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Published July 1, 2010 | Published + Accepted Version
Journal Article Open

High-temperature Photochemistry in the Atmosphere of HD 189733b


Recent infrared spectroscopy of hot exoplanets is beginning to reveal their atmospheric composition. Deep within the planetary atmosphere, the composition is controlled by thermochemical equilibrium. Photochemistry becomes important higher in the atmosphere, at levels above ~1 bar. These two chemistries compete between ~1 and 10 bars in hot-Jupiter-like atmospheres, depending on the strength of the eddy mixing and temperature. HD 189733b provides an excellent laboratory in which to study the consequences of chemistry of hot atmospheres. The recent spectra of HD 189733b contain signatures of CH_4, CO_2, CO, and H_2O. Here we identify the primary chemical pathways that govern the abundances of CH_4, CO_2, CO, and H_2O in the cases of thermochemical equilibrium chemistry, photochemistry, and their combination. Our results suggest that the disequilibrium mechanisms can significantly enhance the abundances of these species above their thermochemical equilibrium value, so some caution must be taken when assuming that an atmosphere is in strict thermochemical equilibrium.

Additional Information

© 2010 The American Astronomical Society. Received 2010 April 19; accepted 2010 May 12; published 2010 June 15. We especially thank Adam Showman for providing us his GCM outputs for temperature and vertical winds, both of which form the basis of our model atmosphere, making it possible for us to determine the eddy diffusion coefficient. We also thank Run-Li Shia, Giovanna Tinetti, Xi Zhang, Konstantin Batygin, Mimi Gerstell, Chris Parkinson, Vijay Natraj, Kuai Le, Mark Swain, Julie Moses, Wes Traub, Pin Chen, Gautam Vasisht, Nicholas Heavens, Heather Knutson, Sara Seager, the anonymous referee, and the Yuk Yung group for very useful discussions and for reading the manuscript. M.R.L. was supported by the JPL Graduate Fellowship (JPLGF). M.C.L. was supported in part by NSC grant 98-2111-M-001-014-MY3 to Academia Sinica. Y.L.Y. was supported by NASA grant NX09AB72G to the California Institute of Technology.

Attached Files

Published - Line2010p10603Astrophys_J.pdf

Accepted Version - 1004.4029.pdf


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