Earth’s tug or asteroid impacts may have generated the ancient lunar magnetic field
External forces beating up the ancient moon may explain how it once maintained a magnetic field for more than 400 million years — longer than scientists had thought such a small object could be magnetized.
Either wobbly rotation produced by Earth’s gravitational tug or asteroids smacking into the lunar surface may have triggered enough turbulence in the moon’s molten core to generate a long-lasting magnetic field, report two teams of scientists in the Nov. 10 Nature.
“This has been a very fundamental question for 40 years,” says study author Christina Dwyer, a graduate student at the University of California, Santa Cruz. Though absent today, this ancient field is recorded in rocks retrieved from the moon’s surface and in magnetized patches of crust spied by orbiting spacecraft. “The moon was magnetized. We don’t know how.”