Scientists have shown that the lunar magnetosphere lasted only about 500 million years, and the later magnetic rocks, which are found on the satellite, appeared without its participation in the plasma of meteorite impacts.
The moon was formed about 4.5 billion years ago, from matter ejected into orbit after the collision of the Earth with a massive celestial body. At first, the satellite was molten and had its own magnetic field, traces of which can be found today in local minerals. Its magnetosphere was much weaker than Earth's and dissipated when the iron-bearing rocks in the interior of the moon cooled. This process took place faster than previously thought, so that the magnetic field disappeared no later than four billion years ago. These are the conclusions reached by the authors of a new article published in the journal Science Advances.
Indeed, the Moon's magnetosphere could not last long. The satellite's iron-containing core is very small and cooled down quickly, losing the ability to generate a magnetic field using the dynamo mechanism. However, until now, the timing of its existence remained unclear. Therefore, the authors of the new work analyzed samples of lunar minerals dated at different times.
In rocks aged from 3, 2 to 3, 9 billion years, traces of magnetism were no longer found. Unexpected magnetism was demonstrated by a sample of volcanic glass formed by a meteorite falling just about two million years ago. However, John Tarduno and his colleagues at the University of Rochester showed that matter could acquire magnetic properties due to temporal fields that briefly appear in the collision plasma.
According to scientists, the appearance of such extremely young magnetized samples may give an incorrect determination of the age of the magnetosphere. However, by themselves, they cannot testify to its existence in such a recent past of the Moon. As a result, Tarduno and his co-authors concluded that the real history of the magnetic field in our satellite lasted only a few hundred million years, and about four billion years ago it had already disappeared.