The basin diameter has an estimated mean of 2,500 km (1,600 mi), the largest confirmed impact structure in the Solar System, almost the size of the Solar System's largest dwarf planet, Pluto, and much larger than the visible side's giant lunar maria, which are large impact craters.
By comparison, the Solar System's second largest confirmed impact crater is roughly 1,200 km in diameter, the Borealis Basin on Mars. The SPA basin is named after the prominent lunar craters Aitken, on its western edge, and the lunar south pole, which is near the center of the SPA basin.
Origin and structure
The SPA basin was created by a massive impact during the Imbrian epoch. Because of the intense bombardment experienced by the Moon in its early era, the crater has been partially masked by later lunar impacts. Subsequent lava flows and ejecta from other craters have covered many of the original details of the SPA basin, and it can best be seen from orbit or in oblique Earth-based telescopic observations.
Subsurface structure
While the SPA basin as a whole has been difficult to study, the Lunar Reconnaissance Orbiter (LRO) has detected large concentrations of a mineral known as anorthosite in two parts of the crater, which are interpreted to be exposed parts of the basin's crust. These detections show that the SPA basin excavated deep enough to expose mantle material, which, once molten beneath the lunar crust, crystallized to form anorthosite when it was thrust to the surface.
The SPA basin contains several major craters within it, including the following:
* Aitken (on the western edge)
* Amundsen (on the northeast edge)
* Boguslawsky (partially overlapped by Amundsen)
* De Gerlache
* Dorsa Burnet (inside Aitken)
* Fermi (partially overlapped by Amundsen)
* Gagarin (partially overlapped by Amundsen)
* Goldschmidt
* Hecataeus (partially overlapped by Gagarin)
* Leibnitz (partially overlapped by Amundsen)
* Oppenheimer
* Pauli
* Schrödinger (partially overlapped by Amundsen)
* Tombaugh (partially overlapped by Dorsa Burnet)
