The Moon Had Liquid Metal Core

The debate on what the lunar core currently looks like is still pretty intense at the moment, although a growing set of arguments seems to attract more and more approval. According to a new paper by scientists at the Massachusetts Institute of Technology, who studied several rock samples brought back from the Moon during the Apollo 17 mission, Earth's natural satellite had, at one point in its history, a liquid metal core, which generated a certain amount of magnetic fields on the body. Over time, however, the fields gradually disappeared, as the core most likely solidified.

Other theories argue that the rocks brought back from the Moon are magnetized because of repeated impacts with asteroids, which melt the surface, and also generate a magnetic field for a short period of time. Repeated impacts would have caused reoccurring shock waves that could have had the strength to magnetize the rocks. But the MIT study shows that their force wasn't nearly enough for this job, and that the rocks brought back showed no signs of alteration from impacts, which was to be expected if the previous theory was to hold.

"This rock was heated up only twice in its history. When rocks cool, they lock in the magnetic fields around them. We found two magnetized events in its history. Impacts that create (magnetic) fields are transient. They don't last long, not more than a day," says Ian Garrick-Bethell, the MIT graduate student who was also the lead author of the new study, published in a recent issue of the journal Science.

According to the scientist, the rock he and colleagues analyzed, estimated to be around 4.2 billion years old, showed signs that the satellite's core cooled down twice over time – the first time for several millions of years, and the second time for only thousands. "It's possible that the moon formed a core. We don't really have enough data to say with any certainty," says Southwest Research Institute planetary scientist Bill Bottke, from Boulder, Colorado.

None of the two magnetization events happened quickly, the researchers say, which essentially rules asteroids and repeated impacts out of the question. The only possibility would be that small asteroids kept pounding on the Moon's surface for thousands and perhaps millions of years, which is highly improbable to have happened.