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Heather Wilson, age 13, of Tempe, Arizona, for her question:

Does the moon have magnetic poles?

As we know, the earth's magnetic poles compel the magnetic .compass needle to point north. From this we can chart the other directions.. However, the moon did not provide this built in convenience for the astronauts. They found that the lunar surface does have patchy magnetic fields, though they vary in intensity.. Apparently, a magnetic compass on the moon would go clear out of its mind.

The earliest space probes failed to detect a magnetic field around the moon. Later probes orbited closer to the surface and carried finer instruments. They reported areas of mild magnetic force and scientists suspected that the moon had a magnetic field about 100 times weaker than the earth's. Our planet's steady magnetism is estimated to measure about 30,000 gamma units at the equator. This built in force comes from a dynamic super magnet in the core of the planet. It reaches out around the earth in an enormous invisible field of energy    the magnetosphere. The two poles of the interior dynamo are the opposite magnetic poles.

At present, our evidence on the moon's magnetism is very scanty and very, very bewildering. Apparently it does not go by the earth's orderly system at all. The Apollo 12 and 14 missions set up sensitive magnetometers to measure the magnetism on two small areas of the moon. The roving Apollo 14 astronauts carried a portable magnetometer. The first instrument promptly relayed a magnetic measurement of 38 gammas. Three days later it changed slightly as the moon swung into the earth's magnetosphere. The portable unit, merely 110 miles from the first site, measured a 43 gamma spot and a 103 gamma spot.

Scientists are computing this data along with other evidence from space probes. Eventually they hope to make some sense of all the bewildering details. But at present they can merely guess the overall pattern and suggest only theories to explain the confusion. Obviously the moon's magnetism is patchy. So far, we know that there are areas where magnetic force comes and goes. Both the permanent and temporary patches are strongly influenced by the solar winds and perhaps also by the changing temperatures of the lunar day and night.

The evidence, of course, is incomplete until the patchy magnetism has been charted over the entire lunar surface. Detailed reports o£ the variations in magnetic force also are needed. These studies will take time. But certainly the moon's magnetic hodgepodge does not resemble the neat, dipolar magnetism of the earth.

As usual, the answer to one question leads to the next one. And solving a big problem tends ao,s4ye several others along the way. It seems that the moon may have been intensely magnetic in the dim past. Perhaps it passed through the earth's or some other strong magnetic field. The answers to these questions promise to help solve many past mysteries of the solar system. Meantime, there is no evidence that the modern moon has magnetic poles strong enough to govern the needle of a magnetic compass.

 

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