On the Origin of Massive Eccentric Planets
On the Origin of Massive Eccentric Planets
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关于大质量偏心行星的起源
DOI：
10.1086/303738
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
S. Ida
中科院分区：
文献类型：
--
作者：
D. Lin;S. Ida
我们提出了一个合并方案，为新发现的太阳系外行星周围70 Vir（马西和巴特勒）和HD 114762（莱瑟姆，斯特凡尼克，和Mazeh;马西和巴特勒）。这些行星的质量Mp sin i = 6.6和9 MJ（其中MJ是木星的质量，i是轨道倾角），轨道半长轴a = 0.43和0.34 Au，离心率e = 0.38和0.35。我们的设想是基于传统的巨行星形成模型（气体吸积到固体核心）和行星系统的长期轨道稳定性理论。我们认为，在一个相对大质量的盘中，可以形成几颗Mp ~ 1- 3 MJ、AU = 1 - 1 Au的巨行星。在盘气体的持续存在下，原巨行星系统在其形成时期（106-107年）是稳定的。但是，在圆盘气体耗尽之后，行星之间的相互引力扰动导致它们的轨道偏心率逐渐增加，直到它们的轨道变得不稳定并开始相互交叉。我们提出的轨道演变导致轨道交叉阶段的数值计算。我们的研究结果表明，内行星有一种趋势，合并成一个大质量的行星，相对较高的e（0.2-0.9）和较小的a（0.5-1 Au）。轨道衰减是外行星引力摄动和碰撞行星相对动能耗散的结果。之后，长期的扰动会略微降低合并体的a，而e会保持较高。合并后的天体的轨道性质与围绕70 Vir和HD 114762的大质量偏心行星的轨道性质一致。行星系统内轨道交叉的起始时间尺度敏感地由行星的质量和分离决定，这可以解释新发现的行星系统之间轨道特性的差异。
We propose a merger scenario for the newly discovered extrasolar planets around 70 Vir (Marcy & Butler) and HD 114762 (Latham, Stefanik, & Mazeh; Marcy & Butler). These planets have mass Mp sin i = 6.6 and 9MJ (where MJ is Jupiter's mass and i is the orbital inclination), orbital semimajor axis a = 0.43 and 0.34 AU, and eccentricity e = 0.38 and 0.35, respectively. Our scenario is based on the conventional formation model of giant planets (gas accretion onto solid cores) and the long-term orbital stability theory of planetary systems. We suggest that in a relatively massive disk, several giant planets can be formed with Mp ~ 1-3MJ and a ≳ 1 AU. Under the persistence of the disk gas, the protogiant planet system is stable during its formation epoch (within 106-107 yr). But, after the depletion of the disk gas, mutual gravitational perturbation between the planets induces a gradual increase in their orbital eccentricities, until their orbits become unstable and begin to cross each other. We present numerical calculations of the orbital evolution leading to the orbit crossing stage. Our results indicate that the inner planets have a tendency to merge into a massive planet with relatively high e (≃0.2-0.9) and small a (≃0.5-1 AU). The orbital decay is a result of the gravitational perturbation by the outer planets and the dissipation of the colliding planets' relative kinetic energy. Afterward, long-term perturbation would slightly reduce the merged body's a, while it would keep its e high. The orbital properties of the merged body are consistent with those of the massive eccentric planets around 70 Vir and HD 114762. The onset timescale for orbit crossing within a planetary system is sensitively determined by the planets' mass and separation, which may explain the diversity in the orbital properties among the newly discovered planetary systems.