<p>Rings are made up of a large number of individual particles, each in elliptical orbits. We see rings as circular because we don't see and follow the individual particles just the overall swarm of particles. Their individual orbits average out and just appear are a circle.</p>

<p>The individual orbits are constantly being changed due to collisions between particles, and gravitational influences for moons. Saturn's F ring is a good example of <a href="http://www.nasa.gov/mission_pages/voyager/PIA_02292_07712.html" rel="nofollow">this.</a> As can be seen from the images the ring is not a circle.</p>

CC BY-SA 3.0
2016-07-27T10:23:03.950Z
Are you saying that individual particles execute noticeably non-circular orbits (note that a circle is an ellipse)? What eccentricities do you think are possible?
ProfRob
CC BY-SA 3.0
2016-07-27T11:40:52.807Z
There will undoubtedly be a range of eccentricities, most will be near circular with number dropping off as the orbits become more elliptical. Due to the huge number of individual particles and their small size its not practical to even attempt to measure them individually, that's without even taking into effect the gravitational and light pressure effects.
James Screech
CC BY-SA 3.0
2016-07-27T16:53:26.753Z
I think you should flesh this out. My understanding is that inelastic collisions circularise orbits and that in rings like Saturn's, the collisional timescale is very short. Saturn's rings look circular because the particles are on circular orbits. The same may not be true of other ring systems where some very small eccentricities have been measured, but there has to be some external "pumping" of the eccentricity.
ProfRob
CC BY-SA 3.0
2016-07-28T01:17:38.980Z
@JamesScreech - there's some guesswork in that answer, and a few facts are wrong. Individual orbits must be very close to circular, otherwise collisions will change them quickly. For the same reason, rings must be very flat. Also, due to precession, rings must be equatorial. Any other configuration is very short-lived.
Florin Andrei
CC BY-SA 3.0
2016-07-27T08:42:15.490Z
2016-07-27T08:42:15.490Z
James Screech
<p>Short answer: no.</p>

<p>Long answer:</p>

<p>There are many collisions within ring systems, and collisions always work, over time, to push orbits to a circular shape (or destroy the rings). Any deviations tend to be quickly corrected.</p>

<p>For the same reason, rings tend to be extremely flat and extremely thin. E.g. Saturn's rings are only dozens of meters thick; given their diameter of 300 thousand kilometers, if you cut a model of the rings from ordinary size printer paper, the paper model would be too thick. (would not represent the thickness of the rings to the correct scale)</p>

<p>Another characteristic of rings is that they are equatorial. If they are not in plane with the equator, precession will drive them towards that configuration.</p>

<p>You could apply a perturbation that makes a ring non-circular, or non-flat, or non-equatorial, but then the system will quickly evolve towards circular, flat, and equatorial (or will be destroyed).</p>

<p><a href="https://www.uwgb.edu/dutchs/AstronPowerPoint/Rings.ppt">https://www.uwgb.edu/dutchs/AstronPowerPoint/Rings.ppt</a></p>

CC BY-SA 3.0
2016-07-28T22:28:32.280Z
If the planet has no equatorial bulge, and very low rotation speed, would the equatorial rule still apply?
userLTK
CC BY-SA 3.0
2016-07-29T01:19:12.597Z
No spin = no precession = no push towards equator.
Florin Andrei
CC BY-SA 3.0
2016-07-28T01:23:04.640Z
2016-07-28T01:23:04.640Z
Florin Andrei
<p>The rings of Saturn and Jupiter are circular. Orbits can be elliptical, so can rings be elliptical?</p>

CC BY-SA 3.0
2016-07-28T16:05:02.570Z
Orbital resonance may be a reason for the circular orbits.
Lelouch
<planetary-ring>
Can there be elliptical rings around a planet?
Gstestso
# Can there be elliptical rings around a planet?

(Asked by: username_0 on 2016-07-27)

The rings of Saturn and Jupiter are circular. Orbits can be elliptical, so can rings be elliptical?

**Tags:** planetary-ring

> **Comments:**
> **username_1**: Orbital resonance may be a reason for the circular orbits.  

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## 2 answers

### Answer by username_4 on 2016-07-28. Score: 9 | Accepted answer

Short answer: no.

Long answer:

There are many collisions within ring systems, and collisions always work, over time, to push orbits to a circular shape (or destroy the rings). Any deviations tend to be quickly corrected.

For the same reason, rings tend to be extremely flat and extremely thin. E.g. Saturn's rings are only dozens of meters thick; given their diameter of 300 thousand kilometers, if you cut a model of the rings from ordinary size printer paper, the paper model would be too thick. (would not represent the thickness of the rings to the correct scale)

Another characteristic of rings is that they are equatorial. If they are not in plane with the equator, precession will drive them towards that configuration.

You could apply a perturbation that makes a ring non-circular, or non-flat, or non-equatorial, but then the system will quickly evolve towards circular, flat, and equatorial (or will be destroyed).

<https://www.uwgb.edu/dutchs/AstronPowerPoint/Rings.ppt>

> **Comments:**
> **username_5**: If the planet has no equatorial bulge, and very low rotation speed, would the equatorial rule still apply?  
> **username_4**: No spin = no precession = no push towards equator.  

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### Answer by username_2 on 2016-07-27. Score: 1

Rings are made up of a large number of individual particles, each in elliptical orbits. We see rings as circular because we don't see and follow the individual particles just the overall swarm of particles. Their individual orbits average out and just appear are a circle.

The individual orbits are constantly being changed due to collisions between particles, and gravitational influences for moons. Saturn's F ring is a good example of [this.](http://www.nasa.gov/mission_pages/voyager/PIA_02292_07712.html) As can be seen from the images the ring is not a circle.

> **Comments:**
> **username_3**: Are you saying that individual particles execute noticeably non-circular orbits (note that a circle is an ellipse)? What eccentricities do you think are possible?  
> **username_2**: There will undoubtedly be a range of eccentricities, most will be near circular with number dropping off as the orbits become more elliptical. Due to the huge number of individual particles and their small size its not practical to even attempt to measure them individually, that's without even taking into effect the gravitational and light pressure effects.  
> **username_3**: I think you should flesh this out. My understanding is that inelastic collisions circularise orbits and that in rings like Saturn's, the collisional timescale is very short. Saturn's rings look circular because the particles are on circular orbits. The same may not be true of other ring systems where some very small eccentricities have been measured, but there has to be some external "pumping" of the eccentricity.  
> **username_4**: @username_2 - there's some guesswork in that answer, and a few facts are wrong. Individual orbits must be very close to circular, otherwise collisions will change them quickly. For the same reason, rings must be very flat. Also, due to precession, rings must be equatorial. Any other configuration is very short-lived.  

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