Researchers at ETH Zurich have investigated whether the Moon ever possessed an internal magnetic field, concluding that a mechanism similar to Earth's geodynamo likely existed on the Moon approximately 4.2 billion years ago. Unlike Earth, the Moon does not currently have a core-generated magnetic field. The study, which utilized data from lunar orbiting probes, focused on the Dewar region on the Moon's far side, where strong magnetic and gravity anomalies were identified.
The findings suggest that beneath the surface of the Dewar region lies a rock body approximately 60 kilometers wide and 9 kilometers deep, which is denser and more magnetized than the surrounding crust. The researchers determined that this structure is likely a solidified magma body, indicating volcanic activity. The estimated magnetic field strength at that time was likely stronger than 10 microtesla, compared to Earth's current magnetic field strength of around 50 microtesla.
The study rules out the possibility that a violent impact caused the magnetic field, suggesting instead that it originated from a long-lasting dynamo generated in the Moon's core. However, the researchers acknowledge that the mechanism behind the Moon's small core generating such a strong magnetic field remains unclear. Additionally, the study provides insights into lunar swirls, which are bright patterns on the Moon's surface associated with magnetic anomalies. These findings may inform future lunar missions and the analysis of lunar samples to better understand the Moon's magnetic history.