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The origin of diversity of extrasolar planets formation of giant gasous planets and orbital evolution

太阳系外行星多样性的起源、气态巨行星的形成与轨道演化

基本信息

批准号：
09440089
负责人：
NAKAZAWA Kiyoshi
金额：
$ 1.09万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

项目摘要

About 30 extrasolar planets have been discovered since 1995. They would be giant planets like Jupiter and Saturn in the Solar system, because the present detection method limits planet mass that can be detectable. About half of them have very short orbital period (shorter than that of Mercury), while the other half have large orbital eccentricity. We have tried to explain the diversity of the extrasolar planets by generalizing the standard theory of the Solar system.This year, we investigated the formation of giant planets and their orbital stability more deeply. Giant planets are formed as follows a solid core with about 10 earth masses accretes from planetesimals and gas of a protoplanetary disk is captured by strong gravity of the core to form massive envelope. We investigated(1) the dependence of formation of a solid core on mass of a protoplanetary disk,(2) time scale of gas infall onto the core, and(3) orbital stability of giant planets in the protoplanetary disk.Regarding (1), we found that in a massive protoplanetary disk, gas giant planets can be formed in inner region. Regarding (2), we found that gas infall can start at less massive core mass than so far considered, but the time scale of gas infall is rather long. Regarding (3), we found that gas drag generally stabilizes the orbits, but the effect is weak if separation distance between the planets is smaller than some critical value. From these results, we conclude that generalization of the standard theory of the Soalr system to different mass protoplanetary disks would account for the diversity of the extrasolar planets.

自1995年以来，大约有30颗太阳系外行星被发现。它们将是太阳系中像木星和土星这样的巨大行星，因为目前的探测方法限制了可以探测到的行星质量。它们中大约一半的轨道周期很短（比水星短），而另一半的轨道离心率很大。我们试图通过推广太阳系的标准理论来解释太阳系外行星的多样性。今年，我们更深入地研究了巨行星的形成及其轨道稳定性。巨行星的形成过程如下：一个大约10个地球质量的固体核心从微行星中吸积，原行星盘的气体被核心的强大引力捕获，形成大质量的外壳。我们研究了（1）固体核的形成与原行星盘质量的关系，（2）气体进入核的时间尺度，（3）原行星盘中巨行星的轨道稳定性，发现在大质量原行星盘中，气体巨行星可以在内部形成。关于（2），我们发现气体侵入可以在比迄今为止考虑的更小的核心质量处开始，但气体侵入的时间尺度相当长。关于（3），我们发现气体阻力通常会稳定轨道，但如果行星之间的距离小于某个临界值，则效果很弱。从这些结果中，我们得出结论，推广的标准理论的Soalr系统不同质量的原行星盘将占太阳系外行星的多样性。