CORVALLIS, Ore., April 12 (UPI) -- New studies indicate many of the lunar rocks returned by the Apollo space missions show signs of melting about 3.9 billion years ago.
Scientists say the analysis suggests the moon -- and its nearby neighbor, Earth -- were bombarded by a series of large meteorites at that time.
The idea that meteorites have hammered the moon's surface isn't new. The lunar surface is pock-marked with large craters produced by the impact of asteroids and meteorites, said Robert Duncan, a professor and associate dean in the College of Oceanic and Atmospheric Sciences at Oregon State University.
But the narrow range of the impact dates suggests a large spike in meteorite activity occurred during a 100-million year interval -- possibly the result of collisions in the asteroid belt with comets arriving from just beyond our solar system.
Results of the study are being published in Geochimica et Cosmochimica Acta, the journal of The Geochemical Society and The Meteoritical Society. The study was funded by NASA.