(戈登•斯坦格的回答)(//www.hoelymoley.com/a/9098/1399)也许已经要领:完全没有理由相信进化的一颗行星在太阳系的一部分应该就是其他星球的镜子。我们看到激烈的成分和类地行星之间的大小差异;为什么其他的性质是相似的吗?我知道的几种可能机制,解释了为什么金星旋转这么慢。# # #重复影响和月球的形成(死亡)金星没有月亮——一个奇怪的事实,只考虑到其他星球上没有一个是水银。你可以把这归因于诸多因素,如质量相对较低和靠近太阳。然而,一些模型表明,周围* *是一个月亮金星,现在不见了。(Alemi &史蒂文森(2006))(http://adsabs.harvard.edu/abs/2006DPS....38.0703A)提出了一个复杂的故事的影响。他们的模型表明,金星遭遇巨大冲击(https://en.wikipedia.org/wiki/Giant_impact_hypothesis)从一个中等大小的行星。就像地球一样,碎片被扔了,月亮合并在轨道上。 This changed Venus' rotation, and began to transfer even more angular momentum to the moon. However, a *second* impact to Venus reversed its rotation, and the moon fell back to the planet, transferring its angular momentum back. This would all happen on the order of ten million years or so, starting and possibly ending during the [Late Heavy Bombardment](https://en.wikipedia.org/wiki/Late_Heavy_Bombardment). The upshot of all this is that Venus emerged with not just a retrograde rotation, but a much longer day. This is, of course, not the sole explanation for the retrograde rotation - exotic scenarios involving 180 degree flips have been proposed; see e.g. [Correia & Laskar (2001)](http://www.nature.com/nature/journal/v411/n6839/abs/411767a0.html) - but the impact hypothesis does have the added advantage of explaining the lack of a moon. ###Atmospheric tides and internal friction Interactions with the Sun have also been proposed as a mechanism affecting not just Venus, but exoplanets like it. [Atmospheric tides](https://en.wikipedia.org/wiki/Atmospheric_tide), generated through heating and cooling from the Sun, could enact a torque on the planet, bringing it into one of several "equilibrium states" (see [Auclair-Desrotour et al. (2016)](https://arxiv.org/abs/1611.05678)). Internal friction could cause more complex interactions in the mantle, further exaggerating the effects on the solid part of the planet. The same thing could happen to any planet orbiting the Sun at roughly the same distance as Venus in the Solar System. It was once proposed that an additional torque was applied to Venus by Earth, complementing the solar atmospheric tides, as there appears to be a coupling between the time between close approaches to Earth and the time of one Venusian day. However, it has since been determined that such a resonance does not, in fact, exist, and should be discounted as a possible reason for the slowing of Venus's rotation (see [Shapiro et al. (1979)](http://adsabs.harvard.edu/abs/1979ApJ...230L.123S)). --- ###Why not Earth? So, why would these effects happen to Venus but not Earth? The chaos of the early Solar System is of course the best answer, but there are other explanations for the specific proposals. The impact theory simply relies on randomness: While Venus and Earth were both likely to suffer major moon-forming collisions, they were not as likely to go through this *twice*. The atmospheric tidal effects, on the other hand, could have been unavoidable, as interactions with the Sun may have been more severe with Venus, for a variety of reasons including distance to the Sun and the exact properties of the atmosphere.