Diffusive Migration of Low-Mass Protoplanets in Turbulent Disks
Diffusive Migration of Low-Mass Protoplanets in Turbulent Disks
复制标题
低质量原行星在湍流盘中的扩散迁移
DOI：
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发表时间：
2006
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通讯作者：
K. Menou
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作者：
Eric T. Johnson;J. Goodman;K. Menou
在原行星盘中，由于磁旋转湍流引起的力矩波动可能会对初生行星的迁移模式和生存概率产生重要影响。假设湍流是一个具有有限振幅和相关时间的平稳随机过程，则由此产生的扩散迁移可以用福克-普朗克方程描述，我们将其简化为对流扩散方程。我们校准现有的磁光盘模拟和平均迁移估计的系数，并解决方程的解析和数值。对于低质量的行星和原行星盘外部区域的行星，扩散倾向于主导平流，无论它们是由最小质量太阳星云（MMSN）还是金牛座T α盘描述。扩散系统地减少了大多数行星的寿命，但它允许它们中的一小部分在大半径下存活更长的时间。平均行星寿命甚至可以是形式上无限的（例如，在无限稳定MMSN中），尽管中值寿命总是有限的。幸存的行星可能会徘徊在特定半径附近，在那里平流和扩散的综合影响被最小化，或者徘徊在大半径处，具体取决于模型的具体情况。湍流盘中迁移的随机性挑战了确定性行星形成的假设，并表明在类似的初始条件下，可能会有各种各样的行星结果。这将有助于（太阳系外）行星系统的多样性。
Torque fluctuations due to magnetorotational turbulence in protoplanetary disks may greatly influence the migration patterns and survival probabilities of nascent planets. Provided that the turbulence is a stationary stochastic process with finite amplitude and correlation time, the resulting diffusive migration can be described with a Fokker-Planck equation, which we reduce to an advection-diffusion equation. We calibrate the coefficients with existing turbulent-disk simulations and mean-migration estimates and solve the equation both analytically and numerically. Diffusion tends to dominate over advection for planets of low mass and those in the outer regions of protoplanetary disks, whether they are described by the minimum mass solar nebula (MMSN) or by T Tauri alpha disks. Diffusion systematically reduces the lifetime of most planets, yet it allows a declining fraction of them to survive for extended periods of time at large radii. Mean planet lifetimes can even be formally infinite (e.g., in an infinite steady MMSN), although median lifetimes are always finite. Surviving planets may linger near specific radii where the combined effects of advection and diffusion are minimized or at large radii, depending on model specifics. The stochastic nature of migration in turbulent disks challenges deterministic planet formation scenarios and suggests instead that a wide variety of planetary outcomes are possible from similar initial conditions. This would contribute to the diversity of (extrasolar) planetary systems.