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arXiv · 1505.00139

Methane Planets and their Mass-Radius Relation

Ravit Helled·Morris Podolak·Eran Vos
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Abstract

Knowledge of both the mass and radius of an exoplanet allows us to estimate its mean density, and therefore its composition. Exoplanets seem to fill a very large parameter space in terms of mass and composition, and unlike the solar-system's planets, exoplanets also have intermediate masses (~ 5 - 50 M_Earth) with various densities. In this letter, we investigate the behavior of the Mass-Radius relation for methane (CH_4) planets and show that when methane planets are massive enough (Mp >~ 15 M_Earth), the methane can dissociate and lead to a differentiated planet with a carbon core, a methane envelope, and a hydrogen atmosphere. The contribution of a rocky core to the behavior of CH_4 planet is considered as well. We also develop interior models for several detected intermediate-mass planets that could, in principle, be methane/methane-rich planets. The example of methane planets emphasizes the complexity of the Mass-Radius relation and the challenge involved in uniquely inferring the planetary composition.

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Ravit Helled, Morris Podolak, Eran Vos. 2015-05-24. Methane Planets and their Mass-Radius Relation. https://doi.org/10.1088/2041-8205%2F805%2F2%2Fl11

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