Architecture of Planetary Systems: Solar and Extrasolar

如果一个人把多颗行星任意放在一颗恒星的轨道上，人们可能会发现这个系统在动力学上是不稳定的：在几个轨道周期的时间尺度上，轨道将以指数形式偏离它们的原始路径。真实的行星系统，至少存活了数百万次轨道，并不是动态不稳定的。在这些长时间尺度上，行星的行为就像它的质量围绕着它的轨道扩散一样，就像围绕恒星的椭圆形环一样。这些环相互引力，导致它们的形状和方向发生缓慢变化，这可能会导致所谓的长期不稳定或长期混乱。该项目的主要研究人员和合作者计划发展一个完整的长期不稳定性理论，使用分析技术以及相互作用的椭圆环的计算机模拟和直接N体模拟。他们的目标是确定长期不稳定性和长期混沌是否能够定量地解释和预测(1)内行星的长期轨道演化，(2)“热木星”系外行星的轨道性质和质量的分布，以及(3)系外行星系统的一般性质。特别是，他们的目标是确定长期混沌是否是形成热木星的盘驱动迁移的可行替代方案，这或许也能够解释相对于恒星赤道的轨道倾角的广泛分布。他们将对太阳系外行星的偏心率和空间做出定量预测，并建立对系外行星系统的观测如何用于约束行星形成物理的理解。该项目将支持和培训一名博士后研究员和两名本科生暑期学生，首席调查员将公开介绍工作结果。

If one were to arbitrarily put multiple planets in orbit around a star, one might find the system to be dynamically unstable: the orbits would deviate exponentially from their original paths on time scales of a few orbital periods. Real planetary systems, which have survived for at least millions of orbits, are not dynamically unstable. On these long time scales, a planet behaves as if its mass were spread around its orbit, like an elliptical ring around the star. These rings pull on each other gravitationally, causing slow changes in their shapes and orientations, which may lead to so-called secular instability or secular chaos. The Principal Investigator and collaborators on this project plan to develop a complete theory of secular instability, using analytic techniques as well as computer simulations of interacting elliptical rings and direct N-body simulations. Their goal is to determine whether secular instability and secular chaos can quantitatively explain and predict (1) the long-term orbital evolution of the Inner Planets, (2) the distribution of orbital properties and masses of "hot Jupiter" exoplanets, and (3) the properties of exoplanet systems in general. In particular, they aim to determine whether secular chaos is a viable alternative to disk-driven migration for the formation of hot Jupiters which may be able also to account for the wide distribution of orbital inclinations with respect to the stellar equator. They will make quantitative predictions for the eccentricities and spacings of extrasolar planets, and build an understanding of how observations of exoplanet systems can be used to constrain planet formation physics. The project will support and train one postdoctoral researcher and two undergraduate summer students, and the Principal Investigator will give public presentations on the results of the work.