Are elliptical rings feasible?
Around a rocky planet or small gas giant, could there be a system of rings that follow an elliptical orbit? I have used a gravity simulator (this one) to test it, but the way it handles its particles doesn't seem like it would work. My question is, can a planet have an elliptical ring system?
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1 answer
It's unlikely, on the whole, for a ring system to maintain a high eccentricity on significant timescales. Dissipative collisions tend to circularize the orbits of individual particles, even if the original constituent body traveled on a fairly eccentric orbit. Therefore, you need some external perturbation keeping the particles on substantially elliptical orbits.
This typically involves another orbiting body - say, a moon - creating, for instance, a Lindblad resonance with a subset of the particles in the ring that have the proper orbital period. These particles will be forced into slightly more eccentric orbits. While this has not occurred stably on a large scale in the present-day Solar System, it might occur in some circumstellar disks around other stars. The star Fomalhaut has a ring of dust of eccentricity
In short, yes, it's quite possible for there to be a ring system that maintains a fairly eccentric shape for long periods of time, but there needs to be a perturbing body (a high-mass moon, for instance) in the proper orbit to force the ring particles to maintain their eccentricities. Otherwise, collisions will very quickly circularize the ring system.
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