Though the Moon lacks a core dynamo magnetic field unlike the Earth, the lunar crust has a remnant magnetisation. But in some areas on the Moon, the localised surface fields extend to hundreds of kilometre and measure up to hundreds of nanotesla or higher. Apollo samples and the lunar crust studies have shown the magnetising field was as high as tens of microtesla before 3.56 billion years ago. Now researchers from Massachusetts Institute of Technology and other institutions have found ( Science Advances, October 2020) a possible answer for the long-standing mystery of the origin of the localised magnetic fields on the Moon. Magnetic fields on the moon may be the remnant of an ancient core dynamo. This might be the “only plausible source” of most magnetisation on the Moon, they say.
Based on computer simulations, the researchers say that the Moon must have had an internal core dynamo in the past. They arrive at this conclusion by ruling out the earlier notion that localised magnetisation was caused by impacts of massive bodies on the Moon surface. While such collisions and ejected material can transiently enhance the field inside the Moon, the resulting fields would be at least three orders of magnitude too weak to explain the localised magnetic field observed on the Moon’s surface.
More research is needed to confirm exactly how the magnetic spots were formed.
