Samples from the Moon’s far side suggest the Moon once generated its own magnetic field more than four billion years ago, according to a new study published in Science Advances on 23 September.

Researchers led by ETH Zurich analysed material brought back by China’s Chang’e-6 mission and found magnetised material at the Dewar anomaly on the lunar far side. The findings suggest an internally generated field of more than 10 microtesla, roughly a fifth to a third of Earth’s current magnetic field.

Scientists have long debated whether the Moon ever had a global magnetic field like Earth’s. Earlier evidence came mostly from the near side, leaving open the question of whether it was local or global. The far-side data strengthens the case for a Moon-wide dynamo in the ancient past.

The magnetic field likely faded billions of years ago as the Moon’s interior cooled. Understanding the ancient field could help scientists piece together how the Moon formed and why it evolved so differently from Earth.

The researchers caution that the evidence supports but does not definitively prove a global lunar field. More samples and analysis will be needed to confirm the picture.