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Title:
Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b
Authors:
Moses, Julianne I.; Visscher, C.; Fortney, J. J.; Showman, A. P.; Lewis, N. K.; Griffith, C. A.; Klippenstein, S. J.; Shabram, M.; Friedson, A. J.; Marley, M. S.; Freedman, R. S.
Affiliation:
AA(Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA ), AB(Lunar and Planetary Institute, Houston, TX 77058, USA ), AC(Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA ), AD(Department of Planetary Sciences and Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721, USA ), AE(Department of Planetary Sciences and Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721, USA ), AF(Department of Planetary Sciences and Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721, USA ), AG(Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439, USA ), AH(Department of Astronomy, University of Florida, Gainesville, FL 32611, USA ), AI(Earth and Space Sciences Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA ), AJ(NASA Ames Research Center, Moffett Field, CA 94035, USA), AK(NASA Ames Research Center, Moffett Field, CA 94035, USA)
Publication:
The Astrophysical Journal, Volume 737, Issue 1, article id. 15, 37 pp. (2011). (ApJ Homepage)
Publication Date:
08/2011
Origin:
IOP
Astronomy Keywords:
planetary systems, planets and satellites: atmospheres, planets and satellites: composition, planets and satellites: individual: HD 189733b HD 209458b, stars: individual: HD 189733 HD 209458
DOI:
10.1088/0004-637X/737/1/15
Bibliographic Code:
2011ApJ...737...15M

Abstract

We have developed a one-dimensional photochemical and thermochemical kinetics and diffusion model to study the effects of disequilibrium chemistry on the atmospheric composition of "hot-Jupiter" exoplanets. Here we investigate the coupled chemistry of neutral carbon, hydrogen, oxygen, and nitrogen species on HD 189733b and HD 209458b and we compare the model results with existing transit and eclipse observations. We find that the vertical profiles of molecular constituents are significantly affected by transport-induced quenching and photochemistry, particularly on the cooler HD 189733b however, the warmer stratospheric temperatures on HD 209458b help maintain thermochemical equilibrium and reduce the effects of disequilibrium chemistry. For both planets, the methane and ammonia mole fractions are found to be enhanced over their equilibrium values at pressures of a few bar to less than an mbar due to transport-induced quenching, but CH4 and NH3 are photochemically removed at higher altitudes. Disequilibrium chemistry also enhances atomic species, unsaturated hydrocarbons (particularly C2H2), some nitriles (particularly HCN), and radicals like OH, CH3, and NH2. In contrast, CO, H2O, N2, and CO2 more closely follow their equilibrium profiles, except at pressures lsim1 mubar, where CO, H2O, and N2 are photochemically destroyed and CO2 is produced before its eventual high-altitude destruction. The enhanced abundances of CH4, NH3, and HCN are expected to affect the spectral signatures and thermal profiles of HD 189733b and other relatively cool, transiting exoplanets. We examine the sensitivity of our results to the assumed temperature structure and eddy diffusion coefficients and discuss further observational consequences of these models.
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