Anatomy of an impact
The Orientale Basin is the youngest and best-preserved multi-ring basin on the Moon. Formed approximately 3.8 billion years ago, its structure resembles a massive bullseye. This feature consists of three main concentric rings of rock. The outermost ring is a mountain range called the Montes Cordillera, which defines the basin's main diameter of about 930 kilometers (580 miles). Inside the Cordillera are two more rings, the Outer and Inner Montes Rook. Unlike many other lunar basins, Orientale is not completely filled with dark volcanic basalt, leaving much of its complex structure visible to spacecraft.
The impact that created Orientale was immense. A body estimated to be 64 kilometers (40 miles) wide struck the Moon at a speed of around 15 km/s (9.3 mi/s). This collision was powerful enough to obliterate any trace of the initial, transient crater, which is estimated to have been between 320 and 460 kilometers across. Data from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission revealed the subsurface structure. The gravity maps show a mass concentration, or "mascon," in the center, which indicates that denser mantle material is closer to the surface because the crust was thinned by the impact. The impact excavated at least 816,000 cubic miles (3.4 million cubic kilometers) of the Moon's crust.