Moon's farside near-zero paleomagnetic field suggests a global lunar dynamo cessation.

Abstract

Recent paleomagnetic studies of Apollo and Chang'e returned samples suggest that the lunar dynamo was active from ∼4.2 billion years ago (Ga) and ceased by ∼1.0 Ga. However, uncertainties remain regarding the temporal and spatial distribution of the lunar paleomagnetic field, as almost all of the returned samples are from the nearside, except for those returned by Chang'e-6. Here, we present the first paleomagnetic analysis of a lunar meteorite, Northwest Africa 15528, which is a feldspathic regolith breccia likely from the farside of the Moon. Our results not only indicate that it recorded a near-zero magnetic field (below a few hundred nanoteslas) at ∼0.7 Ga but also show that lunar meteorites can provide critical paleomagnetic information. Combined with two young Apollo samples from the nearside, Apollo 15015 (formed at ∼0.9 Ga) and Apollo 15465 (formed at ∼0.5 Ga), our findings suggest the absence of a global dynamo-generated lunar magnetic field for the past one billion years.