Planetary atmospheric response to the stellar energetic particles in the habitable zones of TRAPPIST-1-like systems

Habitable zone planets orbiting active stars are expected to be subject to particularly high doses of particle radiation that could affect the evolution of life. We describe test-particle simulations of ∼GeV protons to investigate the propagation of energetic particles accelerated by flares or traveling shock waves within the turbulent and magnetised stellar wind of a TRAPPIST-1-like system. We find that only a few percent of particles injected within half a stellar radius from the stellar surface can escape, and that the escaping fraction increases strongly with increasing injection radius. Escaping particles are strongly focused onto two caps within the fast wind regions and centered on the equatorial planetary orbital plane. Based on a scaling relation between far-UV emission and energetic protons for solar flares applied to M dwarfs, the innermost putative habitable planet, TRAPPIST-1e, is bombarded by a proton flux up to 6 orders of magnitude larger than experienced by the present-day Earth. We present preliminary results of the chemical response of the upper planetary atmosphere to the particle flux at various phases of its orbit around the star.