Observability of signatures of transport-induced chemistry in clear atmospheres of hot gas giant exoplanets

Abstract

Transport-induced quenching, i.e., the homogenisation of chemical abundances by atmospheric advection, is thought to occur in the atmospheres of hot gas giant exoplanets. While some numerical modelling of this process exists, the three-dimensional nature of transport-induced chemistry is underexplored. Here we present results of 3D cloud- and haze-free simulations of the atmospheres of HAT-P-11b, HD 189733b, HD 209458b, and WASP-17b including coupled hydrodynamics, radiative transfer and chemistry. Our simulations were performed with two chemical schemes: a chemical kinetics scheme, which is capable of capturing transport-induced quenching, and a simpler, more widely used chemical equilibrium scheme. We find that transport-induced quenching is predicted to occur in atmospheres of all planets in our sample; however, the extent to which it affects their synthetic spectra and phase curves varies from planet to planet. This implies that there is a “sweet spot” for the observability of signatures of transport-induced quenching, which is controlled by the interplay between the dynamics and chemistry.

A Mini-Chemical Scheme with Net Reactions for 3D GCMs II. 3D thermochemical modelling of WASP-39b and HD 189733b

“…Our results, as well as those presented in Drummond et al (2020) and Zamyatina et al (2023), suggest that non-equilibrium chemistry can affect the conclusions of the physical properties of the atmosphere when drawn from the strength of features in transmission and emission spectra. This may lead to inaccurate interpretation of several atmospheric properties without this 3D non-equilibrium consideration.…”

“…Coupling kinetic models directly to 3D HJ GCM models has been proven to be a challenge and has so far only been attempted by Drummond et al (2020) and Zamyatina et al (2023). Both studies coupled the UM GCM (Mayne et al 2014) to a network of 30 species with 181 reactions published by Venot et al (2019), reduced from the full model of 105 species with ≈1000 reactions from the Venot et al (2012) network.…”

“…In addition to vertical and zonal quenching, their study also showed the importance of meridional quenching effects, suggesting that the 3D dynamical structures present in the atmosphere are a vital consideration in setting the global chemical inventory and spacial distribution. Zamyatina et al (2023) were able to expand the Drummond et al (2020) study by simulating HAT-P-11b and WASP-17b in addition to the canonical HD 189733b and HD 209458b. However, such GCMs with comprehensive chemical network are too computationally expensive to conduct a wider range of numerical survey which is key to improve our understanding of 3D chemical transport.…”

A mini-chemical scheme with net reactions for 3D general circulation models

“…Coupling kinetic models directly to 3D HJ GCM models has been proven to be a challenge and has so far only been attempted by Drummond et al (2020) and Zamyatina et al (2023). Both studies coupled the unified model (UM) GCM (Mayne et al 2014) to a network of 30 species with 181 reactions published by Venot et al (2019), reduced from the full model of 105 species with ≈1000 reactions from the Venot et al (2012) network.…”

“…In addition to vertical and zonal quenching, their study also shows the importance of meridional quenching effects, suggesting that the 3D dynamical structures present in the atmosphere are a vital consideration in setting the global chemical inventory and spacial distribution. Zamyatina et al (2023) were able to expand on the Drummond et al (2020) study by simulating HAT-P-11b and WASP-17b in addition to the canonical HD 189733b and HD 209458b. However, such GCMs with a comprehensive chemical network are too computationally expensive to conduct a wider range of numerical survey, which is key to improve our understanding of 3D chemical transport.…”