2025MNRAS.537.2097L

Galactic cosmic rays (GCRs) may influence the habitability of exoplanets. The recently proposed relationship between GCR intensities at exoplanetary locations and the rotation periods of their host stars is here investigated for several M-dwarf astrospheres, namely Proxima Centauri, TRAPPIST-1, GJ 436, and LHS1140, using a three-dimensional GCR modulation code. This relation, where higher GCR intensities result from enhanced particle transport along astrospheric magnetic fields that are underwound due to longer stellar rotation periods, is found to hold for the astrospheres considered here. The influence of the stellar rotation period on GCR intensities in a Sun-like astrosphere on Earth and Mars-like atmospheres is also investigated and found to directly influence atmospheric ionization and radiation exposure.