Researchers claim that the moon used to have a magnetic core which helped it generate a stronger magnetic field than the Earth currently produces.
Today the moon does not have a global magnetic field, but interest was piqued after moon rock collected during the Apollo missions appeared to suggest that it had one billions of years ago. Scientists still do not fully understand why the magnetic field was so strong and when it ended.
Moon’s magnetic field: Varying theories
Previously scientists did not know whether the moon itself generated the magnetic field, or if it was due to outside forces. However over the past 6 years scientists have used new research methods to discover strong signals that the moon may have had a magnetic core of its own, following analysis of the moon rock which found no evidence of cosmic impacts, another explanation for their magnetization.
The researchers postulate that planets move electrically conducting fluids around themselves, thus generating magnetic fields through a process that they liken to a dynamo. They claim that if the moon had a similar internal dynamo, it would allow us to better understand its inner structure, which has long puzzled scientists.
“Earth’s magnetic field is currently 50 microteslas in strength,” said Benjamin Weiss, co-author of the study. “The early moon may have had a magnetic field that was bigger, maybe up to more than 70 microteslas.” The researchers are perplexed as to how the relatively small core of the moon could generate such a strong magnetic field.
Maintaining the lunar dynamo
The study of planetary magnetic fields has revealed that they are powered by the convection of electrically conducting fluids, but a lunar dynamo of this nature would have cooled relatively quickly given the small size of the moon’s core. One explanation is the presence of less viscous, radioactive material, which would keep it warmer.
Other theories include a series of large asteroid impacts, and the “wobbling” of the moon’s spin, which would have kept the fluids of the core in motion. Another theory draws on the crystallization seen in the Earth’s core, which causes lighter elements to float to the top, and this kind of movement could also have sustained the lunar dynamo.
We still do not know when the moon stopped producing a magnetic field, or why it varied in strength over time. There are evidently huge gaps in our understanding of the lunar core for scientists to ponder for the foreseeable future.