Research Article

On stellar activity cycle-related cosmic ray modulation effects in the astrosphere of Proxima Centauri

¹ Center for Space Research, North-West University, Potchefstroom 2520, South Africa
² Centre for Planetary Habitability (PHAB), Department of Geosciences, University of Oslo, Oslo, Norway

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 3 December 2025
Accepted: 20 March 2026

Abstract

In the heliosphere, solar cycle-related changes in galactic cosmic ray (GCR) intensities have long been known to arise as a direct consequence of solar cyclic changes in, for example, the heliospheric magnetic field and the solar tilt angle. In recent years, an increasing amount of observations of cyclic behaviour (especially in terms of stellar activity cycles like the solar cycle) in other stars has become available. The present study, for the first time, investigates the influence of a stellar activity cycle on the modulation of GCRs, taking as a case study the astrosphere of the exoplanet-hosting M-dwarf Proxima Centauri, using a 3D, physics-first GCR transport code. We demonstrate a modest stellar activity cycle-dependence of GCR proton and Helium intensities at Proxima Centauri b, which qualitatively resembles that seen at Earth. However, drift effect play a more significant role, even during periods of stellar maximum activity. For all levels of stellar activity, GCR intensities remain well above those observed at Earth. The influence of these variations on the atmospheric ionisation and radiation exposure of a presumably Earth-like Proxima Centauri b is also investigated. A moderate but non-negligible cyclic variation of up to 28% is found in the atmospheric ionisation profile at high altitudes. Since atmospheric ionisation and chemistry/climate changes are correlated, and with that might impact atmospheric transmission spectra, more precise information on the GCR-induced atmospheric background ionisation in exoplanetary atmospheres is crucial.