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Title: The puzzling chemical composition of GJ 436B'S atmosphere: Influence of tidal heating on the chemistry

The dissipation of the tidal energy deposited on eccentric planets may induce a heating of the planet that affects its atmospheric thermal structure. Here we study the influence of tidal heating on the atmospheric composition of the eccentric (e = 0.16) 'hot Neptune' GJ 436b, for which inconclusive chemical abundances are retrieved from multiwavelength photometric observations carried out during primary transit and secondary eclipse. We build up a one-dimensional model of GJ 436b's atmosphere in the vertical direction and compute the pressure-temperature and molecular abundances profiles for various plausible internal temperatures of the planet (up to 560 K) and metallicities (from solar to 100 times solar), using a radiative-convective model and a chemical model which includes thermochemical kinetics, vertical mixing, and photochemistry. We find that the CO/CH{sub 4} abundance ratio increases with metallicity and tidal heating, and ranges from 1/20 to 1000 within the ranges of metallicity and internal temperature explored. Water vapor locks most of the oxygen and reaches a very high abundance, whatever the metallicity and internal temperature of the planet. The CO{sub 2}/H{sub 2}O abundance ratio increases dramatically with metallicity, and takes values between 10{sup –5}-10{sup –4} with solar elemental abundances and ∼0.1 for a metallicity 100more » times solar. None of the atmospheric models based on solid physical and chemical grounds provide a fully satisfactory agreement with available observational data, although the comparison of calculated spectra and observations seems to point to models with a high metallicity and efficient tidal heating, in which high CO/CH{sub 4} abundance ratios and warm temperatures in the dayside atmosphere are favored.« less
Authors:
;  [1] ;  [2] ;  [3]
  1. Univ. Bordeaux, LAB, UMR 5804, F-33270 Floirac (France)
  2. Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)
  3. Theoretical Meteorology group, Klimacampus, University of Hamburg, Grindelberg 5, D-20144 Hamburg (Germany)
Publication Date:
OSTI Identifier:
22348137
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 781; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; CARBON DIOXIDE; CARBON MONOXIDE; CHEMICAL COMPOSITION; COMPARATIVE EVALUATIONS; ECLIPSE; HEATING; METALLICITY; METHANE; NEPTUNE PLANET; OXYGEN; PHOTOCHEMISTRY; SATELLITE ATMOSPHERES; SATELLITES; SPECTRA; WATER; WATER VAPOR