A reinforced lunar dynamo recorded by Chang'e-6 farside basalt.

The evolution of the lunar dynamo is essential for deciphering the deep interior structure, thermal history and surface environment of the Moon. Previous palaeomagnetic investigations on samples returned from the nearside of the Moon have established the general variation of the lunar magnetic field. However, limited spatial and temporal palaeomagnetic constraints leave the evolution of the lunar dynamo ambiguous. The Chang'e-6 mission returned the first farside basalts dated at about 2.8 billion years ago (Ga) (refs. ), offering an opportunity to investigate a critical spatiotemporal gap in the evolution of the global lunar dynamo. Here we report palaeointensities (around 5-21 μT) recovered from the Chang'e-6 basalts, providing the first constraint on the magnetic field from the lunar farside and a critical anchor within the large gap between 3 Ga and 2 Ga. These results record a rebound of the field strength after its previous sharp decline of around 3.1 Ga, which attests to an active lunar dynamo at about 2.8 Ga in the mid-early stage and argues against the suggestion that the lunar dynamo may have remained in a low-energy state after 3 Ga until its demise. The results indicate that the lunar dynamo was probably driven by either a basal magma ocean or a precession, supplemented by other mechanisms such as core crystallization.