Ab initio equation of state for hydrogen-helium mixtures with recalibration of the giant-planet mass-radius relation

B. Militzer, W. B. Hubbard

Research output: Contribution to journalArticle

67 Scopus citations

Abstract

Using density functional molecular dynamics simulations, we determine the equation of state (EOS) for hydrogen-helium mixtures spanning density-temperature conditions typical of giant-planet interiors, ∼0.2-9 g cm-3 and 1000-80,000 K for a typical helium mass fraction of 0.245. In addition to computing internal energy and pressure, we determine the entropy using an ab initio thermodynamic integration technique. A comprehensive EOS table with 391 density-temperature points is constructed and the results are presented in the form of a two-dimensional free energy fit for interpolation. Deviations between our ab initio EOS and the semi-analytical EOS model by Saumon and Chabrier are analyzed in detail, and we use the results for initial revision of the inferred thermal state of giant planets with known values for mass and radius. Changes are most pronounced for planets in the Jupiter mass range and below. We present a revision to the mass-radius relationship that makes the hottest exoplanets increase in radius by ∼0.2 Jupiter radii at fixed entropy and for masses greater than ∼0.5 Jupiter mass. This change is large enough to have possible implications for some discrepant "inflated giant exoplanets."

Original languageEnglish (US)
Article number148
JournalAstrophysical Journal
Volume774
Issue number2
DOIs
StatePublished - Sep 10 2013

Keywords

  • methods: numerical
  • planets and satellites: individual (Jupiter, Saturn)
  • planets and satellites: interiors

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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