论文标题
汞旋转轴与耗散引起的精确的卡西尼态的偏差
Deviation of Mercury's spin axis from an exact Cassini state induced by dissipation
论文作者
论文摘要
我们计算了汞旋转轴偏离潮汐耗散引起的精确卡西尼态的偏差，以及核心掩体边界（CMB）和内部核心边界（ICB）处的粘性和电磁（EM）摩擦。 CMB处的粘性摩擦会产生相位的铅，粘性和EM摩擦在ICB产生相位滞后。偏差的大小取决于内部核心的大小，运动场粘度和磁场强度，但不能超过上限。对于一个小的内核，CMB处的粘性摩擦会导致最大相位铅为0.027 ARCSEC。对于大型内核（半径$> 1000 $ km），ICB处的EM摩擦会产生最大的相位滞后，但不超过0.1 ARCSEC。未对准的流体和实心核引起的弹性变形在粘性和EM偶联引起的相位铅/滞后中起一级作用，并导致地幔倾斜的扰动与潮汐变形所引起的相当。潮汐耗散导致相位滞后，其幅度（以Arcsec的单位为单位）由经验关系（80/Q）给出，其中Q是质量因子； Q = 80导致〜1 ArcSec的相位滞后。低粘度为10^{17} pa s或更低阶的大内核会显着影响$ q $，从而影响所得相位滞后。观测值（<10 arcsec）建议的有限地幔相滞后意味着对大约10^{17} pa s的块状粘度的下限。
We compute predictions of the deviation of Mercury's spin axis from an exact Cassini state caused by tidal dissipation, and viscous and electromagnetic (EM) friction at the core-mantle boundary (CMB) and inner core boundary (ICB). Viscous friction at the CMB generates a phase lead, viscous and EM friction at the ICB produce a phase lag; the magnitude of the deviation depends on the inner core size, kinematic viscosity and magnetic field strength, but cannot exceed an upper bound. For a small inner core, viscous friction at the CMB results in a maximum phase lead of 0.027 arcsec. For a large inner core (radius $>1000$ km), EM friction at the ICB generates the largest phase lag, but it does not exceed 0.1 arcsec. Elastic deformations induced by the misaligned fluid and solid cores play a first order role in the phase lead/lag caused by viscous and EM coupling, and contribute to a perturbation in mantle obliquity on par with that caused by tidal deformations. Tidal dissipation results in a phase lag and its magnitude (in units of arcsec) is given by the empirical relation (80/Q), where Q is the quality factor; Q=80 results in a phase lag of ~1 arcsec. A large inner core with a low viscosity of the order of 10^{17} Pa s or lower can significantly affect $Q$ and thus the resulting phase lag. The limited mantle phase lag suggested by observations (<10 arcsec) implies a lower limit on the bulk mantle viscosity of approximately 10^{17} Pa s.
