The Moon today has no inherent magnetism, making the discovery of magnetized rocks on the surface a big problem. Where did they come from? Researchers from the Massachusetts Institute of Technology (MIT) have a bold suggestion: the Moon used to have a weak magnetic field, and then something made it spike. That something was an incredible impact.
Their simulated scenario is as follows. The Earth’s magnetic field is generated deep in its interior by the molten core spinning around. This is the geodynamo. The Moon, too, might have had a similar dynamo, but 50 times weaker, given how much smaller it is compared to Earth.
An impact similar to the one that created the Imbrium basin, the sea of showers on the nearside of the Moon, would have vaporized enough surface material to create a cloud of plasma. The plasma would interact with the weak magnetic fields, creating a spike in magnetism that left an impression in the rocks.
“There are large parts of lunar magnetism that are still unexplained,” lead author Isaac Narrett, a graduate student in the MIT Department of Earth, Atmospheric and Planetary Sciences, said in a statement. “But the majority of the strong magnetic fields that are measured by orbiting spacecraft can be explained by this process – especially on the far side of the moon.”
Rock samples collected by the Apollo astronauts and measurements from orbit have shown this unexpected strength in magnetism. It had been suggested that maybe it was the solar magnetic field and an impact that created the spike, but the simulations don’t seem to support this hypothesis.
The team thinks that the combination of the weak lunar dynamo and the impact plasma shockwave should be enough to explain the high magnetization of some surface rocks. Fortunately, this hypothesis is testable.
There should be rocks showing both impact shock and high magnetism located near the lunar South Pole on the far side of the Moon. This is near the sites that will be visited by the Artemis program when humans go back to the Moon. The answer to this mystery might be just a few years away.
“For several decades, there’s been sort of a conundrum over the moon’s magnetism — is it from impacts or is it from a dynamo?” added co-author Rona Oran, also from MIT. “And here we’re saying, it’s a little bit of both. And it’s a testable hypothesis, which is nice.”
The study is published in the journal Science Advances.
Source Link: The Moon’s Mysterious Magnetic Rocks Might Have A Cataclysmic Explanation