« on: 23/09/2018 11:22:06 »
Quote from: OP
There is a metallic flow but that won't produce a magnetic field, either.The energy source is the heat released by the liquid outer core slowly solidifying, causing the solid inner core to slowly expand over time. This heat release causes convection currents in the liquid outer core.
The magnetic field itself is produced by electrical currents in the liquid nickel/iron, produced by magnetohydrodynamic effects.
In laboratory experiments, two additional factors are needed to kick-start the dynamo:
- Differential rotation of Earth's solid inner core and the mantle
- a "seed" magnetic field (that may have come from the solar magnetic field?)
These effects have been reproduced in the lab using a model with liquid sodium instead of liquid iron. One of the more recent experiments is described here:
the temperature is well over the Curie temperature so the iron and nickel are non-magnetic.Sodium is not ferromagnetic, and yet the effects are reproducible in the laboratory because the metallic flow and electrical currents are similar (just faster).
The Sun also displays a magnetic field - the Sun is composed mostly of a plasma of Hydrogen and Helium; these elements aren't ferromagnetic either.
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