Craters

A crater is a circular or bowl-shaped depression produced by energetic surface processes on a planetary body. Craters are most commonly formed by the impact of meteoroids, comets, or other space debris colliding with a solid surface at high velocity. In some cases, explosive volcanic activity or caldera collapse can create crater-like depressions, but in planetary geology the term usually refers to impact structures.

Impact craters vary widely in size. Simple craters are small and bowl-shaped with smooth walls, while larger craters develop complex features such as terraced walls, a central peak formed by the rebound of the floor, and sometimes a ring or multiple peaks. Surrounding many craters is an ejecta blanket, a outward-spread layer of material excavated during the impact. The morphology of a crater is influenced by the target body's gravity, rock/ice properties, and any post-formation modification by erosion or volcanic infilling.

Crater preservation differs across bodies. Airless or geologically inactive bodies such as the Moon and Mercury best preserve craters over long timescales, whereas atmospheres, weather, and tectonics on planets like Earth or Venus modify or erase features. Erosion, volcanism, and sedimentation progressively obscure older craters, complicating age estimates.

Dating and surface history often rely on crater counting and stratigraphy. The number, size distribution, and density of craters provide insights into relative ages and impact histories of planetary surfaces.

Notable examples include the Chicxulub crater in Yucatán, linked to the dinosaur extinction; Barringer (Meteor) Crater in Arizona; Lonar crater in India; and lunar craters such as Tycho and Copernicus, as well as Martian craters like Gale and Jezero.