Can Moons and Exoplanets Have Ring Systems?

[FtlIsAwesome]

I've been thinking about rings. More massive objects would more likely be able to have rings. I think we'll eventually find superEarths, and even subEarths, that have rings.
All the gas planets in our solar system have rings, but only Saturn has prominent ones.
Exo-ring systems could vary between faint and prominent.

I also think that moons can have rings. Currently astronomers are investigating if Rhea, moon of Saturn, has its own faint rings.

For prominent rings to be in its favor, a moon should be large, a good distance away from its parent planet, the parent planet low in mass, other moons if any not disrupting the rings, and the ringed moon not sharing a rotational or orbital resonance with any of the other moons or the parent planet. Having no other moons will also increase the chances.

The rings will need to be within the object's Hill sphere. They'll need to be outside the Roche limit unless the pieces have the required tensile strength.
My guess is that the rings will usually align with the equator. Can they be inclined relative to the equator?

Saturn's rings are icy, so for planets/moons closer to the local sun the rings will be rocky due to the increased heat.

I found this paper on the detectability of jovian planets with rings, which I only skimmed.
http://arxiv.org/PS_cache/astro-ph/pdf/0510/0510594v1.pdf


I am also interested in rocky thick rings, rings that have much larger rocks that Saturn. Like "asteroid belts" as commonly incorrectly depicted in fiction. Can rings be this way? Will an massive impact on a moon result in this?

Can multiple moons have ring systems?

Instead of a ring system, can planets have torus-shaped or spherical dust clouds?





Thoughts? Corrections?

 

[qraal]

I've been thinking about rings. More massive objects would more likely be able to have rings. I think we'll eventually find superEarths, and even subEarths, that have rings.
All the gas planets in our solar system have rings, but only Saturn has prominent ones.
Exo-ring systems could vary between faint and prominent.

I also think that moons can have rings. Currently astronomers are investigating if Rhea, moon of Saturn, has its own faint rings.

Rhea's putative rings have since been disconfirmed. Rhea does have an oxygen atmosphere, albeit very, very thin.

For prominent rings to be in its favor, a moon should be large, a good distance away from its parent planet, the parent planet low in mass, other moons if any not disrupting the rings, and the ringed moon not sharing a rotational or orbital resonance with any of the other moons or the parent planet. Having no other moons will also increase the chances.

Actually small moons help maintain the rings - witness the various "shepherd moons" which maintain Saturn's.

The rings will need to be within the object's Hill sphere. They'll need to be outside the Roche limit unless the pieces have the required tensile strength.

Saturn's are inside the Roche Limit. An orbiting object's density has a lot to do with its fate.

My guess is that the rings will usually align with the equator. Can they be inclined relative to the equator?

No. They form due to the non-sphericity of a rotating planet. A perfectly spherical planet doesn't form rings from orbiting debris.

Saturn's rings are icy, so for planets/moons closer to the local sun the rings will be rocky due to the increased heat.

Correct.

I found this paper on the detectability of jovian planets with rings, which I only skimmed.
http://arxiv.org/PS_cache/astro-ph/pdf/0510/0510594v1.pdf

I am also interested in rocky thick rings, rings that have much larger rocks that Saturn. Like "asteroid belts" as commonly incorrectly depicted in fiction. Can rings be this way? Will an massive impact on a moon result in this?

Maybe. But only for very young rings. Eventually the chunks either accrete together as mini-moons or grind each other into smaller bits. Thus Saturn's rings.

Can multiple moons have ring systems?

Satellites of satellites are inherently unstable, thus probably don't last long enough to make rings.

Instead of a ring system, can planets have torus-shaped or spherical dust clouds?

For a while, but the debris will eventually form a ring via perturbations from the planet. Rings are the end-state of such debris clouds - the evolution sequence is...

cloud ---> torus/lens ---> rings





Thoughts? Corrections?[/QUOTE]

 

[FtlIsAwesome]

The rings will need to be within the object's Hill sphere. They'll need to be outside the Roche limit unless the pieces have the required tensile strength.

Oops. I was mentally thinking about moons/moonlets. The rings can be within the Roche limit, and usually are.

They form due to the non-sphericity of a rotating planet. A perfectly spherical planet doesn't form rings from orbiting debris.

So is there a correlation between the planet's oblateness and the properties of the rings?

Satellites of satellites are inherently unstable, thus probably don't last long enough to make rings.

A satellite can orbit a moon if the satellite is within the moon's Hill sphere, and the moon doesn't have a orbital/rotational resonance. A satellite could orbit Earth's Moon, but because the Moon is tidally locked the satellites are perturbed.

Actually small moons help maintain the rings - witness the various "shepherd moons" which maintain Saturn's.

True, if we're talking about satellites of the object that has rings. But when a moon has rings, other moons of the parent planet may disturb the rings, especially if there's an orbital resonance like 3 of the Galilean moons.

To the mods: Should this thread be moved to Astrophysics?

 

[Chronos]

Nothing unusual about rings. All planets probably have rings, some more pronounced than others.