Rocks returned by the Apollo missions have signatures that indicate a magnetic field stronger than Earth’s. The mystery has now been solved, with research indicating that the cause was strong, short-lived bursts of magnetism.
A new published in Nature Geoscience may have solved a long-standing mystery about the Moon’s magnetic past. The research suggests that powerful explosions of magnetism short-lived magnetic fields, rather than a permanent magnetic field, may explain the intriguing evidence found in lunar rocks collected during the Apollo missions.
For decades, scientists have been intrigued by samples brought back from the Moon in the late 1960s and early 1970s. Some of these rocks, dating back to about 3.5 billion years ago, contain magnetic signatures as or even stronger than Earth’s current magnetic field. This discovery has been difficult to explain because the Moon is much smaller than Earth and lacks the internal energy and core dynamics needed to sustain a powerful, long-lasting magnetic field.
Researchers at the University of Oxford now suggest that these strong signals may instead reflect brief episodes of intense magnetism triggered by ancient geological processes. According to the study, these explosions may have lasted just a few thousand years, an extremely short period compared to the Moon’s 4.5 billion years.
“Our new study suggests that the Apollo samples are biased towards extremely rare events that lasted a few thousand years,” said planetary geologist Claire Nichols, one of the study’s authors.
The team re-examined volcanic rocks formed from ancient lava flows on the surface, known as lunar mare basalts. By analyzing their composition and magnetization levels, the researchers identified a clear pattern: rocks with stronger magnetic signatures contained significantly higher levels of titanium.
Using computer simulations, scientists then explored how titanium-rich materials could be linked to magnetic activity. Their models suggest that the melting of titanium-rich rocks near the boundary between the Moon’s core and mantle could briefly increase heat flow from the core. This sudden increase in heat could strengthen the process that generates the magnetic field while simultaneously producing titanium-rich lava, which ended up forming the basalts of the lunar maria, explains .
The study also points to a possible sampling bias in the Apollo missions. Astronauts landed mainly in lunar maria regions, where titanium-rich lava flows were common. As a result, the collected rocks may disproportionately represent these rare magnetic events.
“If we were aliens exploring Earth and we landed here just six times, we could eliminate sampling bias similar,” said geoscientist Jon Wade, another author of the study.
Today, the Moon’s magnetic field is extremely weak and irregular, unlike Earth’s strong global field. Although the new hypothesis fits with current evidence, the researchers emphasize that more data is needed.
