According to new study the moon may have possessed a magnetic field for much longer than previously thought, one that was also much stronger than scientists had predicted. Earth’s magnetic field is created by its dynamo, its roiling molten metal core. Scientists have long suspected that the moon once had a dynamo as well, since evidence of magnetism was found in rocks brought back from the moon by Apollo astronauts. But, meteoroids colliding with the moon could have created plasma, which could in turn have generated magnetic fields. To see if a dynamo or meteoroids might be responsible for magnetism on the moon, researchers wanted to examine rocks that had not been influenced by cosmic impacts.
Now an analysis of lunar volcanic rock
returned from the Apollo 11 mission
suggests the moon
did indeed possess a powerful dynamo in its core 3.7 billion years ago. These findings, combined with previous analyses of different 4.2 billion year old lunar rocks
, suggest the lunar dynamo existed for at least a half-billion years. It remains unclear, however, what might have powered this ancient lunar magnetic field.
Scientists had thought that any lunar dynamo that might have once existed was generated much the same way as it is on Earth,
by the cooling of its interior, which would caused the moon’s core to churn as molten metal cooled and sank. However, if the lunar dynamo lasted at least 500 million years, as the current findings suggest, researchers now have to find alternative power sources to explain such a long-lived effect, perhaps impacts from large asteroids
, or shifts in the moon’s
axis of spin.