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30

Every orbiting ring-like structure is unstable due to gravity. Yes, even Saturn's rings and the Asteroid Belt in our Solar System are unstable: they constantly lose and rearrange "particles". The Asteroid Belt is more an intersection of asteroid orbits than some ring structure. There is always a tendency to form some clusters even inside Roche limit. That ...


18

Friction of the fluid against itself as a wave-propagating medium results in local concentrations of density, and ultimately in the continuous material being broken up. The only stable condition for fluid particles is that they must isolate themselves from the wave field through cohesion into local, disconnected bodies or else lose energy to internal motion ...


16

"Can early astronomers determine the gravity of their planet's “moon” without ever going there?" Of course they can. Our Earth-bound astronomers did, and we know how they did it. The distance from the Earth to the Moon and the size of the Moon were known since the Antiquity. The Moon is close enough that the parallax method works well enough with the naked ...


7

Liquid is hard to get in space: you can get either solid or gas. You therefore might get ice particles of various size, or water vapor. Ice would slowly sublimate to gas, and gas would be blown away by the stellar wind. The rate at which this happens would depend on the distance from the star. On the far side of the goldilocks zone ices can live as long as ...


5

Here are a few points Friction: If your water needs to be high up enough so that it isn't affected by the friction of particles in the atmosphere which will slow it down and eventually cause it to rain down. Solar Winds: Your water needs to be in the atmosphere to offer it protection from solar winds. If it is too high, the solar winds will hit your water ...


5

Yes, but probably not on the scale you want. Time dilation exists on earth. According to a study from the National Institute of Standards and Technology, "if one twin spent 79 years living at an altitude 1 foot higher than her sister, the first twin would end up approximately 90 billionths of a second older." We can extrapolate from that that a person ...


4

Yes it is impossible: Liquid water cannot exist at pressures below 0.006Bar so in order to have liquid water in free orbit around a star you would first need a gas torus. Now the highest density we've directly observed in such a torus is around the planet Jupiter it has an amazing 2000 particles per cubic centimetre (that's not in any way measurable as a ...


4

1. Tides the moon would not move in the sky and there would be no tides Wrong. The sun provides tides too (albeit smaller ones than our moon), so the sea still rises and falls on a regular cycle. You'll even get variations in tide height depending on the relative angles of the sun and your "moon", though not to the same extent as spring tides on earth. ...


4

Biology, Not Physics Although we can talk about situations involving speeding up or slowing time and hit an answer, there's a whole other scientific realm available to this answer: biology. And while we don't know how to stop aging exactly (or exactly what causes it), a biology-based answer requires no less handwavium than physics (where we can say what to ...


3

Time Travel Time travel, either back in time from the journey location to the return arrival time or farther along their own personal timeline. If the "traveler" twin is displaced in time as well as space, or goes somewhere where the passage of time differs from that on Earth (in this case it would have to go faster), then they may actually experience more ...


3

At this time the other answers either miss or gloss over the core of the reason why such a structure could not be possible [by natural means]: Fission and materials filtering. With the right star and enough H20 in the correct initial orbits, there isn't a lot to actually stop such a structure from existing for a decent chunk of time on a geological ...


2

No, spare your reputation and your finances and the people of planet Earth--no Kickstarter for this one. A ring satellite would be short-lived: The propagation of waves through the solid material results in nonuniform gravitation, which will generate more waves and hasten the ring's demise. Creating expansion/contraction joints would only transform the ...


1

Such a thing cannot exist, because the ring is not in the lowest energy state, and so it is in an unstable state. Note that the star has nothing whatsoever to do with it. A ring of material is unstable with or without the star, for the exact same reason. So, without loss of generality, simply imagine the situation where there is no star. This ring of ...


1

Here's a solution involving traversable wormholes, which Ash already mentioned as a possibility, but I'll give a little more detail to show how it can be done without violating causality (no one can do anything to exert a causal influence on their own past self). One key thing to understand about traversable wormholes is that time hooks up differently ...


1

Other answers have discussed the methods used by ancient, medieval, and modern pre-spaceflight astronomers to discover the distances, sizes, and masses of various astronomical bodies, from which the surface gravity and escape velocity of those bodies could be calculated once Newton published his laws of physics. Here is another type of answer. Any large ...


1

If you want to augment existing gravity with centrifugation, it is best to place the centrifuge so that it rotates orthogonally with the existing lunar/planetary gravity. The combined net force direction inside the centrifuge then defines a stable "water level" that is always a paraboloid. (This shape can also be shown experimentally, as seen in the ...


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