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The Once and Future Moon

The Moon’s Antipodal Magnetism Mystery

19 Jun 2013, 13:34 UTC
The Moon’s Antipodal Magnetism Mystery
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A magnetic anomaly near the Moon's north pole may be related to an impact basin near its south pole. How can this happen?

North polar area showing location of the Schrödinger basin antipode, magnetized area and grooved terrain in Froelich and Lovelace.
Although the Moon has no global magnetic field like the Earth, small areas on its surface are magnetized. These fields are not systematically distributed and in general are very weak. In trying to explain their mysterious presence and origin, several ideas have been advanced.
Rocks typically acquire magnetism (called remnant magnetism) by cooling in the presence of a magnetic field. At temperatures greater than about 570° C (the so-called Curie point), a rock cannot retain a magnetic signature. But if it cools below the Curie point, it assumes an induced magnetic field oriented in the same direction as the field in which it cooled. Unfortunately, on the Moon most rocks have been dislodged from their original orientations by impact processes, so we do not know whether a given rock cooled in the presence of a global (presumably uniform strength and direction) or local (randomized) magnetic field.
We knew the Moon had no global magnetic field before the Apollo ...

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