NASA Apollo missions brought back samples of lunar rock so that scientists are studying. We have learned a lot during the decades that followed, but a lasting mystery remains. Many of these lunar samples show signs of exposure to magnetic fields strong comparable to that of the earth, but the moon does not have such a field today. So how did the Roches de la Moon get their magnetism?
There have been many attempts to explain this anomaly. The last comes from MIT scientists, who support in a new article published in the journal Science argues that a great asteroid impact briefly stimulated the first low magnetic field of the moon – and that this point is what is recorded in certain lunar samples.
The evidence gleaned from observations in orbit of spaceships, as well as the results announced earlier this year of the China China 5 and Chang’e 6 missions, are largely consistent with the existence of at least a weak magnetic field at the beginning of the Moon. But where does this field come from? These generally form in planetary bodies following a dynamo, in which the molten metals in the nucleus begin to convete thanks to the slow dissipation of heat. The problem is that the small nucleus of the beginning of the moon had a coat which was not much cooler than its nucleus, there would therefore have been no significant convection to produce a sufficiently strong dynamo.
There were hypotheses proposed on the way in which the moon could have developed a central dynamo. For example, an analysis in 2022 suggested that in the first billion years, when the moon was covered with melted rock, giant rocks were formed like the cooled and solidified magma. Dense minerals flow to the heart while lighter minerals formed a crust.
Over time, the authors have argued, a layer of titanium crystallized just below the surface, and because it was denser than the lighter minerals just below, this layer finally broke into small blobs and sank into the coat (gravitational overtake). The temperature difference between the rocks to be colder and the convection generated by the warmer nucleus, creating strong magnetic fields by intermittentness, which explains why certain rocks have this magnetic signature and others not.
Or maybe there is no need for the presence of a dynamo magnetic field. For example, the authors of a 2021 study thought that previous analyzes of lunar samples may have been modified during the process. They re -examined the samples of the 1972 Apollo 16 mission using CO2 Lasers to heat them, thus avoiding any alteration of magnetic carriers. They concluded that all the magnetic signatures of these samples could be explained by the impact of meteorites or comets hitting the moon.
