4
$\begingroup$

Most planets have magnetic poles that align pretty well with their geographical ones. On earth, for example, the magnetic dipole field is tilted about 11 degrees from the rotational axis. As far as I understand, this is a consequence of how the magnetic field is generated. While I am by no means an expert on dynamo theory, here's the gist of what I understood: convection current in the molten outer core generate magnetic fields. The Coriolis effect aligns them into (vaguely) helical flows and thereby aligns the fields into a planet-wide magnetic dipole field. Similar processes also apply to gas giants, but I don't think they are relevant here as the planet in question needs to be habitable for human-like life.

On Uranus, however, this tilt between rotational axis and magnetic field is 59 degrees. This may be because Uranus' magnetic field is generated in a completely different way, closer to the planets surface.

What could cause a stable tilt in the magnetic field of a planet on a similar scale (>35 degrees) while the planet still needs to fulfill the following criteria:

  • It needs to be habitable to life, including intelligent life
  • The tilt of the rotational axis should be similar to earth's, to allow for seasons
  • If necessary, no tides or heavier tides than on earth are acceptable, as long as they still allow for seafaring with late medieval technology (wooden ships)
  • The day/night cycle on this planet should be similar to earths (so no tidal locking with the host star or something similar. Longer or shorter days are acceptable as long as it's not excessive)
  • "stable" in this context means that the magnetic poles should not move by an appreciable amount over thousands of years, so that many generations of intelligent life would see a compass point basically in the same direction. Pole reversals, like we see on earth, are acceptable.

Here is a list of things I have already thought about, and why I discarded them. All of them would be acceptable, if you can make them work somehow:

  • A natural satellite or binary planet with its own magnetic field (from what I can tell, they would either need a ridiculously strong magnetic field or be very close to affect the magnetic field of our planet meaningfully)
  • A planetary ring (Even though in our solar system only the gas giants have rings, smaller/less massive planets could have rings, too. However just having a ring made of ice/rocks would not affect the magnetosphere of the planet on a large scale. Could they be of a material that influences the magnetic field more?)
  • Ring currents (While ring currents can affect the magnetosphere, they are dependent on it in the first place, as they are created by charged particles trapped in the magnetosphere. I see no way to arbitrarily turn the ring current)
  • A solid iron core that cooled down in the presence of a strong magnetic field. This would lock the magnetic field of the core in place and essentially turn it into a permanent magnet. This magnetic field is independent of the axis of rotation and can therefore be misaligned as much as we want. (However, there are some open questions I cannot find answers to: What could reasonably create a magnetic field strong enough for this? Is the resulting field of the permanent magnet considerably weaker than that generated by a molten core? And can a planet with a frozen core harbor life? The Wiki on Planetary habitability mentions a molten core to be at least conducive to life because it is responsible for plate tectonics. Can we go half way and have a big solid inner core responsible for the magnetic field tilt and a thinner molten outer core for tectonics?)
  • A completely different way to generate the magnetic field that allows for such a tilt (I do not know what this could look like, but as long as the list of requirements above is met, anything goes.)

Any solution that might work and is not on this list is, of course, also welcome!

I have, so far, not talked about the reason our world needs this tilt in order to make this post relevant to a wider range of world-builders (I am sure you can come up with many interesting ways such a tilt affects the world and its inhabitants) But for anyone interested, I will outline my own reasons here: This medieval fantasy world has similar climates as earth with frozen poles and warmer climates closer to the equator. With a tilt in the magnetic field, the magnetic poles fall into more temperate climates, which I need. A lot of conflict in the story arises from a religious group seeing this magnetic pole as spiritually important as all compasses lead there and auroras can commonly be seen. They believe this is the origin of the world from which their Creator-God built outward.

This is my first ever post on any StackExchange. I hope I followed any guidelines correctly. I'd appreciate any comments pointing out where I go wrong. I'd also appreciate comments correcting any grammatical errors as english is not my first language.

Thank you for your help!

Improve this question
$\endgroup$
2
  • $\begingroup$ The problem with magnetic field of Earth is that nobody truly knows why and how. There are hypotesis, but not a proved theory. So if you need it for your world - just do it without explanations (but keep in mind that compass is not working in quite a large area near magnetic poles) $\endgroup$
    – ksbes
    Commented Dec 24, 2020 at 12:34
  • $\begingroup$ In 2019 the north magnetic pole of Earth was at about 86° latitude north and 131° longitude west; but in 1859 it was at about 70° latitude north and 96° longitude west. Earth's magnetic poles wander about. $\endgroup$
    – AlexP
    Commented Dec 24, 2020 at 15:04

1 Answer 1

Reset to default
4
$\begingroup$

Your religious group is actually right.

The planet has been terraformed, either by long forgotten ancestors or an unrelated alien race. As the planet had no molten (or an insufficiently ferrous) core the terraformers found it necessary to create one, plumbing vast field generators deep into the planet’s crust. They did this at the two most opposite locations on the planet that were also easiest to land at and work in, so somewhere temperate makes a lot of sense.

The generators are buried deep, repair themselves and are defended by Clarkian machines, so none of your characters know they actually exist past rumours, and of course the level of know how and sheer power required to set up a self-maintaining geomagnetic field generator is... well... godlike.

So: the idea of the pole being the work of creator gods is not actually far from the truth...

Improve this answer
$\endgroup$
10
  • $\begingroup$ Hi and thanks for the quick response. This is not the type of solution I expected, but a very interesting one. Could you elaborate on what Clarkian machines are? I am not familiar with the concept, sorry $\endgroup$
    – Vollkornkeks
    Commented Dec 24, 2020 at 13:59
  • 1
    $\begingroup$ @Vollkornkeks Science so advanced that everyone is convinced it is magic. .. in detail: en.wikipedia.org/wiki/Clarke%27s_three_laws , but really it's the third one that bites. $\endgroup$
    – PcMan
    Commented Dec 24, 2020 at 14:25
  • $\begingroup$ And what is a "field generator"? It cannot simply be a huge (electro- or permanent) magnet because that would have both a north end and a south end and would not project a field out across the planet. You'd need two antipodal generators, each a huge magnetic monopole, one of each polarity. Not only would that not behave exactly like a singular iron core, it is physically impossible to create such a thing: it'd take a whole universe's worth of energy to keep one held together. Moreover, do magnetic monopoles even exist? How do you create them? Are they stable? $\endgroup$
    – Harry Wilson
    Commented Dec 24, 2020 at 16:02
  • $\begingroup$ @HarryWilson: two suitably large electromagnets slapped across a ferrous core (even if frozen) should create a single big magnetic field in the right shape. Otherwise: See PcMans comment on Clarkian magic. $\endgroup$
    – Joe Bloggs
    Commented Dec 24, 2020 at 18:21
  • $\begingroup$ Two large electromagnets would not create a field anything like a central iron core -- it would create a field like two big magnets! Think of two magnets at opposite ends of a table vs one magnet in the centre. If you're going to claim "it's just technology that's indistinguishable from magic" you might as well just claim that the poles are at a funny angle because of magic. That would actually leave less to be explained than your answer, since at least that's established physics. $\endgroup$
    – Harry Wilson
    Commented Dec 24, 2020 at 18:27

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .