# Planetary Magnetic Field ReplacementJanuary 4, 2007 4:08 AM   Subscribe

The magnetic field of the earth isn't that strong, right? So what would it take to replace it?

I'd just been reminded of this whole "magnetic field flip" scare and wondered if the resources are available to 'fake' it, should the need arise. The size of the (electro)magnet will (?) need to be continent-scale, but could we give it enough power to matter outside the ionosphere? And what configuration would be most effective?
posted by Tzarius to Science & Nature (12 answers total) 1 user marked this as a favorite

Over what volume?

Anything more serious than sticking a magnet near your mate's compass is going to run smack-bang into the inverse cube law.
posted by pompomtom at 5:05 AM on January 4, 2007

i really doubt we could fake a full-scale planetary magnetic field. Our field may be weak, but it's big. Inverse cube sounds right for sure.
posted by clord at 5:36 AM on January 4, 2007

Earth's field strength at the surface ranges from .3 to .6 gauss. But the field is very large, so the total energy contained is very large as well.

(Warning. Googling this hits an amazing amount of nutbar pages.)

Trying the math, I'm getting a total energy of 7 exajoules -- that's 7,000,000,000,000 joules. Or, just so I can write more zeros, 70,000,000,000,000,000,000 ergs, which is 70 yottaergs.

Warning -- I may have shanked the math badly. Take with a yottagrain of salt. I'm confident that I'm within a couple of order of magnitude, so we're certainly talking a staggering amount of energy.

Thus, replacing that field would require another source of a staggering amount of energy.

However, I'm not worried. The total dipole strength of the field is dropping, but the non-dipole component has been rising. Given the periodic flip of the dipole field, this isn't surprising. Total energy is remaining the same, so even with a flip, there will still be a very large magnetic field around the planet. We'll just need to look at the white arrow to find north on a compass.

Of course, until we figure out the new declination maps, getting true from magnetic is going to be a problem.
posted by eriko at 6:06 AM on January 4, 2007

I think this question is analogous to asking, "What's the big deal with this global warming thing raising temperatures by a few degrees? Can't we just install a big A/C unit somewhere if it's only a couple of degrees?" "A couple of degrees" is trivial when you're talking about a cup of coffee, but not when you are talking about the entire surface of the planet, and the same is true for magnetic fields.
posted by Rhomboid at 6:18 AM on January 4, 2007 [1 favorite]

To create a comparable field it would be necessary to wrap a wire around the equator multiple winds, and then pour a lot of current through it. That's not impossible (it doesn't violate any laws of physics) but it's a nontrivial engineering problem.

Lessee, 5 winds of an inductor with a radius of 6,378 kilometers with a ferromagnetic core... That's a lot of henrys, I think.
posted by Steven C. Den Beste at 6:36 AM on January 4, 2007

The magnetic field of the earth isn't that strong, right?

Wrong, though I guess everything is relative. Our magnetic field is vastly stronger than that of every other planet except the gas giants. See here.

That's not impossible (it doesn't violate any laws of physics) but it's a nontrivial engineering problem..

You're not kidding. Is there enough conductive metal on the earth to make enough wire to wrap the earth that much AND thick enough to carry that much current? Yikes.
posted by Pastabagel at 8:24 AM on January 4, 2007

(From the wonderful film The Core, by the way.)
posted by The Deej at 8:33 AM on January 4, 2007

I'm pretty sure that in order to really imitate the earth's natural magnetic field, the magnet would have to be placed in the center of the planet, at the core. (not sure if wrapping wire around the equator, on the surface, would work quite the same)
posted by Green Eyed Monster at 9:18 AM on January 4, 2007

More reasons to get into space.
posted by emptyinside at 9:46 AM on January 4, 2007

Bah. You are all crazy. All we need to do is rub the surface of the earth from pole to pole with a giant magnet. We'll be fine!
posted by chairface at 9:56 AM on January 4, 2007

I'm glad I live in a lower level apartment. Suck the sun, 2nd and 3rd floor tenants!!!!!
posted by The Deej at 10:42 AM on January 4, 2007

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