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Earth Science

Building a Miniature Magnetic Earth 150

Posted by CmdrTaco
from the don't-bring-your-laptop-near-there dept.
Doofus writes "There was an interesting story on NPR this morning about a geophysicist who has constructed a miniature earth to model the earth's dynamo effects. Dan Lathrop, a geophysicist at the University of Maryland, has constructed a 10-foot diameter stainless steel sphere. He intends to fill the sphere with molten sodium and spin the sphere to examine the propensity for the system to generate its own magnetic field. The article includes both video, in which Lathrop spins up the sphere, and audio, including the conversion of magnetic wave functions in prior experiments into audible sound: literally the music of the spheres."
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Building a Miniature Magnetic Earth

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  • by Ecuador (740021) on Monday June 02, 2008 @10:36AM (#23626767) Homepage
    Wait, don't fill it up with anything. The model is accurate right now!
  • We're going to go create our own dome, a dome within a dome. So don't come knockin on our door!
  • by X0563511 (793323) on Monday June 02, 2008 @10:46AM (#23626881) Homepage Journal
    A 10-foot sphere filled with sodium? Damn... talk about playing with fire.
    • They actually did have a small file when some leaked out. The fire department was called, but they couldn't do anything.
      • by SpinyNorman (33776) on Monday June 02, 2008 @11:07AM (#23627141)
        You can't use water or CO2 (reacts with sodium) on a sodium fire, but if you're messing with large quanties of liquid sodium you'd think they'd have done their homework and know what to use (as well as to inform the fire dept that it's a sodium fire they're being called for).

        http://www.ilpi.com/safety/extinguishers.html#Picking [ilpi.com]
        • Re: (Score:2, Insightful)

          by Talderas (1212466)
          Later on though, they say you should have a non-magnetic fire extinguisher if you're going to be using it in an area with magnetics.

          I can only surmise that they need non-magnetic Class D fire extinguishing equipment. You don't know if their experiment will generate a magnetic field or not.
          • by Pope (17780)
            If it's anything like a crystal skull, it'll only be selectively magnetic, like when you look directly at it.
        • by evanbd (210358) on Monday June 02, 2008 @11:56AM (#23627757)

          For many types of fires, including reactive metal fires, best procedure is to just let it burn if possible. In this case, I imagine you'd build the setup so that that *was* possible, and then focus your efforts on making sure you could get everyone out of the way efficiently. A huge pool of burning sodium is certainly dramatic, but if there's no person or property in danger then there's no necessarily anything wrong with it. The caustic lye dust should fall out of the air rapidly; don't stand down wind.

          When it comes to exotic fires, there are techniques to fight them -- but by far the preferred one is to not fight it at all. Besides, suppose you did put it out -- you now have a damaged sphere of molten sodium that already caught fire once. Are you planning to approach it? I'd rather stand back and wait for it to go out if at all possible.

          I'm sure they've informed the fire department, and I'm sure the fire department intends to get involved only if there's an immediate danger to life, or a risk of the fire spreading -- in which case they'll likely try to contain it without putting it out.

          • While I'm sure they have informed the fire department, as a resident of College Park, I can assure you that the fire department is your typical two engine operation. I seriously doubt they have the capacity to handle a ten foot sphere of sodium.
            • as a resident of College Park ... I seriously doubt they have the capacity to handle a ten foot sphere of sodium

              It's like this.

              You could inhale a load of ash and need serious and expensive medical attention. Then again ,you could get pro-active and install a water tank somewhere uphill from the sphere, with say a 10 Kl capacity. If there is a problem, you release the water.

