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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."
I hope the sprinkler system doesn't go off.
I've had this sig for three days.
I sure don't want to be around when lightning strikes one of the scientists during one of the experiments. The reign of Magneto is coming, only he won't be a mutant like we expected.
Don't blame Durga. I voted for Centauri.
The picture made me think of 3 evil magical ones in Charmed preparing a really noxious potion ...
Look closely, one of them is even clearly hunched 8)
It takes 40+ muscles to frown, but only four to extend your arm and bitchslap the motherfucker
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
Eat the Path.
I can think of one way to get really rich of this idea.....
.... profit!!!
Sell air plane fuel? Install one of these puppies near an airport. Ideally a faily busy one like LAX or O'Hare. Turn on the machine. As it takes more fuel for the planes to take off
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.
If they can simulate iron with sodium, we should be able to figure out a way to simulate irony with sodiumy!
Sheesh, evil *and* a jerk. -- Jade
That theory is treated with serious skepticism for a reason. (Well, lots of reasons, really.) I can recall having this discussion here before and I forget the details of the theory, but I recall that the author showed an accute lack of understanding of planetary science among other things. (Jupiter is unlikely to have much more of a given metal than the Earth, oddly enough. The core is only at most about 10 Earth masses, and that's mostly ices. Also, the reactor theory doesn't explain field reversals or why the Sun has a field while dynamo theory explains both fairly naturally. Mind you, no one pretends to understand the details of theory since it's wickedly non-linear, but the basics of the theory seem to be fairly solid.)
Just in your post, I can say that it's unlikely that the field would stop because of build-up of wastes. For one thing, the wastes would either build up or they'd continually be lost. If they *did* build up, they'd slow the reactor down which would cool the system, leading to more sluggish convection and less mobile atoms. That would tend to freeze the wastes in place, not remove them.
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
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.
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.
That theory is treated with serious skepticism for a reason. (Well, lots of reasons, really.) I can recall having this discussion here before and I forget the details of the theory, but I recall that the author showed an accute lack of understanding of planetary science among other things. (Jupiter is unlikely to have much more of a given metal than the Earth, oddly enough. The core is only at most about 10 Earth masses, and that's mostly ices. Also, the reactor theory doesn't explain field reversals or why the Sun has a field while dynamo theory explains both fairly naturally.
Actually, while the original poster's linked model is indeed bunk, it turns out that many of these objections aren't entirely accurate.
For one, the model doesn't dispute that the field arises from a dynamo. All it disputes is the nature of the heat source driving it (near-critical ball of uranium vs. a mixture of radioactives in far subcritical spontaneous decay mode). The mechanism for setting up the field is the same.
For another, if the model's tenets are accepted, field reversals aren't mysterious. The dynamo is shut down and restarted; there's no reason for it to restart with the same field orientation as before. All of the core material is far past the Curie point for holding a residual field, so I'd expect the restarted orientation to be random (constrained only by how the earth's rotation axis affects dynamo flow patterns).
What I find dubious about the model are the claims that a) lithophyllic elements like uranium would be concentrated in the core material, and b) material would diffuse preferentially towards the core strongly enough to result in fractioning, as opposed to just slightly increased concentrations. kT is big, and gravitational potential energy change with location is small down there, so I'd expect material to diffuse anywhere it pleased.
As far as Jupiter is concerned, I can't find references that say that the "icy" chemicals are in the core. As jupiter is expected to be molten throughout (as far as I can find), I'd expect them to diffuse out. Most sources say that carbon and nitrogen are mostly bound as methane and ammonia above the layers of liquid hydrogen. Some of the oxygen is bound as water in the atmosphere, and some of it as silicates in the "rocky" part of the core (which is presumably fractioned into silicates on top of a [molten] iron inner core, as in Earth).
Moot point re. the original article, of course, as you are definitely correct about the rocky core's mass.
Just in your post, I can say that it's unlikely that the field would stop because of build-up of wastes. For one thing, the wastes would either build up or they'd continually be lost. If they *did* build up, they'd slow the reactor down which would cool the system, leading to more sluggish convection and less mobile atoms. That would tend to freeze the wastes in place, not remove them.
My understanding was that the model proposed that they built up, shut down the core, froze in place, kept the core shut down until they decayed enough for the core to be near-critical again, and then dispersed as the hotter core allowed for faster diffusion away from the reactor area. Still pretty dubious, but I'd want to see a fairly detailed model of temperature, reaction rate, and mobility changes before writing that aspect off as outright impossible.
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.
Yeah, I considered that the restarted dynamo would be randomly oriented. That was actually the objection, although I didn't want to go on about it in the original post. You'd expect, in reactor case, to see the new field aligned the same way as before the (dipole!) fieldless period as often as anti-aligned. You don't see that, however. It actually reverses. That requires explanation in the model and the reactor doesn't manage that. A simple, continuous dynamo does it well. (You can get a dynamo with feedback to do this, never mind one as complex as Earth's. And besides, the Sun does it. And we know that the Sun's energy source doesn't shut off every 11 years ;-)
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.)
That said, no, there probably ices there if there is, in fact, a core. (We don't know for certain that there is as the data are sketchy. Oddly, it's easier to tell at the other giant planets.) Under the kinds of pressures at the center of Jupiter, rock and ice would be slushy, we think. We really don't understand the physics all that well for those pressures and temperatures, alas. (Which are, obviously, difficult to reproduce and to model since we have no good equations of state.)
Even if there aren't any ices, you're right that it's a moot point: there's not that much uranium in the planet unless our cosmochemistry is seriously wacked. (That is to say, unless there's a lot MORE uranium in Jupiter than in the Earth and in the galaxy at large. Which then requires an explanation as to where it all came from and how it got enriched in the giant planets.)
What's worse is that you need a lot more uranium than Earth has to generate your heat that way. Jupiter puts significantly more heat that it takes in from the Sun. (Earth takes in about 1360 W/m^2 and adds an additional 0.01 W/m^2 to the outgoing flux due to internal heat. Jupiter's internal heat is of order the same as what it takes in from the Sun. The latter being about 1/30 of what the Earth recieves.)
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 you want other objects, I gots 'em. Like the fact that you need a LOT of uranium to make this work. (Again, where is it coming from?) And that the primorial Earth would have been wickedly active. (Take the heat for formation, heat of differentiation, and add in not the radioactive decay buy a nuclear generator with a LOT more fuel and therefore a much more vigorous reactor. 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. One would need to look at the model to see how hot, but I wouldn't be surprised, say, 3 billion years ago there would be too much heating to leave solid rock lying around.
You raised another of mine, how the uranium headed downward rather than sticking around with the silicates.
stuff
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.
IWARS.
People, in general, disappoint me. Politicians even more so.
Speaking of the earths magnetic field, tonite the Aurora Borealis
was spotted in Southern Ontario from about 6pm Eastern to 3:00AM Eastern.
What a treat.
I'm a big retard who forgot to log out of Slashdot on Mike's computer! LOOK AT ME.
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.
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.
Welcome to the land of the free...pay toll ahead...no photography...please open your bag...
You see, I'm with the nonlinear dynamics and chaos research group.
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.
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.)
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.
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.
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.