Grain opacity and the bulk composition of extrasolar planets II. An analytical model for grain opacity in protoplanetary atmospheres

We investigate the grain opacity [Kappa][subgr] in the atmosphere (outer radiative zone) of forming planets. This is important for the observed planetary mass-radius relationship since [Kappa][subgr] affects the primordial H/He envelope mass of low-mass planets and the critical core mass of giant pl...

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Bibliographic Details
Published inAstronomy and astrophysics (Berlin) Vol. 572; pp. 1 - 34
Main Author Mordasini, C
Format Journal Article
LanguageEnglish
Published 01.12.2014
Subjects
Astronomy
Atmospheres
Extrasolar planets
Grains
Iron
Mathematical analysis
Opacity
Planets
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Summary:We investigate the grain opacity [Kappa][subgr] in the atmosphere (outer radiative zone) of forming planets. This is important for the observed planetary mass-radius relationship since [Kappa][subgr] affects the primordial H/He envelope mass of low-mass planets and the critical core mass of giant planets. The goal of this study is to derive a simple analytical model for [Kappa][subgr] and to explore its implications for the atmospheric structure and resulting gas accretion rate. In agreement with earlier results, we find that [Kappa][subgr] is typically much lower than in the ISM. In retrospect, this suggests that classical giant planet formation models should have considered the grain-free case to be as equally meaningful as the full ISM opacity case. This corroborates the result that core accretion can explain the observed increase of the giant planet frequency with stellar [Fe/H].
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ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201423702