Warren, you've left out the Coriolis force. It surely plays an important role. Gene
--I find that hard to believe because the flow velocities are very small, and Coriolis force is proportional to velocity.
And I would expect the molten iron to have much higher conductivity than molten silicon rock. But the theory can't just be about fields and rotating conductors, otherwise you could produce a field just by rotation an iron ball.
--A rigidly rotating solid body by itself, can never be a dynamo, as is easy to see. (Also, it would have no way to generate power, vs: convection is continuously powered by radioactive heat.)
The theory must depend on the conductors being carried by the molten convection as well as rotation of the Earth. Brent Meeker
--it indeed does. As I explained in one of my latest posts, molten iron convects up toward poles and down from equator, which is a decidedly non-rigid-body kind of liquid flow, and which IS a dynamo. Furthermore, the rotation of the Earth plays an important role in stabilizing that particular flow configuration as opposed to its time-reverse (which would have been an anti-dynamo featuring negative feedback -- useless). So my current picture, which took a while for me to find, seems to explain a lot plus clearly will produce large enough field numbers: 1. explains why field is normally points parallel or antiparallel to rotation axis 2. explains why Venus no field (not rotating) 3. explains why Mercury<Earth<Saturn<Jupiter in terms of fields 4. explains why Moon has no field (slow rotation, only very small liquid core region) But I would now say I do not understand why Mars has only a tiny field given that Mars is believed to have a liquid metal core and rotates reasonably fast. However, I'm not sure they know a damn thing about Mars' core. Earthquakes and seismic clues tell us what is inside. Moon quakes are not powerful enough to see the Moon's core with the seismic sensors Apollo put on the Moon, and so its presence is less certain. For Mars presumably things are still less certain and I do not think they really know if it has a liquid core, nor do they have any accurate estimate of its size. All they have are models constrained by gravitational measurements, which is not good enough. Both Moon & Mars geo-tectonically dead and hence have only tiny quakes. So it might be that Mars contradicts my picture, but I do not think that will be clear until at least 2016 when they plan to land a seismometer there.