Every solid body in the solar system suffers from impact cratering. An impact crater is produced when a projectile, travelling at a very high velocity, hits the surface of a solid body such as a planet or natural satellite forming a large hole in the ground.
The study of impact craters is very important in order to gain an understanding of the history and properties of the body on which the impact has occurred. On Earth, this is made very difficult by the erosion that occurs as a result of both the weather and geological activity, and so relatively few craters can be well studied. In contrast, the Moon has no weathering, so craters there are well preserved. Lunar impact craters date back to just after the formation of the Moon itself, and have shown that the number of impacts occurring in the past was much greater than the number occurring today.