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Formation on the surface of nearly all the bodies of the solar system with a solid crust. You can be distinguished from impact craters (generated by the impact of meteorites) and volcanic craters (volcanic). The former are, in general, by far the most numerous. On all interior of the solar system planets are impact craters. Their density, which varies from planet to planet and, for the same planet, from region to region, is used to establish the era in which they were formed planetary surfaces. The dating is done by comparison with the lunar surface, by which the rock samples taken in the Apollo missions, made it possible to perform absolute dates. The uncertainties of the method are mainly related to the assumption that the intensity of the meteor shower on the various planets was the same as that which hit the Moon. On Earth, in particular, there are numerous volcanic calderas and rare are the easily recognizable impact craters. The traces of the intense meteorite bombardment that must have struck the Earth, as well as on the Moon, in the first 800 million years of his life were completely erased by subsequent geological upheavals. However, the most recent surveys, which make use of artificial satellite observations have led to the identification of at least thirty very ancient fossil craters, generated by impacts also occurred 1 or 2 billion years ago. The outer planets do not have solid surfaces and, therefore, have no craters. Numerous c. impact, on the other hand, were observed by the Voyager probes of various satellites of Jupiter, Saturn and Uranus, with an icy crust. This suggests that even in the outer regions of the solar system there has been a meteor bombardment primal intensity similar to the one that hit the inner planets.