Planetary rings

[Chris]

Looking at the Cassini images of Saturn's rings, I was wondering, is it theoretically possible for a planet to have elliptical rings (highly eccentric) with the planet in one focus of the ellipse, or would such an arrangement be unstable?
Thanks.

Chris

[Russ]

Looking at the Cassini images of Saturn's rings, I was wondering, is it theoretically possible for a planet to have elliptical rings (highly eccentric) with the planet in one focus of the ellipse, or would such an arrangement be unstable?
Thanks.

Chris

It is possible for a planet to have an eliptical ring system, just not for very long. As you surmise, the elipse would be unstable.

[Evan]

Elliptical rings? Sure. Our sun has elliptical rings such as the debris trail left by comet Tempel-Tuttle which extends throughout the 33 year long orbital path.

[Emspak]

I think he was referring to rings as coherent (and spectacular) as Saturn's.

Russ is right that those would be less stable. But a ring of crumbly stuff would last a while, if whatever was in that orbit was breaking up. Like a comet, as Evan noted.

Part of the reason is the difference in speeds that particles in orbits (elliptical ones) have. If I have an even slightly more massive particle (a rock, say) than one nearby it will zing around the planet with a lot more oomph than the smaller, lighter one if the orbit is approximately the same radius. (I'm assuming all the other vectors are equal).

Anyhow, point is that the more eccentric the orbit, the harder it is to keep lots of little particles aligned becuase the speeds they move at will differ more, if that makes any sense. A tiny change at perihelion (or peri-whatever planet) will mean a much bigger differnce in the shape of the orbit if it is highly eccentric.

So if your ring particles are all different sizes (even within a narrow range) if they knock each other around at all (and they will) an eccentric orbit will show a pattern of lots of them in a narrow band at closests approach, but a wide one further away. So your ring would get smeared out at apastron.

Yeah, it's way oversimplified but I am too tired to show the math.

[Chris]

Thanks.

Chris