March 17, 1999
Web posted at: 3:41 p.m. EST (2041 GMT)

(CNN) -- NASA says data from its Lunar Prospector spacecraft support a theory that the bulk of the Moon was ripped away from the Earth.

Based on information first gathered during the Apollo era, scientists suggested that the Moon formed when a Mars-sized body hit the Earth during its earliest history.

"This impact occurred after the Earth's iron core had formed, ejecting rocky, iron-poor material from the outer shell into orbit," said Dr. Alan Binder, principal investigator for the Lunar Prospector mission. "It was this material that collected to form the Moon."

Similarities in the mineral composition of the Earth and the Moon indicate that they share a common origin. However, if they had simply formed from the same cloud of rocks and dust, the moon would have a core similar in proportion to the Earth's.

The new Lunar Prospector findings, presented in a series of papers at a scientific meeting in Houston, show that the lunar core contains less than 4 percent of the moon's total mass, a very small ratio compared with the Earth, which has about 30 percent of its mass in its iron core.

"Further analysis of Lunar Prospector data to refine the exact size of the lunar core and the amounts of elements like gold, platinum, and iridium in lunar rocks -- all of which are concentrated with metallic iron -- is required," Binder added. "This will do much to pin down for good if the 'giant impact' model of the formation of the Moon is correct, or if the moon formed in a different manner."

Binder said that the $63 million mission, which is being directed by NASA's Ames Research Center in California, could provide the data necessary to reach a firmer conclusion as the small Prospector spacecraft continues to sweep the Moon in a very tight orbit, mapping and gathering information.

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