Impact craters are geological structures formed when an asteroid, comet or meteorite hits a planet or satellite. The Earth has suffered more impacts than the Moon, but most craters have been erased by erosion, tectonic activity and volcanism.
The first of these geological structures was catalogued in 1920. It was the Meteor Crater, in Arizona, discovered by a group of workers who found meteorite fragments inside.
For years, the only way to recognize impact craters was to find these cosmic fragments. Most of the time, however, the impact is so brutal that any trace of the body that produced it is erased.
Today the chemical and magnetic footprints of meteorites and comets can be recorded, so the number of classified impact craters has increased to more than 150.
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