The Explosive History of Orientale Basin

Orientale Basin and its multiple rings formed about 3.8 billion years ago, at the end of the conjectured Late Heavy Bombardment. None of the rings are the initial crater itself, which would fall somewhere between the sizes of the two innermost rings. The initial crater would have been obliterated by rebounding of the surface that occurred in the impact, an event that demonstrates the violence of the tremendous impacts that form basins and illustrates how basin rings might form.

A photo of the Moon's Orientale impact basin. It is colored in to show free-air gravity differentiations. There are yellow areas (average gravity), green and blue areas (below average) and red areas (above average).
This computer model of Orientale basin shows the terrain in high relief, as it would be just after sunrise. Gravity anomalies measured by the Gravity Recovery and Interior Laboratory (GRAIL) mission are depicted in different colors on the right side of the image. Red indicates areas of higher gravity, or excess mass, and blue indicates lower gravity or areas of mass deficits. The GRAIL data reveals the structure of the basin beneath the surface. The red in the center of the basin, for example, shows that the crust is particularly thin there, and that denser mantle material is closer to the surface.
NASA's Scientific Visualization Studio

One study theorizes that the basin’s three concentric rings ― the largest three times the width of Massachusetts ― formed when around 816,000 cubic miles (3,401,236 cubic km) of ejecta, or around 135 times the combined volume of the Great Lakes, was blasted into the sky by a 40-mile-wide (64 km) impactor and came crashing back to the Moon’s surface.
The material would have risen like a tidal wave around 62 miles (100 km) above the surface ― more than 11 times the height of Mount Everest ― before collapsing, creating faults so deep they reached through the crust to the mantle. The material then sloshed back and forth for two hours, eventually settling into the two outer rings. Finally, the inner ring would have formed from the collapse of a central peak that was too massive to be stable.

Detailed view of lunar surface with many craters. In the center, a large crater has a dark, patchy floor.
The Orientale basin is the youngest of the large lunar basins. The distinct outer ring is about 590 miles (950 km) from east-to-west.
NASA/GSFC/Arizona State University

Writer: Tracy Vogel; Science Advisors: Daniel P. Moriarty (University of Maryland at College Park), Natalie M. Curran (NASA's Goddard Space Flight Center)

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