Le séminaire a lieu le jeudi 29 avril 2004 de 13h45 à
15h00
dans la salle de réunion
du PHC (Observatoire de Nice).
Phase separations
and the evolution of giant planets
We present the first models of giant planets to couple their evolution to both a
radiative-atmosphere grid and to high-pressure phase diagrams of hydrogen with helium
and other admixtures. The purpose of these models is to quantify the evolutionary
effects of phase separation in giant planet deep interiors. For Saturn, which is 50%
more luminous that homogeneous models predict, we find that prior calculated phase
diagrams in which Saturn’s interior reaches a region of predicted He immiscibility
do not allow enough energy release to prolong the planet’s cooling to its known age
and effective temperature. We explore modifications to published phase diagrams that
would lead to greater energy release, and find a modified H-He phase diagram that is
physically reasonable, leads to the correct extension of Saturn’s cooling, and predicts
an atmospheric He mass fraction Yatmos = 0.185, in agreement with recent estimates.
We also explore the possibility of internal separation of elements heavier than He, and
find that, alternatively, such separation could prolong Saturn’s cooling under a realistic
phase diagram and heavy element abundance. We extend our models and calculate
the effects of He phase separation on the luminosity, Teff, radii, and dectability of
extrasolar giant planets in the 0.15 to 3.0 MJup mass range. These planets can have
luminosities 2 X greater than homogeneous models predict.