New chemical scheme for giant planet thermochemistry: Update of the methanol chemistry and new reduced chemical scheme

Abstract

Context. Several chemical networks have been developed to study warm (exo)planetary atmospheres. The kinetics of the reactions related to the methanol chemistry included in these schemes have been questioned. Aims. The goal of this paper is to update the methanol chemistry for such chemical networks based on recent publications in the combustion literature. We also aim to study the consequences of this update on the atmospheric compositions of (exo)planetary atmospheres and brown dwarfs. Methods. We performed an extensive review of combustion experimental studies and revisited the sub-mechanism describing methanol combustion in a scheme published in 2012. The updated scheme involves 108 species linked by a total of 1906 reactions. We then applied our 1D kinetic model with this new scheme to the case studies HD 209458b, HD 189733b, GJ 436b, GJ 1214b, ULAS J1335+11, Uranus, and Neptune; we compared these results with those obtained with the former scheme. Results. The update of the scheme has a negligible impact on the atmospheres of hot Jupiters. However, the atmospheric composition of warm Neptunes and brown dwarfs is modified sufficiently to impact observational spectra in the wavelength range in which James Webb Space Telescope will operate. Concerning Uranus and Neptune, the update of the chemical scheme modifies the abundance of CO and thus impacts the deep oxygen abundance required to reproduce the observational data. For future 3D kinetics models, we also derived a reduced scheme containing 44 species and 582 reactions. Conclusions. Chemical schemes should be regularly updated to maintain a high level of reliability on the results of kinetic models and be able to improve our knowledge of planetary formation.