Lunar samples returned by China’s Chang’e 6 mission contain rare, highly magnetic iron allotrope

China’s Chang’e 6 lunar mission has returned samples from impact craters that contain γ-iron – an allotrope normally stable only above 912°C. Researchers believe that the magnetic fields recorded in the particles could have been generated by lunar impacts and may explain areas of unusually high magnetic intensity on the moon.

Debate over whether the moon ever had a liquid metal core capable of generating strong magnetic fields, a so-called dynamo, and how long it lasted, has flourished since Apollo mission samples were found to be magnetised. This led to the theory of a historical lunar dynamo, explains John Tarduno, a geophysicist at the University of Rochester in the US who wasn’t involved in the analysis. ‘But there’s always been this looming issue … the lunar core is tiny and it’s very hard to generate a long-lived magnetic field in that tiny core.’