A systematic retrieval analysis of secondary eclipse spectra. III. Diagnosing chemical disequilibrium in planetary atmospheres

Michael Line, Yuk L. Yung

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

Chemical disequilibrium has recently become a relevant topic in the study of the atmospheres of transiting extrasolar planets, brown dwarfs, and directly imaged exoplanets. We present a new way of assessing whether or not a Jovian-like atmosphere is in chemical disequilibrium from observations of detectable or inferred gases such as H2O, CH4, CO, and H2. Our hypothesis, based on previous kinetic modeling studies, is that cooler atmospheres will show stronger signs of disequilibrium than hotter atmospheres. We verify this with chemistry-transport models and show that planets with temperatures less than ∼1200 K are likely to show the strongest signs of disequilibrium due to the vertical quenching of CO, and that our new approach is able to capture this process. We also find that in certain instances a planetary composition may appear in equilibrium when it actually is not due to the degeneracy in the shape of the vertical mixing ratio profiles. We determine the state of disequilibrium in eight exoplanets using the results from secondary eclipse temperature and abundance retrievals. We find that all of the planets in our sample are consistent with thermochemical equilibrium to within 3σ. Future observations are needed to further constrain the abundances in order to definitively identify disequilibrium in exoplanet atmospheres.

Original languageEnglish (US)
Article number3
JournalAstrophysical Journal
Volume779
Issue number1
DOIs
StatePublished - Dec 10 2013
Externally publishedYes

Fingerprint

planetary atmosphere
planetary atmospheres
eclipses
disequilibrium
retrieval
extrasolar planets
atmospheres
atmosphere
planet
planetary composition
planets
mixing ratios
coolers
vertical mixing
mixing ratio
quenching
analysis
chemical
chemistry
temperature

Keywords

  • astrochemistry
  • planets and satellites: atmospheres
  • planets and satellites: composition

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

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AB - Chemical disequilibrium has recently become a relevant topic in the study of the atmospheres of transiting extrasolar planets, brown dwarfs, and directly imaged exoplanets. We present a new way of assessing whether or not a Jovian-like atmosphere is in chemical disequilibrium from observations of detectable or inferred gases such as H2O, CH4, CO, and H2. Our hypothesis, based on previous kinetic modeling studies, is that cooler atmospheres will show stronger signs of disequilibrium than hotter atmospheres. We verify this with chemistry-transport models and show that planets with temperatures less than ∼1200 K are likely to show the strongest signs of disequilibrium due to the vertical quenching of CO, and that our new approach is able to capture this process. We also find that in certain instances a planetary composition may appear in equilibrium when it actually is not due to the degeneracy in the shape of the vertical mixing ratio profiles. We determine the state of disequilibrium in eight exoplanets using the results from secondary eclipse temperature and abundance retrievals. We find that all of the planets in our sample are consistent with thermochemical equilibrium to within 3σ. Future observations are needed to further constrain the abundances in order to definitively identify disequilibrium in exoplanet atmospheres.

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