A thermospheric circulation model for extrasolar giant planets

T. T. Koskinen, A. D. Aylward, C. G.A. Smith, S. Miller

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


Several models of extrasolar giant planet (EGP) atmospheres have been developed recently. Many of them are one-dimensional or concentrate on the lower or middle atmosphere. Three-dimensional hydrodynamic models are needed to study the horizontal variations in temperature and composition of EGP atmospheres. Circulation models for the upper atmosphere are particularly important as they can be used to study the thermal structure due to stellar irradiation, radiative cooling, and atmospheric circulation in the thermospheres of close-in EGPs and hence the rate of evaporation of their atmospheres. We present a generic gas giant model that is capable of generating three-dimensional, self-consistent global simulations of stable EGP thermospheres at different orbital distances. Calculations performed by this model indicate that IR emissions from H 3+ ions may play a significant role in cooling the thermospheres of EGPs at least in the range of 0.2-1 AU from a solar-type host star. In this range thermal dissociation of H2 is negligible and ion densities are small compared to the overall neutral density. Inside 0.2 AU thermal dissociation and dissociative photoionization of H2 may prevent the effective formation of H3+. In the absence of radiative cooling from H3+ the upper atmospheres reach temperatures well above 10,000 K within ∼0.5 AU. In this case the upper thermospheres are entirely converted into atomic hydrogen and the temperatures are high enough for significant atmospheric loss to take place. Our model is capable of calculating the IR signal strengths for various vibrational transitions of H3+ based on the thermal state and the composition of the atmosphere. Potential detection of such signals would thus provide a validation of some of our results.

Original languageEnglish (US)
Pages (from-to)515-526
Number of pages12
JournalAstrophysical Journal
Issue number1 I
StatePublished - May 20 2007


  • Hydrodynamics
  • Infrared: general
  • Instabilities
  • Planetary systems
  • Plasmas

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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