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."

Comments

who says it's molten iron

[austad]

Several articles have been written lately about the possibility of our core being a natural nuclear reactor. Dead natural reactors have been discovered before, I believe in Nevada. It would only make sense that when the earth was forming, the heavier elements would migrate towards the core. Supposedly the reason our magnetic field changes every several thousand years is that the reactor poisons itself with byproducts and nearly stops... over time, these byproducts migrate outwards because they are lighter than the uranium, and the reactor starts up again with a magnetic field oriented differently from the one before it.

Here is a site with a ton of info on it. Interesting stuff, but it makes more sense to me than an iron core simply because of the whole mass/gravity issue.

Re:who says it's molten iron

[Undefined Parameter]

I just so happen to be taking a Geology course, this semester. As I understand it, while Geologists are rather certain that radioactive materials provide the majority of the Earth's internal heat, they are equally certain that the core consists mostly of iron. The "liquid" outer sphere of iron produces the magnetic field through its motion.

As for the study itself: Wouldn't the Earth's own magnetic field interfere with the experiment, somehow? I saw nothing about this in the article, but I'm assuming that the Earth's magnetic field would either fail to significantly effect the results or the scientists are countering for it somehow, either in the experiment itself or in their calculations.

At any rate, I wish them the best of luck.

~UP

Re:who says it's molten iron

[Christopher Thomas]

I'd like to see your sources on the core of Jupiter. I can cite a lot of sources to back up my statement, if you like. "The New Solar System" is an easily accessable book that covers the topic adequately. If you want something more detailed, "Protostars and Planets IV" has a nice discussion of this. I'd bet that the new Jupiter book from Cambridge University Press covers it, but my copy hasn't arrived yet.

If you're not finding references that say that the core is mainly ice, I'm curious where you're looking. (No, really: I'm curious.)

About half an hour of looking for all of the web sources I could find (starting with Nasa, then moving to wikipedia and then exhaustive Googling). I figured that if that if there was a new or at least more detailed model that asserted that there were definitely light elements in the core, that at least one page on Jupiter's structure would mention it. Everything I could find said rocky core, then metallic hydrogen, then supercritical fluid hydrogen, then gaseous hydrogen mixed with small amounts of icy material and trace amounts of things like phosphine and hydrogen sulphide.

Any of the books I have lying around that talk about gas giant structure are old enough that they're still speculating about whether a rocky core exists at all, so they weren't much help.

I'm not disputing your sources, as you appear to have ones that are both more recent and more detailed than what I could dig up. Crawling through an astronomy publication archive would have taken me longer than half an hour :).

What's worse is that you need a lot more uranium than Earth has to generate your heat that way.

I realize that. My older sources on Jupiter mainly say that its heat source is from things like latent heat of fusion as materials continue to fraction out. Is this still thought to be the case?

While I'm at it, is heat of crystallization still thought to be making any significant contribution to Earth's heating? I recall that that was the competing model for Earth's heat generation before radioactive decay became widely accepted.

And you can't restart the reactor by letting the uranium daughter istopes decay. What do you think that they decay into? Lead, mainly. If thorium stops the reactions, I'm pretty sure that lead will, too.

If the core is conjectured to be a ball of mostly-pure uranium, you actually get a fast-neutron reactor type of process, which means most of your material is fissioned instead of decaying by alpha emission. This gives you all kinds of junk lighter than lead, instead of the slow decay chain you'd find in a subcritical radiothermal source.

Even a slow-neutron reactor should breed U238 and thorium into things that will fission. The whole point of a reactor is to speed up the rate of decay by either triggering it directly (as with fissile materials in a slow-neutron reactor or any material in a fast-neutron reactor) or by transmuting materials into ones that can be induced to decay rapidly (breeder reactors of all types). Mostly the end result is fission, again giving light daughter products.

Basically, what the reactor model does is speed the burn rate. Which means, since we know the present heating rate of the Earth pretty well, you have to make it a lot hotter in the past with the reactor model than with pure decay.

Quite a valid objection.

Re:who says it's molten iron

[CheshireCatCO]

Any of the books I have lying around that talk about gas giant structure are old enough that they're still speculating about whether a rocky core exists at all, so they weren't much help.

Actually, they're not that old necessarily. We still don't know if there's a core. The problem is that we don't have a good equation of state for materials at those pressures and temperatures and that the data from the Voyager flybys and Galileo orbits isn't that strong a constraint. (You're forced to use minor deflections in the trajectories to determine the deep interior structure. But that structure is, of course, shielded by many Earth-masses of overlying hydrogen and helium.)

