Formation of the Giant Planets

The structure of a gaseous envelope surrounding a protoplanet has been investigated in connection with the formation of the giant planets. Under the assumptions of spherical symmetry and hydrostatic equilibrium, the structure has been calculated for the regions of Jupiter, Saturn, Uranus and Neptune. Energy transfer in the envelope has been taken into account precisely.

When the core mass increases beyond some critical value, the envelope cannot be in hydrostatic equilibrium and collapses onto the core. The most remarkable result is that a common relation between the core mass and the total mass holds irrespectively of the regions in the solar nebula. Therefore, at the collapse, the core mass becomes almost the same regardless of the regions in the nebula. This is consistent with the conclusion obtained from the theory of internal structure of the present giant planets. The grain opacity in the envelope should be about 1cm²/g in order to explain the estimated core mass (about 10 Earth's mass) of the giant planets. The value of the grain opacity is larger than that expected before.