MOVES - IV. Modelling the influence of stellar XUV-flux, cosmic rays, and stellar energetic particles on the atmospheric composition of the hot Jupiter HD 189733b

Hot Jupiters provide valuable natural laboratories for studying potential contributions of high-energy radiation to pre-biotic synthesis in the atmospheres of exoplanets. In this fourth paper of the Multiwavelength Observations of an eVaporating Exoplanet and its Star (MOVES) programme, we study the effect of different types of high-energy radiation on the production of organic and pre-biotic molecules in the atmosphere of the hot Jupiter HD 189733b. Our model combines X-ray and UV observations from the MOVES programme and 3D climate simulations from the 3D Met Office Unified Model to simulate the atmospheric composition and kinetic chemistry with the STAND2019 network. Also, the effects of galactic cosmic rays and stellar energetic particles are included. We find that the differences in the radiation field between the irradiated dayside and the shadowed nightside lead to stronger changes in the chemical abundances than the variability of the host star's XUV emission. We identify ammonium (NH4+) and oxonium (H3O+) as fingerprint ions for the ionization of the atmosphere by both galactic cosmic rays and stellar particles. All considered types of high-energy radiation have an enhancing effect on the abundance of key organic molecules such as hydrogen cyanide (HCN), formaldehyde (CH2O), and ethylene (C2H4). The latter two are intermediates in the production pathway of the amino acid glycine (C2H5NO2) and abundant enough to be potentially detectable by JWST.

Automated summary

This study shows that high-energy radiation has an enhancing effect on the abundance of organic and pre-biotic molecules in the atmosphere of the hot Jupiter HD 189733b. Differences in irradiated dayside and shadowed nightside, as well as the ionization of the atmosphere by galactic cosmic rays and stellar particles, play crucial roles in the chemical abundances. Various types of high-energy radiation, including X-ray and UV emissions, have the potential to impact the production of key organic molecules in exoplanetary atmospheres.