View Full Version : Mega-Magnet, a Hypothetical Situation

2014-Mar-02, 09:45 PM
Suppose that Luna was instantaneously replaced by a spherical neodymium magnet of equal mass, what would be the effects?

2014-Mar-02, 10:23 PM
Maybe not too much the man in the street would notice. Strength of a magnet falls off fairly fast from the surface, and IIRC even a magnetar (http://en.wikipedia.org/wiki/Magnetar) would only be strong enough to, for example, wipe credit cards within half the distance to the Moon. I expect a lot of high sensitivity experiments that are on going would return weird results.

2014-Mar-02, 10:27 PM
Neil Armstrong and Buzz Aldrin would be very cross with us for sending them up there.

2014-Mar-02, 11:44 PM
Since magnetic force is much stronger than the gravitational force, the orbits would alter. Earth's molten iron core is non magnetic but there are sufficient solid iron in the crust to affect the orbit (IMHO).

2014-Mar-03, 01:01 AM
For a really rough approximation using the surface field and inverse cube law...the surface magnetic field of Earth is 0.25-0.65 gauss...call it 0.5 gauss for convenience. A neodymium sphere magnet from K&J Magnetics has a surface field of 8815 gauss. At Earth's distance of 221 lunar radii, the moon's magnetic field would be around 0.0008 gauss.

This isn't very accurate, but is hopefully accurate enough. We wouldn't notice much.

2014-Mar-03, 05:14 AM
I stand corrected James.
I didn't realize that inverse square law of gravity was much stronger at large distances than the inverse cube of dipoles.