Did the Moon once have Its own magnetic field?

For decades, the history of the Moon's magnetic field has been a point of contention. The central question is whether the Moon once possessed an internal dynamo-a molten core generating a global magnetic field-or if its magnetism is merely a remnant of debris ejected from Earth during ancient collisions.

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Partial lunar eclipse

Researchers from the Chinese Academy of Sciences have examined lunar regolith from the far side to find a physical record of these ancient processes. Using electron holography to create 3D microscopic images, the team analyzed impact glass-material forged by the instant melting of rock during meteorite strikes.

Within this glass matrix, the physicists detected nanoscale particles of gamma-iron. Normally, this cubic atomic structure of iron is unstable, existing only at extreme temperatures before reverting to standard iron as it cools.

The researchers found that the specific conditions of a meteorite impact-intense pressure combined with carbon impurities and near-instantaneous cooling-trapped the gamma-iron within the glass, freezing it in place for billions of years.

The Magnetic Archive

The team focused on the magnetic properties of these particles. They observed that the larger gamma-iron crystals exhibit a stable single-vortex magnetic state, where internal magnetic fields are twisted into a spiral.

This specific configuration acts as a shield, allowing the crystals to retain their magnetization across eons without being erased by external interference. Professor Du Haifeng and his colleagues suggest that these structures serve as natural archives of ancient magnetic records.

If these particles recorded a consistent global field, they provide evidence for the lunar dynamo effect. However, the interpretation remains a subject of debate: some scientists argue these samples did not originate on the Moon, but were instead transported from Earth via asteroid impacts, meaning the magnetic signals they carry are terrestrial, not lunar.