Quenching-driven equatorial depletion and limb asymmetries in hot Jupiter atmospheres: WASP-96b example

Abstract

Transport-induced quenching in hot Jupiter atmospheres is a process that determines the boundary between the part of the atmosphere at chemical equilibrium and the part of the atmosphere at thermochemical (but not photothermochemical) disequilibrium. The location of this boundary, the quench level, depends on the interplay between the dynamical and chemical timescales in the atmosphere, with quenching occurring when these timescales are equal. We explore the sensitivity of the quench level position to an increase in the planet’s atmospheric metallicity using aerosol-free 3D GCM simulations of a hot Jupiter WASP-96b. We find that the temperature increase at pressures of ∼104–107 Pa that occurs when metallicity is increased could shift the position of the quench level to pressures dominated by the jet, and cause an equatorial depletion of CH4, NH3 and HCN. We discuss how such a depletion affects the planet’s transmission spectrum, and how the analysis of the evening-morning limb asymmetries, especially within ∼3–5 µm, could help distinguish atmospheres of different metallicities that are at chemical equilibrium from those with the upper layers at thermochemical disequilibrium.