For decades, a debate has raged about whether the moon ever had a strong magnetic field, or if it was always weak. Now, a new analysis of Apollo-era moon rocks suggests the moon's magnetic field might be mostly weak, despite brief outbursts of strong activity — potentially solving the mystery for good.

The research, published Thursday (Feb. 26) in the journal Nature Geoscience, shows that the moon's magnetic field amped up for brief periods in its early history, roughly 3.5 billion to 4 billion years ago, but for most of the moon's 4.5 billion-year-old history, the magnetic field was weak.