The effect of dense cores on the structure and evolution of Jupiter and Saturn

The evolutionary and static models of Jupiter and Saturn were calculated with homogeneous solar composition mantles and dense cores of material consisting of solar abundances of SiO2, MgO, Fe, and Ni. Evolutionary sequences for Jupiter were calculated with cores of mass ranging from 2 to 8% of the Jovian mass; the Saturn sequences ranged from cores of mass of 16 to 22% of total mass. Two envelope mixtures representative of the solar abundances were used: they contained mass fraction of 0.74 and 0.77 of hydrogen, respectively, and 0.24 and 0.21 mass fractions of helium. For Jupiter, the observations of the temperature at 1 bar pressure, of radius and of internal luminosity were best fit by evolutionary models with a core mass of about 6.5% and chemical composition of 0.77 mass fraction of hydrogen and 0.21 mass fraction of helium. The cooling time calculated for Saturn was 2.6 x 10 to the 9th yr, almost a factor of 2 less than the percentage of the solar system.