The Influence of Strong Stellar Particle Events and Galactic Cosmic Rays on Exoplanetary Atmospheres (INCREASE)

Exoplanetary diversity is as fascinating as it is wide-ranging. Bulk properties vary from low-density ultra hot Jupiters, proposed gas-ice-rock mixtures such as GJ1214b, and worlds such as LHS1140b with over twice Earth’s density. The mass-radius relation suggests that the planetary mass can vary widely for a given radius, and vice-versa covering sizes from sub-Earth up to several Jupiter radii. Recent highlights include the proposed Neptunian desert and a radius gap between the population of terrestrial Super-Earths and Mini Gas Planets known as the Fulton gap.

Much remains to be learned about the atmospheres of richly diverse exoplanets. For some favoured systems such as GJ1214b, Proxima Centauri b, and TRAPPIST-1 first atmospheric observations are either present or will come in the next few years. To interpret these observations, dedicated model studies of planetary atmospheres are necessary considering atmospheric escape, outgassing, climate, photochemistry, and air shower physics as well as consistent treatments of the stellar electromagnetic radiation and the transport of the stellar cosmic rays and Galactic cosmic ray (SCRs and GCRs) within stellar astrospheres and planetary magnetic fields.

To achieve the above in this project, we will apply and further expand our newly developed model suite for exoplanetary atmospheres to calculate evolutionary snapshots of the observables planetary radii, atmospheric albedo, and spectra. We will address the following science questions:

Q1: What processes determine whether (rocky) worlds around cooler stars can retain their atmospheres?
Q2: How do different atmospheres evolve for cool star systems?
Q3: How do results from our study compare with observations for some favoured systems?

In particular, we will carry out model studies over a wide range of possible exoplanetary atmospheres and stellar environments. We will analyse these results with regard to the impact of SCR and GCR fluxes on planetary climate, atmospheric density and composition, surface radiation and the planets’ radiation dosage.