Moon with a once strong magnetic field? Mystery from Apollo program solved
It is generally considered certain that the Moon did not have a strong magnetic field in its early days. However, samples contradicted this. Now it is clear why.
Harrison Schmitt (Apollo 17) next to a large rock on the moon
(Image: NASA)
Even though the soil samples from the Apollo missions suggested the opposite, the Moon never had a strong magnetic field for a long time after its formation. A research group from the University of Oxford has found this out, thus providing the answer to an old question about our Earth's satellite. It had ignited on the rock that the astronauts of the US lunar missions brought back. All these samples indicated that the Moon was once surrounded by a strong magnetic field. This should have persisted for hundreds of millions of years given the amount of samples – unless the samples were much less representative than assumed. But that is precisely the case.
No clear victory for one side
Despite the strong magnetism of the rock samples, many researchers were sure that the Moon had no or only a weak magnetic field in its early history. However, the findings could not explain this. This is because they are extreme exceptions, believes the research group led by study director Claire Nichols. According to them, the rocks obtained their extremely strong magnetism during periods of only a few thousand years in which the Moon had an extremely strong magnetic field – even stronger than that of the Earth. But precisely in that rock at the landing sites of the Apollo missions, the stones were strongly overrepresented for geological reasons. This should be confirmed by future manned missions.
For their work, the group examined the composition of a specific basalt from the Moon, from which the rock samples originated. Each piece with particularly strong magnetism also had a particularly high proportion of titanium, and that was the solution to the puzzle. The group believes that the episodes with a strong magnetic field are related to the melting of material with a high titanium content in the interior of the early Moon. This then also deposited the strongly magnetized rock with a lot of titanium in the basalt. Where this basalt forms the surface, however, ideal conditions for manned lunar landings would also prevail. That is why so many comparatively many were found.
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Co-author Jon Wade believes that similar mistakes would happen if aliens were to explore the Earth only during six short visits to shallow locations. If the US astronauts had landed in different locations, the debate about a possibly much stronger magnetic field would never have arisen. But then they might not have found out that there were indeed episodes with a strong magnetic field, only that they were very short on geological scales. Now it is possible to predict exactly which rock samples are likely to have preserved these episodes. This can be checked during the manned Artemis missions, and the history of the Moon can be understood even better. The research group's work has been published in Nature Geoscience.
(mho)
