The Nitrogen Chemistry in Hot Jupiters Atmosphere
Résumé
The atmosphere of hot Jupiters can be probed by primary transit and secondary eclipse spectroscopy. In order to constrain the atmospheric thermal structure and composition from observables, chemical models are necessary. Due to the intense UV irradiation, mixing and circulation, the chemical composition is maintained out of equilibrium and kinetic photochemical models must be applied with kinetics valid at the high temperatures prevailing in hot Jupiters atmospheres. We study the steady state atmospheric composition of HD 189733b one of the most observed hot Jupiters by implementing a new kinetic network in a 1D time-dependent chemical model including photodissociations and vertical diffusion. We confirm that the atmospheric composition of the planet is maintained out of the equilibrium by photodissociations and vertical quenching. The core and novelty of this study is the chemical scheme. It was produced in close collaboration with experts of applied high-temperature kinetics and methodically validated over a range of temperatures and pressures typical of the atmospheric layers influencing the observations of hot Jupiters. In addition to our nominal chemical scheme, we implemented other reaction sub-networks for nitrogen-bearing species that are commonly used in the field of combustion, and investigate the sensitivity of the predicted abundances and spectra to the network. We found that the abundances of NH3 and HCN can vary by 2 orders of magnitude. A spectral feature of NH3 at 10.5 μm is sensitive to these abundance variations and thus to the chemical scheme.