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I was contemplating the impact of doping an Earth-like planet's core with a substance that alters its magnetic permeability. Specifically, I considered a scenario where the planet has an improved magnetic permeability by a factor of 2 compared to Earth. I don't care if this is unobtainium.

My initial thought was that this would result in a stronger magnetic field, causing a more powerful deflection of stellar wind. However, I am uncertain about whether this would lead to brighter or fainter auroras. I believe that this would not have a significant impact on technology, and hence, would not disrupt civilization.

On the other hand, I am concerned about the magnetohydrodynamics of the planet's outer core. Would the stronger magnetic field result in greater heating of the core material, leading to increased volcanism or continental drift? Alternatively, could the different core cause the energy balance to shift the other way, cooling the material and resulting in fewer of these effects?

Are there any physicist out there who would hazard a guess?

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  • $\begingroup$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. $\endgroup$
    – Community Bot
    Sep 2, 2023 at 6:24
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    $\begingroup$ I am sorry to disappoint you, but the inner core of Earth is not ferromagnetic, although it is indeed made of iron and nickel. Much too hot. The Curie point of iron is 770 °C (1418 °F). $\endgroup$
    – AlexP
    Sep 2, 2023 at 7:36
  • $\begingroup$ @AlexP: the Curie point will vary depending on pressure, and the Core's likely some entirely different phase that can't even exist at the surface, so that precise value probably has no meaning...but yeah, the magnetic properties are still going to be entirely different, and I'd be surprised if it's still ferromagnetic (or rather, if it becomes ferromagnetic again). At any rate, varying details of the convection would likely make a far bigger difference... $\endgroup$ Sep 2, 2023 at 18:18
  • $\begingroup$ @ChristopherJamesHuff: Doesn't the Curie temperature decrease with pressure? Anyway, we know that the core is not ferromagnetic -- Earth's magnetic field would be very different if it was. (And yes, there is an exotic allotrope of iron which might exist at those immense pressures.) $\endgroup$
    – AlexP
    Sep 2, 2023 at 19:30
  • $\begingroup$ @AlexP From what I've gathered, pressure increases kinetic energy of the atoms, disrupting the magnetic ordering, but it also decreases the volume, strengthening the magnetic ordering. Whether the Curie temperature increases or decreases depends on what effect dominates. And the pressure at the core is so high that iron crystallizes out at the center. I just wouldn't base my expectations of how iron behaves at the core on how it behaves at the surface, in a very different region of its phase diagram. That said, it probably isn't strongly ferromagnetic, just because few things are... $\endgroup$ Sep 2, 2023 at 19:36

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Just look at the terrestrial planets in the solar system:

  • Venus is slightly smaller than Earth and has no intrinsic magnetic field, likely due to insufficient heat flux to sustain the core convection currents required.
  • Mars has a fully liquid core, and its crust has weak remnants of a past magnetic field, but no present one. Possibly again due to reduced heat flux through its largely inert crust.
  • Mercury has a relatively large core for its size, likely with a solid inner core. It has a global magnetic field like Earth's, though weaker.
  • Earth's own magnetic field is highly variable over time, with repeated periods of it having no strong, organized global field, sometimes reorganizing with the opposite polarity afterward. Just 2000 years ago, it was about 35% stronger. It's the strongest of the planetary magnetic fields in the inner system, but it probably isn't at the limit of how strong an Earthlike planet's magnetic field can be.

In short, you really don't need to dope the core with some sort of unobtainium. It's not obviously unrealistic for an Earthlike world to have a magnetic field that's twice as strong.

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