Formation of Close Giant Planets

沿行星形成标准模型的巨行星的形成被认为是在原行星盘状星云的最内层区域，那里的湍流已经衰减。研究表明，如果在最内层区域存在足以形成质量约为地球10倍的地核的尘埃物质和相应数量的气体，则可以在那里形成质量略大于木星的巨大行星。我们还研究了双星周围行星轨道的稳定性，以MACHO 97-BLG-41为例，这是一颗在双星系统中通过引力微透镜探测到的系外行星。我们对不同初始条件下的共面椭圆受限三体问题进行了长时间的数值积分，目的是观察在积分过程中，什么样的初始条件能产生大约300万年稳定的行星轨道。我们的数值模拟结果允许我们估计双星偏心率的上限，这保证了稳定的行星轨道运动，在行星的圆形初始轨道的情况下，大约为0.5。在行星初始轨道为椭圆的情况下，发现行星轨道运动不太稳定；因此，估计双星偏心率的上限要小于行星初始轨道为圆形的情况。对于稳定的行星运动，估计初始行星离心率的上限约为0.4。对逆行轨道的类似积分结果表明，行星逆行轨道比顺行轨道更稳定。

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.