It's easier to tell what's going on at the other planets, being lighter, since the temperatures and pressures are lower and there is less material over the core. (Also, Saturn's rings provide an interesting constraint, as I recall.)

My older sources on Jupiter mainly say that its heat source is from things like latent heat of fusion as materials continue to fraction out. Is this still thought to be the case?

I don't think I've ever seen anyone speculate about heat of fusion. (For anyone who doesn't know, this isn't nuclear fusion, it's the latent heat released when your go from liquid to solid phase. It's probably unfortunate that the chemists use the word "fusion" here.) Differentiation has been considered, but I don't think it's held in favor. The planet has probably had ample time for most kinds of differentiation to occur. (Saturn still has some differentiation occuring, we think. But in this case, it's helium rain in the atmosphere. But the conditions only appear to be right for this at Saturn and nowhere else.) However, it does seem that Jupiter could still be contracting, which also releases heat.

Even using a fast-neutron raction, I'd wager (feel free to fill in the nuclear physics here, though) that if the daughter isotopes moderate the reaction enough to stop it, then their daughter products probably will as well. Lighter elements aren't necessarily incapable of this, after all. (Carbon is a good moderator, as I recall.)

Re:who says it's molten iron

[Christopher Thomas]

We still don't know if there's a core. The problem is that we don't have a good equation of state for materials at those pressures and temperatures and that the data from the Voyager flybys and Galileo orbits isn't that strong a constraint. (You're forced to use minor deflections in the trajectories to determine the deep interior structure. But that structure is, of course, shielded by many Earth-masses of overlying hydrogen and helium.)

Out of curiosity, did anyone manage to get seismic data by looking at how Jupiter's envelope moved after Shoemaker-Levy 9's fragments hit?

Even using a fast-neutron raction, I'd wager (feel free to fill in the nuclear physics here, though) that if the daughter isotopes moderate the reaction enough to stop it, then their daughter products probably will as well Lighter elements aren't necessarily incapable of this, after all. (Carbon is a good moderator, as I recall.)

Actually, moderation (thermalizing of neutrons by a light material that scatters neutrons more readily than it absorbs them) could even speed it up. It's absorption that's the problem. There isn't a strong relation between the absorption characteristics of the initial daughter products and what they alpha or beta decay to. I'd either have to crunch through an ungodly-huge number of possible decay chains, or find a nuclear physicist who has.

I'm pretty sure this question has been answered at some point, though, as you get very similar material coming out of conventional fast neutron reactors in the form of spent fuel.

Re:who says it's molten iron

[CheshireCatCO]

Out of curiosity, did anyone manage to get seismic data by looking at how Jupiter's envelope moved after Shoemaker-Levy 9's fragments hit?

Kind of. I think some groups looked at it, but they were only looking for atmosphere-level diagnostics. (I think the farthest down they thought they might be able to sense was the metallic hydrogen transition.) I don't recall any results from that, actually, so I'm not sure if they really panned out. Certainly I've heard nothing that says we learned about the core.

I'm pretty sure this question has been answered at some point, though, as you get very similar material coming out of conventional fast neutron reactors in the form of spent fuel.

Ooo, good point. Unless they do something to the spent fuel that I don't know about, I've never heard of a worry about the spent fuel restarting itself. Which is probably saying something for our purposes.

Re:who says it's molten iron

[Christopher Thomas]

I'm pretty sure this question has been answered at some point, though, as you get very similar material coming out of conventional fast neutron reactors in the form of spent fuel.

Ooo, good point. Unless they do something to the spent fuel that I don't know about, I've never heard of a worry about the spent fuel restarting itself.

The spent fuel is dissolved in glass (vitrified), which is then encapsulated as glass pellets sheathed in carbon composites for structural strength, to limit possible accidents during handling. These are put in extremely strong barrels, and the plan is to put these in deep mine shafts in non-porus rock and plug the holes with clay.

What's actually done now is storing them as fuel bundles in pools of water, as an interim measure until we can agree on whose mine shaft the waste gets dumped into, but that's another discussion.

Upshot is that the short-term storage doesn't have to worry about the fuel reactivating, and the long-term storage doesn't have enough in one place, and has enough other crud around it, to not have to worry about reactivation.

A construct amounting to a several-mile sphere of radioactive waste, on the other hand, probably _would_ have to worry about it, though a more plausible scenario is a steady-state burn where the rate of outward diffusion of lighter wastes matches their rate of production.

ObDisclaimer about having to run lots of numbers before being able to say what would actually happen in a situation like this.

Re:Measuring the Earth's core?

