Four Billion Years Ago, the Moon May Have Taken a Punch from a Protoplanet

Mare Imbrium. Image: NASA/Lunar Reconnaissance Orbiter
Mare Imbrium, the lunar impact crater that forms the right eye of the pareidolic “Man in the Moon,” may have been formed by a protoplanet-sized object colliding with the young Moon, according to a study published Wednesday in Nature.

By Becky Ferreira | MOTHERBOARD

Authored by Pete Schultz, professor of planetary sciences at Brown University, and David Crawford of Sandia National Laboratories, the new research estimates that an object measuring about 275 kilometers (170 miles) in diameter impacted the lunar surface about 3.8 billion years ago, during a period known as the Late Heavy Bombardment, when planetary collisions were much more common than they are today.

This new size estimate is much larger than previous calculations of the Imbrium impactor’s dimensions, challenging prevailing theories about this chaotic era in the history of the solar system.

“We find that the Imbrium basin was formed by an object at least three times larger in diameter, or 30 times more massive [than previous estimates],” Schultz told me. “This has implications for the sizes of even larger impact basins on other planets, not to mention the Earth where the evidence has been largely erased” by geological processes like erosion and plate tectonics.

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