Photochemical Effects of High Energy Particles in (Exo)Planetary Atmospheres

Grenfell, J. L.¹, Wunderlich, F.^1,2, Sinnhuber, M.³, Herbst, K.⁴, Lehmann, R.⁵, Scheucher, M.^2,6, Arnold, G.¹, Rauer, H.^1,2,7

We investigate the photochemical effect of air shower events due to galactic and solar cosmic rays in the
atmospheres of terrestrial planets in the Solar System and beyond. First, we investigate the Martian atmosphere. Results suggest that the high energy particles can break up molecular nitrogen and lead to the formation of several parts per billion of nitrous oxide (N2O). This compound is a potential biosignature produced on Earth by microorganisms. Therefore, our results suggest that care is needed when interpreting biosignature signals on atmospheres under the influence of cosmic rays. Second, we review recent results from our group simulating air showers on a hypothetical planet with an Earth-like atmosphere in the habitable zone of the M-dwarf star AD Leonis. Results suggest that the breakup of N2 and O2 by high energy particles can lead via gas-phase chemistry to the formation of nitric acid (HNO3). Detection of the spectral signal of this species via transmission spectroscopy could therefore represent an indicator of cosmic ray activity in Earth-like atmospheres. Finally, we discuss future aims to simulate air showers in the atmosphere of Proxima Centauri b.