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A widely accepted theory for how the Earth's magnetic field is generated is the dynamo theory. Dynamo theory describes how molten magma convection currents containing metal are locally spun the same direction by Coriolis forces, producing a magnetic field.

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If Earth's outer core was solid, this effect would go way. However, the metals in the interior would still be moving (though all together) due to the Earth's rotation. Would Earth still produce a magnetic field? If so, how would it compare to our current field? Would it still help shield the atmosphere from charged particles?

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    $\begingroup$ Very cool question! There are two uncommented votes to close so far and they might be about topicality. I think that this is the type of question that can be simultaneously on-topic here in Astronomy SE as well as in Earth Science SE and Physics SE because understanding why Earth's molten core produces a magnetic field is important for planetary science, but how a portable generator makes electrical power without permanent magnets nor a molten core is a nifty Physics question. $\endgroup$ – uhoh Dec 3 '20 at 1:18
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    $\begingroup$ @uhoh If it gets closed, maybe I will try to re-post in different terms. I never took an electromagnetics course and I am very curious about these processes. $\endgroup$ – Connor Garcia Dec 3 '20 at 2:19
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    $\begingroup$ This is clearly Astronomy AND Earth science. That can happen sometimes. Astronomers are very interested in what gives a planet a magnetic field. I also think it's an area that's still being studied. On the one hand the liquid core and motion of the hot plasma temperature iron in the outer core generates the field. I've also heard it argued that the Moon plays a key role and Earth's crust rotates slower than it's inner core, creating a kind of drag. Earth might maintain it's magnetic field for a long time because of the Moon - but I don't think anyone really knows. $\endgroup$ – userLTK Dec 3 '20 at 2:32
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    $\begingroup$ To answer part of your question, this answer says that the flow must be complex, so a solid core just rotating would probably not generate a magnetic field. It would if it was charged but if it was solid, I don't believe it would hold a charge of any significance. When it flows it can maintain temporary charges and in a sense, interact with itself, the electric charge generates magnetism, the magnetism guides the electric charge, it's self sustained by the turbulence. physics.aps.org/story/v19/st3 But I'm a little out of my depth to turn this into an answer. $\endgroup$ – userLTK Dec 3 '20 at 2:39
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    $\begingroup$ I took the liberty to change "interior" by "outer core" in the title and question, as the Earth's most interior part, the inner core, is solid. $\endgroup$ – Jean-Marie Prival Dec 3 '20 at 11:21
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We have an excellent reference of what would happen to the Earth's magnetic field if it had a solid core: we can look at Venus' magnetosphere. Its internal magnetic field is dominated by the remanent crustal magnetization and its external magnetic field by the induced currents and their magnetic field in the ionosphere. The magnetic field mostly misses any dynamo part due to Venus' very slow rotation (even though it also has a similar internal structure like Earth).

Thus as a result, the Earth's magnetosphere would shrink considerably had it as little rotation and/or no liquid outer core. With only a solid core remaining, it would also only be able to produce some small remanent magnetization which is usually MUCH less than any self-feedback dynamo like Earth, Jupiter, Sun,... are able to produce. Erosion of the upper atmosphere would be much stronger and we could enjoy polar lights about continuously and even at low lattitudes as we'd loose considerable magnetic field strength, especially of the dipole moment.

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  • $\begingroup$ +1 This is a pretty good answer, but I think it would be even better with some estimates of magnetic field strength for the solid vs liquid outer core and an explanation of how they are computed and the physics behind it. For example, I can't tell from your answer if a slowly rotating solid earth would generate a weaker magnetic field than a faster rotating solid earth. $\endgroup$ – Connor Garcia Dec 3 '20 at 23:00
  • $\begingroup$ Explaining planetary dynamos is certainly interesting, but more a separate question question IMHO $\endgroup$ – planetmaker Dec 3 '20 at 23:11
  • $\begingroup$ The magnetic moment of a rotating magnet - and a solid earth would be nothing else - is the same as a non - rotating. You can try that on your table with toy magnets. No dynamo, no dependence of the magnetic moment on rotation. $\endgroup$ – planetmaker Dec 3 '20 at 23:15

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