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Piggybacking on this question: Could soft matter infused with nano or pico sized magnets be used to clump together so that we could create environments with it?

...So we have a planet that has lower gravity than Earth, low enough for people to float/fly in the sky (so it does have an atmosphere- like Earths), with an ocean that is held together with the use of nano-magnets evenly spread throughout (the ocean covers the planet).

But how do we keep the place from evaporating into space or freezing over?

I think that the atmosphere itself will keep it from evaporating, and I think that having it close to the sun will keep it warm so it doesn't freeze (the planet could be somewhere a bit farther out than Earth is to our sun, but not as far as Mars, or maybe it needs to be closer?).

This planet is artificial so we can literally build it anywhere to achieve our results. I like to believe that its placement in the solar system (again assuming a sun like ours) solves the problem, but I might be missing other aspects.

I also accept that the place is probably not stable, but I'm hoping for a scenario that could give us maybe a million years or so before falling apart.

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    $\begingroup$ Carbon dioxide? $\endgroup$ – RonJohn Mar 5 '18 at 19:05
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    $\begingroup$ While heat does determine the phase of a given substance so does pressure. The two tend to go hand in hand in a given environment. Higher heat is associated with higher pressure. Lower heat is associated with lower pressure. $\endgroup$ – Englishman Bob Mar 5 '18 at 19:09
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    $\begingroup$ CO2 is a greenhouse gas. That keeps the "planet" from freezing. A magnetosphere keeps the escape of atmosphere into space to a minimal trickle. Distance from the central star keeps it from overheating. $\endgroup$ – RonJohn Mar 5 '18 at 20:08
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    $\begingroup$ evaporation from Earth's oceans and bodies of water doesn't cause any problems, the evaporated water floats in the atmosphere until it condenses and falls as rain. If the constructed planet has a low escape velocity and will lose water vapor, it will also lose it's oxygen atmosphere. So you should put an airtight roof over the planet when you build it.. $\endgroup$ – M. A. Golding Mar 5 '18 at 21:43
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Without something to 1) keep the atmosphere from just floating away (solved by gravity on Earth), and 2) prevent solar wind from stripping away lighter gases (solved by a magnetosphere on Earth), your planet is doomed to an airless, frozen fate.

Handwaving how "nano magnets" would hold water together or why people who can float in the air would want a planet without any solid surfaces, the solution is an artificial shell or envelope to contain the atmosphere. If your gravity is already so low that humans can float around in it, we're talking about a planetoid with negligible mass and size, so constructing such a thing isn't out of the question.

To keep the planet and shell centred and prevent them from drifting and colliding you'll want a number of stanchions anchored to the rocky surface and supporting the shell. These stanchions would also be a logical place to construct entry/exit facilities. Then fill the volume to your desired depth of water and density of atmosphere.

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  • $\begingroup$ Thank you for your answer. I assume you think the set-up suggested in worldbuilding.stackexchange.com/questions/106061/… is totally off? $\endgroup$ – Len Mar 5 '18 at 19:54
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    $\begingroup$ @Len Foglets make sense for constructing things out of foglets, but I don't think they'd be useful for containing individual molecules of water. $\endgroup$ – rek Mar 5 '18 at 20:02
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    $\begingroup$ @rek - yes, putting some sort of roof over a world that might otherwise lose its atmosphere is always a good idea, and if you're able to construct worlds it should be feasible. $\endgroup$ – M. A. Golding Mar 5 '18 at 21:40
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I would suggest

  • A Planet with 0.7 Earth masses and 0.85 Earth radii
  • surrounded by a transparent Dyson sphere with a CO2 rich atmosphere
  • Orbiting a young Type-K white dwarf(no solar wind AND huge magnetosphere to protect from galactic winds)
  • with a 3:2 orbital resonance (mercury style) to prevent destruction from tidal forces (the white dwarf has 0.5 Sol masses) and excessive baking of one side of the planet

For the planet decaying to death after a million years or so, I would suggest that after some time, the planets gets fully locked in 1:1 resonance. One side gets baked and the gases there leave local gravity and float towards the dwarf, adding to it's mass and causing a nova explosion.

But I would say that the organisms from your previous question capable of flying and swimming would be impossible, physiologically.

Air flight is dependent on moving large pockets of fluid to move, and a body shape designed for an upward thrust.

Swimming in water doesn't require thrust because buoyancy (which is manipulated in fish using air bladders) and water is so dense walking through it is tough when in the pool, let alone "flying"(because the organism would have to repurpose their air adaptations for water).

All of the flora on the planet will adapt themselves to max out on either running flying or swimming, because each have their own unique set of challenges with unique solutions and survival of the fittest will chose the ones who excel in one rather than ones who can just do a bit of everything.

Footnote:

Penguins are flightless birds who can swim in water without air bladders, but they can only swim for short periods, and all the extra fat and insulation for swimming won't carry well into flying.

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  • $\begingroup$ Thank you for your response. Very helpful. As for the flying/swimming organisms... Your points are well taken, and I'm still working on them. In their defense, it turns out that in my story that the planet AND the creatures that live in it are all artificially manipulated by hand wave alien science. A kind of grand experiment. In that case do you think there are scenarios that might allow for them? Again, thanks. $\endgroup$ – Len Mar 7 '18 at 15:28
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    $\begingroup$ @Len If you are not going for hard sci-fi, then the thing I would suggest is to just abandon going for some specific coherent science, and take up science that seems coherent and doesn't break the readers experience $\endgroup$ – Varad Mahashabde Mar 7 '18 at 16:59
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    $\begingroup$ @Len the reason why the animals work will largely depend on why the aliens are doing this. E.G. the animals can dynamically change their bodies to suit their environment, because the aliens are looking to implement that I their own population to have an edge in a decaying ecosystem, and they want to know if there are any unforeseen consequences. They do this in a small time dilated region of space to cover the million years of the planets orbital decaying in like 20 years $\endgroup$ – Varad Mahashabde Mar 7 '18 at 17:00
  • $\begingroup$ Varad, yeah, there is a reason that would come out in the story. I would love to discuss this with you (for that matter with anyone who was interested to) privately so as to not occupy comment or site space, but I don't know if that's allowed. Anyway, thanks for your attention. $\endgroup$ – Len Mar 7 '18 at 17:06

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