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Building a Miniature Magnetic Earth
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."
Wait, don't fill it up with anything. The model is accurate right now!
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WTF? Mythbusters created their own planet? Where the fuck do I sign up? I've been worshiping Kari for a long time now, but I didn't know her deity status had been made official!
A 10-foot sphere filled with sodium? Damn... talk about playing with fire.
For large sets, this will be our guide even unto death, for the LORD will work for each type of data it is applied to...
A group at New Mexico Tech 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 Their group page is a bit out of date, though.
My first thought upon reading the summary here was "Man, I really hope they disabled the sprinkler system...
What I'm listening to now on Pandora...
we can throw it in a lake when he's finished? That's a *lot* of sodium.
Do you have ESP?
> An interesting story on NPR this morning, about
> a geophysicist who has constructed a miniature earth
"Everything was modeled with exacting proportionality, including Pamela Andersons fake breasts, approximately 1cm in diameter on the beach-ball sized planet."
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
shouldn't you be commenting on youtube videos or something?
This guy now seems to bring this "sodium party" thing to a new, unprecedented level...
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I hope they remember to dry it out before they put in the sodium.
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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.
Not to study the gross effects of turbulent conductive metal. Simple experiments first, complex experiments later.
"I'm no geophysicist, but I have a hunch gravity has a huge impact on the equation when it comes to the generation of the Earth's magnetic field."
Only in that the earth's core's flow is driven by convection (both/either thermal and compositional)
The static pressure field in a fluid cancels out gravitational effects, so in our experiment (I'm one of the graduate students who's been building the thing) there's just a slight increase in pressure as you go deeper in the sodium that doesn't change its electrical or hydrodynamic properties at all.
In the earth, buoyancy forces are important to stir up the core. In our experiment, we use differential rotation between a pair of spheres to drive the flow. That aspect is not particularly earthlike, but easier to put a lot of energy in.
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.
;-) Looks like we'd also have to coat the sphere with something to prevent corrosion, but honestly, we never considered gallium so I didn't even know that ;-)
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
It's used in a few smaller MHD experiments (as is the eutectic Galinstan); it's convenient (you can build the experiments out of acrylic) and some labs consider it worth the price, but it really doesn't scale well. Sodium is the way to go for large volume MHD experiments.