Grid of pseudo-2D chemistry models for tidally locked exoplanets – II. The role of photochemistry

Robin Baeyens*, Thomas Konings, Olivia Venot, Ludmila Carone, Leen Decin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Citations (Scopus)
8 Downloads (Pure)


Photochemistry is expected to change the chemical composition of the upper atmospheres of irradiated exoplanets through the dissociation of species, such as methane and ammonia, and the association of others, such as hydrogen cyanide. Although primarily the high altitude day side should be affected by photochemistry, it is still unclear how dynamical processes transport photochemical species throughout the atmosphere, and how these chemical disequilibrium effects scale with different parameters. In this work we investigate the influence of photochemistry in a two-dimensional context, by synthesizing a grid of photochemical models across a large range of temperatures. We find that photochemistry can strongly change the atmospheric composition, even up to depths of several bar in cool exoplanets. We further identify a sweet spot for the photochemical production of hydrogen cyanide and acetylene, two important haze precursors, between effective temperatures of 800 and 1400 K. The night sides of most cool planets (Teff < 1800 K) are shown to host photochemistry products, transported from the day side by horizontal advection. Synthetic transmission spectra are only marginally affected by photochemistry, but we suggest that observational studies probing higher altitudes, such as high-resolution spectroscopy, take photochemistry into account.
Original languageEnglish
Pages (from-to)4877–4892
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date26 Mar 2022
Publication statusPublished - Jun 2022


  • Planets and satellites: atmospheres
  • Planets and satellites: composition


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