Rock samples from the moon's far side, collected by China's Chang'e-6 lunar probe, have revealed groundbreaking insights into the evolution of the moon's magnetic field.

Published in Nature on Thursday, the analysis shows that the moon's magnetic field experienced a surprising resurgence in strength 2.8 billion years ago, following a significant decline around 3.1 billion years ago. This discovery challenges the prevailing theory that the lunar dynamo remained in a low-energy state after its earlier weakening.

These results mark the first-ever paleomagnetic data obtained from the moon's far side, shedding light on intermediate stages of the lunar dynamo – a geophysical process responsible for generating the moon's magnetic field in the past.

On June 25, Chang'e-6 returned to Earth with 1,935.3 grams of samples from the moon's far side, a previously unexplored region.

Researchers from the Institute of Geology and Geophysics (IGG) under the Chinese Academy of Sciences analyzed four basalt fragments from the Chang'e-6 mission and detected an increase in paleomagnetic field strength. This suggests a possible reactivation of the lunar dynamo after its initial decline. The resurgence may have been caused by changes in the dynamo's energy sources or a revival of its driving forces, according to the study.

Researcher hypothesized that the dynamo's resurgence could be attributed to alterations in its primary energy sources or a reinvigoration of the initial driving forces, according to the study.

Satellite and lunar surface data that the moon no longer possesses a global dipole magnetic field. Earlier studies of lunar samples revealed that the moon's magnetic field, once comparable to Earth's between 4.2 and 3.5 billion years ago, underwent two significant declines before ultimately ceasing entirely sometime after 1 billion years ago. 

However, questions remain regarding the precise timeline, duration, and mechanisms driving the moon's magnetic field, highlighting the gaps in understanding the moon's far side.

"Understanding the evolution of the lunar dynamo is of great significance for revealing the moon's internal structure, thermal history and surface environment," said Cai Shuhui from the IGG, the corresponding author of the study.

A peer-reviewer of the paper stated that the team's "highly original results" fill a billion-year-long gap in the lunar paleomagnetic record and provide "the first paleomagnetic measurements from the lunar far side," representing "a major advance in our understanding of lunar magnetism."

These findings build on other major discoveries from Chang'e-6. In November, an IGG team reported two volcanic events on the moon's far side, occurring 2.8 billion and 4.2 billion years ago, also published in the journal Nature.

Another study, published in the journal Science, confirmed that the low-titanium samples collected by Chang'e-6 are approximately 2.83 billion years old, offering further evidence of volcanic activity on the moon's far side.

(With input from Xinhua)