H2S and SO2 detectability in hot Jupiters Sulphur species as indicators of metallicity and C/O ratio

Context. The high cosmic abundance, the intermediate volatility, and the chemical properties of sulphur allow sulphur-bearing species to be used as tracers of the chemical processes in the atmospheres of hot Jupiter exoplanets. Nevertheless, despite their properties and relevance as tracers of the giant planets' formation histories, little attention has been paid to these species in the context of hot Jupiter atmospheres. Aims. In this paper, we provide an overview of the abundances of sulphur-bearing species in hot Jupiter atmospheres under different conditions and explore their observability. Methods. We used the photochemical kinetics code VULCAN to model hot Jupiter atmospheric disequilibrium chemistry. Transmission spectra for these atmospheres were created using the modelling framework ARCiS. We varied model parameters such as the diffusion coefficient K-zz, and we studied the importance of photochemistry on the resulting mixing ratios. Furthermore, we varied the chemical composition of the atmosphere by increasing the metallicity from solar to ten times solar. We also explored different C/O ratios. Results. We find that H2S and SO2 are the best candidates for detection between 1 and 10 mu m, using a spectral resolution that is representative of the instruments on board the James Webb Space Telescope (JWST). H2S is easiest to detect at an equilibrium temperature of similar to 1500 K, and with C/O ratios between 0.7 and 0.9, with the ideal value increasing slightly for increasing metallicity. SO2 is most likely to be detected at an equilibrium temperature of similar to 1000 K at low C/O ratios and high metallicities. Nevertheless, among these two molecules, we expect SO2 detection to be more common, as it is detectable in scenarios more favoured by formation models. Conclusions. We conclude that H2S and SO2 will most likely be detected in the coming years with the JWST, and that the detection of these species will provide information on atmospheric processes and planet formation scenarios.

Automated summary

In this paper, the abundances of sulphur-bearing species in hot Jupiter atmospheres are discussed, and their observability is explored. It is found that H2S and SO2 are the most likely species to be detected in the coming years with the JWST.