Magnets are pretty common here on Earth, and magnetism in general is a constant thanks to the geomagnetic field. On the moon, however, things are different. The moon does not have a magnetic field, though astronomers believe it did at some point in the past.

What is weird, however, is that when scanning the moon from orbit or looking at moon rocks collected in the past, there is magnetism present where it is not expected. Scientists have been trying to figure out what could have caused these magnetic rocks so that they can better understand the history of the moon and its future.

Researchers at the Massachusetts Institute of Technology (MIT) think they have the answer. In a study published in Science Advances, they propose that the magnetism was created by a cataclysmic impact, likely from an asteroid.

In the moon’s past, it likely had a similar geodynamo creating a magnetic field that is a lot weaker than Earth’s, because of its size. If an impact occurred on the moon that was significantly large, it would have vaporized a large amount of the surface material to create plasma. This plasma would then interact with the moon’s weak magnetic fields, creating a spike.

The spike would have magnetized these rocks before calming down and leaving the moon to eventually solidify completely, eliminating its own magnetic field.

In a statement on the study, Isaac Narrett, a graduate student in the MIT Department of Earth, Atmospheric and Planetary Sciences, said:

“There are large parts of lunar magnetism that are still unexplained. 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.”

So, this large impact event would explain much of the current magnetism that researchers don’t understand. Their simulations support their hypothesis much better than previous hypotheses that say it could have been a solar magnetic field with an impact that created the spike.

Another advantage that the theory from the MIT researchers has is that it is much more testable. If they are right, there should be rocks that show the high magnetism as well as the impact shock somewhere near the South Pole of the moon. The Artemis program is already planning to send humans to this part of the moon, so collecting some rocks for testing won’t be difficult.

So, we might get firm answers to this old question within the next decade.

If you thought that was interesting, you might like to read about a second giant hole has opened up on the sun’s surface. Here’s what it means.