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Is it necessarily a given that a compass (as they magnetically function on Earth) could be made to function similarly on an alternate, Earth-like, ringed planet?

Another way of asking: is it feasible that the magnetic attributes of another planet could be different than Earth's (possibly making an instrument like a compass nonexistent in that world) and that planet still support flora and fauna similar to Earth?

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  • $\begingroup$ smh, google 'Earth's Magnetic Poles' $\endgroup$ – anon Nov 8 '18 at 23:33
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    $\begingroup$ In short: Yes. Doesn't need a full answer. As long as the rings aren't made of magnetized material, there's no reason why a compass shouldn't function as far as I know. That said, your question comes across slightly unclear. I assume you're asking about a ringed planet like Saturn but with Earth's environment, composition, and atmosphere. If you mean a planet that is a ring, then I don't know. $\endgroup$ – Sora Tamashii Nov 8 '18 at 23:33
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    $\begingroup$ I believe they're asking for a way to make compasses not work, rings and other conditions aside. $\endgroup$ – B.fox Nov 8 '18 at 23:52
  • $\begingroup$ In that case it should be stated more clearly. Either way, my comment does explain how to do that then... So... shrugs $\endgroup$ – Sora Tamashii Nov 9 '18 at 0:09
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The requirement of a compass behaving sensibly is that a planet has a reasonably smooth bi-polar magnetic field. Under such circumstances the lines of force always point towards one of the magnetic poles on the planet's surface, and therefore the compass always points in the same direction.

You also mentioned fauna. The Earth's magnetic field is a vital part of maintaining the biosphere because it acts to deflect molecule-shredding cosmic rays of varying sorts. Maintaining life without having feasible compasses thus leaves us with a problem to solve.

Non-working compasses and living fauna require either:

  • No proper magnetic field, and highly radiation resistant lifeforms
  • No proper magnetic field, and subterranean lifeforms
  • Something funky about the magnetic field that maintains deflection of cosmic radiation & solar winds, but messes up the compass.

Things that could interfere with the a compass:

  • Large, frequent, random deposits of ferromagnetic material causing localised distortions in the EM field (compass won't reliably point in a single direction)
  • A multi-polar magnetic field. That said, this is a tough sell: we don't know if this is possible in the long term, or if the magnetohydrodynamics planetary bodies force a dipole. The planets in the solar system with magnetic fields are not like this
  • The planet is iron-poor. There are no ferromagnetic materials readily available, so no society can invent the compass.
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    $\begingroup$ In the case of having rings of highly ferromagnetic materials circling the globe, could this ring, in theory, offset the magnetic pull of the compass significantly enough to make compasses effectively useless? (Basically, the equivalence of having two magnets messing with a compass, is what I'm getting at.) $\endgroup$ – Sora Tamashii Nov 9 '18 at 0:12
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    $\begingroup$ @SoraTamashii the reason magnets make compasses useless is because they are too close to serve as useful reference points. The ring you describe certainly modifies the shape of the magnetic field, making compass reading less straightforward, but still dependent on stable reference points which you can base navigation on. $\endgroup$ – Alexis Nov 9 '18 at 0:19
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    $\begingroup$ My instinct is that any highly magnetized ring material will, itself, be deflected by Earth's magnetic field until it's no longer part of the ring (either ejected or deorbited). I don't have any math to back that up, though. $\endgroup$ – Cadence Nov 9 '18 at 0:41
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    $\begingroup$ A magnetic orbiter would be generally unstable yes. The only marginally stable orbit is that perpendicular to the magnetic field axis, but it is an unstable equilibrium (and magnetic fields fluctuate and the magnetics poles move). $\endgroup$ – Mark_Anderson Nov 9 '18 at 5:14
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    $\begingroup$ On the rings specifically, they are actually quite hard to make magnetically active. It's the tyranny of Newton's Laws: if they are magnetic enough to have interesting effects and push things around, then the rings experience significant magnetic pushes on themselves (from their interactions with the planet's magnetic field). Under such circumstances it is very hard to get a stable orbit, if not actually impossible. $\endgroup$ – Mark_Anderson Nov 9 '18 at 17:14
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If you want to use a magnetic compass the way we use it on Earth, you need two conditions:

  • a stable bipolar magnetic field
  • the axis of the above magnetic field shall be aligned with the rotation axis of the planet.

If the latter condition is not satisfied, you compass will be pointing you at a different direction as the time passes by, significantly lowering the usefulness of such an instrument.

You can still use a gyroscopic compass, though, which would not be influenced by the magnetic field.

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  • $\begingroup$ The second point is much insightful, I must say. Pole-switching takes a few thousand years and has your poles pointing in weird, not-opposite, rotationally mis-aligned ways, so yeah, enough time to have a story And the Gyroscopic compass, I learnt something new $\endgroup$ – Varad Mahashabde Nov 9 '18 at 10:25

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