Formation of Close Giant Planets

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Formation of giant planets along the standard model of planetary formation is considered in the innermost region of protoplanetary disk nebulae where turbulence has already decayed. It is shown that if dust material enough to form a core with about ten times Earth mass and the corresponding amount of gas exist in the innermost region, a giant planet with mass somewhat larger than our Jupiter can form there.We also investigate the stability of planetary orbits around a binary stars, whose example is MACHO 97-BLG-41, an extrasolar planet detected in a binary system by gravitational microlensing. We performed long-term numerical integrations of the coplanar elliptic restricted three-body problem with various initial conditions in order to see what initial conditions produce stable planetary orbits during the integration for about three million years. The result of our numerical simulation permit us to estimate the upper limit of binary eccentricity, which ensures stable planetary orbital motion, to be about 0.5 in the cases of circular initial orbits of the planet. In the cases of elliptic initial orbits of the planet, the planetary orbital motion is found to be less stable; hence, the upper limit of the binary eccentricity is estimated to be smaller than that in the cases of circular initial orbits of the planet. The upper limit of the initial planetary eccentricity is estimated to be about 0.4 for stable planetary motion. The results of similar integrations for retrograde orbits indicate that the planetary retrograde orbits are more stable than the prograde ones.