Spirit Research

Study points to an ancient internal magnetic field on the Moon 4.2 billion years ago

A new study supports the idea that the Moon once generated its own internal magnetic field, Futurity reports. Researchers from ETH Zurich, working with colleagues at the Institute of Space Research, DLR and the Technical University of Berlin, concluded that 4.2 billion years ago, several hundred million years after the Moon formed, it had a magnetic field driven from within.

The team did not rely on Apollo rock samples but on orbital data, including gravity measurements from NASA's GRAIL probes and magnetic field models built from the Lunar Prospector and Kaguya missions, according to Futurity.

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Why the Dewar swirl mattered#

The Moon has no core-generated magnetic field today, unlike Earth, where moving liquid iron in the outer core produces one, Futurity reports. Geophysicist Anna Mittelholz of ETH Zurich said researchers have long disagreed over whether a strong magnetic field existed between 4.25 and 3.5 billion years ago, with some finding no evidence for it at all.

Mittelholz called the Dewar region, on the far side of the Moon, "a genuine stroke of luck" because one of the strongest magnetic anomalies there overlaps with a distinct gravity anomaly, letting the team estimate the density of the material beneath the surface, Futurity and Discover Magazine both report.

Discover Magazine reports the Dewar swirl sits atop a buried mass of rock 37 miles wide and 6 miles deep, thought to be a volcanic complex of solidified magma that formed roughly 4.2 billion years ago.

Two rival explanations for lunar magnetism#

Besides an internal dynamo, the mechanism that converts a planet's mechanical motion into a magnetic field, researchers have also proposed that impacts from large meteorites or asteroids magnetized lunar rock, Futurity reports. The new study, published in Science Advances, comes down in favor of the dynamo explanation.

Discover Magazine reports that Claire Nichols, who holds a position studying planetary processes at the University of Oxford, said the findings show the young Moon could run a strong internal dynamo, and that the result gives added reason to keep watching for magnetic clues during upcoming missions such as Artemis and Chang'e.

Separately, researchers led by professor Du Haifeng at the High Magnetic Field Laboratory of the Hefei Institutes of Physical Science identified a rare iron phase, face-centered cubic gamma-Fe, in impact-glass particles from Chang'e-6 lunar soil samples, marking the first time this iron form has been found in natural lunar material, Phys.org reports. Researcher Li Long called the discovery a "tiny magnetic fossil" that may help clarify the Moon's ancient magnetic history.

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