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Q & A: magnets and gravity

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Most recent answer: 10/22/2007
Q:
On Wikipedia, under the subject of Earthís magnetic field,it states that the magnetic field on the surface of the Earth is 60,000 microtesla, or 0.6 Gauss. How large of a BAR MAGNET would be required on the Moon to produce a similar magnetic field? Would it be 1 mile long (in segments, letís say). A shaft would be drilled down the core of the moon and a bar magnet inserted. What would be the specifications for this bar magnet, if I had to manufacture one? The purpose is to build an atmosphere on a planet, to keep oxygen, co2 and nitrogen in. Thank you. Susan
- Susan (age 27)
New York, NY, USA
A:
Susan-
Before getting to your question, it's important to examine your assumption. The Earth's magnetic field has nothing to do with the gravity that holds our atmosphere. In fact, our magnetic field has briefly dropped to very low values at times, and the Earth did not lose its atmosphere. (Those times may be rough for organisms because the magnetic field helps shield us from some types of radiation, but that's another story.) Gravity is an entirely different effect.

If you're still interested in the magnet question, we can try to answer it. Roughly speaking, if you wanted a big magnet on the Moon to allow standard Earth compasses to work, the magnet would have to be huge, almost 10% of the diameter of the Moon. I got that by using that the magnetic field falls off as the cube of the distance from the magnet, and that standard magnetic materials only have a few thousand times the surface field of the Earth.

Mike W.

(published on 10/22/2007)

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