Impact craters

Impact craters in the Solar System: Top-left: 500-kilometer large crater Engelier on Saturn's moon Iapetus Top-right: Recently formed impact crater on Mars showing a pristine ray system of ejecta Bottom-left: 50,000-year-old Meteor Crater east of Flagstaff, Arizona, U.S. Bottom-right: The prominent crater Tycho in the southern highlands of the Moon

An impact crater is an approximately circular depression in the surface of a planet, moon, or other solid body in the Solar System or elsewhere, formed by the hypervelocity impact of a smaller body. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than the surrounding terrain. Although Meteor Crater is perhaps the best-known example of a small impact crater on Earth, impact craters range from small, simple, bowl-shaped depressions to large, complex, multi-ringed impact basins.

Impact craters are the dominant geographic features on many solid Solar System objects including the Moon, Mercury, Callisto, Ganymede and most small moons and asteroids. On other planets and moons that experience more active surface geological processes, such as Earth, Venus, Mars, Europa, Io and Titan, visible impact craters are less common because they become eroded, buried or transformed by tectonics over time. Where such processes have destroyed most of the original crater topography, the terms impact structure or astrobleme are more commonly used. In early literature, before the significance of impact cratering was widely recognised, the terms cryptoexplosion or cryptovolcanic structure were often used to describe what are now recognised as impact-related features on Earth.

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