For decades, scientists have wrestled with a simple question: what happened to the Moon’s magnetism? Instruments on orbiting spacecraft once detected strong magnetic signatures in lunar surface rocks, indicating a powerful field in the past. Yet the moon itself has no inherent magnetism today.

Researchers at MIT now believe they may have uncovered the answer. Their hypothesis suggests that the Moon once possessed a faint magnetic field, and when a massive impact occurred, it produced a burst of plasma that temporarily strengthened this field, particularly on the far side of the Moon.