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Formation of heavy-element rich giant planets

Genda, H (Tokyo Institute of Technology)
Tuesday 18 August 2009, 14:40-15:00

Meeting Room 2, CMS


More than twenty extrasolar planets are known to transit their star. >From planetary radius observed by the transit method and planetary mass observed by the radial velocity method, one can determine the densities of the extrasolar planets. The density of the planet informs us about the planetary interior. According to calculation of the interior structure of gas giant planet by Guillot et al. (2006), the core mass and core mass ratio in the planets increases with the metallicity of their star ([Fe/H]). This dependency seems to be reasonable, because the star with higher [Fe/H] had the protoplanetary disk with enough solid materials to form more heavy element-rich planet. However, the simple formation theory of gas giant planets cannot fully explain this dependency. We have performed the smoothed particle hydrodynamic (SPH) simulations of collisions between two gas giant planets. Changes in masses of the ice/rock core and the H/He envelope due to the collisions are investigated. The main aim of this study is to constrain the origin and probability of a class of extrasolar hot Jupiters that have much larger cores and/or higher core/envelope mass ratios than those predicted by theories of accretion of gas giant planets. A typical example is HD 149026b. Theoretical models of the interior of HD 149026b (Sato et al. 2005; Fortney et al. 2006; Ikoma et al. 2006) predict that the planet contains a huge core of 50-80 Earth masses relative to the total mass of 110 Earth masses. Our SPH simulations demonstrate that such a gas giant is produced by a collision with an impact velocity of typically more than 2.5 times escape velocity and an impact angle of typically less than 10 degrees, which results in an enormous loss of the envelope gas and complete accretion of both cores.

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