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

Abstract

The evolution of the lunar dynamo is essential for deciphering the deep interior structure, thermal history, and surface environment of the Moon^1-4. Previous palaeomagnetic investigations on samples returned from the nearside of the Moon have established the general variation of the lunar magnetic field^5-7. 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 ca. 2.8 billion years ago (Ga)^8,9, offering a unique opportunity to investigate a critical spatiotemporal gap in the evolution of the global lunar dynamo. Here we report palaeointensities (~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 and 2 Ga. The new results record a rebound of the field strength after its prior sharp decline around 3.1 Ga, which attests to an active lunar dynamo at ca. 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 result suggests the lunar dynamo was most likely driven by either a basal magma ocean and/or precession, probably supplemented by other mechanisms such as core crystallisation.