China Focus: Chang'e-6 samples reveal rebound in moon's magnetic field

BEIJING, Dec. 19 (Xinhua) -- Rock samples collected from the moon's far side by China's Chang'e-6 lunar probe have provided groundbreaking insights into the evolution of the lunar body's magnetic field.

Analysis of the samples, published on Thursday in the journal Nature, indicates the unexpected resurgence in strength of the moon's magnetic field 2.8 billion years ago, following a sharp decline around 3.1 billion years ago. The find challenges the prevailing theory that the moon's lunar dynamo remained in a low-energy state after that decline.

It marks the first-ever paleomagnetic data obtained from the moon's far side, and provides critical insights into the intermediate stages of the evolution of the lunar dynamo, the geophysical mechanism that generated the moon's magnetic field in the past.

On June 25 this year, the Chang'e-6 lunar probe returned to Earth with 1,935.3 grams of lunar samples collected from the previously unexplored far side of the moon.

The 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 found an increase of paleomagnetic field strengths, which indicates a possible lunar dynamo reactivation following an initial rapid decline.

They 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 show no global dipole magnetic field on the moon today. Previous research on lunar samples has revealed that the moon's magnetic field, similar to Earth's around 4.2 to 3.5 billion years ago, experienced two sharp declines and shut down sometime after around 1 billion years ago.

However, current data concentrates predominantly on the era before 3 billion years ago, offering little insight into the evolution of the moon's magnetic field in its middle-to-late phases, and providing virtually no details about 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 said that the team's "highly original results" fill in 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."

The results are the latest published findings arising from samples returned from Chang'e-6. In November, an IGG team reported two volcanic events that occurred on the moon's far side 2.8 billion years ago and 4.2 billion years ago, which was also published in the journal Nature.

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