any of a class of geologic features that have been observed on various planets and satellites in the solar system. A multiringed basin typically resembles a bull's-eye and may cover an area of many thousands of square kilometres. The outer rings of the basins are clifflike scarps that face inward. Because of the gradation of smaller examples into ordinary craters and because of the apparent ejecta-blanket patterns of radially striated terrain surrounding them, multiringed basins are believed to be giant impact features. The rings probably were formed as part of the crater-forming process during impact, although some hypotheses suggest that they were formed, or were enhanced, by post-impact collapse. Transitional structures between bowl-shaped craters and multiringed basins include craters with central peaks and larger craters with central rings of peaks. Partly owing to the unfortunate placement, relative to the Moon's visible face, of the most prominent lunar examples, multiringed basins were only slowly recognized as coherent geologic features by geologists and astronomers.