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Fluid helium at conditions of giant planetary interiors

  1. Raymond Jeanloz??§
  1. *Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom; and
  2. Departments of ?Earth and Planetary Sciences and
  3. §Astronomy, University of California, Berkeley, CA 94720
  1. Contributed by Raymond Jeanloz, May 16, 2008 (received for review December 19, 2007)

Abstract

As the second most-abundant chemical element in the universe, helium makes up a large fraction of giant gaseous planets, including Jupiter, Saturn, and most extrasolar planets discovered to date. Using first-principles molecular dynamics simulations, we find that fluid helium undergoes temperature-induced metallization at high pressures. The electronic energy gap (band gap) closes at 20,000 K at a density half that of zero-temperature metallization, resulting in electrical conductivities greater than the minimum metallic value. Gap closure is achieved by a broadening of the valence band via increased s–p hydridization with increasing temperature, and this influences the equation of state: The Grüneisen parameter, which determines the adiabatic temperature–depth gradient inside a planet, changes only modestly, decreasing with compression up to the high-temperature metallization and then increasing upon further compression. The change in electronic structure of He at elevated pressures and temperatures has important implications for the miscibility of helium in hydrogen and for understanding the thermal histories of giant planets.

Footnotes

  • ??To whom correspondence may be addressed. E-mail: l.stixrude{at}ucl.ac.uk or jeanloz{at}berkeley.edu
  • Author contributions: L.S. and R.J. designed research; L.S. performed research; L.S. and R.J. analyzed data; and L.S. and R.J. wrote the paper.

  • The authors declare no conflict of interest.

  • See Commentary on page 11035.

  • Received December 19, 2007.

Freely available online through the PNAS open access option.

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