Heavily cratered surfaces emphasize the important geologic role of impacts on almost all planetary bodies. Large impacts (referred to as “hypervelocity” to indicate velocities of tens of kilometers per second) produce micro-, meso-, and macroscale deformations that can influence the structures of planetary crusts. Crater morphologies are described as simple, complex, and multi-ring, and correlate with crater size and inversely with gravity of the target body. Crater formation is envisioned in three stages: contact/compression, excavation, and modification, each characterized by different processes and geologic features. Shock metamorphism has affected all Solar System bodies, producing breccias containing planar deformation features, high-pressure polymorphs, and melts. Craters provide the basis for planetary stratigraphy and chronology. Massive impacts on the Earth have potential consequences for damaging the planetary ecosystem and biosphere.
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