crater

A circular feature on the surface of a planetary body. The word literally means "cup", and craters are typically shaped like a shallow cup, lower in the centre than the surrounding terrain, with raised walls. The vast majority of craters observed on planets and their satellites are now known to have resulted from the impact of meteorites and the word is often treated as synonymous with "impact crater". However, volcanic craters (calderas) also occur, on Mars, for example. Craters range in size from the smallest discernible to hundreds of kilometres across. The largest impact features are often termed basins. The detailed forms of craters depend on many factors, including the composition of the planetary surface, the speed, mass and direction of the impacting body and subsequent weathering or geological activity. They may contain a central peak, or a depression.