Influence of Magma on the Atmospheric Chemical Abundances of Hot Sub-Neptunes

Atmospheres of hot sub-Neptunes are being characterised by the James Webb Space Telescope (JWST). Recent modelling efforts suggest that the magma-atmosphere coupling of hot sub-Neptunes strongly impacts their atmospheric chemistry, enriching the atmosphere with gases formed from magma-bearing elements, e.g., SiO, SiH4. We implement an equilibrium chemistry reaction network at the magma-atmosphere boundary with a new Python-based code, Atmodeller, to simulate gas-gas reactions, magma-atmosphere reactions, gas solubility in magma and real gas behaviour. We demonstrate significant effects of ideal gas versus real gas assumptions and gas solubility in magma for sub-Neptunes. We also advocate for more laboratory experiments to be conducted to understand the chemical composition of sub-Neptunes. These populations should exhibit distinct atmospheric signatures that are potentially detectable with JWST now and with ARIEL in the future.