For 'Man in the Moon,' a bump in the head

The ''Man in the Moon" mentioned in Charles Dickens's ''David Copperfield" has always been the object of human dreams. Its shape and size, its core and light have always been a mystery.

Ohio State University planetary investigators now think they know what caused the earth-facing bulge on the moon.

Reporting in a recent issue of the journal Physics of the Earth and Planetary Interiors, they suggest that a large object hit the moon's far side sending a shock wave through its core to the Earth-facing side. As the crust recoiled, it produced the scars dubbed the ''Man in the Moon."

Laramie Potts, a postdoctoral student, and Ralph von Frese, a professor of geological sciences at Ohio State, based their results from gravity fluctuations measured by NASA.

The ''Man in the Moon" is a collection of dark plains on the earth-facing side of the moon, where magma from the moon's mantle once flowed onto the surface and flooded lunar craters. The moon has since cooled, von Frese explained, but the dark plains are a remnant of that early active time -- ''a frozen magma ocean."

Chris Matzner, assistant professor at the University Of Toronto department of astronomy and astrophysics, said that impacts such as the one that caused the shock wave ''were common in the early solar system and represent the end of the planet-building process, as the last pieces were collected onto larger bodies or cast into space by the giant planets. The moon itself probably formed in a major collision between the proto-earth and another proto-planet."

Potts and von Frese are now looking into gravitational anomalies at the site of the Chicxulub Crater buried underneath Mexico's Yucatan Peninsula. A giant asteroid struck the spot some 65 million years ago and is believed to have set off the environmental chain reaction that may have killed the dinosaurs.