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.
By the Numbers
Estimated diameter of the Chicxulub impactor, which struck modern-day Mexico approximately 66 million years ago and contributed to the demise of the dinosaurs.
Estimated diameter of the asteroid that formed South Africa's Vredefort Crater, the largest confirmed crater on Earth's surface.
Newly estimated diameter of the asteroid that created the moon's Imbrium Basin.