Phase separation in giant planets: Inhomogeneous evolution of Saturn

Jonathan J. Fortney, William B. Hubbard

Research output: Contribution to journalArticlepeer-review

106 Scopus citations


We present the first models of Jupiter and Saturn to couple their evolution to both a radiative-atmosphere grid and to high-pressure phase diagrams of hydrogen with helium and other admixtures. We find that prior calculated phase diagrams in which Saturn's interior reaches a region of predicted helium immiscibility do not allow enough energy release to prolong Saturn's cooling to its known age and effective temperature. We explore modifications to published phase diagrams that would lead to greater energy release, and propose a modified H-He phase diagram that is physically reasonable, leads to the correct extension of Saturn's cooling, and predicts an atmospheric helium mass fraction Yatoms = 0.185, in agreement with recent estimates. We also explore the possibility of internal separation of elements heavier than helium, and find that, alternatively, such separation could prolong Saturn's cooling to its known age and effective temperature under a realistic phase diagram and heavy element abundance (in which case Saturn's Yatoms would be solar but heavier elements would be depleted). In none of these scenarios does Jupiter's interior evolve to any region of helium or heavy-element immiscibility: Jupiter evolves homogeneously to the present day. We discuss the implications of our calculations for Saturn's primordial core mass.

Original languageEnglish (US)
Pages (from-to)228-243
Number of pages16
Issue number1
StatePublished - Jul 1 2003


  • Atmospheres, composition
  • Jupiter, evolution
  • Jupiter, interior
  • Saturn, evolution
  • Saturn, interior

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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