Lunar rocks hint at fleeting magnetism

摘要

A lunar magnetic field may have persisted for only a blip in geologic time, a new study suggests.Shortly after the moon formed about 4.5 billion years ago, it may have begun generating a magnetic field, a protective sheath that can deflect charged particles from the sun. Now, analyses of moon rocks suggest that any lunar magnetic field was gone by at least 4 billion years ago, researchers report August 4 in Science Advances.Magnetized lunar rocks brought back by Apollo astronauts decades ago were the first indication that the moon may have once had an internal dynamo-in which molten, iron-rich rock swirls inside the core of a celestial body, giving rise to a magnetic field (SN: 12/17/11, p. 17). But how long such a lunar dynamo may have lasted has been unclear.The moon's core is "really small," says geophysicist John Tarduno of the University of Rochester in New York. It's not clear how that core could have sustained a dynamo for long before cooling, he says.