Moon rocks from China’s Chang’e 6 mission test Apollo views on lunar magnetic field

Rocks brought back indicate lunar magnetic field may have shot up about 2.8 billion years ago, Chinese study in Nature says

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A view of the lunar surface as taken by the Chang’e-6 probe in June. Photo: EPA-EFE

Published: 10:00am, 21 Dec 2024

The strength of the lunar magnetic field may have shot up about 2.8 billion years ago, a Chinese study of samples from the far side of the moon suggests.

The study, published online on Thursday in the journal Nature, challenges the prevailing view that the lunar magnetic field sharply declined around 3.1 billion years ago and has remained weak ever since.

Studies of US Apollo mission samples earlier indicated that a lunar dynamo was relatively active between 4.2 and 3.5 billion years ago before gradually fading. However, the precise timeline and mechanisms of this decline remained subjects of debate.

A dynamo magnetic field, like that of the Earth, is generated by the flow of liquid metal in the planet’s core. This field protects the planet’s atmosphere and water from solar wind erosion. Similarly, the moon’s ancient dynamo might have shielded its surface environment, potentially influencing its early evolution.

While satellite observations and surface measurements confirm that the moon does not have a global dipole magnetic field today, its crust retains extensive magnetisation. This suggests that it might once have had a dynamo-generated magnetic field or a field induced by massive impacts.

The latest Chinese study looked at the first-ever samples from the moon’s far side, collected by the Chang’e 6 mission last year. The researchers – from the Institute of Geology and Geophysics (IGG) under the Chinese Academy of Sciences, in collaboration with the National Astronomical Observatories – analysed 4mm-sized basalt rock fragments returned by the mission.

They said the samples recorded an ancient magnetic field with strengths ranging from 5 to 21 microteslas (with a median value of about 13 microteslas). The value is close to the present level of the Earth’s magnetic field.