37th DPS Meeting, 4-9 September 2005
Session 28 Extrasolar Planets
Oral, Tuesday, September 6, 2005, 4:20-6:00pm, Law LG19

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[28.05] On the Atmospheric and Interior Structure of New Transiting Planet HD 149026b

J.J. Fortney (NASA Ames), D. Saumon (LANL), M.S. Marley (NASA Ames), K. Lodders (Washington Univ.), R. Freedman (NASA Ames/SETI Inst.)

The planet HD 149026b was recently discovered by Sato et al.~(2005) in a 2.8 day orbit around a bright G0 IV star. The planet was seen in transit and its mass and radius have been pinned at 0.36 MJ and 0.73 RJ, respectively. This small radius, considering its mass and proximity to its parent star, leads to the conclusion that the planet has an enormous supersolar abundance of heavy elements. Here we compute models of the atmosphere and interior of this planet. Assuming the planet is able to reradiate absorbed stellar flux over the day and nights sides, we estimate an effective temperature of 1700-1750 K and a Bond albedo < 0.1. For an atmosphere enriched in heavy elements (``metals'') near 10 times solar, the atmosphere is everywhere warmer than the condensation curve of CaTiO3, leading to free gaseous TiO high in the planet's atmosphere. Strong absorption of stellar flux by TiO and VO produces a hot stratosphere of T~ 2000-2500 K at mbar pressures. We compute IR planet/star flux ratios in anticipation of Spitzer observations, which will help to determine if a hot stratosphere exists. The detection of planetary limb brightening would support the existence of a hot stratosphere. We compute thermal evolution models of the planet's interior with advanced equations of state for the H/He envelope and ice/rock core. We find that the planet is likely composed of 65-80 M\oplus of heavy elements, out of a total planet mass of 114 M\oplus (similar to Sato et al). The current intrinsic effective temperature is 80-100 K. We compare possible interior structures to those of our solar system's giant planets, and find that HD 149026b seems to be a hybrid between the gas giants and ice giants. JJF supported by an NRC Fellowship.

The author(s) of this abstract have provided an email address for comments about the abstract: jfortney@arc.nasa.gov

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.