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M-C. Liang, C. Parkinson, Y. Yung (Caltech)
The tentative detection of atomic hydrogen near HD 209458b, a Jupiter-size planet located at 0.05 AU from its parent star, suggests that the atmosphere is hydrodynamically unstable. This hydrogen in the atmosphere of HD 209458b can readily escape by a process that is similar to that responsible for the loss of an ocean on the early Venus. The ongoing hydrodynamic loss in the atmospheres of planets similar to HD 209458b would tell us for the first time how this process is triggered, as well as how the planets evolve. A photochemical study suggests that the hydrogen is produced via an H2O-mediated process, and the mixing ratio of atomic hydrogen in the upper atmosphere can be as high as unity, suggesting that the upper atmosphere is unstable. This is the direct consequence of high temperature in the atmosphere, where the H2O can be present in gas phase. Because of the high abundance of atomic hydrogen in such high temperature conditions, the production of aerosols is unfavorable. The aerosols can be formed only locally. A possible candidate is poly-sulfur. To study this possibility, we explore a three-dimensional circulation model. Using the EPIC model, we rule out this possibility. Therefore, we would be able to detect the atmospheric constituents down to the Rayleigh limit or cloud tops of high temperature condensates.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.