Impact Crater

Crater formed by high-speed impact of a meteoroid, asteroid, or comet on a solid surface. Craters are a common feature on most moons (an exception is Io), asteroids, and rocky planets, and range in size from a few cm to over 1,000 km across. There is a general morphological progression from large to small craters: large craters often have several rings and smooth floors; intermediate complex craters tend to have a central peak (formed by melting and rebounding of the crust) and smooth floors; small simple craters have a rough bowl-shaped floor. Craters have been classified into three categories: simple craters, complex craters, and impact basins.

Because impact craters degrade at different rates depending on their environment, they are valuable indicators of the age of a surface and the extent to which resurfacing has taken place. On Earth, for example, craters are rapidly degraded and destroyed by weathering processes; ~120 are known, very few older than 1 Ga. Mercury, which lacks an atmosphere and is geologically inert, has a landscape peppered with craters dating to over 4 Ga.

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Some or all content above used with permission from J. H. Wittke.