cratering

Cratering is the process by which impact events create depressions, or craters, on solid planetary surfaces. These features form when a solid body such as a meteoroid or comet collides at hypervelocity with a surface, producing shock waves, ejecta, and a circular or near-circular basin. On bodies with thin or no atmospheres, craters tend to be well preserved; on worlds with thick atmospheres, erosion, weathering, and tectonics can modify or erase craters over time.

The formation of a crater proceeds in stages. An impact generates a shock pulse that creates a transient crater, larger than the incoming body. Material is excavated and ejected in an outward blast, forming an ejecta blanket. The transient crater may then undergo modification: walls slump, the floor may relax, and in larger craters a central peak, a peak ring, or terraced rims can develop. Craters are broadly categorized as simple or complex; simple craters are bowl-shaped with smooth rims, while complex craters are larger and exhibit central peaks, terraced walls, and flatter floors. The transition diameter between simple and complex craters depends on gravity and the strength of the target rock.

Crater morphology includes rims, ejecta patterns, central peaks or peak rings, terraces, and, for very large basins, multiple rings. Ejecta rays and secondary craters may accompany fresh impacts. Crater counts are a fundamental tool in planetary geology, used to estimate surface ages and to interpret resurfacing histories, although secondary craters and erosion can complicate interpretations.

Notable examples include Meteor Crater in the United States and the Chicxulub crater in Mexico, both contributing to the understanding of impact processes and their ecological and geological consequences. Cratering remains a central concept in the study of planetary surfaces across the solar system.