Scientists at Brown University in the United States have proposed an explanation for the mystery of the lunar rocks, which store evidence of a powerful magnetic field, which in ancient times competed with the Earth’s in strength. The results of the study, published in the journal Nature Astronomy, demonstrate that the ancient moon could generate a field thanks to its own magnetic dynamo.
A magnetic dynamo is the effect of self-generation of a magnetic field due to the presence of a metal core (for large planets) rotating in a liquid molten mantle. The researchers showed that in the case of the Moon, a strong magnetic field could be generated by internal convection caused by the passage of giant rock formations through the moon’s mantle. Such a field is not able to exist for a long time, but it appears periodically and has a high intensity.
The Moon currently has no magnetic field. Core models show that Earth’s satellite is too small and lacks the convective force to create a constant strong field like Earth’s. This requires intense convective mixing due to the temperature difference between the core and the mantle. The early Moon had a mantle not much colder than the core, so convection was not strong.
As the magma ocean on the early Moon began to cool and solidify, rocks with the minerals olivine and pyroxene sank toward the core, while less dense minerals floated up to form the crust. The titanium-bearing rocks solidified later, but were found to be denser than the minerals underneath. Over time, the titanium formations sank into the less dense mantle rock. When each of the clumps up to 60 kilometers in size reached the core, they gave impetus to the Moon’s dynamo, increasing convection.