Carbon monoxide–methane quenching Created 2026-09-28 Updated 2026-11-05
Carbon monoxide–methane quenching preserves a transported carbon partition after local reactions become too slow to restore thermochemical equilibrium. A useful net reaction isThis is a net stoichiometric balance, rather than a single elementary reaction whose rate can simply be read from the equation. Temperature, pressure and the kinetic pathway determine the preferred composition and conversion time.
In models of hot Jupiters, vertical transport can maintain methane away from its local equilibrium abundance, while atmospheric photochemistry removes it at higher levels.[ref]
Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b by Julianne I. Moses and others. Abstract: transport-induced methane enhancement and high-altitude destruction
A methane band therefore probes both chemistry and circulation, rather than acting as a unique local temperature measurement. Disequilibrium chemistry in an exoplanet atmosphere Created 2026-09-24 Updated 2026-11-05
Disequilibrium chemistry in an exoplanet atmosphere occurs when transport or externally driven reactions prevent the composition from reaching local thermochemical equilibrium. Deep gas brought upward can retain its earlier composition if chemical reactions become too slow in cooler layers. At higher altitudes, atmospheric photochemistry can instead destroy or create species using stellar photons.
Models coupling chemical kinetics with vertical diffusion for HD 189733 b and HD 209458 b demonstrate that chemical quench levels and photochemical destruction can affect the same molecule at different heights.[ref]
Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b by Julianne I. Moses and others. Abstract: transport-enhanced methane/ammonia followed by high-altitude photochemical removal
An atmospheric retrieval that assumes equilibrium everywhere can consequently infer a different composition or atmospheric pressure-temperature profile from one that allows transport. Julianne I. Moses 2026-11-05
Julianne I. Moses coauthored models of disequilibrium atmospheric chemistry on strongly irradiated exoplanets. Chemical reactions, vertical mixing and irradiation can maintain compositions different from local equilibrium, so a spectrum probes both chemistry and transport.[ref]
Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b by Julianne I. Moses and others. author list and the described study’s abstract or introductory account
Nitrogen–ammonia quenching Created 2026-09-28 Updated 2026-11-05
Nitrogen–ammonia quenching occurs when transport preserves a nonequilibrium partition between molecular nitrogen and Ammonia. Their net conversion may be writtenbut its actual relaxation time depends on a multistep reaction network. Near a chemical quench level, that time exceeds the eddy mixing time, so the abundance can retain a deeper value instead of following local thermochemical equilibrium.
Coupled diffusion and chemistry models illustrate ammonia enhancement by transport and destruction at high altitudes by atmospheric photochemistry.[ref]
Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b by Julianne I. Moses and others. Abstract: ammonia mole fractions and the distinct effects of mixing and photochemistry
Interpreting an ammonia feature therefore requires an atmospheric pressure-temperature profile and a transport model, not only a molecular identification.