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 coprecessing 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.

中文翻译：

---

流体核和固体核对卡西尼状态汞的影响

我们提出了一个卡西尼水星状态的模型，该模型包括一个内芯，一个流体芯和一个地幔。我们的模型包括内部区域之间的惯性和重力转矩，以及在流体核心边界处的粘性和电磁（EM）耦合。我们表明，水星内部区域之间的耦合足够强，以致地幔自转轴的倾角与刚性行星的倾角相差不超过0.01 arcmin。内倾角随内核尺寸的增加而减小，但大内核与无内核之间的变化限制为0.015 arcmin。EM耦合在内核内部边界处比粘性耦合强，并且，如果内核磁场强度大于0.3 mT，则将流体和固体内核锁定为共同的进动。由于地幔与内核之间的强引力耦合，内核越大，该共处理核与地幔的对准就越多，并且极惯性矩的倾角越接近于预期的惯性矩。刚性行星。极惯性矩和地幔自旋轴之间的失准随内芯尺寸的增加而增加，但限制为0.007 arcmin。我们的结果表明，测得的地幔自转轴的倾斜度和极惯性矩应在当今的测量误差水平上一致，并且不能与刚性行星的倾斜度区分开。极惯性矩的倾角越接近刚性行星所期望的倾角。极惯性矩和地幔自旋轴之间的失准随内芯尺寸的增加而增加，但限制为0.007 arcmin。我们的结果表明，测得的地幔自转轴的倾斜度和极惯性矩应在当今的测量误差水平上一致，并且不能与刚性行星的倾斜度区分开。极惯性矩的倾角越接近刚性行星所期望的倾角。极惯性矩和地幔自旋轴之间的失准随内芯尺寸的增加而增加，但限制为0.007 arcmin。我们的结果表明，测得的地幔自转轴的倾斜度和极惯性矩应在当今的测量误差水平上一致，并且不能与刚性行星的倾斜度区分开。