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 kine
tic 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 photodissoci
ations 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-bearin
g 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
NH
3
and HCN can vary by 2 orders of magnitude. A spectral feature of NH
3
at
10.5
μ
m is sensitive to these abundance variations and thus to the chemical scheme.