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What evidence suggests that the Moon once had a magnetic field?
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Moon
(Left) Near side of Earth's Moon, photographed by the Galileo spacecraft on its way to Jupiter. (Right) Far side of the Moon with some of the near side visible (upper right), photographed by the Apollo 16 spacecraft.
While the Moon does not currently possess a global magnetic field, scientific evidence indicates that it experienced periods of magnetic activity in the past.12
The primary evidence for this ancient magnetism is the presence of remanent magnetism found in certain lunar surface rocks. Additionally, researchers have identified large magnetic anomalies in the lunar crust, such as the region associated with the Reiner Gamma formation, which are characterized by distinct light-colored, swirling patterns. These findings suggest that the Moon was once subject to magnetic forces, though the exact mechanisms and duration of this activity remain subjects of ongoing study.123