论文标题
流体核心和固体内核对汞的Cassini固定的影响
The influence of a fluid core and a solid inner core on the Cassini sate of Mercury
论文作者
论文摘要
我们提出了一个Cassini汞状态的模型，该模型包括内核，流体核心和地幔。我们的模型包括内部区域之间的惯性和重力扭矩，以及在流体核心边界处的粘性和电磁（EM）耦合。我们表明，汞内部区域之间的耦合足够强，以至于地幔旋转轴的斜率偏离刚性行星的斜率不超过0.01 arcmin。地幔斜率随着内部核心的大小增加而减小，但是大和无内核之间的变化限制为0.015 arcmin。 EM耦合比内核边界处的粘合耦合强，如果核心磁场强度高于0.3 MT，则将流体和固体核心锁定到一个共同的进动运动中。由于地幔与内核之间的强力耦合强，内核的越大，将共同核心的核心与地幔的对齐程度越多，并且对固定行星预期的惯性矩的倾斜度越大。惯性和地幔旋转轴极矩之间的错位随着内核的大小增加，但限制为0.007 arcmin。我们的结果表明，测量的旋转轴和惯性的极矩的倾斜度应在当今测量误差的水平上重合，并且不能与刚性行星的斜率区分开。
We present a model of the Cassini state of Mercury that comprises an inner core, a fluid core and a mantle. Our model includes inertial and gravitational torques between interior regions, and viscous and electromagnetic (EM) coupling at the boundaries of the fluid core. We show that the coupling between Mercury's interior regions is sufficiently strong that the obliquity of the mantle spin axis deviates from that of a rigid planet by no more than 0.01 arcmin. The mantle obliquity decreases with increasing inner core size, but the change between a large and no inner core is limited to 0.015 arcmin. EM coupling is stronger than viscous coupling at the inner core boundary and, if the core magnetic field strength is above 0.3 mT, locks the fluid and solid cores into a common precession motion. Because of the strong gravitational coupling between the mantle and inner core, the larger the inner core is, the more this co-precessing core is brought into an alignment with the mantle, and the more the obliquity of the polar moment of inertia approaches that expected for a rigid planet. The misalignment between the polar moment of inertia and mantle spin axis increases with inner core size, but is limited to 0.007 arcmin. Our results imply that the measured obliquities of the mantle spin axis and polar moment of inertia should coincide at the present-day level of measurement errors, and cannot be distinguished from the obliquity of a rigid planet.
