New chemical scheme for giant planet thermochemistry

Update of the methanol chemistry and new reduced chemical scheme

¹ Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR CNRS 7583, Université Paris-Est-Créteil, Université de Paris, Institut Pierre Simon Laplace, Créteil, France
e-mail: olivia.venot@lisa.u-pec.fr
² Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, Pessac 33615, France
³ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
⁴ Laboratoire Réactions et Génie des Procédés, LRGP UMP 7274 CNRS, Université de Lorraine, 1 rue Grandville, BP 20401, 54001 Nancy, France
⁵ Maison de la Simulation, CEA, CNRS, Univ. Paris-Sud, UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
⁶ Université de Bordeaux, 351 Cours de la Libération, 33400 Talence, France

Received: 13 September 2019
Accepted: 13 December 2019

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.