How the Man in the Moon Got His Enormous Right Eye

A new estimate for the impactor that created the Imbrium Basin puts the rock at the size of New Jersey

A map showing the location of Mare Imbrium.

WIKIPEDIA, CC BY-SA 3.0

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The Man in the Moon has an enormous right eye: the crater known as the Imbrium Basin, which is 1,200 kilometers across. The cavity was created roughly four billion years ago during a collision with something big. How big? “About the size of New Jersey,” says Peter H. Schultz, a planetary geoscientist at Brown University who published a new estimate of the object's heft in Nature. To figure out the impactor's dimensions, Schultz and his colleague David A. Crawford turned to the surface features of the moon—in particular the grooves that emanate from the collision site, which were carved by flying chunks of the impactor. The researchers usedmeasurements of those grooves and laboratory experiments to calculate the rock's size, speed and impact angle. The updated magnitude is 10 times more massive than previous estimates, which were based on computer simulations, and is a reminder of how little we know about the early solar system, Schultz says.

Credit: AMANDA MONTAÑEZ; Source: "Origin and Implications of Non-Radial Imbrium Sculpture on the Moon," by Peter H. Schultz and David A. Crawford, in Nature, Vol. 535; July 21, 2016 (Imbrium Basin outline and diameter); "The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary," by Peter Schultz et al., in Science, Vol. 327; March 5, 2010 (Chicxulub impactor diameter); "Constraints on the Size of the Vredefort Impact Crater from Numerical Modeling," by E. P. Turtle and E. Pierazzo, in *Meteoritics & Planetary Science*, Vol. 33, No. 3; May 1998 (Vredefort Crater asteroid diameter)

By the Numbers

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10 kilometers

Estimated diameter of the Chicxulub impactor, which struck modern-day Mexico approximately 66 million years ago and contributed to the demise of the dinosaurs.

10 kilometers

Estimated diameter of the asteroid that formed South Africa's Vredefort Crater, the largest confirmed crater on Earth's surface.

250 kilometers

Newly estimated diameter of the asteroid that created the moon's Imbrium Basin.

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