The Apollo missions from NASA brought Moon Rock monsters back for scientists to study. We have learned a lot in the following decades, but there is still one permanent mystery. Many of those lunar samples show signs of exposure to strong magnetic fields that are comparable to the earth, but the moon does not have such a field today. So how did the lunar rocks get their magnetism?
Many attempts have been made to explain this anomaly. The newest comes from MIT scientists, who argue in a new article published in the magazine Science, promotes that a large asteroid impact briefly has increased the early weak magnetic field of the moon – and that this peak is recorded in some moon samples.
Proof from the turning of the observations of spacecraft, as well as results announced earlier this year from China's Chang'e 5 and Chang'e 6 missions, is largely consistent with the existence of at least a weak magnetic field on the early moon. But where did this field come from? These usually form in planetary bodies as a result of a dynamo, in which melted metals in the core begin to convecate thanks to slowly dissipating heat. The problem is that the small core of the early moon had a cloak that was not much cooler than the core, so there would have been no significant convection to produce a sufficiently strong dynamo.
Hypotheses have been proposed about how the moon could have developed a core dynamo. For example, an analysis of 2022 suggested that in the first billion years, when the moon was covered with melted rock, giant rocks were formed when the magma cooled and solidified. Denser minerals fell in the core, while lighter formed a crust.
Over time, the authors argued, crystallized a titanium layer just below the surface, and because it was poet than lighter minerals just below, that layer eventually broke into small blobs and dropped through the cloak (gravity overwhelms). The temperature difference between the cooler sinking rocks and the hot core generated convection, creating intermittent magnetic fields – which explains why some rocks that have magnetic signature and others don't.
Or perhaps there is no need for the presence of a dynamo-driven magnetic field. For example, the authors of a 2021 study thought that previous analyzes of lunar samples could have changed during the process. They re-examined samples of the 1972 Apollo 16 mission using Co2 Lasers to heat them, so that every change in the magnetic carriers is avoided. They concluded that any magnetic signatures in those samples can be explained by the impact of meteorites or comets that touch the moon.
