As on the Moon, the extent of large impact cratering serves as an age indicator for the Martian surface.
和在月球的一样，大型撞击陨石坑的范围之广可以显示出火星表面的年龄。
2
The Mariner spacecraft found that the surface of Mars, as well as that of its two moons, is pitted with impact craters formed by meteoroids falling in from space.
水手号宇宙飞船发现火星表面，还有它的两个卫星表面，都有由太空坠落的流星体造成的陨石坑。
3
The impact of raindrops on the loose soil tends to transfer fine clay particles into the tiniest soil spaces, sealing them and producing a surface that allows very little water penetration.