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A major new study published in Nature Geoscience has finally resolved a long-standing scientific debate: the Moon did not maintain a strong global magnetic field for hundreds of millions of years in its early history. Instead, it experienced rare, short-lived bursts of intense magnetism lasting only a few thousand years each — and the confusion arose because Apollo astronauts landed in exactly the wrong places to see the Moon’s typical weak field.

Lead author Claire Nichols of the University of Oxford explained in a press release: “Our new study suggests that the Apollo samples are biased to extremely rare events that lasted a few thousand years — but up to now, these have been interpreted as representing 0.5 billion years of lunar history. It now seems that a sampling bias prevented us from realising how short and rare these strong magnetism events were.”

The research team analyzed mare basalts — dark volcanic rocks formed from ancient lava flows — and found a striking pattern: every sample recording a strong magnetic field also contained high levels of titanium (above ~6%). Low-titanium samples consistently showed only weak magnetism. This correlation points to temporary supercharging of the lunar dynamo during specific geological events, rather than a long-lived powerful field.

The Moon’s small core — just one-seventh of its radius — has long puzzled researchers, as it seemed too tiny to sustain a strong dynamo like Earth’s for extended periods. The new findings reconcile this: intense but brief pulses, likely triggered by internal processes, produced the strong signals preserved in titanium-rich rocks.

The bias stems from Apollo landing sites. All six missions touched down in relatively flat, safe lunar mare regions — vast plains of ancient lava — which happen to be rich in titanium-heavy basalts. These areas preserved evidence of rare magnetic surges, while most of the Moon’s surface (highlands, far side) would likely show only weak field records.

Co-author Jon Wade compared it to an alien survey of Earth: “If we were aliens exploring the Earth, and had landed here just six times, we would probably have a similar sampling bias especially if we were selecting a flat surface to land on.”

The study’s models predict that random sampling across the lunar surface would reveal overwhelmingly weak magnetism — a hypothesis Artemis missions can test by landing in diverse, non-mare regions.

Co-author Simon Stephenson added: “We are now able to predict which types of samples will preserve which magnetic field strengths on the Moon. The upcoming Artemis missions offer us an opportunity to test this hypothesis and delve further into the history of the lunar magnetic field.”

The findings reshape our understanding of planetary dynamos and how sampling location can profoundly skew scientific conclusions — even for missions as historic as Apollo.