Understanding Earth's Magnetic Field 58
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."
Fire in the hole! (Score:5, Funny)
Re:Fire in the hole! (Score:1)
Re:Fire in the hole! (Score:2)
Re:Fire in the hole! (Score:1)
Magneto, for sure. (Score:4, Funny)
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.
Re: (Score:1, Interesting)
Re:who says it's molten iron (Score:4, Interesting)
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 (Score:5, Informative)
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:who says it's molten iron (Score:1, Informative)
Re:who says it's molten iron (Score:5, Insightful)
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.
Re:who says it's molten iron (Score:5, Insightful)
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.
Re:who says it's molten iron (Score:5, Insightful)
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.
Re:who says it's molten iron (Score:4, Interesting)
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 (Score:3, Interesting)
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 defle
Re:who says it's molten iron (Score:3, Interesting)
Out of curiosity, did anyone manage to get seismic data by looking at
Re:who says it's molten iron (Score:3, Interesting)
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
Re:who says it's molten iron (Score:3, Interesting)
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
Re:who says it's molten iron (Score:5, Informative)
Re:Measuring the Earth's core? (Score:5, Interesting)
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.
you sure they're scientists ? (Score:3, Funny)
Look closely, one of them is even clearly hunched 8)
Blinded me with science (Score:2)
But it would take a scientist to explain--- eh? Oh, nevermind!
Re:A question (Score:3, Informative)
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 mor
Potential of untold riches (Score:4, Funny)
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
Re:Potential of untold riches (Score:3, Funny)
Then cough up for the energy used to start and keep the thing running. Declare bankruptcy. Move onto street, drink from liquor bottle in brown paper bag.
Re:Potential of untold riches (Score:2, Funny)
Cool! (Score:2, Funny)
If they can simulate iron with sodium, we should be able to figure out a way to simulate irony with sodiumy!
Re:Considering (Score:5, Informative)
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.
Note to self.... (Score:2)
You wouldn't have time to hear the extremly loud KABOOM.
"Earth's" magnetic field? (Score:2, Insightful)
Re:"Earth's" magnetic field? (Score:5, Informative)
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.
look up (Score:4, Interesting)
Speaking of the earths magnetic field (Score:2, Informative)
was spotted in Southern Ontario from about 6pm Eastern to 3:00AM Eastern.
What a treat.
More to it than the article states (Score:3, Interesting)
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 (Score:2, Interesting)
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
Re:More to it than the article states (Score:4, Informative)
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 (Score:1, Troll)
Are you certain there is no connection between ozone and the earth;s magnetic field?
Are you certain there is no connection between the loss of ozone in the upper atmosphere and the increase at ground level (due to human activity?)
And you are incorrect about the constituency of ozone: Ozone, according to my understanding, IS dissociated oxygen -- that is, an unbonded, single oxygen atom instead of a pair forming a molecule.
Ozo
Re:More to it than the article states (Score:1, Informative)
Re:More to it than the article states (Score:2)
Re:More to it than the article states (Score:3, Insightful)
Indeed, if you get picky there is bound to be some connection between the various things we are talking about, but I do maintain that, from my wide reading over a long period, that the accepted view of the scientific community based on decades of observation and experiment is that any such connections are very tiny, and are swamped, for instance, by random variations due to
Re:More to it than the article states (Score:2)
Stratospheric ozone is generated by solar UV light interacting with atmospheric oxygen. Neither is affected by or has an effect on the magnetic field. Stratospheric ozone will be very slightly increased by diffusion of ground ozone, but few ozone molecules will survive that trip...it's
Re:More to it than the article states (Score:2)
There's actually remarkably little relationship between ground-level ozone and stratospheric ozone. Stratospheric ozone is the product of
Re:More to it than the article states (Score:2)
All electric motors produce ozone. All wires that carry varying currents will produce ozone, as ozone is produced be electrical current (any moving magnetic field) in the presence of gaseous oxygen.
I've learned a lot of detail in this discussion, but nothing that daunts my pursuing the answer to my IF proposition, as you quoted above. To me, if the total amount of ozone
I wonder... (Score:3, Interesting)
Re:I wonder... (Score:1)
Re:I wonder... (Score:2)
Cool party chat-up line... (Score:4, Funny)
another possible experiment (Score:2)
Re:another possible experiment (Score:1)
Re:another possible experiment (Score:2)