The Moon, the natural satellite of the Earth, has a surface a lot more impacted than the Earth’s. This is due because the Earth has a much more developed atmosphere than the Moon. This causes that the meteorites, in their entrance in the Earth’s atmosphere, they disintegrate, forming a luminescent cue behind it. This is what we call a shooting star. Every day, there are many meteorites that disintegrate when they enter in the Earth’s atmosphere, but the reason because we don’t see many shooting stars, is because the most part of meteorites are so small that we don’t see them.
All what I have just explained is what happens in the Earth, but, in the Moon, there is a so weak atmosphere, that, in practical effects, it is considered that there isn’t any atmosphere. For this reason, the meteorites can impact into its surface without any problem. Consequently, the Moon’s surface is recovered with an enormous quantity of craters. There are craters of very different sizes. The smaller of them are called micro-meteorites, and they are so small that we can’t see them at first sight. In addition, inside the lunar craters, there are even smaller craters, and in this way successively.
Beside the small craters, there are big craters too. The basin of the South Pole-Aitken (SPA), is the conserved crater of big impact of the Moon and maybe the biggest impact structure of the solar system. Moreover, the basin of the SPA is one of the oldest structures of the Moon. We think that this crater of impact, of 2 500 km wide and some kilometres of depth was created by a big asteroid that crashed into the Moon 4 000 millions of years ago.
Even if this crater is the biggest of the Moon, it isn’t visible from the Earth, because it is in the hidden face of the Moon, which is a part of the Moon that we can never see from the Earth.
In the Moon, like I’ve said before, there isn’t an atmosphere. Because of this, there can’t be either rain or air. Then, because there isn’t any type of erosion, the craters will never disappear. If the Moon had a small atmosphere, the most part of the craters, in exception of the biggest of them, would disappear due to the erosion that there would be in the Moon’s surface.