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A Systematic Retrieval Analysis of Secondary Eclipse Spectra III: Diagnosing Chemical Disequilibrium in Planetary Atmospheres

Line, Michael R. and Yung, Yuk L. (2013) A Systematic Retrieval Analysis of Secondary Eclipse Spectra III: Diagnosing Chemical Disequilibrium in Planetary Atmospheres. Astrophysical Journal, 779 (1). Art. No. 3. ISSN 0004-637X.

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Chemical disequilibrium has recently become a relevant topic in the study of the atmospheres of 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 H_2 O, CH_4, CO, and H _2. 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 3-sigma. Future observations are needed to further constrain the abundances in order to definitively identify disequilibrium in exoplanet atmospheres.

Item Type:Article
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URLURL TypeDescription Paper
Line, Michael R.0000-0002-2338-476X
Additional Information:© 2013 American Astronomical Society. Received 2013 September 25, accepted for publication 2013 October 25. Published 2013 November 14. We thank Dave Stevenson, Pin Chen, Gautam Vasisht, and Channon Visscher for useful discussions. We also thank Julie Moses and Jonathan Fortney as well as the Yuk Yung group for meticulously reading the manuscript. This research was supported in part by an NAI Virtual Planetary Laboratory grant from the University of Washington to the Jet Propulsion Laboratory and California Institute of Technology. YLY was supported in part by NASA NNX09AB72G grant to the California Institute of Technology.
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University of Washington NAI Virtual Planetary LaboratoryUNSPECIFIED
Subject Keywords:astrochemistry; planets and satellites: atmospheres; planets and satellites: composition
Record Number:CaltechAUTHORS:20131015-104013706
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Official Citation:A Systematic Retrieval Analysis of Secondary Eclipse Spectra. III. Diagnosing Chemical Disequilibrium in Planetary Atmospheres Michael R. Line and Yuk L. Yung 2013 ApJ 779 3
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41917
Deposited By: Tony Diaz
Deposited On:15 Oct 2013 20:35
Last Modified:20 Aug 2017 00:41

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