Formation of Hot Planets by a Combination of Planet Scattering, Tidal Circularization, and the Kozai Mechanism
Formation of Hot Planets by a Combination of Planet Scattering, Tidal Circularization, and the Kozai Mechanism
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DOI：
10.1086/529369
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发表时间：
2008-01
期刊：
影响因子：
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通讯作者：
M. Nagasawa;S. Ida;T. Bessho
中科院分区：
文献类型：
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作者：
M. Nagasawa;S. Ida;T. Bessho
我们通过轨道积分研究了相互散射耦合效应、Kozai机制和潮汐圆化作用下近距离太阳系外巨行星的形成。近距离气体巨星最初可能是在原行星盘冰线以外的几个天文单位形成的，然后迁移到它们的主星附近。虽然由于行星-磁盘相互作用导致的II型迁移可能是迁移的主要渠道，但我们表明这种散射过程也会产生不可忽略的贡献。我们进行了三颗行星与木星质量的轨道积分，直接包括潮汐圆化的影响。我们发现，在大约30%的运行中，近距离行星形成了，这比以前的研究表明的要高得多。三颗行星的轨道相交通常会导致一颗或两颗行星的抛射。潮汐圆化经常发生在三行星轨道相交期间，但以往的研究只监测了抛射后的最后阶段，大大低估了形成概率。我们已经发现外行星中的Kozai机制是近地行星形成的原因。在三行星轨道交叉期间，Kozai激励被重复，并且离心率经常特别地增加到足够接近统一的值，以便潮汐圆化将内行星转变为近行星。由于中等偏心率可以保留在近地行星上，这一机制可能解释了观测到的具有中等偏心率且附近没有副行星的近地行星。由于这些行星的轨道倾角也很大（甚至是逆行的），这个过程的贡献将通过对凌日行星的罗西特-麦克劳克林效应的更多观察来澄清。
We have investigated the formation of close-in extrasolar giant planets through a coupling effect of mutual scattering, the Kozai mechanism, and tidal circularization, by orbital integrations. Close-in gas giants would have been originally formed at several AU beyond the ice lines in protoplanetary disks and migrated close to their host stars. Although type II migration due to planet-disk interactions may be a major channel for the migration, we show that this scattering process would also give a nonnegligible contribution. We carried out orbital integrations of three planets with Jupiter mass, directly including the effect of tidal circularization. We have found that in about 30% of the runs close-in planets are formed, which is much higher than suggested by previous studies. Three-planet orbit crossing usually results in the ejection of one or two planets. Tidal circularization often occurs during three-planet orbit crossing, but previous studies have monitored only the final stage after the ejection, significantly underestimating the formation probability. We have found that the Kozai mechanism in outer planets is responsible for the formation of close-in planets. During three-planet orbital crossing, Kozai excitation is repeated and the eccentricity is often increased secularly to values close enough to unity for tidal circularization to transform the inner planet to a close-in planet. Since a moderate eccentricity can retain for the close-in planet, this mechanism may account for the observed close-in planets with moderate eccentricities and without nearby secondary planets. Since these planets also remain a broad range of orbital inclinations (even retrograde ones), the contribution of this process would be clarified by more observations of Rossiter-McLaughlin effects for transiting planets.