Washington: A team of scientists at the University of California has shed light on the presence of magnetized rocks on the surface of the moon that has no global magnetic field, which has been a mystery since the days of the Apollo program.
They have proposed a novel mechanism that could have generated a magnetic field on the moon early in its history.
Christina Dwyer, a graduate student in Earth and planetary sciences at the University of California, Santa Cruz and her co-authors describe how an ancient lunar dynamo could have arisen from stirring of the moon’s liquid core driven by the motion of the solid mantle above it.
“This is a very different way of powering a dynamo that involves physical stirring, like stirring a bowl with a giant spoon,” Dwyer said.
At close distances, tidal interactions between the Earth and the moon caused the moon’s mantle to rotate slightly differently than the core. This differential motion of the mantle relative to the core stirred the liquid core, creating fluid motions that, in theory, could give rise to a magnetic dynamo.
“The moon wobbles a bit as it spins—that’s called precession--but the core is liquid, and it doesn’t do exactly the same precession. So the mantle is moving back and forth across the core, and that stirs up the core,” explained planetary scientists Francis Nimmo at UC Santa Cruz.
The researchers found that a lunar dynamo could have operated in this way for at least a billion years.
Eventually, however, it would have stopped working, as the moon got farther away from the Earth.
“The further out the moon moves, the slower the stirring, and at a certain point the lunar dynamo shuts off,” Dwyer said.
The study appeared in the Nov. 10 issue of Nature.