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J. I. Moses (LPI), A. G. Sharp (Harvard), B. Fegley, Jr. (Washington U.), M. S. Marley (NASA Ames), A. J. Friedson (JPL), K. Lodders (Washington U.), K. A. Rages (SETI Inst.)
The atmospheric composition and spectral properties of extrasolar giant planets will depend in large part on disequilibrium processes like photochemistry, chemical kinetics, diffusive transport, and haze formation. We have developed a photochemical kinetics, radiative transfer, and 1-D vertical transport model for extrasolar giant planets (EGPs) and brown dwarfs. The chemical reaction list contains H-, C-, O-, N-, P-, and S-bearing species and is designed to be valid for atmospheric temperatures ranging from 100-3000 K at pressures from 0-50 bar. Here we examine the effect of stellar distance (e.g., ultraviolet flux, atmospheric temperature) on the composition and other physical/chemical properties of EGPs. Our focus will be on comparing photochemical models for Jupiter with those for very close-in EGPs (e.g., the recently discovered transitting planet HD209458b at 0.045 AU) and for intermediate-temperature EGPs (e.g., generic Class II and III EGPs at \le 1-3 AU, as described by Sudarsky et al. 2003, ApJ 588, 1121-1148). The closer the giant planet is to its central star, the fewer elements that are tied up in condensed phases deep in the troposphere. First ammonia, then hydrogen sulfide, then water become available in the gas phase as the stellar distance decreases. The photochemistry of ``warm'' and ``hot'' EGPs will be more complex than the simple methane-based photochemistry that dominates on the cold giant planets in our own solar system. We will identify the possible observational consequences of disequilibrium chemistry and diffusive transport in EGPs.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.