The mystery of the Moon"s magnetic field solved by scientists for the first time

An international team of scientists has proposed an explanation for one of the long-standing mysteries of lunar geology: why some rocks brought to Earth by the Apollo missions indicate the existence of a powerful lunar magnetic field in the past. The study has been published in the journal Nature Geoscience.

Today, the Moon's magnetic field is extremely weak and only local in nature — unlike Earth's powerful global field. However, lunar rock samples approximately 3.5 billion years old tell a very different story: in the distant past, our satellite's magnetic field may have been incomparably stronger, at times even comparable to the modern Earth's field. This finding long puzzled researchers. The Moon is significantly smaller than Earth and simply does not possess the internal processes and energy reserves that sustain Earth's magnetic field.

Specialists from the University of Oxford put forward an unexpected hypothesis: the strong magnetic signals in lunar rocks are linked not to the prolonged existence of a powerful field, but to rare and short-lived bursts of magnetic activity.

The team reanalyzed so-called mare basalts — volcanic rocks formed in ancient lunar lava plains. They discovered a curious pattern: the most strongly magnetized samples contained elevated amounts of titanium.

Following this, the researchers conducted computer simulations to determine how the formation of such rocks could have affected the Moon's magnetic field. The results were striking: the melting of titanium-rich rocks near the core-mantle boundary could have dramatically increased the heat flux from the core. This, in turn, temporarily triggered or intensified the dynamo process — the mechanism that generates a magnetic field.

At the same time, these processes triggered eruptions of lava with a high titanium content. It was precisely these rocks that were collected by the Apollo mission astronauts.

According to geologist John Wade, the results obtained may have been skewed due to the limited set of samples. "If aliens came to Earth only six times and collected samples from just one type of terrain, they would have a similar data bias," he noted.

According to the new hypothesis, periods of a strong magnetic field on the Moon may have lasted only a few thousand years — a negligibly short time compared to the satellite's age.

The authors acknowledge that the model is based on a limited amount of data, since scientists have only a small number of lunar samples at their disposal. However, future missions could help test this hypothesis.

"We can now predict which types of rocks should preserve traces of different levels of the Moon's magnetic field," emphasized geophysicist Simon Stevenson. According to him, upcoming missions of the Artemis program will open up the opportunity to collect new samples and significantly advance our understanding of the history of the lunar magnetic field.