Multi-ringed basin



A multi-ringed basin (also a multi-ring impact basin) is not a simple bowl-shaped crater, or a peak ring crater, but one containing multiple concentric topographic rings; a multi-ringed basin could be described as a massive impact crater, surrounded by circular chains of mountains resembling rings on a bull's-eye. A multi-ringed basin may have an area of many thousands of square kilometres.

An impact crater of diameter bigger than about 180 mi is referred to as a basin.

Structure
In adjacent rings, the ratio of the diameters approximates √2:1 ≈ 1.41 to 1.

Formation


To start, a peak ring crater has


 * one peak-ring, i.e., a crater rim, which is generally circular, and
 * a mountainous region which surrounds the basin center.

A multi-ringed basin has an important difference, which is multiple peak-rings.

In extremely large collisions, following the impact the rebound of the surface can obliterate any trace of the initial impact point. Usually, a peak ring crater has a high structure with a terrace and has slump structures inside of it. In 2016, research brought forward new theories about the formation of the lunar mare called Mare Orientale on Earth's Moon.

Multi-ring basins are some of the largest, oldest, rarest and least understood of impact craters. There are various theories to explain the formation of multi-ringed basins, however there is currently no consensus.

Examples

 * Mare Orientale on Earth's Moon is a multi-ringed basin created by an impactor perhaps 40 mi in diameter traveling at 9 mi/s, or about 32,400 mph
 * Anubis on Ganymede, the largest moon of Jupiter
 * Valhalla on Callisto, a moon of Jupiter
 * Evander on Dione, a moon of Saturn
 * Caloris Basin, surrounded by Caloris Montes, on Mercury
 * Burney on Pluto, a dwarf planet in the Kuiper belt

Chicxulub crater in Mexico has a sufficient area to have been a multi-ringed basin,