The far side of the moon may hold clues about its ancient magnetic field, suggesting that the moon might have once had a magnetic field generated by its core, much like Earth does today. On Earth, the movement of liquid iron in the outer core generates a global magnetic field, a process known as the geodynamo. This mechanism is similar to a bicycle dynamo, which converts motion into electricity. However, unlike Earth, the moon no longer has a magnetic field generated by its core. A recent study by researchers from ETH Zurich, in collaboration with institutions in Germany, suggests that the moon did have a magnetic field about 4.2 billion years ago, shortly after its formation. This conclusion comes from data collected by lunar orbiters, rather than from rock samples brought back by Apollo astronauts, which had previously led to conflicting interpretations. The study focuses on a region on the moon's far side called Dewar, an area that is not visible from Earth. This region is notable for having both a strong magnetic field and a distinct gravity anomaly, suggesting the presence of dense and strongly magnetized rock beneath the surface. By combining data on magnetic fields and gravity, the researchers were able to create a detailed model of the subsurface structure. They identified a buried volcanic complex, approximately 60 kilometers wide and extending to a depth of about 9 kilometers, made of solidified magma. The study estimates that the magnetic field on the moon at that time was stronger than 10 microtesla, which is about a fifth of Earth's current magnetic field strength. The researchers ruled out the possibility that a meteorite impact caused this magnetic field, as the Dewar region is not in an area typically associated with such events. While the findings support the existence of an early lunar dynamo, the exact mechanism by which the moon's small core could have generated such a strong magnetic field remains unclear. The study also sheds light on mysterious features on the moon's surface known as lunar swirls—bright, curved patterns that appear in areas with magnetic anomalies. These swirls may be protected from solar wind by the horizontal magnetic field, which shields the surface from erosion. Understanding these features could be crucial for future lunar missions, as they might help identify safe landing sites or areas of scientific interest. The methods used in this study could also be applied to other celestial bodies, such as Mars, to study their magnetic histories using orbital data.