Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aas...20313608f&link_type=abstract
American Astronomical Society Meeting 203, #136.08; Bulletin of the American Astronomical Society, Vol. 36, p.583
Astronomy and Astrophysics
Astronomy
Scientific paper
The planet Saturn is currently over 50 % more luminous than one would predict for a homogeneous adiabatic hydrogen-helium planet. However, homogeneous adiabatic evolutionary models of Jupiter predict that planet's current luminosity fairly accurately. Recently we have attempted to explain this discrepancy by calculating detailed evolutionary models of Jupiter and Saturn that include a phase separation of helium from liquid metallic hydrogen in Saturn's deep interior. If the immiscible helium rains down to deeper layers inside the planet, this process can be a substantial additional energy source. See Fortney & Hubbard (2003), Icarus, vol. 164, pg. 228.
Here we extend our calculations to investigate the effects that helium phase separation may have on various hypothetical extrasolar giant planets (EGPs) in the mass range from 0.15 to 3.0 Jupiter masses, for ages up to 10 Gyr. The energy provided by helium raining down within the planet's interior can lead to planet luminosities twice the value calculated with homogeneous models, if the planets are very far from their parent stars. The trend of monotonically decreasing radii with age may reverse at the onset of helium phase separation, for planets 1 Jupiter mass or greater. Since the planets do not cool as quickly as one would predict with homogeneous models, the onset of ammonia cloud formation will be delayed by several billion years. The detectability of these old low-mass EGPs will also be discussed. JJF is supported by a NASA GSRP grant & WBH by a NASA PG&G grant.
Fortney Jonathan J.
Hubbard William B.
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