Going off of my other question here, I guessed that a cube planet could work out. BUT, would it be possible for the planet to exist and function as a (relatively) normal planet with life on it without having tectonic plates? I know that tectonic plates with a cube don't really work out too well in life's favor.
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$\begingroup$ A cubic planet can be treated as a planet with very high mountains, but mountains cannot be too heigh. We would have to use material with strength about 1000 bigger than rocks (unless the planet would be smaller). I don't know whether such materials can exist. $\endgroup$– BartekChomCommented Jan 16, 2015 at 10:28
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1$\begingroup$ Blame it on the Ancients $\endgroup$– The ManCommented Jan 16, 2015 at 12:58
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$\begingroup$ OK, so there is no problem. The Ancients can also prevent water and air from escaping or sinking in. Possibility of this is probably the main reason some people say that planets with life must have plate tectonics. $\endgroup$– BartekChomCommented Jan 16, 2015 at 13:22
3 Answers
Artificial planet made by Ancients is your only option.
If your planet was "nature made", without plate tectonics and with crust thick enough to support your gigantic mountains, such planet would have very little mantle (melted core). But turbulence of such core creates magnetic field protecting the atmosphere.
Mars has no atmosphere because its atmosphere was swiped away by solar wind: Mars also lacks strong enough magnetosphere (protective magnetic shield) - which is direct consequence of its cold core (which prevents mountains from sinking into the mantle).
So Ancients need to take care for magnetic field - not only to protect atmosphere from solar wind, but also protect life from radiation from space.
Yes, such planet is very carefully engineered project - most likely PhD in planet engineering from advanced race.
Some interesting reading about why mountains on Earth have theoretical limit on height of about 49K feet (15km). Another unexpected (for me) force grinding mountains down: glaciers eroding valleys.
The cube would have to be artificial and relatively recent. It can't be created by natural process and eventually tidal forces will break it apart. As such any life on it would have to be either created artificially or imported from elsewhere. You can simply assume that the planet was created or given maintenance recently enough that the planet still works as planned.
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1$\begingroup$ I guess in lore wise for it, ancients could make it. $\endgroup$– The ManCommented Jan 16, 2015 at 3:12
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1$\begingroup$ @ShadowZ. Yup, if it is planet sized and it is not a sphere... the Ancients did it. $\endgroup$ Commented Jan 16, 2015 at 3:16
Forget about cube planets, by now, and go for a real planet: Mars.
Mars has no tectonic plates, but for it being habitable it just needs some more atmosphere and heat.
In fact, if Mars were where Earth is, it would surely have basic life (at least) on its own, since polar caps would be smaller and there would be more water on them. A lake is enough to create life, from where bacteria would have colonized the planet's soil.
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$\begingroup$ So if Mars was created in the same way that it has been, but in Earth's spot, it would have had no tectonic plates, but still habital? $\endgroup$– The ManCommented Jan 16, 2015 at 12:57
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$\begingroup$ Yes. Not as habitable as Earth, because its minor size implies minor gravity, and that's one of the causes of Mars having way less atmosphere than Earth, but yes, it will be naturally habitable and in fact most probably inhabited by some forms of life. $\endgroup$– EnviteCommented Jan 16, 2015 at 13:09
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2$\begingroup$ That is not true. Atmosphere was swiped away by solar wind because Mars also lacks strong enough magnetosphere (protective magnetic shield) - which is direct consequence of its cold core (which prevents mountains from sinking into the mantle) $\endgroup$ Commented Jan 16, 2015 at 13:43
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$\begingroup$ Just check in Wikipedia: Possible causes for the depletion of a previously thicker Martian atmosphere include: Gradual erosion of the atmosphere by solar wind, possibly helped by Mars's magnetic-field irregularities; Catastrophic collision by a body large enough to blow away a significant percentage of the atmosphere; Mars's low gravity allowing the atmosphere to "blow off" into space by Jeans escape. $\endgroup$– EnviteCommented Jan 16, 2015 at 13:55
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$\begingroup$ Seems that making a habitable Mars would be much less of an engineering project than a cube planet. Swipe some water off one of Jupiter's moons plus maybe a bit of nitrogen & ammonia from Triton, add some orbital mirrors to warm it up some, seed it with microorganisms, and you're done. Hardly counts as a senior project at Advanced Alien Tech :-) $\endgroup$– jamesqfCommented Jan 16, 2015 at 18:46