Is a cuboid planet possible?

The force of gravity crushes planets into a spherical shape. However would it be possible for some large cube to resist the force of gravity if it were made from a strong substance? For example crystals are often cube shaped, could a giant crystal planet retain it's cuboid shape?

 

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I'll happily defer to astrophysicists and earth scientists on this, but I'm inclined to think not. This is on the grounds that a rocky planet like the Earth is composed of crystalline rocks which, in bulk, over geological timescales, nevertheless exhibit plastic deformation, due to convection in the mantle - something that is is driven by density differences, i.e. differences in weight, between rocks in different regions. This suggests to me that crystals must be shearing and reforming under the pressures, creating this "creep" of the rocks, i.e. a crystal lattice is not strong enough to resist these immense forces of tonnes of rock. So I'd have thought that the vertex of a cube, projecting as it would like some monstrous mountain, would collapse under its own weight. Bear in mind also that a single crystal in one structural form may be stable at atmospheric pressure, but under the extreme pressures encountered deep in a planetary interior, different forms are likely to be the stable ones. So there will probably be phase changes, that will tend to break up and reform any hypothetical initial giant crystal. So I think it will settle down into a sphere in the end.

 

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You can think of a cuboid planet as a spherical planet with eight extremely high mountains stuck on.

According to How high can mountains be?, the maximum height is roughly:

\(h_max \approx \sigma_c/\rho g\)
\(\sigma_c\) is the compressive strength of the rock.
\(\rho\) is the density of the rock.
g is acceleration due to gravity.

This is a very rough back of the envelope equation. As the author notes, the shear strength of the material is also relevant.
That's all I have time for right now... might do some calcs later.

 

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My guess is that such a planet would be extremely unstable, is it will try to reach a spherical shape.

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when pouring sand or other material out into a mound it will form a cone shaped mound.
the angle of the sides is called the "angle of repose".
don't know if it's relevant or applies but it might help some.

 

Theoretically isn't it possible, but unlikely?

 

No. As others have said, or implied, the strength of the bonds formed in a crystal lattice is not without limit. In other words, the crystal can only become so large that eventually the effects of gravity breaks those bonds and the material come tumbling down.

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So another suggestion...a hollow cube planet, or rather an inversion space underneath each of the "4 mountains" edges of the cube planet to equalize the gravity effects. How one would engineer such a thing, is beyond me.

TrES-4 is the largest planet in universe, supposedly 70% bigger than Jupiter but less massive than Jupiter.

Maybe if we put constraints on this cuboid planet of ours, it would be easier to figure out the engineering of such planet. I propose a terrestrial cuboid planet engineered with the same density of 5.52 g/cm^3. A rocky cuboid planet with seas, possible or no?

One constraint I can think of for our planet is:

constrain 1: Mass of the planet < 0.06 Sun mass (to avoid formation of a star)

 

Sure. At some size gravity will overcome any realistic material strength, so it would have to be below a certain size. But below that size, yes, you could manufacture a cubical planet.

 

No. The definition or "planet" is as follows.
"A planet is an astronomical object orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals." - Wikipedia

 

and who here denies that such a cuboid planet will indeed be rounded by its own gravity over a questionable period of time?

 

Until it does, it is not a planet. When it does, it is not a cuboid. So, no. It is not possible to make a cuboid planet.

 

fine you are just playing with words. Pluto is not a planet and etc fanatics.

A rephrase of the OP would be a "massive cuboid satellite" or maybe "cuboid dwarf planet"

 

Whatever. Every single satellite we've ever seen via probe is more or less (and considerably *more* than less) round. Pardon my bluntness but this cube business is just plain infantile and clearly ignorant. Gravity will NOT permit it. <shrug>

 

A friend of mine once sought cuboid planets - he was assimilated 27 times after encountering a fleet of borg ships.

 

In the absence of erosion, and given the proper structure, it will not be. In most real world cases, erosion (caused by interplanetary gas, dust, meteor impacts etc) will "round it up" over millions of years.

 

The rounding of a planet has nothing to do with erosion. It is purely gravitational stress versus properties (strength, creep rate, etc.) of materials. Erosion smooths the negligible wrinkles only.

 

Hence the statement "given the proper structure."

 

In a crystal, the intermolecular forces are much larger than the gravitational forces. In a gigantic pile of crystals - e.g. a planet - the opposite is true. Gravitational forces will determine the shape of the planet even if individual crystals are cubic.

 

Larry means a single planet-sized cubic crystal.
The forces in question aren't the gravitational forces between adjacent atoms, but the internal stresses due to the weight of eight colossal mountains (ie the corners of the cube) sticking out of the planet.
That force is larger than the crystal's ionic bonds, and the sides of the mountains (corners) would shear off and slide down onto the faces, until crumbling the huge crystal into the aforementioned spherical pile of small crystals