Stopping inward planetary migration by a toroidal magnetic field
Stopping inward planetary migration by a toroidal magnetic field
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通过环形磁场阻止行星向内迁移
DOI：
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发表时间：
2003
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影响因子：
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通讯作者：
C. Terquem
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文献类型：
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作者：
C. Terquem
我们计算了行星在圆形轨道上对含有环形磁场的圆盘施加的线性扭矩。所有的流体扰动在所谓的磁共振处都是奇异的，其中扰动的多普勒频移频率与沿着磁力线传播的慢MHD波的频率相匹配。它们位于自转半径的两侧。波在Lindblad共振之外传播，也在磁共振周围的受限区域传播。磁共振会产生一个重要的全球力矩，就像林德布莱德力矩一样，在S轨道内部(外部)是负(正)的。由于这些共振比Lindblad共振更接近行星，如果磁场足够大，它们贡献的扭矩将主导Lindblad扭矩。此外，如果β=c^2/v_A^2随半径增加得足够快，则外磁共振变得不那么重要，总扭矩为负，由内磁共振主导。这导致了地球向外迁移。即使在大旋时β=100，也可能获得负扭矩。一颗行星穿过圆盘的非磁化区域向内移动时，当到达磁化区域时，就会失速。然后，它将能够成长为一颗类地行星或一颗巨大行星的核心。在湍流磁化圆盘中，大尺度的场结构变化非常缓慢，行星可能会交替向内和向外迁移，这取决于遇到的场的梯度。然后，它的迁移可能会变得扩散，或者仅限于小规模。
We calculate the linear torque exerted by a planet on a circular orbit on a disc containing a toroidal magnetic field. All fluid perturbations are singular at the so--called magnetic resonances, where the Doppler shifted frequency of the perturbation matches that of a slow MHD wave propagating along the field line. These lie on both sides of the corotation radius. Waves propagate outside the Lindblad resonances, and also in a restricted region around the magnetic resonances. The magnetic resonances contribute to a significant global torque which, like the Lindblad torque, is negative (positive) inside (outside) the planet\'s orbit. Since these resonances are closer to the planet than the Lindblad resonances, the torque they contribute dominates over the Lindblad torque if the magnetic field is large enough. In addition, if beta=c^2/v_A^2 increases fast enough with radius, the outer magnetic resonance becomes less important and the total torque is then negative, dominated by the inner magnetic resonance. This leads to outward migration of the planet. Even for beta=100 at corotation, a negative torque may be obtained. A planet migrating inward through a nonmagnetized region of a disc would then stall when reaching a magnetized region. It would then be able to grow to become a terrestrial planet or the core of a giant planet. In a turbulent magnetized disc in which the large scale field structure changes sufficiently slowly, a planet may alternate between inward and outward migration, depending on the gradients of the field encountered. Its migration could then become diffusive, or be limited only to small scales.