Rotational Period of the Planet Mercury
Rotational Period of the Planet Mercury
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DOI：
10.1038/208575a0
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发表时间：
1965-11
期刊：
影响因子：
64.8
通讯作者：
Giuseppe Colombo;Giuseppe Colombo
中科院分区：
文献类型：
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作者：
Giuseppe Colombo;Giuseppe Colombo
在最近的一次通信中，S。J. Peale和T. Gold 1根据雷达多普勒扩散测量确定的水星自转周期为59 ± 5天2，并考虑到水星轨道的大偏心率和潮汐摩擦的1/r6依赖性（r是太阳与行星的距离），用太阳潮汐力矩效应来解释。他们从一个非常简短的讨论中得出结论，在从更高的直接角速度减慢后，行星的最终自转周期将在56到88天之间，具体取决于耗散函数的假设形式。然而，从他们的讨论中，根本不清楚为什么永久变形意味着在减速过程之后的88天作为最终旋转状态。58.65恒星日周期，即轨道周期的2/3的非常接近匀速的旋转运动确实可能是稳定的周期解。这种旋转运动的最小转动惯量轴在每一个近日点都几乎与太阳-水星半径矢量对齐。近日点的轨道角速度（2φ/56.6天）接近2φ/58.65天，导致最小惯性矩轴与半径矢量近似对齐，在近日点周围的弧中相互作用最强。水星惯性椭球的轴向不对称性可能会产生一个抵消潮汐扭矩的扭矩，使水星在这个方向上稳定运动，周期为轨道周期的三分之二。因此，水星有可能具有比皮尔和戈尔德所允许的更高的永久刚度。
IN a recent communication by S. J. Peale and T. Gold1the rotational period of Mercury, determined from radar Doppler-spread measurements to be 59 ± 5 days2, has been explained in terms of a solar tidal torque effect, taking into account the large eccentricity of Mercury's orbit, and the 1/r6dependence of the tidal friction (rbeing the Sun–planet distance). They conclude from a very brief discussion that after slowing down from a higher direct angular velocity, the planet will have a final period of rotation between 56 and 88 days, depending on the assumed form of the dissipation function. However, from their discussion it is by no means clear why permanent deformations would imply a period of 88 days as a final rotation state after a slowing-down process. A very nearly uniform rotational motion of 58.65 sidereal-day period, that is 2/3 of the orbital period, may indeed be a stable periodic solution. This rotational motion could have the axis of minimum moments of inertia nearly aligned with the Sun–Mercury radius vector at every perihelion passage. The orbital angular velocity at perihelion (2φ/56.6 days) is close to 2φ/58.65 days, leading to an approximate alignment of the axis of minimum moment of inertia with the radius vector in an arc around perihelion where the interaction is strongest. The axial asymmetry of Mercury's inertia ellipsoid may result in a torque that counterbalances the tidal torque, giving a stable motion with this orientation and with a period two-thirds of the orbital period. It would therefore be possible for Mercury to have a higher permanent rigidity than that permitted by Peale and Gold.