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Abstract EANA2024-94


Stellar Storms and Cosmic Rays: Exploring Exoplanet Chemistry in Extreme Environments

Nanna Bach-Møller (1, 2), Christiane Helling (2), David Lewis, Martin Bødker Enghoff (3), and Uffe Gråe Jørgensen (1)
(1) Niels Bohr Institute, University of Copenhagen, Denmark (2) Space Research Institute, Austrian Academy of Sciences, Austria (3) National Space Institute, Danish Technical University, Denmark


Since the discovery of exoplanets, we have been aware that planets can exist in environments dramatically different from the Solar System. One such difference is the amount and type of high-energy radiation reaching the planet. On Earth we know that high-energy radiation can have significant, and sometimes unforeseen, effects on the atmosphere through processes such as photo-chemical reactions, and ionisation of the upper atmosphere. In order to understand and analyse the chemistry of exoplanet atmospheres, it is therefore crucial to understand the effect of the radiative environment on the atmosphere.

In this talk, I address some of the effects high-energy radiative environments can have on the complex chemistry of exoplanet atmospheres. 
This study focuses on two sources of high-energy radiation: 1) the host star, through XUV radiation and stellar energetic particles (SEPs), and 2) the galactic environment through galactic cosmic rays (GCRs). 
We model the effect of these radiation sources on the disequilibrium chemistry of a hot-Jupiter using the 1D photo-chemistry and diffusion code, ARGO, in combination with the chemical kinetic network, STAND2020. STAND2020 excels by its complexity in H/C/N/O chemistry, which allows us to study the effect of the irradiation on larger complex molecules. 

We present a grid of models run for host stars of the seven main sequence spectral types, under influxes of GCRs ranging from highly shielded systems with no GCRs, to highly exposed systems with GCR fluxes estimated for high-energy environments in the galaxy.

This grid over radiative environments allows us an insight into the effects of high-energy radiation on atmospheric chemistry, and can help guide our analysis of exoplanet atmosphere observations based on the host star and the environment the system is located in. This might be especially interesting for future missions such as PLATO, that focuses on different exoplanet host stars, and HWO, that will study the habitability of exoplanets, and it might also be interesting in relation to missions such as Athena, that is set to focus on the high-energy environments in galaxies and our universe as a whole.