Stellar energetic particle and cosmic ray effects in exoplanetary atmospheres

TL;DR

This paper models how stellar energetic particles and cosmic rays ionize hydrogen in exoplanet atmospheres, especially around GJ436 b-like planets, impacting atmospheric chemistry and future spectral observations.

Contribution

It introduces a Monte Carlo model for energetic particle transport and ionization in hydrogen-dominated exoplanet atmospheres, focusing on GJ436 b-like conditions at various orbital distances.

Findings

High ionization rates caused by stellar energetic particles in close-in exoplanets.

Results support including energetic particle effects in atmospheric chemical models.

Implications for future JWST and Ariel spectral observations.

Abstract

Energetic particles, in the form of stellar energetic particles and cosmic rays, can lead to disequilibrium chemical effects in exoplanetary atmospheres. In Earth-like atmospheres, energetic particles can drive the formation of prebiotic molecules, the building blocks of life. Here instead, I study the transport of energetic particles through a hydrogen-dominated exoplanet atmosphere and calculate the resulting ionisation rate of molecular hydrogen using a Monte Carlo energetic particle transport model. I focus on a GJ436 b-like atmosphere at orbital distances between 0.01-0.2 au which includes the orbital distance of the exoplanet GJ436 b (0.028 au). I found that stellar energetic particles lead to high ionisation rates in a GJ436 b-like atmosphere between 0.01-0.2 au. These results motivate the use of chemical models of gas giant atmospheres including energetic particle ionisation to ultimately produce synthetic James Webb Space Telescope (JWST) and Ariel transmission spectra in the future.