Original title: Energy deposition in planetary and exoplanetary atmospheres induced by cosmic rays
Jesse Polman, Ingo Leya · September 2026
High-energy particles from space, called cosmic rays, can change the chemicals in a planet's upper air, including signs of life. To see how much they change things, scientists must know how planetary magnetic fields block these incoming particles. Researchers used a computer model named CosmicTransmutation to test two particle types: galactic cosmic rays and stellar energetic particles. Because these two types carry different energy levels, magnetic fields steer them away differently. On an Earth-like planet with no magnetic field, stellar particles dump far more energy into the air. However, a field of 30 μT or higher reduces this difference, making both energy fluxes comparable. The team also discovered that particles do not plunge as deep into high-pressure air as older, simpler models predicted, regardless of atmospheric composition. Tests on the larger exoplanet K2-18b showed similar results, proving both particle sources matter.
Someone waters two garden beds with two hoses: one gives a steady mist, the other fires short bursts. A tall hedge stands between the hoses and the beds, but it blocks the mist almost completely while the bursts fly over the top, so you cannot predict the wetness from the hose settings alone. In this paper the hedge is a planet's magnetic field, the two hoses are the two kinds of incoming particles from space, and the water that lands is the energy the particles deposit in the atmosphere.
If telescopes look for life by scanning a planet's air, they are really looking for biosignature molecules. Cosmic rays change how many of those molecules are present, and this work shows a planet's magnetic field decides how much incoming particle energy reaches the atmosphere and how deep it goes. Reading an atmosphere without modeling this could lead to a wrong answer about whether life is there.
This work does not yet predict actual chemical abundances or biosignature changes, since it reports energy fluxes and penetration depths rather than atmospheric chemistry. The authors also note that full latitudinal and longitudinal dependencies will require general circulation models, so the magnetic-field treatment here is not complete in that spatial detail.
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Energy deposition in planetary and exoplanetary atmospheres induced by cosmic rays — Jesse Polman, Ingo Leya
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.