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arXiv 1012.0266astro-ph.EP
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随机力对行星系和土星环演化的影响

The effects of stochastic forces on the evolution of planetary systems and Saturn's rings

Hanno Rein

摘要:

太阳系外行星数量的增加为研究行星系的形成提供了新的机会。共振系统是特别感兴趣的,因为它们的动态配置提供了不可观测的形成和迁移阶段的约束。在这篇论文中,行星系HD 128311和HD 45364的编队方案。N体模拟的两个行星和二维流体动力学模拟的原行星盘被用来模拟迁移阶段和捕获到共振。结果表明,原行星盘的表面密度比以前认为的要大。原行星暴露在随机力中,由圆盘中的密度波动产生。一个通用的模型,一个单一的行星,两个行星的共振,被随机强迫。例如,GJ 876系统在合理的随机力强度下是稳定的,但行星较轻的系统可能会被破坏。即使它们没有被完全破坏,随机力也会产生特征性的、可观察到的天平动模式。湍流在行星形成过程的早期阶段也起着重要作用。核心吸积模型中的引力坍缩由于尺度分离大,很难用数值方法模拟。提出了一种缩放方法,通过考虑相关的小尺度过程,可以正确处理边缘碰撞系统中的自重力。有趣的是,这个系统在动力学上与土星环非常相似。还研究了土星环中小天体的随机迁移。的小卫星/螺旋桨与环粒子的相互作用的分析预测相比,碰撞N-体模拟多达一百万个粒子。随机游走的速度足够快,可以被卡西尼号航天器直接观测到。

英文摘要:

The increasing number of extra-solar planets opens a new opportunity for studies of the formation of planetary systems. Resonant systems are of particular interest because their dynamical configuration provides constraints on the unobservable formation and migration phase. In this thesis, formation scenarios for the planetary systems HD128311 and HD45364 are presented. N-body simulations of two planets and two dimensional hydrodynamical simulations of proto-planetary discs are used to model the migration phase and the capture into resonance. The results indicate that the proto-planetary disc has a larger surface density than previously thought. Proto-planets are exposed to stochastic forces, generated by density fluctuations in the disc. A generic model of both a single planet, and two planets in resonance, being stochastically forced is presented. The system GJ876, for example, is stable for reasonable strengths of the stochastic forces, but systems with lighter planets can get disrupted. Even if they are not disrupted completely, stochastic forces create characteristic, observable libration patterns. Turbulence plays also an important role during the early phases of the planet formation process. Due to the large separation of scales, the gravitational collapse in the core accretion model is very hard to model numerically. A scaled method is presented, that allows for the correct treatment of self-gravity in a marginally collisional system by taking into account the relevant small scale processes. Interestingly, this system is dynamically very similar to Saturn's rings. The stochastic migration of small bodies in Saturn's rings is also studied. Analytic predictions of the interactions of a moonlet/propeller with ring particles are compared to collisional N-body simulations with up to a million particles. The random walk is fast enough to be directly observable by the Cassini spacecraft.

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