Multi-ringed basin

More common peak ring craters have: (1) a peak-ring, i.e., a crater rim, which is generally circular, and; (2) a mountainous region which surrounds the center of the crater basin. In contrast, a multi-ringed basin has multiple peak-rings displaying as further concentric circles. In extremely large collisions, the rebound of the surface after impact 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 adjacent rings, the ratio of the diameters approximates :1 ≈ 1.41 to 1. ==Formation==

, on Earth's Moon Multi-ring basins are some of the largest, oldest, rarest and least understood of impact craters. There are various hypotheses to explain the formation of multi-ringed basins, including harmonic oscillations as is observed when a pebble is dropped on calm water, and brittle terrace faulting; however, there is currently no consensus. In 2016, research brought forward new hypotheses about the formation of the lunar mare called Mare Orientale on Earth's Moon. Prior to this research, the most accepted explanation was the 'slumping/megaterrace' model, which suggested that a deep bowl-shaped basin forms during the impact and that subsidence along faults later produces the ring formations, though this hypothesis was always considered problematic because of evidence that the rings were produced simultaneously with the impact that formed the basin. The new research produced a model confirming instantaneous formation of all rings, a mechanism in which ductile subsurface rocks flowed towards the center of the basin as the crust rebounded, causing concentric cracking and slippage that formed the outer rings, and that the unstable central peak collapsing formed the inner ring. ==Examples==

• Mare Orientale on Earth's Moon is a multi-ringed basin created by an impactor perhaps in diameter traveling at , or about • 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. ==See also==