The Mutual Influence of Disequilibrium Composition and Temperature in Exoplanet Atmospheres
We have developed a 1D planetary atmosphere model that solves in a self-consistent manner the evolution of temperature and disequilibrium chemistry in the vertical direction.
Thermochemical kinetics is based on a reaction network built from scratch that includes 164 gaseous species composed of H, C, N, O, S, Si, P, Ti, He, and Ar, connected by 2352 forward reactions. The model is applied to the well-known gas giant exoplanets WASP-33b, HD209458b, HD189733b, GJ436b, and GJ1214b, and to secondary atmospheres that exoplanets characterized in the future may plausibly have.
For irradiated gas giants with solar or supersolar metallicity, the corrections to the temperature due to disequilibrium chemistry are relatively small, on the order of 100 K at most, in agreement with previous studies. Although the atmospheric composition of some of these planets deviates significantly from chemical equilibrium, the impact on the temperature is moderate because the abundances of the main atmospheric species that provide opacity, such as H2O, CO2, CO, and/or CH4, are not seriously modified by disequilibrium chemistry.
An impact on the temperature greater than 100 K appears in hot Jupiters due to TiO, which is predicted to be seriously depleted by UV photons in the upper layers. However, the extent of this depletion, and thus of its impact on the temperature, is uncertain due to the lack of knowledge about TiO photodestruction. In secondary atmospheres, the impact of disequilibrium chemistry on the temperature depends on the composition.
In atmospheres dominated by H2O and/or CO2 the temperature is not affected to an important extent. However, reducing atmospheres dominated by CH4 and oxidizing atmospheres dominated by O2 see their temperature being seriously affected due to the important processing of the atmospheric composition induced by disequilibrium chemistry.
Calculated dayside composition in five gas giants and three plausible secondary atmospheres (hot volcano-like, hot reducing N2/CH4, and warm oxidizing N2/O2 atmosphere). Dotted lines correspond to the initial composition (chemical equilibrium for the gas giants and equal uniform abundances for secondary atmospheres), dashed lines to a calculation where the initial temperature does not further evolve (only for the gas giants), and solid lines to a self-consistent calculation where temperature and chemical composition evolve together. — astro-ph.EP
Marcelino Agundez
Comments: Accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2506.11658 [astro-ph.EP] (or arXiv:2506.11658v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2506.11658
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Submission history
From: Marcelino Agundez
[v1] Fri, 13 Jun 2025 10:39:39 UTC (233 KB)
https://arxiv.org/abs/2506.11658
Astrobiology,
