Tidal Interactions Between Planets and Host Stars
Tidal Interactions Between Planets and Host Stars
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行星与主恒星之间的潮汐相互作用
DOI：
10.1093/acrefore/9780190647926.013.191
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发表时间：
2020
期刊：
影响因子：
64.8
通讯作者：
G. Ogilvie
中科院分区：
文献类型：
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作者：
G. Ogilvie
已经知道有数百颗行星的轨道只比它们所在的恒星宽几倍。行星和其宿主星星之间的潮汐相互作用是形成这些系统的观测到的属性分布的主要因素之一。行星的潮汐消散倾向于使轨道呈圆形，以及使行星的自转与轨道同步和对齐，并可以显着加热行星，潜在地影响其大小和结构。星星的耗散通常会导致行星向内轨道迁移，加速星星的旋转，并在某些情况下摧毁行星。
潮汐演化的一些基本特征可以从自旋和轨道之间通过引力场进行角动量和能量交换以及能量耗散的基本原理来理解。例如，大多数短周期系外行星系统的角动量太小，无法达到潮汐平衡状态。
理论研究的目的是通过求解恒星和行星在周期性潮汐力作用下的流体和固体力学方程来定量解释潮汐耗散。平衡潮汐是一种近似流体静力学的膨胀，由大规模的流动围绕着天体，可以通过对流或流体动力学不稳定性或行星固体区域的粘弹性耗散来阻尼。动力潮汐是一个附加的组成部分，它通常采取内波的形式，由旋转和分层流体中的科里奥利力和浮力恢复。如果波被共振放大，当它们达到非常短的波长时被有效地阻尼，或者因为它们超过临界振幅而破裂，则会导致显著的耗散。
热潮汐是在行星大气中由星星辐射的可变加热激发的。它们可以对抗引力潮汐，防止潮汐锁定，从而对地球的气候和可居住性产生影响。
对凌日系外行星的持续观测提供了关于轨道周期和偏心率以及星星的旋转度（自旋-轨道错位）和行星大小的信息。这些数据揭示了几个潮汐过程的工作，并提供了各种恒星和行星的潮汐耗散效率的限制。
Hundreds of planets are already known to have orbits only a few times wider than the stars that host them. The tidal interaction between a planet and its host star is one of the main agents shaping the observed distributions of properties of these systems. Tidal dissipation in the planet tends make the orbit circular, as well as synchronizing and aligning the planet’s spin with the orbit, and can significantly heat the planet, potentially affecting its size and structure. Dissipation in the star typically leads to inward orbital migration of the planet, accelerating the star’s rotation, and in some cases destroying the planet.
Some essential features of tidal evolution can be understood from the basic principles that angular momentum and energy are exchanged between spin and orbit by means of a gravitational field and that energy is dissipated. For example, most short-period exoplanetary systems have too little angular momentum to reach a tidal equilibrium state.
Theoretical studies aim to explain tidal dissipation quantitatively by solving the equations of fluid and solid mechanics in stars and planets undergoing periodic tidal forcing. The equilibrium tide is a nearly hydrostatic bulge that is carried around the body by a large-scale flow, which can be damped by convection or hydrodynamic instability, or by viscoelastic dissipation in solid regions of planets. The dynamical tide is an additional component that generally takes the form of internal waves restored by Coriolis and buoyancy forces in a rotating and stratified fluid body. It can lead to significant dissipation if the waves are amplified by resonance, are efficiently damped when they attain a very short wavelength, or break because they exceed a critical amplitude.
Thermal tides are excited in a planetary atmosphere by the variable heating by the star’s radiation. They can oppose gravitational tides and prevent tidal locking, with consequences for the climate and habitability of the planet.
Ongoing observations of transiting exoplanets provide information on the orbital periods and eccentricities as well as the obliquity (spin–orbit misalignment) of the star and the size of the planet. These data reveal several tidal processes at work and provide constraints on the efficiency of tidal dissipation in a variety of stars and planets.