So how did γ-Fe survive on the lunar surface? The researchers proposed that the violent and unusual conditions of meteorite impacts played a key role. Several factors could stabilize the structure: small amounts of carbon and other elements mixed into the iron, the rapid cooling of molten material splashed out during an impact, and the protective cage of surrounding glass that shields the particles from later disturbance.

How the team found it

To examine the samples, the researchers used focused ion beam preparation, a technique that carves out ultrathin slices of material, along with transmission electron microscopy and chemical analysis. These methods revealed numerous nanoscale iron particles scattered throughout the glassy material.

Closer inspection showed something unexpected: in the two impact-glass samples studied, γ-Fe was actually the dominant form of iron.

The team then turned to a technique called off-axis electron holography, which maps magnetic fields at the nanoscale, to probe the magnetic behavior of individual γ-Fe nanoparticles.

The results were striking. Relatively large γ-Fe particles formed a stable single-vortex magnetic state — a swirling arrangement of magnetization that, unlike a simple bar-magnet configuration, resists being scrambled. The particles also retained a consistent magnetic response when the researchers exposed them to an external magnetic field.

That stability is crucial. A mineral that reliably holds its magnetic signature can preserve a record of the field conditions present when it formed — in this case, potentially the magnetic environment on the Moon at the moment of an ancient impact.

A new window on lunar history

The discovery broadens the known variety of magnetic minerals in lunar samples. Because γ-Fe and α-Fe form under different conditions and behave differently in magnetic terms, each could record information from separate stages of lunar impact events. Together, they may offer a more detailed timeline of the Moon's magnetic past than either mineral alone.

The researchers caution that the work is still early. Future studies will need to determine exactly how much these minerals can reveal about the Moon's ancient magnetic field and how that field evolved over time.

The study also examined only two impact-glass samples, so it remains to be seen how widespread γ-Fe is across the Chang'e-6 collection and other lunar materials.

Still, the identification of a previously unrecognized magnetic recorder in natural Moon samples gives planetary scientists a fresh tool. Each nanoscale iron grain encased in glass is, in effect, a tiny data archive — one that waited decades for a mission capable of retrieving it and microscopes capable of reading it.