Lunar Probe Data Uncover Massive Magnetized Rock, Reviving Moon Dynamo Debate

A team of researchers analyzing archival data from NASA’s Lunar Prospector (1998), Japan’s Kaguya (2007) and NASA’s GRAIL (2011) identified a dense, strongly magnetized formation beneath the far-side region known as Dewar. The buried structure spans roughly 60 km (37 mi) in width and extends about 9 km (5.6 mi) deep. The study, published on September 23 in *Science Advances*, argues the rock likely solidified from magma around 4.2 billion years ago, when the Moon’s magnetic field may have been between one-fifth and one-third the strength of Earth’s present field.

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Since Apollo-era samples in the 1970s suggested a magnetic record, scientists have debated whether the Moon ever sustained a core-driven dynamo. Recent re-analyses of Apollo material have found no magnetic signal for parts of the same interval, prompting some researchers to question the existence of an early dynamo. The new orbital-data approach sidesteps the handling-induced disturbances that can scramble magnetic records in rock samples.

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• Anna Mittelholz – Lecturer, Swiss Federal Institute of Technology Zurich (ETH Zurich); co-author who emphasized the advantage of combining magnetic and gravity data.

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• Adrien Broquet – Researcher, German Aerospace Center, Berlin; co-author who highlighted the Moon’s distinct geological history.

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• Xi Yang – Doctoral student, ETH Zurich; lead author who noted a possible link between magnetic anomalies and lunar swirls.

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• Claire Nichols – Associate professor of geology of planetary processes, University of Oxford; external commentator on the study’s implications.

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The researchers merged magnetic field maps with gravity-derived density models, allowing them to pinpoint the buried structure rather than infer a generic magnetic source. Their analysis suggests the Moon once generated a “intense dynamo” early in its history, though the study could not determine the dynamo’s duration or the exact mechanism by which a small lunar core could produce such a field. The observation that magnetic anomalies often coincide with bright lunar swirls supports the hypothesis that localized magnetism can deflect solar wind, potentially preserving surface material.

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The results shift the scientific conversation from “whether” the Moon had a dynamo to “how” it operated.

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• “Earth and the moon had drastically different geological histories. The moon was smaller and fully molten for a long time. It also had a lot of volcanism early on, and there are many questions we cannot exactly answer if we don’t know how the moon looked like back then,” — Adrien Broquet, a researcher at the German Aerospace Center in Berlin

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