Impact Basin

Mare Orientale. Image Source: Lunar Orbiter Images

Very large impact structure, typically many tens to hundreds of kilometers in diameter, consisting of one or more concentric rings of peaks. Impact basins are proportionally shallower relative to their diameter compared with simple and complex craters. Basins are subdivided into central peak, peak ring and multi-ring basins. Mare Orientale on the Moon (photograph) is perhaps the archetypal multi-ring impact basin. Orientale contains four concentric rings with the inner ring bordering the mare basalt fill. The outer ring, known as the Cordillera Mountains, has a diameter of 920 km. The main two internal rings form the Rook and Inner Rook Mountains. The mountains in the rings rise up to 2–5 km above the surrounding plain.