Of course, computer simulations can say only whatcould have happened, not what did. For that,physical evidence is required. Some suggestiveevidence does exist, though. For a start, the cruston the far side of the moon is indeed much thickerthan that on the nearside. Also, because the secondmoon would have been smaller than the main one, itwould have cooled and solidified more quickly,meaning that its rocks would be older. Sure enough,different parts of the present moons crust,recovered by various missions to the lunar surface,differ in age by up to 200m years, a fact that has long puzzled selenologists but which theimpact theory neatly explains. Moreover, such a huge collision on the far side would haveshifted much of the magma ocean that then underlay the moons surface to the near side,which led to the formation of the maria.
当然,计算机模拟只能估计已经发生的情形,而不是确实发生的情况。为此,实物证据是需要的。虽然,某些提示性的证据确实存在。因为从一开始,较远那侧的月球外壳确实比较近侧的外壳要厚实的多。此外,因为这第二个月球应该比最大的月球要小的多,所以这个月球应该冷却、凝固要快得多。这也意味着这个月球的岩石要年久的多。果真如此,现在月球外壳的不同部分,各次去月球表面的探测任务发现,这些岩石年代的不同达到 2亿年之久。一个长期困扰月球学家的客观事实被碰撞理论巧妙地解释了。此外,在月球较远那侧如此巨大的一次碰撞应该迅速移动很多岩浆洋,然后在月球表面一直铺到近地侧,这就导致了月海的形成。
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