专家:地球曾有两个月亮

　　The 'second' moon is also thought to have been generated by the giant impact, remaining in orbit for tens of millions of years. The two moons collided relatively slowly, according to the theory described today in the journal Nature. Such low velocity impacts do not produce craters or cause much melting. Instead, most of the colliding material is piled onto the impacted hemisphere as a thick new layer of solid crust. This could have formed the mountainous region now seen on the far side of the moon. 'Our model works well with models of the moon-forming giant impact, which predict there should be massive debris left in orbit about the Earth, besides the moon itself,' said lead researcher Professor Erik Asphaug, from the University of California at Santa Cruz.

　　“第二个月亮”的理论获得许多科学家的认同，据《自然》杂志称，两个月亮碰撞过程相对缓慢。此外，月球的年龄大约有46亿年，和地球同岁，也有壳、幔、核等分层结构。然而，月球永远都是一面朝向我们，这一面习惯上被称为“正面”。另外一面，除了在月面边沿附近的区域因天秤动而中间可见以外，绝大部分不能从地球看见。在没有探测器的年代，月球的“背面”一直是个未知的世界。各种猜测、各种推测层出不穷。专家Erik Asphaug说：“我们当今的工作就是模拟月球撞击时的景象，并预测在碰撞轨道上还有可能遗留地球或者月球的残骸。”