The interaction of energetic particles with the winds of cool stars

Abstract

Energetic particles, such as stellar energetic particles and Galactic cosmic rays, are an important part of space weather for exoplanets orbiting cool stars and the young Earth. Energetic particles bombard exoplanetary atmospheres, leading to unique chemical effects that may be detectable with JWST. The flux of energetic particles reaching an exoplanet depends on the stellar wind properties which vary with stellar age, as the star spins down. This means it is important to constrain the stellar wind properties of other stars. I will present our results which modelled the energetic particle flux reaching Earth at different ages, such as when life is thought to have begun (approximately 3.8Gyr ago). I will discuss how, at this time, our model shows that stellar energetic particles dominated over Galactic cosmic rays up to GeV energies. At these energies, energetic particles can cause particle showers in the planet atmosphere that can reach the surface of the planet. At the same time, to connect with upcoming observations we need to consider exoplanets orbiting stars with well-constrained stellar winds. For instance, the stellar mass-loss rate is important in determining the size of the astrosphere. Thus, I will also discuss our recent results for the Galactic cosmic ray fluxes reaching the habitable zone and exoplanets of a number of nearby stars. Finally, I will discuss our ongoing efforts to connect these energetic particle fluxes closely to upcoming JWST observations