              Sure, it'll cause a larger, more violent reaction, bathing you in sodium hydroxide and turning you into soap, but at least you will t

            • by sumdumass (711423)
              Sometimes, even more sophisticated fire departments can be found lacking when it comes to certain unusual or non-typical fires. I remember getting called to a Hazmat scene when I work at an environmental services company. There was two different township stations (the typical two engine stations) and a city station with sent three of their 6 engines. It was near a large city area just outside of town too. I won't name the city because of does us no good but it has an international airport and profesional sp
          • by rossdee (243626)
            A tanker of liquid nitrogen would do a pretty good job. I don't think Sodium reacts with it and it would cool it down pretty quickly. Of course liquid Helium would do an even better job but would be very hard to obtain.
        • by Firehed (942385) on Monday June 02, 2008 @11:59AM (#23627821) Homepage

          if you're messing with large quanties of liquid sodium you'd think they'd have done their homework and know what to use

          A new pair of running shoes?
          • Re: (Score:2, Funny)

            by R2.0 (532027)
            "A new pair of running shoes?"

            More likely a spare pair of underwear.
    • Re: (Score:1, Informative)

      by Jay Maynard (54798)
      No kidding. A 10-foot diameter sphere has a volume of 14,826,654 cc. I couldn't find a figure for density of molten sodium, but even if it is (as is likely) less dense than the solid form's 0.97 grams per cc, that's still upwards of 10,000 metric tonnes of molten sodium.

      Where is this? I'm staying the hell out of that city...
      • Re: (Score:1, Informative)

        by Anonymous Coward
        Check your math.
        • by VanessaE (970834)
          For the benefit of the GP above who got the last equation wrong, and anyone else who cares to read:

          The volume of a sphere: Volume = (4/3) * (pi * r^3)

          Since the sphere is 10 feet in diameter, the radius is 5 feet (let's assume that's the inside radius).

          5 cubed is 125, so: Volume = (4 / 3) * (3.14159265 * 125)

          Which works out to about 523.598775 cubic feet. Google's calculator says that's about 14.8266662 cubic meters.

          Wikipedia says that, in liquid form, sodium has a density of about 0.927 kg per c

      • No problem, his next research program can be into liquid metal fast breeder reactors [wikipedia.org].
        • by hkfczrqj (671146) on Monday June 02, 2008 @11:15AM (#23627245)
          Just FYI, one of the technicians working in this experiment used to work in a nuclear submarine, I presume taking care of the cooling of a reactor. I don't know what kind of reactors they use in the Navy, but Dr. Lathrop told me that this guy knows how to handle liquid sodium. (Disclaimer: I'm in a collaboration with Lathrop's lab, though in another experiment.)
          • Re: (Score:3, Interesting)

            by Otter (3800)
            Just FYI, one of the technicians working in this experiment used to work in a nuclear submarine, I presume taking care of the cooling of a reactor. I don't know what kind of reactors they use in the Navy, but Dr. Lathrop told me that this guy knows how to handle liquid sodium.

            The only US sub with such a reactor was the Seawolf in the 1950s. If the tech is Russian -- Alfa's have lead-cooled reactors, not sodium-cooled, IIRC.

          • by treeves (963993) on Monday June 02, 2008 @02:38PM (#23629647) Homepage Journal
            US Navy uses all Pressurized (light) Water Reactors.
            I was on a boat with an S5W reactor (S for submarine, W for Westinghouse). I did my prototype training (the hands on training that nucs do before going out to the fleet) in upstate NY at the D1G reactor (G for General Electric, D for destroyer). Also at that facility were a couple of interesting reactor designs, one of which used liquid sodium as coolant (it was no longer in operation by the time I got there in 1987) and another, called MARF, that used gadolinium-lined, well I don't know what to call them, but they were like toilets, and they were neutron moderators, so when you wanted to SCRAM the reactor you dumped the water out of them, like flushing a toilet, and reactivity immediately dropped to subcritical.
      • by hkfczrqj (671146) on Monday June 02, 2008 @11:10AM (#23627183)
        Dan Lathrop works at the University of Maryland... probably you already have other reasons to stay out of thar region of the US.
      • by mapsjanhere (1130359) on Monday June 02, 2008 @11:20AM (#23627303)
        googling "density liquid sodium" would have given you 927 kg/m^3 as the correct number
        doing your unit conversions correctly would have given you 13.77 tons
        and I get scared with a kilo in my reactions - I'm a wimp
        • Hm. Somehow, I couldn't turn up that number.

