Origins of Eccentric Extrasolar Planets: Testing the Planet-Planet Scattering Model
Origins of Eccentric Extrasolar Planets: Testing the Planet-Planet Scattering Model
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DOI：
10.1086/590926
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发表时间：
2007-03
期刊：
影响因子：
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通讯作者：
E. Ford;F. Rasio
中科院分区：
文献类型：
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作者：
E. Ford;F. Rasio
在具有两个或更多巨行星的行星系统中，动力学不稳定性可能会通过强烈的行星散射而导致碰撞或喷射。先前对两颗等质量行星初始条件的研究揭示了模拟结果与观测到的系外行星轨道之间的两个差异：巨行星之间潜在的频繁碰撞和最终偏心率的狭窄分布。我们表明，对两颗质量不等的行星在近圆形轨道上进行的模拟预测，碰撞会减少，最终偏心率范围也会扩大。因此，两行星散射模型可以通过行星质量比的合理分布来重现观察到的偏心率。该模型还预测最大偏心率为≃0.8，与行星质量比的分布无关，前提是两颗行星最初都位于接近圆形的轨道上。这与观测结果相比较，并将通过未来行星发现的检验。此外，行星间散射和潮汐圆化的结合可以解释一些轨道周期非常短的巨行星的存在。行星散射引起的轨道迁移可以在解释径向速度测量发现的轨道周期分布方面发挥重要作用。我们还重新检查并讨论了系外行星的偏心率和其他特性之间的各种可能的相关性。我们发现，径向速度观测结果与行星偏心率一致，而行星偏心率与行星表面的逃逸速度相对于行星所在位置的主恒星的逃逸速度之比相关。我们证明，观测到的行星质量、周期和偏心率的分布可以为行星形成和演化模型提供约束。
In planetary systems with two or more giant planets, dynamical instabilities can lead to collisions or ejections through strong planet-planet scattering. Previous studies for initial conditions with two equal-mass planets revealed two discrepancies between the results of simulations and the observed orbits of exoplanets: potentially frequent collisions between giant planets and a narrow distribution of final eccentricities. We show that simulations with two unequal-mass planets starting on nearly circular orbits predict fewer collisions and a broader range of final eccentricities. Thus, the two-planet scattering model can reproduce the observed eccentricities with a plausible distribution of planet mass ratios. The model also predicts a maximum eccentricity of ≃0.8, independent of the distribution of planet mass ratios, provided that both planets are initially placed on nearly circular orbits. This compares favorably with observations and will be tested by future planet discoveries. Moreover, the combination of planet-planet scattering and tidal circularization may explain the existence of some giant planets with very short period orbits. Orbital migration due to planet scattering could play an important role in explaining the distribution of orbital periods found by radial velocity surveys. We also reexamine and discuss various possible correlations between eccentricities and other properties of exoplanets. We find that radial velocity observations are consistent with planet eccentricities being correlated with the ratio of the escape velocity from the planet's surface relative to the escape velocity from the host star at the planet's location. We demonstrate that the observed distribution of planet masses, periods, and eccentricities can provide constraints for models of planet formation and evolution.