[Christopher Thomas]

I don't see how measuring the effects on a 10-foot diameter sphere (filled with Na) can be equivalent to the effects on the central core of a 6400km-radius ball of rock (filled with many different elements). If they want to figure out more about the Earth's magnetic field, I suggest they take measurements, etc... on the EARTH.

The nice thing about building our own sphere of molten metal is that we a) know its structure and composition in detail, b) can put sensors inside, and c) can alter parameters (temperature gradient, rate of spin) and see what happens. None of these are practical for Earth, though we do have a reasonably good idea of what its composition and large-scale internal structure are.

The patterns of motion they're setting up are common to a very wide range of fluid systems - you don't need something as big as Earth to generate them. It's very hard to measure fluid flows and magnetic fields deep within the earth (all that's easy is density change boundaries), and the Earth's field isn't likely to flip within our lifetimes (or the next several centuries, minimum, even if the wierdness we're seeing _does_ represent the start of a flip). A small-scale mock-up run in the same turbulence modes that the core has will flip many times during the course of observation, and tell us a _lot_ about how the flipping occurs.

In short, we'll learn a lot more about the geomagnetic field from this experiment than we would from more studies of the Earth itself.

look up

[carambola5]

If they're in Northern USA or Canada, alls they gotta do is look up tonight. Killer auroras in the skies... at least in my neck of the woods.

More to it than the article states

[Anna Merikin]

In the article, it is reported that the earth's magnetic field has been measured to have decreased by ten per cent in 150 years; other articles (from BBC, f'rexample) announced other scientists using tree-sections, have determined the field's strength-loss began about three hundred years ago, and now totals about fifteen per cent decrease.

There also have been reports that the earth's magnetic field within the Ozone Hole has already reversed.

This information does not fit with the nuclear-generator theory, but fits better with the destruction of the ozone layer in the upper atmosphere.

As an FCC-licensed radio/TV engineer, I know that ozone is always produced with electrical current. The article quotes (I paraphrase) an "expert" who says motion, magnetism and electricity are a trinity: where two are found, the other will be too. He should have included ozone and made it a quadernity as this is also true of ozone.

During lighting strikes to earth, ozone first rises from the ground to the cloud, and only then is a conductive path to earth made, enabling the lighting strike.

Also, IF it is true, as contended by many scientists, that the ozone hole is related to the increase in ground ozone caused by human activity (electrical production and photochemical smog, largely) then it MIGHT be that there is only a finite amount of ozone that can be produced (or supported) by the earth's magnetic field, and humanity may fairly be seen as the cause.

But I doubt this is true, as the records in the trees show the magnetic field having begun its decrease three hundred years ago -- before Watt and the industrial revolution.

In any case, this is not an easy study as information is scanty and largely the reserve of specialists rather than the generalists who seem to be the only ones with a large enough world-view (weltenshauung, in German) to grasp the problem and explain it to us.

And I doubt strongly that the subjects of the article have any real klew as to what is happening -- not to say I do.

Re:More to it than the article states

[Anna Merikin]

Since you asked (I don't usually reply to follow-ups) I am an FCC First-Class Radio and Television engineer. I started in 1969 and continued until 1982, when I began writing fulltime. I left the field because I was being asked to falsify data to the FCC.

I agree no one but me has suggested a relationship between ground-level ozone and upper-atmosphere ozone. But a fixed earth mag field would produce (was produced by?) a fixed amount of ozone. It is a reasonable possibility, I think, until disproven. Think about it: there is less and less upeer ozone and more and more lower.

Yes, the researchers are trying hard; I am not trying to insult them (or you) it's just no one seems to see the larger view that the earth is a living system and ozone is its breath (metaphor).

I got my news about the weakening magnetic field from the BBC natural science pages. However, a search of the site has produced nothing.

I sent a friend an email about this subject with a link to a BBC article; it's on a Knoppix partition right now, though, and I'm on my new SuSE installation, so it will be some hours till I MIGHT be able to get the link to the reversed field in the ozone hole off New Zealand.

Here, though, are some other links to support my thesis and informtation.

http://www-istp.gsfc.nasa.gov/Education/FAQs2.ht ml
http://www.theozonehole.com/magnetic.htm
http:/ /www.sciforums.com/showthread.php?t=11632

I wonder...

[charlie763]

I wonder if there is any correlation between the reversal of the poles and evolution. An increased exposure to cosmic radiation may increase the normal rate of mutation of a species. It would be interesting to look at the fossil record and compare the pole reversals with the arrival of new species or, perhaps, even the end of a species.