<p>The recent paper <a href="https://arxiv.org/abs/1905.12566" rel="nofollow noreferrer">Thermal Emission from the Uranian Ring System</a> has <a href="https://news.berkeley.edu/2019/06/20/astronomers-see-warm-glow-of-uranuss-rings/" rel="nofollow noreferrer">been in the news</a> recently. The introduction mentions:</p>
<blockquote>
<p>The ε ring, the brightest and most massive of the narrow rings, <strong>was shown to maintain an appreciable eccentricity (e = 0.00794)</strong> and an azimuthally-varying width; the ring is five times wider and ∼2.5 times brighter in reflected sunlight at apoapsis than at periapsis (French et al. 1988<sup>1</sup>; Karkoschka 2001a<sup>2</sup>). However, many fundamental parameters about the ring system remain unknown, including the filling factor, composition, thickness,</p>
<p><sup>1</sup>French, R. G., Elliot, J. L., French, L. M., et al. 1988, Icarus, 73, 349, doi: 10.1016/0019-1035(88)90104-2</p>
<p><sup>2</sup>Karkoschka, E. 2001a, Icarus, 151, 51, doi: 10.1006/icar.2001.6596</p>
</blockquote>
<p>I've read in Wikipedia's <a href="https://en.wikipedia.org/wiki/Rings_of_Uranus#%CE%B5_ring" rel="nofollow noreferrer">Rings of Uranus</a> that several rings are expected to be fairly young, and there may be interaction with some small moons, but I am surprised that the rings could maintain a significant eccentricity, and do not circularize or smear out due to collisions.</p>
<p><strong>Question:</strong> What kind of dynamical effects can maintain Uranus' rings' eccentricities?</p>
<p>Uranus itself has a <a href="https://nssdc.gsfc.nasa.gov/planetary/factsheet/uranusfact.html" rel="nofollow noreferrer">huge J2</a> and so any ring that isn't perfectly equatorial should have an eccentricity-dependent precession. The paper states that the apoapsis of the rings is five times wider than the periapsis, so there's definitely a population of different eccentricities and semi-major axes within the ε ring.</p>
<p>List of <a href="https://nssdc.gsfc.nasa.gov/planetary/factsheet/uraniansatfact.html" rel="nofollow noreferrer">rings and their orbital parameters</a></p>

<orbital-mechanics><planetary-ring><eccentric-orbit><uranus><eccentricity>
What kind of effects can maintain Uranus' rings' eccentricities?
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# What kind of effects can maintain Uranus' rings' eccentricities?

(Asked by: username_0 on 2019-06-22)

The recent paper [Thermal Emission from the Uranian Ring System](https://arxiv.org/abs/1905.12566) has [been in the news](https://news.berkeley.edu/2019/06/20/astronomers-see-warm-glow-of-uranuss-rings/) recently. The introduction mentions:

> The ε ring, the brightest and most massive of the narrow rings, **was shown to maintain an appreciable eccentricity (e = 0.00794)** and an azimuthally-varying width; the ring is five times wider and ∼2.5 times brighter in reflected sunlight at apoapsis than at periapsis (French et al. 19881; Karkoschka 2001a2). However, many fundamental parameters about the ring system remain unknown, including the filling factor, composition, thickness,
>
> 1French, R. G., Elliot, J. L., French, L. M., et al. 1988, Icarus, 73, 349, doi: 10.1016/0019-1035(88)90104-2
>
> 2Karkoschka, E. 2001a, Icarus, 151, 51, doi: 10.1006/icar.2001.6596

I've read in Wikipedia's [Rings of Uranus](https://en.wikipedia.org/wiki/Rings_of_Uranus#%CE%B5_ring) that several rings are expected to be fairly young, and there may be interaction with some small moons, but I am surprised that the rings could maintain a significant eccentricity, and do not circularize or smear out due to collisions.

**Question:** What kind of dynamical effects can maintain Uranus' rings' eccentricities?

Uranus itself has a [huge J2](https://nssdc.gsfc.nasa.gov/planetary/factsheet/uranusfact.html) and so any ring that isn't perfectly equatorial should have an eccentricity-dependent precession. The paper states that the apoapsis of the rings is five times wider than the periapsis, so there's definitely a population of different eccentricities and semi-major axes within the ε ring.

List of [rings and their orbital parameters](https://nssdc.gsfc.nasa.gov/planetary/factsheet/uraniansatfact.html)

**Tags:** orbital-mechanics, planetary-ring, eccentric-orbit, uranus, eccentricity


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## 0 answers

