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Dorocche t1_j5ave5l wrote

Rings are under a lot of pressure from all kinds of conflicting and chaotic forces. So they need to be able to move fairly fluidly.

If they melded into a single solid structure, they would immediately be ripped apart again unless they were made of a fantasy super-strong material.

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rabbitwonker t1_j5by3tj wrote

Alternatively, if they were to get dense enough to even approach being solid, they’d collapse into one or more moons.

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Dorocche t1_j5c10dy wrote

Isn't that a function of distance from the planet (the Roche limit) rather than the total mass of the rings?

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andygates2323 t1_j5pku54 wrote

The ring will have its own urge to turn into moons, and if has lots of mass, that moony limit will apply.

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Dunbaratu t1_j5e5e0r wrote

Even if you had such a fantasy strong material to build it from, a rigid ring doesn't have a stable orbit. Once the tiniest thing knocks it slightly off center, like a single meteor impact, or even the gravity of a passing meteor that doesn't even hit it, the ring would quickly shift further and further off center until one side hits the planet. The orbit isn't self-correcting once you make the object rigid. Quite the opposite - whichever side is closer to the planet gets a stronger pull that pulls it even closer to the planet.

If you wonder why that doesn't happen to individual orbiting satellites, that's because individual orbiting objects that are knocked closer the the planet take on an eccentric elliptical orbit shape which is still stable. But a rigid ring is still stuck in a circle shape even when the "proper" orbit that would remain stable should be an eccentric ellipse.

This raises an interesting question of whether a ringworld that was flexible such that it could be deformed into any ellipse could keep a stable orbit. It still probably couldn't because the same energy orbit that was a circle, when it deforms into an ellipse, ends up being an ellipse with a larger circumference than it had as a circle - so it would have to be both infinitely flexible and infinitely stretchy. That's why a field of rocks and dust can form a stable orbit ring shape (they can form a shape that is infinitely flexible and stretchy since they're not really one joined object.) While a single-object ring really can't.

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Whookimo t1_j5jz3ex wrote

Is this also why the Halo rings from, well, halo, aren't really feasable?

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Kamiyoda t1_j5o35ua wrote

Not really because Halo's don't orbit around things the same way a ringworld would. Not that that makes it any more feesable, its just not THAT particular reason it would be a problem.

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Dunbaratu t1_j5lx8st wrote

I never played Halo and don't know the game lore, so I can't really answer the question - I don't know what halo rings are supposed to be.

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