Implications of three-dimensional chemical transport in hot Jupiter atmospheres: Results from a consistently coupled chemistry-radiation-hydrodynamics model

Abstract

We present results from a set of simulations using a fully coupled three-dimensional (3D) chemistry-radiationhydrodynamics model and investigate the effect of transport of chemical species by the large-scale atmospheric flow in hot Jupiter atmospheres. We couple a flexible chemical kinetics scheme to the Met Office Unified Model which enables the study of the interaction of chemistry, radiative transfer and fluid dynamics. We use a newly-released "reduced" chemical network comprising 30 chemical species that has been specifically developed for application in 3D atmosphere models. We simulate the atmospheres of the well-studied hot Jupiters HD 209458b and HD 189733b which both have dayside-nightside temperature contrasts of several hundred Kelvin and superrotating equatorial jets. We find qualitatively quite different chemical structures between the two planets, particularly for methane (CH4), when advection of chemical species is included. Our results show that consideration of 3D chemical transport is vital in understanding the chemical composition of hot Jupiter atmospheres. 3D mixing leads to significant changes in the abundances of absorbing gas-phase species compared with what would be expected by assuming local chemical equilibrium, or from models including 1D -and even 2D -chemical mixing. We find that CH4, carbon dioxide (CO2) and ammonia (NH3) are particularly interesting as 3D mixing of these species leads to prominent signatures of out-of-equilibrium chemistry in the transmission and emission spectra, detectable with near-future instruments.

The Hubble WFC3 Emission Spectrum of the Extremely Hot Jupiter KELT-9b

“…Disequilibrium processes, such as vertical or horizontal mixing could also play an important role in distributing metal oxide/hydrides on the day-side of KELT-9 b (Kitzmann et al 2018;Komacek et al 2019;Drummond et al 2020). To investigate those processes, one should compare the timescales of the creation and destruction reactions with the timescales of dynamical processes.…”

Atmospheric Dynamics of Hot Giant Planets and Brown Dwarfs

“…5. Chemical disequilibrium between CH4 and CO was suggested as a possible culprit for HD 189733b and HD 209458b (Knutson et al 2012;Zellem et al 2014), but recent GCM experiments rule out this explanation (Steinrueck et al 2019;Drummond et al 2018aDrummond et al , 2020. More likely is that the discrepancies result from clouds and/or hazes, although this possibility remains to be quantified in detail.…”

“…As a consequence the final atmospheric abundances are determined by the vertical mixing strength on the dayside atmosphere and the pressure and temperature at the quench point, where the vertical mixing timescale equals the chemical timescale. Drummond et al (2018a) and Drummond et al (2020) additionally showed that the meridional circulation could also mix the chemical composition latitudinally, meaning that the 3D nature of the atmospheric mixing by the circulation should not be ignored. Finally, differences between chemical schemes (e.g.…”

Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: effects of rotation

“…When the chemical conversion timescales is close to or longer than dynamical timescales, the potential correlation between horizontal distribution of chemical species (therefore their radiative feedback) and large-scale dynamics may play a similar role as a dynamically active tracer, contributing to the heating/cooling rates that shape the circulation. Such radiative feedback by chemical quenching on the general circulation has been investigated for hot Jupiters (e.g., Steinrueck et al 2019;Drummond et al 2020), and will be an interesting topic in future studies for BDs and directly imaged EGPs.…”