A research team discovered that the Moon had a weak dynamo magnetic field, measuring around 2 to 4 microteslas, approximately 2 billion years ago. The finding suggests that the lunar dynamo continued to function at least into the Moon's middle age. This study was published as a cover article in Science Advances on Jan.1, 2025. 

Understanding the strength, structure, and evolution of the Moon's magnetic field is essential for uncovering its internal structure, thermal history, and surface environment. Most of the knowledge about the ancient lunar magnetic field has come from samples collected during the Apollo missions, which primarily focus on the Moon's early history, particularly more than 3 billion years ago. However, much less is known about how the lunar magnetic field evolved during the middle to late stages of the Moon's history. This leaves important questions unresolved, such as whether the Moon sustained a long-lasting magnetic field, known as a "dynamo."

The Chang'e-5 mission returned the youngest lunar basalt samples from Oceanus Procellarum, a mid-latitude region on the Moon. These rocks provided an opportunity to explore the Moon's magnetic history during its middle age. The research team led by Prof. ZHU Rixiang from the Institute of Geology and Geophysics of the Chinese Academy of Sciences (IGGCAS), in collaboration with researchers from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) and China University of Geosciences (Wuhan), conducted a detailed magnetic study on these Chang'e-5 basalt samples.

The researchers recovered weak paleointensities of ~2 to 4 microtesla from the Chang’e-5 basalt clasts at 2 billion years ago and they also discovered that thermal convection in the Moon's deep interior may have persisted during this period, supplying extra heat for volcanic activity later in the Moon's history. 

Furthermore, the weak magnetic field found in the Chang'e-5 samples suggested the existence of a protective magnetic shield, or "paleomagnetosphere," at that time. This finding offers valuable insights for research on space weathering and the presence of volatile materials on the lunar surface during the Moon's midlife.

This study was supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences.

The Chang'e-5 basalts reveal a weak lunar dynamo magnetic field 2 billion years ago, indicating that the Moon's interior still retained some level of activity during the midstage (Image by IGGCAS)