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Pretty self explanatory question...can the Cube Earth described at the link below support a spherical core and a magnetic field?

How would a civilization that has been living on a "cube" Earth differ from one on a "spherical" Earth?

(intent of this question is whether or not a cube planet could support the magnetic field required to protect life from harmful exposure to space and the various rays the Earths magnetic field protects us from. Lack of magnetic field likely means a pretty barren cube.)

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  • $\begingroup$ Many many questions needs to be answered before any answer would be just WAG: How tall are passes between ridges? How high is the atmosphere? Is your planes perfect cube, or are there anomalies to create some landscape? How much water there is on each side? Same amount of water or are there differences? Axis of rotation over corners, faces, different? Tilt? $\endgroup$ – Peter M. Jan 17 '15 at 0:51
  • $\begingroup$ You've pretty much thrown away our physics wholesale to have a cube planet in the first place, so what's one more handwave? Of course, if the cube is your big lie, unless your mechanism for having a cubical planet forces the core to not be spherical, it will be spherical, as that's the lowest energy shape. Everything is as close to the center as it can be. $\endgroup$ – Leliel Nov 24 '16 at 19:12
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Yes.

Assuming, of course, that the otherwise impossible cube world exists there is no reason it can not have a spherical, rotating iron core with a magnetic field. Think of a sphere contained inside the cube.

As noted in my answer for that previous question, there would only be a relatively small habitable space in the center of each face of the cube (ignoring climate). This area would be just as protected as the a spherical Earth.

Actually the only interesting difference, in the case of a cube with its magnetic axis through two corners, there would be no auroras.

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Those huge corner mountains would sink into natural molten core and mantle.

But there are cool ways to create magnetic field for my Mars question - some usable also for cubic planet.

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No.

At the moment, I can't answer the part about the shape of the core. I can answer the part about the magnetic field.

The Earth rotates, and because of that its shape is that of an oblate spheroid, so any body that rotates must take this shape. Now, you can object, saying that the body in question is not originally a sphere but a cube, and so it will not become an oblate spheroid. However, there will be some elongation along the equatorial axis, and so the planet will become a rectangular prism.

Furthermore, a rotating object must have approximate axial symmetry - in other words, if you look down on it from the axis of rotation, it should appear the same shape in all directions. So now we've shown that the planet must be at least a cylinder. However, we already said that the object will bulge out along the equator, and so it will become an oblate spheroid.

You could object to this, saying that the planet doesn't have to rotate. Ah, but it does, if you want a substantial magnetic field like the one you're thinking about. The Earth's magnetic field (and that of other planets) can be thought of using dynamo theory. As Wikipedia says,

In the case of the Earth, the magnetic field is induced and constantly maintained by the convection of liquid iron in the outer core. A requirement for the induction of field is a rotating fluid. Rotation in the outer core is supplied by the Coriolis effect caused by the rotation of the Earth. The Coriolis force tends to organize fluid motions and electric currents into columns (also see Taylor columns) aligned with the rotation axis.

Therefore, you need a rotating planet to have a magnetic field, and a cube-shaped planet could not have a magnetic field.


Note

I am, admittedly, a bit late to this interesting series of spherical-planets-questions (I wish I hadn't missed most of it!). Samuel had a nice explanation of the reasoning for a cube-shaped rotating planet:

The cube is sustained 'magically'. It was shown previously that a cubic world would be impossible otherwise. That was what my stated assumption was addressing.

See, this is what I get for coming in late. :-) It seems the original idea (after some searching) was of jamesqf, in a nice answer here. The point was a bit of a buzz-kill, and to keep the whole scenario magic of some sort had to be invoked.

I'll stick with my guns on this one, especially because of the use of the tag. I'm much more reluctant than most people to use magic - which is why many of my answers are a wee bit disappointing - but I do believe that a given situation should use as much science as possible, especially with this tag choice. But if magic is allowed, then feel free to invalidate this answer! I'll be disappointed, but I'll understand. I suppose life needs a bit of magic to it, though I prefer the metaphorical kind.

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  • $\begingroup$ I was under the impression the cube world did rotate from the linked question $\endgroup$ – Twelfth Jan 17 '15 at 0:40
  • $\begingroup$ A non rotating Cube planet would never be even remotely Earth-like. $\endgroup$ – Oldcat Jan 17 '15 at 0:40
  • $\begingroup$ @Twelfth Well, you'd have to explain why it's still a cube. The scenario of a non-rotating cube-shaped planet is impossible. $\endgroup$ – HDE 226868 Jan 17 '15 at 0:41
  • $\begingroup$ So is a rotating cube like planet without unreasonable materials. So assume unreasonable materials for the moment. $\endgroup$ – Oldcat Jan 17 '15 at 1:44
  • $\begingroup$ This is not quite true - you can have non-spherical rotating objects. A cube will spin quite happily either around the center of one of the faces or around the line passing between two opposing corners. $\endgroup$ – Tim B Jan 17 '15 at 9:57
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It depends on why your world is a cube to begin with. In short, the answer is no.

Is it because it was formed that way by the birth of the solar system, or is it because it was engineered to be that way?

I will assume you intend that it was formed by the birth of the solar system, as in naturally occurring.

If this is true then the physics of that universe are different from our own, and all planetary bodies would be cubes instead of an oblate speroid. Since the cube world would still be rotating that makes it an oblate cube. To truly be an equidistant cube it would not be rotating, and then you'd have no magnetic field and no life since the rotation of magma is what makes the field. So I will assume you intend that the cube world is an oblate rotating cube. In this reality the sun and the other planets would also be cubular, and so would the core of the planet, because the nature of what makes a sphere has been supplanted with what makes a cube. And the planetary rotation influences the core rotation to boot.

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