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This is an earth-sized planet, unable to produce an adequately protective magnetic field. Could a moon with a hot, iron/nickel core produce a magnetosphere large enough to encompass the planet and protect it from solar winds and ionizing radiation, to a degree that the planet would be habitable?

In this scenario, I define habitability as 'humans could live here without worry of imminent death, without the use of controlled suits or habitats.'

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  • $\begingroup$ flowing current produce magnetic field, Mars' core somehow cooled at a much faster rate than Earth's. i suppose to speed up the current in the mantle like a boiling kettle requires more energy than some tidal heating🌑 $\endgroup$
    – user6760
    Jan 21 at 9:19

2 Answers 2

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  • The moon magnetic field would protect the moon from the flow of charged particles coming from the star. Only in certain configuration of the moon - planet - star the moon could incidentally shield a bit of the planet from that flow, but not structurally. It could also be that the moon would focus the charged particles on the planet, depending on the specific parameters of the set up.
  • The moon core, due to the smaller size of the moon with respect to the planet, would cool down way faster. Even if the moon offered some protection, it would fade away pretty quickly as the core cooled down.
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  • $\begingroup$ A more realistic configuration would have a habitable moon shielded by a large planet's magnetic field, but even then you'd have to keep the moon out of the radiation belts or the planet will do the opposite of shielding it. $\endgroup$ Jan 21 at 17:28
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The sunward section of the Earth magnetic field is about 64,000 kilometers thick; the side facing away from the sun is 1,300,000 kilometers thick. The moon is 400,000 kilometers away from earth, so its safe at full moon and goes out of safety each month.

If moon was at 36,000km from Earth, it could have a geostationary orbit. Not sure it would last very long though, as the gravitational forces at such a small distance may be too strong and destructive for both, but Roshe limit is 18,261 km so its possible for moon to be at same place on sky without destroying planet with tidal forces.

Now, to our case - if moon will create magnetosphere same as Earth does, planet will be able to remain inside it without reaching Roshe limit. Sometimes planet will go inside polar cusps but even that could be avoided if planet is tidelocked to sun (but its usually bad thing). How long such state will last is hard to tell. enter image description here

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