Meteorite Craters

When a meteorite impacts with Earth or with other comparatively large solid bodies such as the Moon, other planets and their satellites, or larger asteroids and comets, a depression results that is called a meteorite crater. For this discussion, the term meteorite crater is considered to be synonymous with impact crater. As such, the colliding objects are not restricted by size to meteorites as they are found on

Earth. Rather, they include chunks of solid material of the same nature as comets or asteroids and in a wide range of sizes—from small meteoroids up to comets and asteroids themselves.

Meteorite crater formation is arguably the most important geologic process in the solar system, as meteorite craters cover most solid-surface bodies, Earth being a notable exception. Meteorite craters can be found not only on rocky surfaces like that of the Moon but also on the surfaces of comets and ice-covered moons of the outer planets. Formation of the solar system left countless pieces of debris in the form of asteroids and comets and their fragments. Gravitational interactions with other objects routinely send this debris on a collision course with planets and their moons. The resulting impact from a piece of debris produces a surface depression many times larger than the original object. Although all meteorite craters are grossly similar, their appearance varies substantially with both size and the body on which they occur. If no other geologic processes have occurred on a planet or moon, its entire surface is covered with craters as a result of the impacts sustained over the past 4.6 billion years since the major bodies of the solar system formed. On the other hand, the absence or sparseness of craters on a body's surface, as is the case for Earth's surface, is an indicator of some other geologic process (e.g., erosion or surface melting) occurring during the body's history that is eliminating the craters.

Four impact craters imaged by spacecraft on different solid bodies of the solar system and reproduced at the same scale. They are (clockwise from upper left) Golubkhina crater on Venus, Kepler crater on the Moon, an unnamed crater on Jupiter's moon Ganymede, and an unnamed crater on Mars. (Venus and Moon) Robert Herrick/Lunar and Planetary Institute; (Mars) Calvin Hamilton/Los Alamos National Laboratory; (Ganymede) Paul Schenk/Lunar and Planetary Institute

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