![Atmospheric energy deposition profiles of GCRs and SEPs in the atmosphere of K2-18b for different magnetic field strengths. The profiles have been smoothed to improve visual clarity. For visibility, the deposited energy corresponding to B=300 µT has been multiplied by a factor of 10. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/09/Energy-.png?fit=1200%2C674&ssl=1)
[astro-ph.EP] Cosmic rays can significantly alter the abundances of certain species in the upper layers of planetary atmospheres, especially in terms of their biosignatures. To fully understand the extent of this effect, it is essential to accurately model the interactions of cosmic rays with planetary magnetic fields.
We used the CosmicTransmutation code to study the effect of a planetary magnetic field on the flux of galactic cosmic rays and stellar energetic particles. We found that both particle sources are significantly affected by magnetic fields, even though the effects are different due to the varying energy ranges that characterize each source.
The stellar energetic particle energy flux is significantly higher for an Earth-like planet with no magnetic field, but with a magnetic field of 30μT or higher, the energy flux of the two sources becomes comparable.
We find that the atmospheric pressures the cosmic rays reach are significantly lower than those found in previous studies using simpler models and that the effect of the atmospheric composition on this outcome is small.
We found similar results using the model for the exoplanet K2-18b, even though the radius is significantly larger than Earth’s. Because the two cosmic ray sources cover different energy ranges and are affected by the magnetic field in different ways as a result, both sources should be considered.
Future studies should focus on combining an accurate modelling procedure of the interaction between cosmic rays and planetary magnetic fields with atmospheric chemistry models. This will require general circulation models to capture the latitudinal and longitudinal dependencies in full.
Jesse Polman, Ingo Leya
Comments: Accepted to A&A. 13 pages, 9 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); High Energy Astrophysical Phenomena (astro-ph.HE)
Cite as: arXiv:2609.10688 [astro-ph.EP] (or arXiv:2609.10688v2 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.10688
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Related DOI:
https://doi.org/10.1051/0004-6361/202661406
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Submission history
From: Jesse Polman
[v1] Wed, 9 Sep 2026 18:00:04 UTC (269 KB)
[v2] Wed, 16 Sep 2026 07:12:19 UTC (268 KB)
https://arxiv.org/abs/2609.10688
Astrobiology,
