Journal
ASTRONOMICAL JOURNAL
Volume 162, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/1538-3881/abfdad
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Funding
- California Institute of Technology, Jet Propulsion Laboratory, Exoplanet Science Initiative
- National Aeronautics and Space Administration [80NM0018D0004]
- Sao Paulo Research Foundation (FAPESP) [2018/09984-7]
- California Institute of Technology Jet Propulsion Laboratory Exoplanet Science Initiative
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The literature on exoplanet atmospheric disequilibrium chemistry theory is extensive, but observationally it is still lacking. In a study of 62 Hubble Space Telescope exoplanet transit spectra, it was found that about half of the atmospheres exhibit disequilibrium chemistry, suggesting its importance in determining the composition of exoplanet atmospheres. While very hot atmospheres tend to prefer equilibrium chemistry, there is a preference for disequilibrium in the 1200-1800 K temperature range, possibly due to the role of UV-augmented thermochemistry.
Literature on the theory of exoplanet atmospheric disequilibrium chemistry is rich, although its observational counterpart has yet to emerge beyond the hints provided by a few targets in dedicated studies. We report results from an uniform data reduction and analysis for a catalog of 62 Hubble Space Telescope exoplanet transit spectra where we assess the atmospheric model preference for disequilibrium chemistry (i.e., water vapor is not the dominant absorption spectral signature) over thermal equilibrium chemistry in a comparative planetology context. Where model preference assessment is possible, we find that disequilibrium occurs in about half of the atmospheres, indicating that disequilibrium processes play an important role in the composition of exoplanet atmospheres. While very hot atmospheres, over 1800 K, prefer equilibrium chemistry, we find a clustering of preference for disequilibrium in the 1200-1800 K temperature range. We suggest that UV-augmented thermochemistry may play a significant role for those atmospheres.
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