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Is it possible for a planet to have a liquid ring rather than a ring made of solid particles?

If it is, how long would it be stable for? If not, is there any other configuration of a liquid that could form a ring such as droplets or a mist etc? Else what happens to liquids in orbit (especially liquids with a high boiling point at low temperatures which will only evaporate very slowly).

Assume any configuration of planet and ring and the liquid does not have to be water. Any materials and conditions may be used, but no magic.

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  • $\begingroup$ Any "liquids with a high boiling point at low temperatures" would be awesomely wondrous. Seriously, AFAIK, there is no substance able to exist in liquid phase in a vacuum. $\endgroup$
    – AlexP
    Sep 19, 2017 at 19:43
  • $\begingroup$ Mercury would work I guess. $\endgroup$
    – A. C. A. C.
    Sep 19, 2017 at 19:44
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    $\begingroup$ I just want to point out that Saturn's rings are already mostly water, so obviously that doesn't produce liquid rings. Do you want any possibility for them to form naturally? $\endgroup$
    – Raditz_35
    Sep 19, 2017 at 19:45
  • $\begingroup$ Wouldn't a liquid evaporate under the near-vacuum conditions? You'd end up with gas rings, I'd think, unless you had something with van der Waals bonding high enough to keep the molecules together in a liquid. I could be wrong, my chemistry is pretty rusty. $\endgroup$
    – Chris M.
    Sep 19, 2017 at 19:53
  • $\begingroup$ worldbuilding.stackexchange.com/questions/59399/… $\endgroup$
    – Karl
    Sep 19, 2017 at 20:29

4 Answers 4

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No, impossible.

Firstly, the internal friction would let it collapse, because the parts at different altitude have to rotate at different speeds. The frictional heat can be nothing else than transformed potential energy, and the whole thing goes down ...

Secondly, the surface tension would disintegrate the ring into droplets, which would coalesce into a smaller number of (liquid) moons. Those moons can't grow very much, however, because of the Roche limit. So they would probably split again from time to time, until they have lost so much angular momentum due to the tidal forces that they crash into the planet atmosphere.

And yes, ionic liquids have the required vanishingly low gas pressure, and would be liquid in space, as long as they stay in the sun and warm enough. See my answer on How to flood the entire lunar surfaces? Also ionic liquids are totally unnatural.

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  • $\begingroup$ Why don't rings made of solid particles coalesce into a moon? I don't see why having having different parts of the ring rotate at different speeds imposes different problems for a liquid ring than a solid one, either. $\endgroup$
    – Nuclear Hoagie
    Sep 19, 2017 at 20:36
  • $\begingroup$ @NuclearWang Because even the zillions of particles making up the Saturns rings have quite a lot of vacuum between them. They're, compared to a liquid ring, not interacting. $\endgroup$
    – Karl
    Sep 19, 2017 at 20:48
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    $\begingroup$ So a continuous film ring is not possible, but presumably a ring of orbital globules and droplets would be? $\endgroup$
    – Slarty
    Sep 19, 2017 at 21:25
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    $\begingroup$ @NuclearWang Rings made of solid particles don't coalesce because they're inside the Roche limit - the gravitational pull between particles to coalesce into a moon is overridden by the tidal force of the orbited body. $\endgroup$
    – Chris M.
    Sep 19, 2017 at 21:35
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    $\begingroup$ @Karl When the Roche limit is reached an object is disrupted because tidal forces overcome the internal gravitational attraction of the body. But it’s normally applied to solid objects. A liquid body might well behave differently. The earth’s crust is moved by much less than the oceans by the passage of the moon (en.wikipedia.org/wiki/Earth_tide). A liquid body could be distorted and stretched out by tidal forces very easily in orbit as it has no mechanical strength. I suggest this would happen well before the Roche limit was reached thus reforming the ring. $\endgroup$
    – Slarty
    Sep 20, 2017 at 12:25
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Not in liquid form. It would be gas or ice. I am going to echo another sentiment--you could certainly create technology that allowed for artificial liquid rings, if they are necessary to worldbuilding.

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    $\begingroup$ A gas ring would immediately expand until the gas in it had a mean free path lenght of a few thousand kilometers. Pressure in the order of 10^-10bars $\endgroup$
    – Karl
    Sep 21, 2017 at 17:59
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A gas torus sounds more similar to what you want then a standard planetary ring. It might be possible at least in theory to have a thick enough torus that along its core the gas could condense. You would need the planet to have a very strong magnetic field (or even better, replace it with a neutron star). You also need a moon inside the torus that constantly leaches atmosphere into the torus to compensate for what it loses to space. In order to get liquids from the planet into the torus significant volcanism might be an answer.

An example of this concept taken to its extreme is the The Integral Trees. In it the torus is mostly composed of gas, but it does have globules of liquid water interspersed so I guess it in itself would serve as an answer to your question.

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  • $\begingroup$ Came here to see if anyone had mentioned that book. I thought it was alright. Haven't read the sequels. $\endgroup$
    – Phiteros
    Sep 19, 2017 at 22:34
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One mongo molecule to rule them all.

I will venture here into heady speculation, because I want a liquid ring.

A liquid should have a boiling point. The higher the molecular weight, the higher the barrier to turn these molecules to gas. Consider hydrocarbons. Low molecular weight hydrocarbons are volatile, like gasoline. High molecular weight hydrocarbons are nonvolatile, like asphalt. For really big polymers the heat necessary to boil is in excess of that which breaks down the intermolecular bonds - especially in the presence of oxygen.

So: we can have long polymers which do not boil. I propose the ring be made of such molecules. The ring may, in fact, be one enormous planet-girdling cross linked polymeric molecule. Boilproof. Are enormous macroscopic single molecules possible? Go look at your car's tires. How big could a car tire be?

But it must be liquid. That can be achieved by tweaking the flexibilty of the main chain and the strength of the crosslinks between loops of this asphalt like polysilane-like chain. Heat will be imparted by any nearby heat source, like a star or the planet. With no volatility, shedding heat will rely on radiation alone, and this giant polymer ring in orbit will become very warm. Warmed to a fluctuant fluidity!

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  • $\begingroup$ Unfortunately as Karl has pointed out different parts of the ring orbit at different velocities so the inner part of the ring is moving a lot faster than the outer part causing shearing forces across the ring so sadly I don’t think a solid ring (which I think such a large molecule would be) would work. Interesting idea though perhaps a series of orbiting hoops? Although I fear slight disturbances in such an arrangement would cause collision and chaos. $\endgroup$
    – Slarty
    Sep 20, 2017 at 8:17
  • $\begingroup$ Why would shearing forces be a problem for a liquid ring? $\endgroup$
    – Willk
    Sep 20, 2017 at 11:55
  • $\begingroup$ I think it would create friction slowing some areas down and causing the ring to break up and clump into droplets or globules. This would give a Saturn like ring but with droplets instead of solid grains. Seems as if a liquid ring of globules is possible, but will wait to see if anyone else has a view on that. $\endgroup$
    – Slarty
    Sep 20, 2017 at 12:03
  • $\begingroup$ One benefit of using a huge macromolecule is that its viscosity would oppose the tendency of shearing forces to break it up. It would be very gooey. The shear forces would still exist but would hopefully be dispersed as heat, keeping the goo warm. $\endgroup$
    – Willk
    Sep 20, 2017 at 13:15
  • $\begingroup$ @Will This heat is energy, which will come from the potential energy of the ring. Going down .... $\endgroup$
    – Karl
    Sep 20, 2017 at 19:26

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