Theory of the Earth-synchronous rotation of Venus
Theory of the Earth-synchronous rotation of Venus
复制标题
金星地球同步自转理论
作者：
T. Gold;S. Soter
CARPENTER1在1966年指出，对金星自转周期的雷达观测给出了一个非常接近金星在每一个较低的交会处向地球呈现相同方位的图形。Goldreich和Peale2讨论了这是地球对金星永久横向四极矩施加的引力对的可能共振，但他们指出，由于太阳作用于固体潮汐，这样的引力对预计会比这小得多。由于潮汐摩擦，自转将继续减慢，不可能在共振中停止。因此，我们提出，热力大气层潮汐上的太阳对可能会对金星的自转产生加速，从而与体潮摩擦减速相反。(在这个意义上，地球也会受到影响。)这两个相反的力矩对金星的自转速度有不同的依赖关系，并可能在一个特定值上保持平衡。当自转速度接近这个值时，捕获进入共振所需的扭矩将变得非常小，届时地球施加的影响可能就足够了。一天只有1毫巴的压力波就可以平衡体潮。Ingersoll和Dobrovolskis重新考虑了这一建议，并尝试对大气潮汐进行定量计算。尽管他们的结果似乎支持这一理论，但我们在这里表明，他们的方法是无效的。Ingersoll和Dobrovolskis考虑了一个每日受热的准静态大气，然后计算了质量分布，从而得出了太阳电偶。但对于金星上的已知情况，准静态假设是不合理的。风速必须是预期的，而且确实已经观测到6，这种风速引起的热量平流速度大大快于太阳以下点在地表的运动速度(∼4 m S−1)；在这种情况下，大气质量分布将由对流大气的动力学决定。(影响压力和密度水平变化的主要因素是加速度项，而不是温度。)只有从行星对流的详细理论或直接观测中知道流动模式和速度，才能得到可靠的结果。
CARPENTER1 noted in 1966 that the radar observations of the rotation period of Venus gave a figure remarkably close to one at which Venus would present the same aspect to the Earth at each inferior conjunction. Goldreich and Peale2 discussed this as a possible resonance with a gravitational couple exerted by the Earth on a permanent transverse quadrupole moment of Venus, but noted that such a couple would be expected to be much smaller than that due to the Sun acting on the solid body tide. The rotation would continue to slow down due to tidal friction, and could not have been arrested in the resonance. We therefore proposed3 that the solar couple on thermal atmospheric tides might be expected to apply an acceleration to the spin of Venus, thus opposing the body tidal frictional deceleration. (An effect in that sense occurs for the Earth.) The two opposed torques would have a different dependence on the rotation speed of Venus, and might balance at a particular value. As the rotation speed approached this value, the torque necessary for capture into a resonance would have become very small, and the effect exerted by the Earth might then be sufficient. A diurnal pressure wave of as little as 1 mbar could balance the body tide. Ingersoll and Dobrovolskis4 have reconsidered this suggestion, and attempted a quantitative calculation of the atmospheric tide. Although their result seems to favour the theory, we show here that their approach is not valid. Ingersoll and Dobrovolskis consider a quasi-static atmosphere heated diurnally, and then calculate the mass distribution and hence the solar couple that results. But the quasi-static assumption is not justified for the known circumstances on Venus. Wind speeds must be expected5, and have indeed been observed6, that cause an advection of heat substantially faster than the motion of the subsolar point over the surface (∼4 m s−1); in these circumstances the atmospheric mass distribution will be determined by the dynamics of the convecting atmosphere. (The acceleration terms rather than temperature make the main contribution to horizontal variations of pressure and density.) A secure result cannot be obtained until the flow patterns and velocities are known, from a detailed theory of planetary convection, or from direct observation.