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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.
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.
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