference: The 23rd Cambridge Workshop on Cool Stars, Stellar Systems and the Sun (CS23), Tokyo, Japan (2026)
Related DOI:
https://doi.org/10.5281/zenodo.22031841
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Submission history
From: Juan Pablo Hidalgo
[v1] Fri, 21 Aug 2026 10:15:08 UTC (3,618 KB)
https://arxiv.org/abs/2608.20949
Astrobiology, exoplanet,
