Circular depression in the surface of a planetary body. Most craters are the result of impacts of meteorites or of volcanic explosions. Meteorite craters are more common on the Moon and Mars and on other planets and natural satellites than on Earth, because most meteorites either burn up in the Earth's atmosphere before reaching its surface or erosion soon obscures the impact site. Craters made by exploding volcanoes (e.g., Crater Lake, Ore.) are more common on the Earth than on the Moon, Mars, or Jupiter's moon Io, where they have also been identified.

This entry comes from Encyclopædia Britannica Concise.
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