DISEQUILIBRIUM CARBON, OXYGEN, AND NITROGEN CHEMISTRY IN THE ATMOSPHERES OF HD 189733b AND HD 209458b

Journal Article · Wed Aug 10 00:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/737/1/15· OSTI ID:21580000

Moses, Julianne I ^[1]; Visscher, C ^[2]; Fortney, J J ^[3]; Showman, A P; Lewis, N K; Griffith, C A ^[4]; Klippenstein, S J ^[5]; Shabram, M ^[6]; Friedson, A J ^[7]; Marley, M S

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1. Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States)
2. Lunar and Planetary Institute, Houston, TX 77058 (United States)
3. Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
4. Department of Planetary Sciences and Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States)
5. Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439 (United States)
6. Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)
7. Earth and Space Sciences Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

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 CH{sub 4} and NH{sub 3} are photochemically removed at higher altitudes. Disequilibrium chemistry also enhances atomic species, unsaturated hydrocarbons (particularly C{sub 2}H{sub 2}), some nitriles (particularly HCN), and radicals like OH, CH{sub 3}, and NH{sub 2}. In contrast, CO, H{sub 2}O, N{sub 2}, and CO{sub 2} more closely follow their equilibrium profiles, except at pressures {approx}<1 {mu}bar, where CO, H{sub 2}O, and N{sub 2} are photochemically destroyed and CO{sub 2} is produced before its eventual high-altitude destruction. The enhanced abundances of CH{sub 4}, NH{sub 3}, 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.

• OSTI ID: 21580000
• Journal Information: Astrophysical Journal, Vol. 737, Issue 1; Other Information: DOI: 10.1088/0004-637X/737/1/15; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABUNDANCE
AMMONIA
CARBON
CARBON MONOXIDE
EQUILIBRIUM
HYDROCYANIC ACID
METHANE
NITRILES
NITROGEN
ONE-DIMENSIONAL CALCULATIONS
OXYGEN
PHOTOCHEMISTRY
PLANETARY ATMOSPHERES
PLANETS
QUENCHING
STARS
THERMOCHEMICAL PROCESSES
WATER
ALKANES
ATMOSPHERES
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMISTRY
ELEMENTS
HYDRIDES
HYDROCARBONS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS