Understanding Earth's Magnetic Field

neutron_p writes "Researchers from the University of Maryland's nonlinear dynamics and chaos research group are seeking to solve a major scientific mystery: How is the Earth's magnetic field formed and what causes changes in the field? To find answers, they are recreating on a small scale the forces that produce Earth's own magnetic field. Scientists have constructed a series of "geodynamos" - metal spheres filled with liquid sodium that emulate conditions of the Earth's spinning, churning molten iron core. This project involves more than 14 tons of sodium metal and a 10-foot stainless steel sphere."

Re:who says it's molten iron

[CheshireCatCO]

Radioactive materials aren't the same as a nuclear reactor. Unstable elements (like uraniam) or isotopes will break down regardless. A reactor has nearby radioative atoms triggering fission in their neighbors. For this, you need a fairly high density of radioative elements in close proximity. That's why they have to purify uranium ore, for example, to make fuel rods. (And further purify the isotopes to make weapons-grade uranium.)

The interiorof the Earth is almost certainly not a reactor. That theory has a lot of holes (we've argued this before on Slashdot, I know). The Earth's interior is more like an RTG on a spacecraft: you let the atoms decay at their own pace and use the heat rather than trigger a chain-reaction.

Re:A question

[CheshireCatCO]

Actually, in a direct sense, the ground currents are caused by Earth's field. It's when the field snaps back from CME*-induced distortions that we get those nasty currents. The Sun is driving it, but it's via a CME, which then messes with Earth's field, which then causes the currents.

That said, if Earth's magnetic field didn't exclude the Sun's, would there be an EMF? Yeah, I should think so. But the Sun's field is mainly in the plane of Earth's orbit and varies comparatively slowly. (Over hours or more, rather than, say, seconds.) So I wouldn't expect a lot of induced EMF as per Faraday's law. (Caveat: This is from memory. I have the details about the solar wind and interplanetary magnetic field in my texts in my office, but I'm (happily) not there at the moment.)

* Coronal Mass Ejection

Re:Considering

[Christopher Thomas]

That the Earth's core is not molten sodium, nor is it made of stainless steel, this is a pretty poor experimental model, but, hey, I'll bet the grant money was pretty good.

Considering that magnetic field generation depends only on the pattern of fluid flow and the fact that the fluid is conducting, I'd say this is actually a pretty good experimental model. See my previous post about why it's really handy to have a dynamo you can change the parameters of.

Re:"Earth's" magnetic field?

[Christopher Thomas]

As I understand it, the universe has only one megnetic field and the Earth (and other masses) merely distorts that field. Same goes for gravity. Is this not true? I realize this doesn't change the sense of the article at all, but it always bothers me to hear people talk of the "Earth's" magnetic field like it is somehow unconnected to anything else.

The answer to this is "sort of".

The short answer is, the Earth's magnetic field is best thought of as belonging to Earth, as opposed to being a disturbance in a larger universal field. ObCaveats about the interaction between the Earth's field and the Sun's field and the Milky Way's field giving important effects; all of these can still be considered fields local to the objects generating them.

The long answer is that the electromagnetic force can be thought of as charges disturbing a field of virtual photons that does indeed fill the universe. However, saying that there's a magnetic field pervading the universe doesn't really make sense, as the measured magnetic and electric field strengths without charges and currents disturbing the virtual photon field will be zero, and these disturbances for unchanging fields have a very limited range of effect (or rather, an unlimited range but a strength that drops off very fast with distance).

In summary, "Earth's magnetic field" is probably the best description.

Re:who says it's molten iron

[krymsin01]

The natural reactor you speak of is Oklo, you can find more information about it here [curtin.edu.au]. You're wrong about the location, unless you are speaking of some other natural nuclear reactor that hasn't been brought to acedemic attention. From the site:

Location: Natural fossil reactors have (so far) only been found in the country of GABON in equatorial Africa. All but one of the reactors are located at a place known as the OKLO uranium deposit located in the south eastern corner of the country. Another fossil reactor has also been discovered in Gabon at another U deposit at Bangombe, some 35 km south east of the OKLO mine. For more information about Gabon;

Speaking of the earths magnetic field

[seann]

Speaking of the earths magnetic field, tonite the Aurora Borealis [mtu.edu]
was spotted in Southern Ontario from about 6pm Eastern to 3:00AM Eastern.

What a treat.

Re:who says it's molten iron

[hplasm]

Unfortunately, Faraday cages only shield out the electrical component of EM waves. To protect a volume from magnetic effects requires a high permittivity material, such as mumetal, which diverts the field through itself, and around the area to be protected.

Re:More to it than the article states

[stevelinton]

The ozone in the stratosphere is created by solar ultraviolet dissociateing oxygen
This produces free oxygen atoms which latch onto basically anything they can find. If what they find is an oxygen molecule then you have ozone. This happens wherever there is sunlight and oxygen and there is no electrical current involved.

Over the poles, during the winter, in the presence of chlorine (which is mainly there due to human activity) there is a chemical reaction which breaks down the ozone causing the holes.

None of this has anything to do with the Earth's magnetic field, which is generated far underground, or with surface ozone, which is mainly man-made.

Re:More to it than the article states

[Anonymous Coward]

Ozone is O3.