My premise involves a habitable planet with a dual core: it has two masses similar in composition to Earth's core, which revolve around each other over the course of hundreds of thousands of years. The revolving motion creates electrical anomalies on the surface of the planet.

My goal is to have the dual-core dynamics working in such a way that they psychologically and physically affect the folks living on the planet, while still providing a habitable environment, with ample flora and fauna. Part of the conceit for the plot is that the core dynamics flare up every once in an eon or so, and that one of these flares occurs during the course of the story.

Regarding the actual possibility of such an event occurring, if the idea gets anyone's juices flowing I can live with it.

That being said, how plausible is this premise?

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    $\begingroup$ Is your goal to have two cores or is your goal to have a chaotic (sun-like) magnetic field? $\endgroup$
    – Tritium21
    Nov 5, 2014 at 23:08
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    $\begingroup$ Very good point by @Tritium21 Also, the effects would be primarily magnetic in nature, although interactions with the solar wind could create "electrical anomalies" high in the atmosphere. $\endgroup$
    – HDE 226868
    Nov 5, 2014 at 23:25
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    $\begingroup$ I'd wonder if two separate magnetic fields would be generated by this setup (so two magnetic Norths would exist on the globe). $\endgroup$
    – Twelfth
    Nov 6, 2014 at 0:14
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    $\begingroup$ I've got just one question. On a planet with dual cores, do you get a measureably improved CPU performance? $\endgroup$
    – Zibbobz
    Nov 6, 2014 at 15:21
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    $\begingroup$ @Zibbobz, will it run Crysis? $\endgroup$ Nov 6, 2014 at 16:46

6 Answers 6


The Earth has a core for much the same reason that it's a spheroid: Gravity.

When you have as much stuff as there is in the Earth, it's own gravity is so great that it simply isn't strong enough to hold its shape. All it can do is fall until there's nowhere to fall to, which leads to a sphere.

Similarly, dense materials sink while lighter ones float on top of them. With the enormous forces involved, solid rock acts in some ways as if it were a very very thick liquid. (most of the Earth's mantel is "plastic" rock like this rather than outright molten)

Iron and nickle are the heaviest materials that make up a significant portion of Earth's mass, and so that's what we find at the centre. Two cores would require having something less dense between them that they could displace to reach a lower equilibrium.

You could spin the planet until the cores are in equilibrium, but then anything above them would be moving FASTER than orbital speed and so the planet would fly apart.

You could move them at a different rate from the rest of the planet, but the friction would be staggering. It would very cause the cores and the planet to sync up, the cores would then merge together. The heat produced would probably melt the surface of the planet.

You could make the planet hollow with two giant balls orbiting each other inside each other. I'm not sure but I think the co orbiting balls inside would be stable with respect to one another, but would not be stable with respect to the sphere in the same way a Ringworld is unstable relative to the star it contains. You would need active attitude control to maintain distance.

There are also problems with building a planet sized hollow shell that can hold up under its own weight, or a pair of cores able to withstand spinning around each other that fast.

Such a thing is obviously not a naturally occurring phenomenon, and the cores would spin around each other in minutes, not hundreds of thousands of years.

That all aside, Earth's magnetic field is pretty complicated without needing multiple cores. Among other things it seems to occasionally drop into chaotic behaviour as if the core were several cores (there's only one but different parts of it are behaving differently) and then can re-emerge with the field running in either direction. This happens chaotically on the order of millions to hundreds of thousands of years apart, with the chaotic transition periods taking hundreds of years to tens of thousands of years. This is called a Geomagnetic Reversal

At least one science fiction writer has used this as a plot point: Robert J. Sawyer's Neanderthal Parallax trilogy involves a geomagnetic reversal.

  • $\begingroup$ +1 I was going to answer similarly with less detail. I would add though that, especially in a not-too-high technology, the people could think they understand that their planet has two balls rolling inside it, even if it doesn't really. $\endgroup$
    – Dronz
    Nov 6, 2014 at 6:06
  • $\begingroup$ One correction: the material separating the cores would have to be more dense in order to provide the buoyant force to keep the two cores apart. $\endgroup$
    – dotancohen
    Nov 6, 2014 at 16:44
  • $\begingroup$ @dotancohen That's not quite what I was talking about. I did consider the case of a high density disc of material separating two hemispheres, but the whole thing was already getting rather silly and so I left it out. I'll clarify, and maybe add diagrams when I have some time. $\endgroup$
    – smithkm
    Nov 6, 2014 at 22:49
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    $\begingroup$ The shell theorem says that a hollow planet will be neutrally stable with respect to anything inside (that is, displace the planet and it'll stay in its new position), where a ringworld is unstable (displace the ring, and the displacement will tend to get worse). $\endgroup$
    – Mark
    Nov 7, 2014 at 0:58
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    $\begingroup$ @Taemyr, that's positive stability. Negative stability means a displacement introduces forces that act to increase the displacement, while neutral stability means a displacement introduces no forces, or the forces introduced cancel out (as happens inside a hollow planet). $\endgroup$
    – Mark
    Oct 29, 2015 at 9:31

I don't know how realistic a scenario this is. I would think that if two cores formed in Earth (this could happen in the early solar system, if another moderately-sized protoplanet hit Earth), they would collide and merger, forming a slightly bigger core. For there to be two cores, they would have to stably "orbit" each other inside the planet. Given the extreme conditions down there, I doubt this is possible.

