Researchers at the Massachusetts Institute of Technology and Rutgers University have found that the moon's ancient magnetic field was generated by a giant dynamo, similar to Earth's. Scientists came to this conclusion, having determined that the magnetism of the satellite lasted one billion years longer than previously thought. An article with the results of scientific work was published in the journal Science Advances.
Experts analyzed samples of lunar rocks collected during the Apollo 15 mission. It turned out that they formed 1-2.5 billion years ago in the presence of a relatively weak magnetic field, the induction of which was five microtesla (T). This is about 10 times weaker than the Earth's magnetic field, but 1000 times stronger than the fields in interplanetary space. However, 3-4 billion years ago, the magnetism of the Moon was two orders of magnitude stronger.
The discovery made it possible to identify the mechanisms that powered the magnetic dynamo. At first, the field was maintained by rotating the metal core. In the early stages of its existence, the Moon was close enough to the Earth for the latter's gravity to act on the bowels of the satellite and set them in motion. Over three billion years, however, the Moon moved away from the planet, which greatly reduced the latter's influence.
After that, another mechanism comes into play, which is characteristic of the Earth itself. The core of the satellite began to slowly cool down, giving rise to convection, in which warm layers of matter float up and cold ones descend. The streams of molten metal rocks were twisted by Coriolis forces, creating electric currents, which, in turn, generated a magnetic field. In principle, the mechanism resembles a dynamo launched in the opposite direction.
A dynamo is a device that generates electricity that uses a magnetic field and a coil that spins inside it. The energy of motion was thus converted into direct current.