Ohio State University planetary researchers have found the remains of ancient lunar impacts that may have helped create the surface feature usually called the "man in the moon".

Their study suggests that a large object hit the far side of the moon and sent a shock wave through the moon's core and all the way to the Earth-facing side. The crust recoiled -- and the moon bears the scars from that encounter even today.

The finding holds implications for lunar prospecting, and may solve a mystery about how past impacts on Earth affect it's geology today.

The early Apollo missions revealed that the moon isn't perfectly spherical. Its surface is warped in two spots; an earth-facing bulge on the near side is complemented by a large depression on the Moon's far side. Researchers have long wondered whether these surface features were caused by Earth's gravity tugging on the moon early in its existence, when its surface was still molten and malleable.

As per Laramie Potts and Ralph von Frese, a postdoctoral researcher and professor of geological sciences respectively at Ohio State , these features are instead remnants from ancient impacts.

Potts and von Frese came to this conclusion after they used gravity fluctuations measured by NASA's Clementine and Lunar Prospector satellites to map the moon's interior. They reported the results in a recent issue of the journal Physics of the Earth and Planetary Interiors.

They expected to see defects beneath the moon's crust that corresponded to craters on the surface. Old impacts, they thought, would have left marks only down to the mantle, the thick rocky layer between the moon's metallic core and its thin outer crust. And that's exactly what they saw, at first.

Potts pointed to a cross-sectional image of the moon that the researchers created using the Clementine data. On the far side of the moon, the crust looks as though it was depressed and then recoiled from a giant impact, he said. Beneath the depression, the mantle dips down as he and von Frese would expect it to do if it had absorbed a shock.

Evidence of the ancient catastrophe should have ended there. But some 700 miles directly below the point of impact, a piece of the mantle still juts into the moon's core today.

That was surprising enough. "People don't think of impacts as things that reach all the way to the planet's core," von Frese said.



Source: Ohio State University

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