          Yeah, my conversion from grams to tonnes was off, too...but even so, 13.77 tonnes of liquid sodium is something I want to be nowhere close to.
      • M=D x V
        M=0.97g/cc * 14,826,654cc = 14,381,854.38g = 14,381.85438kg ~ 14.4 tonnes
      • by oodaloop (1229816)
        10,000 metric tonnes? What?

        If it were filled with water, it would about 6,500 lbs. I think your math is a *little* off.
    • by mangu (126918) on Monday June 02, 2008 @11:25AM (#23627373)
      Here [theodoregray.com] are some interesting (true) stories on what happens when sodium hits water. But those are about small blocks, one kilo or so, and solid at ambient temperature.


      This guy now seems to bring this "sodium party" thing to a new, unprecedented level...

    • Re: (Score:2, Informative)

      by Anonymous Coward
      Working for a small fire department, I can just about guarentee that consulting and preplanning with the fire department would be about the last thing anyone in this project did.

      Many many people have a disaster plan that reads 'if something goes wrong, call fire department' without ever considering whether the fire department is equipped to deal with their particular problem.

      I have two agricultural chemical companies in my area that deal with chemicals that they measure in tons. I went to visit them to try
  • Couldn't he have gone to the local fairground and used one of those cyclotron things where you get stuck to the side of a giant drum? Take the people out, fill it with sodium. Or one of those candy sugar spinny things that makes clouds on a stick? They're awesome. Science is awesome and has lots of sugar. Wait, salt is sodium chloride, he could make candy floss out of salt? What has science done!
  • Been Done (Score:5, Informative)

    by Stranger4U (153613) on Monday June 02, 2008 @10:47AM (#23626903)
    A group at New Mexico Tech [nmt.edu] was working on a similar experiment using a cylindrical chamber filled with liquid sodium and a way to introduce turbulence to create magnetic fields. This was started over ten years ago. Their group page [nmt.edu] is a bit out of date, though.
    • by timster (32400)
      Isn't this experiment an expansion and continuation of that sort of research? Not really so much something that's "Been Done"? Are you saying that the previous work has already answered all these questions?

      The story mentions that this guy has worked with smaller simulations before, so it's not as if we're being told that this is some brilliant new idea. It's just sort of cool that somebody built such a large sphere for this purpose.
  • by Otter (3800) on Monday June 02, 2008 @10:48AM (#23626905) Journal
    Sodium becomes liquid at stovetop temperatures and conducts electricity well, but it's flammable. A sodium fire can't just be put out with water. Water can actually make things worse -- Lathrop's team has disabled the sprinkler system.

    My first thought upon reading the summary here was "Man, I really hope they disabled the sprinkler system...

    • Re: (Score:2, Insightful)

      by X0563511 (793323)
      Class D fires are not fun.
    • by Chris Burke (6130)
      My first thought upon reading the summary here was "Man, I really hope they disabled the sprinkler system...

      Yeah, no kidding. That little caveat there about water making things worse is kinda an understatement too. More like "Water can actually make things kaboom". Or, at least if you're watching from a safe distance, it would also be accurate to say "Water can actually make things awesome."
      • by pragma_x (644215)

        Water can actually make things awesome.
        Being someone who lives just over the county line from College Park (I can hear the Terps play half the time and see the light pollution from the stadium), I couldn't agree more.
  • ...the start of a howie mandel joke?
  • Well, sass that hoopy. Bypass construction notwithstanding, should be an interesting project. Frood really seems to know where his towel is at.

    (Too easy)
  • any chance (Score:5, Interesting)

    by Trailer Trash (60756) on Monday June 02, 2008 @10:57AM (#23627017) Homepage
    we can throw it in a lake when he's finished? That's a *lot* of sodium.
  • He's got Balls of Steel!
  • I gotta wonder if they thought about installing and FM-20 or other extinguisher system in the room, and disabled the sprinklers. If they didn't, someone let me know what building it's in so I can stay away. Far away.
  • solid core? (Score:2, Insightful)

    by Gothmolly (148874)
    Don't you need the solid iron core, so that you have the 2 iron pieces separated by the liquid (sodium) mantle ?
  • It would be music of the sphere. Singular. Sounds much less enchanting for some reason. Must be an innate preference for plurality.
  • by Jerry (6400) on Monday June 02, 2008 @11:57AM (#23627787)
    So, how is spinning a neutral liquid metal going to create an electric field?

