# Thread: I may as well ask the question : magnetic fields: iron core, or mantle convection?

1. ## I may as well ask the question : magnetic fields: iron core, or mantle convection?

I'm doing a collab with someone and he needs to clarify something before we move on.

How widely accepted is the idea that mantle convection rather than core rotation is the driving force behind a magnetic field, and if it is the case, does that mean that a terrestrial planet or similar body need not possess an iron core to generate a magnetic field?

He seems to think that the mantle convection idea is widely believed. I'm not sure myself.

2. Originally Posted by parallaxicality
I'm doing a collab with someone and he needs to clarify something before we move on.

How widely accepted is the idea that mantle convection rather than core rotation is the driving force behind a magnetic field, and if it is the case, does that mean that a terrestrial planet or similar body need not possess an iron core to generate a magnetic field?

He seems to think that the mantle convection idea is widely believed. I'm not sure myself.
This is the first I have ever heard of the mantle convection idea.

3. Originally Posted by Hornblower
This is the first I have ever heard of the mantle convection idea.
Definitely not mantle convection.

Maybe it was outer core convection? That's the generally accepted theory, partly based on Gauss's calculations that put the source deep within the earth, but not as deep as the solid inner core. (By core rotation, did they mean outer core onvection, or inner core rotation? -- there's not much possibility of it being inner core rotation, because the field rotates with the earth.)

4. Here is a February 2017 webpage about it from Natural Resources Canada

The actual process by which the magnetic field is produced in this environment is extremely complex, and many of the parameters required for a complete solution of the mathematical equations describing the problem are poorly known. However, the basic concepts are not difficult. For magnetic field generation to occur several conditions must be met:

1. there must be a conducting fluid;
2. there must be enough energy to cause the fluid to move with sufficient speed and with the appropriate flow pattern;
3. there must be a "seed" magnetic field.

All these conditions are met in the outer core. Molten iron is a good conductor. There is sufficient energy to drive convection, and the convective motion, coupled with the Earth's rotation, produce the appropriate flow pattern.
There are apparently some ideas about how the mantle (which is just outside of the outer core) might affect things.

Science Daily 2012

Above the liquid outer core is the mantle, the rock in which behaves plastically deformable due to the intense heat and high pressure. At the boundary between Earth's core and mantle at 2900 km depth there is an intense heat exchange, which is on the one hand directed from Earth's core into the mantle. On the other hand, processes within Earth's mantle in turn also affect the heat flow. The interesting question is how the much slower flow in the solid mantle influences the heat flow and its spatial distribution at the core-mantle boundary, and how this will affect the Earth's magnetic field which is produced due to the much faster currents in Earth's core.

5. Originally Posted by Swift
There are apparently some ideas about how the mantle (which is just outside of the outer core) might affect things.
Those sort of things can stabilize the field, or contribute to the field characteristics during a "flip"

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