But that's overly boring, as are a lot of my answers to "What-if" questions. So let's dig deeper. Earth's core is, of course, the source of its magnetic field. Its field forms by the circulation of molten liquid in the outer core, driven in part by Earth's rotation. This creates a dipole magnetic field.

Wikipeda talks briefly about creating a quadrupole field - that is, creating four poles. Two would be "North", and two would be "South". Here is a good visualization. Unfortunately, that one isn't loading here, so I'll go with this one instead: enter image description here
Image courtesy of Wikipedia user Geek3 under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Here is the caption:

Magnetic field lines of an idealized quadrupole field in the plane transverse to the nominal beam direction. The red arrows show the direction of the magnetic field while the blue arrows indicate the direction of the Lorentz force on a positive particle going into the image plane (away from the reader)

The caption for the other image is this (emphasis mine):

Example of a quadrupole field. This could also be constructed by moving two dipoles together. If this arrangement were placed at the center of the Earth, then a magnetic survey at the surface would find two magnetic north poles (at the geographic poles) and two south poles at the equator.

I doubt you'd see any electrical effects, but you might see an interesting aurora. An aurora is caused by the solar wind interacting with Earth's atmosphere, but the solar wind can also interact with Earth's magnetosphere to create some cool effects. A change in Earth's magnetic field means a change in the magnetosphere, which means some awesome aurora-like events. You can see this question for some more information.

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    $\begingroup$ good answer. Could be possible that you'd get 'northern lights' occurring on the magnetic north pole that's centered somewhere near the equator of the globe. $\endgroup$
    – Twelfth
    Nov 6, 2014 at 0:50
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    $\begingroup$ @Twelfth That actually made me laugh. Yep, think we'd see equatorial "northern" lights. $\endgroup$
    – HDE 226868
    Nov 6, 2014 at 0:52
  • $\begingroup$ In fact, there's a nowadays fairly generally accepted theory that such a collision between the Earth and a protoplanet did happen early in the history of the solar system. As you'd expect, the cores indeed simply merged, producing the somewhat unusually large iron core Earth has today. A bit more surprisingly, the outer layers did not merge completely: a substantial fraction of them was ejected into space by the force of the impact, and some of the ejected material, it is believed, coalesced in orbit to form the Moon. $\endgroup$ Nov 6, 2014 at 7:42
  • $\begingroup$ @IlmariKaronen I almost put that in, but didn't. Do you want to post that as an answer? $\endgroup$
    – HDE 226868
    Nov 6, 2014 at 12:31
  • $\begingroup$ Honestly, I'm not sure how my comment above would actually answer the question. OK, it does add some credibility to the claim that the collision of two protoplanets should not result in a planet with two cores, but that's not really something one should reasonably doubt in the first place. That said, it does provide an mildly interesting, if somewhat tangential, footnote to your answer; feel free to edit it in, if you like. $\endgroup$ Nov 6, 2014 at 12:42

The two cores would coalesce due to gravity. You cannot have an "orbit" in an environment with friction, i.e. in a planetary body.

One solution would be to have the magnetic i.e. ferrous cores suspended in a super-core of non-magnetic material of higher density than the ferrous cores. The material would need to have the following properties:

  • Denser than iron
  • Semi-plastic at very high temperature and pressure
  • Plausibly be created during planet formation
  • Non-magnetic

Note that on the surface of the planet the location of the north and south magnetic poles would not change, in fact a system with such high angular momentum would seem to be more stable than our current magnetic fields which do in fact wander. The field lines would be about the center of rotation of the two cores.

If you want eccentric magnetic fields on the planet, then you might want to consider a more liquid core. This is completely plausible, and you could have phenomenon in which multiple poles appear for a few years or decades. I would suggest giving the planet a thicker atmosphere to protect the inhabitants, and don't give it a moon so that the planet's wobble will be more eccentric.


Like many of the other posters, friction will kill you every time in a system like this. Engineers work very hard to make internal revolving systems efficient. However, the mention of a more engineering like system might actually work very well. However, as mentioned, hollow just doesn't make sense. I recommend filling the inside of such a structure with something with little/no friction even at high densities. Basically, I recommend a superfluid. A super massive (and super cold) gas giant with a superfluid helium core that caught large solid bodies might be able to support this. However, only in a gas giant, so people would come later as space travelers.


To have a "core" you need a sharp edge to define as "this is the edge of the core." The Earth doesn't think it has a "core," but we find it useful to abstract the Earth into a molten core and a non-molten outer body.

The first question would be what defines this edge, and how does it progress over time. It would be easy for the edge to get fuzzy, and slowly migrate into the center.

The second question would be what prevents the two cores from mixing over time. You need something to do it.

For some inspiration, I'd consider looking at Jupiter's big spot. It is a storm that has been raging for a tremendously long time, and it has a very clearly defined edge. Something stormy and chaotic like that could provide a core with enough oomph to remain split into two dueling cores for a very long time.

  • $\begingroup$ Actually, the Earth has a solid inner core, and a liquid outer core, and then a rocky mantle outside of that. $\endgroup$
    – Oldcat
    Nov 13, 2014 at 23:32

Some bodies in our solar system seem to exhibit superrotation. That might be a more plausible way to get such effects, especially if you make the skin, lumpy like ours with contenents thicker than basins, have interaction with the inner rigid body, with another ocean in between.


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