    Are they hoping that rotating Sodium will be like moving a solid piece of Iron through the magnetic field of the earth, inducing current in the Sodium, which then creates a secondary EMF, which then creates a secondary magnetic field...?

    Without Earth's magnetic field are they lifting themselves by their own bootstraps?
    • Re: (Score:3, Insightful)

      by pclminion (145572)

      Are they hoping that rotating Sodium will be like moving a solid piece of Iron through the magnetic field of the earth, inducing current in the Sodium, which then creates a secondary EMF, which then creates a secondary magnetic field...? Without Earth's magnetic field are they lifting themselves by their own bootstraps?

      I don't see why it's a problem. The same arguments apply to Earth itself. Could the Earth's magnetic dynamo have formed without the influence of the sun's magnetic field? It's a legitima

  • Why sodium? (Score:4, Interesting)

    by Fallen Andy (795676) on Monday June 02, 2008 @11:58AM (#23627805)
    Anyone out there can explain to me why he wouldn't use e.g. Gallium ? Sodium sure isn't the safest stuff to have around molten.

    Andy

    • Re:Why sodium? (Score:4, Informative)

      by njh (24312) on Monday June 02, 2008 @01:03PM (#23628567) Homepage
      At a guess, price. Metallic sodium cost about $1/kg I think, Gallium costs perhaps $2000/kg.

      Mercury is probably too heavy, Tin is an option, though it needs to be hotter. Finally, metals are different, perhaps sodium is the most like molten iron/nickle in electronic structure or something.
      • by evanbd (210358)
        As you say, I'm sure price is the primary reason. But mercury? You have to be kidding. The toxicity and environmental issues make the sodium look easy to handle. It also costs ~10x the price of sodium per kg, and is 14 times as dense -- so it's 140x as expensive if they care about volume rather than mass (I'm guessing they do, but I don't know). And yes, I know metallic mercury is the least problematic form -- but that doesn't make it harmless, especially in the eyes of safety inspectors and insurance
        • by njh (24312)
          Yes, metallic mercury isn't too bad, as long as it doesn't get into the water ways (if it does it is readily converted to methylmercury, nasty stuff). There are gold mining towns that still have mercury puddles lying around after 150 years without significant problems. But they are dry places.

          I agree though: Mercury is expensive, particular given its density (and hence multiplier for volumetric uses). Tin is a similar price.

          (Then there is the whole terror of mercury thing, which is strange considering ho
    • Re: (Score:3, Informative)

      by n3umh (876572)
      Three major reasons:

      1)Price. Like others have said, it's a kilobuck a kilogram. Sodium is cheap, they just electrolyze salt in a plant in Niagara Falls where they can get cheap hydro power.

      2) Density. I think a Gallium filled sphere would weigh 95 tons. Our campus structural engineer already had us shore up the floor for this one.

      3) Electrical conductivity. Sodium is a factor of 10 more electrically conductive than Gallium.
      • by njh (24312)
        3) Electrical conductivity. Sodium is a factor of 10 more electrically conductive than Gallium.

        incidently, what a scale corrections for this are you using? Magnetic reynolds/permitivity etc?
  • Sounds like an interesting experiment. However, I have to wonder how accurately it can possibly represent the mechanisms in Earth's core. Just a few things off the top of my head:

    • Density of sodium is nothing like that of iron
    • Conductivity of sodium is different
    • Viscosity of sodium is different
    • Various constants of electromagnetic self-interaction are different for sodium vs. iron
    • The pressure at Earth's core is much larger than anything achievable in this experiment
    • The scale isn't even close

    I wouldn'

    • by Chuckstar (799005)
      Another thought I had is that the effect of the sodium's weight on Earth could perturb the experiment.

