疏散星团中双行星系统热木星形成机制研究

On the formation of hot Jupiters in two-planet systems within open clusters

  • 摘要: 有鉴于疏散星团中恒星动力学长期演化背景,通过n体数值模拟,探讨了双行星系统中热木星的形成过程.模拟时,考虑邻近恒星引力扰动的影响,2颗行星均取木星质量,初始处于共面圆轨道,内侧行星半长轴固定为5 ua,外侧行星半长轴变化范围为10~100 ua,在时间尺度为1 Ga上跟踪系统演化.结果表明:伴星在触发高偏心率迁移并形成热木星的过程中发挥重要作用;行星−行星散射表现出促进与抑制并存的双重效应,当外侧行星初始半长轴较小时,增强的散射过程会干扰长期摄动驱动的偏心率增长,从而降低热木星形成效率,当外侧行星初始半长轴约为30 ua时,系统热木星形成效率达到峰值,并高于单行星参考组;随着外侧行星初始半长轴进一步增大,双行星系统与单行星系统的演化结果逐渐趋于一致.疏散星团环境下热木星的形成受伴星扰动、长期引力作用及行星−行星散射共同控制,不同动力学机制之间的竞争关系决定了系统的最终演化结果.

     

    Abstract: Within the dynamical environment of open clusters, we investigate the formation of hot Jupiters in two-planet systems through long-term N-body simulations. The systems are initialized with two Jupiter-mass planets on coplanar circular orbits, with the inner planet fixed at 5 ua and the outer planet placed between 10 and 100 ua. The orbital evolution is followed over a timescale of 1 Gyr while including perturbations from neighbouring stars. The results show that stellar companions play a key role in triggering high-eccentricity migration and promoting hot-Jupiter formation, whereas planet–planet scattering exhibits both positive and negative effects depending on the initial orbital configuration. When the outer planet is initially located at small separations, enhanced scattering tends to disrupt the long-term growth of orbital eccentricity and reduces the formation efficiency of hot Jupiters. The formation rate reaches its maximum when the initial semi-major axis of the outer planet is around 30 ua and remains higher than that of the single-planet reference systems. As the orbital separation increases further, the evolutionary behaviour of two-planet systems gradually approaches that of the single-planet case. These results suggest that hot-Jupiter formation in open clusters is jointly regulated by companion perturbations, long-term gravitational interactions, and planet–planet scattering, with the final outcome determined by the competition among these dynamical processes.

     

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