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Understanding Earth's Magnetic Field 58

Posted by michael
from the hot-and-wet dept.
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."
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Understanding Earth's Magnetic Field

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  • by addaon (41825) <addaon+slashdot.gmail@com> on Sunday November 07, 2004 @07:12PM (#10749543)
    I hope the sprinkler system doesn't go off.
  • by AtariAmarok (451306) on Sunday November 07, 2004 @07:23PM (#10749629)
    "This project involves more than 14 tons of sodium metal and a 10-foot stainless steel sphere."

    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.

  • by austad (22163)
    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 lighte
    • by Undefined Parameter (726857) <[moc.oohay] [ta] [modeerf4leuf]> on Sunday November 07, 2004 @07:55PM (#10749865)
      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
      • by CheshireCatCO (185193) on Sunday November 07, 2004 @08:41PM (#10750259) Homepage
        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.
    • by CheshireCatCO (185193) on Sunday November 07, 2004 @08:57PM (#10750391) Homepage
      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.
      • by Christopher Thomas (11717) on Monday November 08, 2004 @12:28AM (#10751761)
        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.
        • by CheshireCatCO (185193) on Monday November 08, 2004 @01:14AM (#10752003) Homepage
          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.
          • by Christopher Thomas (11717) on Monday November 08, 2004 @11:29AM (#10754602)
            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 defle

              • 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
                • 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.

                    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
    • by krymsin01 (700838) on Monday November 08, 2004 @02:52AM (#10752363) Homepage Journal
      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;
  • by da5idnetlimit.com (410908) on Sunday November 07, 2004 @07:36PM (#10749728) Journal
    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)
  • "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?"

    But it would take a scientist to explain--- eh? Oh, nevermind!
  • by failedlogic (627314) on Sunday November 07, 2004 @08:08PM (#10749983)
    I can think of one way to get really rich of this idea.....

    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 .... 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 .... profit!!!

      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.
  • Cool! (Score:2, Funny)

    by Black Parrot (19622)


    If they can simulate iron with sodium, we should be able to figure out a way to simulate irony with sodiumy!

  • ...Don't accidentally tip the (imaginary) precariously perched buck-o-water into that thing.

    You wouldn't have time to hear the extremly loud KABOOM.
  • 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.
    • by Christopher Thomas (11717) on Monday November 08, 2004 @12:40AM (#10751831)
      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.
  • look up (Score:4, Interesting)

    by carambola5 (456983) on Monday November 08, 2004 @03:14AM (#10752464) Homepage
    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.
  • 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.
  • by Anna Merikin (529843) on Monday November 08, 2004 @08:39AM (#10753410) Journal
    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.

    • by stevelinton (4044) <sal@dcs.st-and.ac.uk> on Monday November 08, 2004 @10:24AM (#10753982) Homepage
      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.

      • Wow! I ususally don't reply to followups, but I HAVE to ask you some questions.

        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
        • by Anonymous Coward
          Ozone is O3.
        • I'm not unshakingly, go to my death protesting it, deep-rootedly certain of these points from my own personal knowledge and experience.

          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
    • Ground ozone is generated by human activity, and is independent of the magnetic field. The ozone molecule itself is neutral and exists in extremely tiny concentrations, and can have no measurable effect on the magnetic field.

      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
    • 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.

      There's actually remarkably little relationship between ground-level ozone and stratospheric ozone. Stratospheric ozone is the product of

      • ...you'll only get ozone around high voltage equipment (where there is corona discharge) or where circuits are being opened and closed.

        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)

    by charlie763 (529636) on Monday November 08, 2004 @09:41AM (#10753708) Homepage
    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.
    • There would be a rather large delay between a cosmic-radiation triggered mutation and the point where it would become common enough in a species to leave its mark in the fossil record. Probably a significant fraction of the average time between field pole reversals (which is about 200,000 years). That would make finding a pattern near impossible.
    • This is true. However, there may be much faster mechanisms for *die*-offs than radiation-induced mutations, such as if a species or superset of species specifically rely on Earth's magnetic field for migration, etc. If the field suddenly reduces in strenth or changes direction, the migration paths of these animals may be radically altered, with the result that they may migrate to low- (or higher-) food areas, into areas with fewer predators, into areas where parasites are able to take advantage of them, etc
  • by jpop32 (596022) on Monday November 08, 2004 @09:43AM (#10753723)
    You see, I'm with the nonlinear dynamics and chaos research group.

  • spinning 14 tons of molten Na is impressive - but sodium metal is not not very paramagnetic - the atoms have only one unpaired electron per atom, unlike iron. What's wrong with doing experiment with molten iron? I wonder if somebody tried to bring a magnetometer into a steel mill - to detect the changes in magnetic fields generated by hundreds tons of molten iron flowing around. While this may not be as controlable experiment as playing with the sodium sphere I think it is more relevant to the actual condit

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