      I was originally going to write "the gravitional field from Earth could perturb the experiment", but its not really the field that's the issue. The Earth's magnetic field formed in the Sun's gravitational field. But the Earth's core is in free fall around the sun, so does not feel any weight. (In the Earth's core, down is toward the center. In this experiment, down will be towards some direction outside of
      • by pclminion (145572)

        I was originally going to write "the gravitional field from Earth could perturb the experiment", but its not really the field that's the issue. The Earth's magnetic field formed in the Sun's gravitational field. But the Earth's core is in free fall around the sun, so does not feel any weight. (In the Earth's core, down is toward the center. In this experiment, down will be towards some direction outside of the sphere.)

        Good point as well. It would be interesting to see the difference in results if the ex

  • by dpbsmith (263124) on Monday June 02, 2008 @12:10PM (#23627957) Homepage
    I hope they remember to dry it out before they put in the sodium.
    • by ultranova (717540)

      I hope they remember to dry it out before they put in the sodium.

      Why ? You need a heat source for the whole thing to be authentic, right ?

  • A miniature ball with its own force of gravity. Who else thought this is a Katamari Damacy in the making?!
  • I noticed the article mentioned the Earth's internal turbulence. Would the way the Sun's and Moon's gravitational pull deform the earth's geometry be a partial cause of turbulence within the earth's molten core?

    If no, why not?

    If yes, is this experiment accounting for something like that?

    Would something like this even have an effect on the magnetic field?
  • by peter303 (12292) on Monday June 02, 2008 @12:38PM (#23628295)
    Several groups such as Glatzmeir at Harvard have tried computer simulations. Since it is a non-linear, turbelent phenomena they have to make a very small grid with a large number of grid cells. It took 80 days of NSF supercomputer time in the mid-1990s.

    Plus there are some uncertainties:
    (1) The equations of state at the high pressures and temperatures inside the earth arent well known. People have squished minerals in diamond presses or in super-guns to measure the equations of state. However a Berkeley group claims the inner-most core is twice as hot as others claim. A factor of two uncertainty is not good.
    (2) The coupling of elastic equations with magnetic equations is not well thought out either. People have done each independently fairly comprehensively, but not both together.

    The Harvard guy got some interesting results:
    (1) There is an inter-play between the solid inner iron core and liquid iron outer core. The solid holds magnetisation better than the liquid. So he sees over a hundred thousand year simulation a "flickering" as the field looks like it might reverse then really doesnt. Then eventually it reverses about every 40,000 years. This is a little faster than observed in rocks. Currently the earth's magnetic field is abotu 10% weaker than meaured right around 1800. People think is this more likely a "flicker" than an impending reversal, but who knows?
    (2) The model predicted convection spins the whole core once time extra about every 400 years. Convection is driven by both thermal and magnetic force. Seismologists have looked for this "extra core day" and think they have found it. There has been comprehensive global seismic data for about 45 years, or about a tenth of a rotation. Seismologists have see inner core velocity anomalies moving about this rate. You know a theory is really fabulous when it predicts something completely unexpected such as extra core days, and then scientists verify it.
  • n/t
  • I was reminded of the novel "Richter 10" by A. C. Clarke and Mike McQuay, where they use a somewhat similar (albeit much more complex) device to predict earthquakes.
  • There's a eutectic alloy of sodium and potassium that's liquid at room temperature. I guess they're not using gallium, which is safer than sodium, because it's incompatible with steel.
    • Re: (Score:3, Informative)

      by n3umh (876572)
      I'm fairly certain NaK is a significant autoignition risk compared to Sodium. Sodium at the temperatures we run the experiments at just slowly forms a white oxide crust as it freezes. I think NaK might just catch fire.

      As far as gallium goes, if you've got $100 million dollars to spare and maybe another $5 million to upgrade our floor to take an extra 80 tons of load or so, we can talk ;-) Looks like we'd also have to coat the sphere with something to prevent corrosion, but honestly, we never considere

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