Magnetic Properties of the Moon

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The Moon has no global magnetic field as does Earth. Some lunar rocks are weakly magnetic, indicating that they solidified in the presence of a magnetic field. The Moon has small, local magnetic fields that seem to be strongest in areas that are on opposite hemispheres from large basins. The origin of these local magnetic fields is unknown. Some scientists speculate that the magnetic fields were induced by the extreme shock pressures associated with the large asteroid collisions that created the basins. Others believe that the Moon originally had a global magnetic field generated by the movement of liquid metal in the core as on Earth. This global field shut down for some reason and only remnants of it exist in certain places on the lunar surface, preserved in material ejected by the asteroid collisions. The “fossil” magnetism found in some lunar rocks supports the former global field model, whereas the regional distribution of the magnetic surface anomalies tends to support the local field model. Regions of strong magnetic fields repel the charged particles that stream from the Sun in the solar wind. Scientists believe that interaction with the solar wind darkens the Moon, and that some lighter swirl-shaped regions of the Moon are protected by local magnetic fields.

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