The energetic particle environment of a GJ 436 b-like planet

Abstract A key first step to constrain the impact of energetic particles in exoplanet atmospheres is detect chemical signature ionisation due stellar and Galactic cosmic rays. We focus on GJ 436, a well-studied M dwarf with warm Neptune-like exoplanet. demonstrate how maximum particle momentum can be estimated from X-ray luminosity. model transport through atmosphere hypothetical at orbital distances between = 0.01 − 0.2au including 436 b’s distance (0.028 au). For these we find that, top-of-atmosphere, ionise molecular hydrogen rate $\zeta _{\rm StEP,H_2} \sim 4\times 10^{-10}-2\times 10^{-13} \mathrm{s^{-1}}$. In comparison, rays alone lead GCR, H_2}\sim 2\times 10^{-20}-10^{-18} At 10au that equals particles: GCR,H_2} \zeta 7\times 10^{-18} \rm {s^{-1}}$ for top-of-atmosphere rate. distance, ion-pair production occurs pressure P ∼ 10−3bar while dominate > 102 bar. These high pressures are similar what expected post-impact early Earth atmosphere. The results presented here will used quantify signatures atmospheres.