How can the rings of Saturn exist?

[CaptainPanic]

I just can't understand why the rings of Saturn are stable...

 

My knowledge of the theory of gravity, which may be limited, is that there is only an attraction force (when we look at macroscopic things like rocks and planets). These rings seem to defy everything I know of gravity. Why don't the rings form a few moons, or at least larger lumps of rock? Any disturbance in the homogeneity of the rings should irreversibly cause the formation of lumps of rock. There are plenty of disturbances (even from outside, in the form of asteroids and comets), but also moons, and a size distribution in the rocks (they are not all equally big).

 

Can anyone explain to me how the popular sciences see this? (I have read some theories where electricity and magnetism were included together with the theory of gravity to explain it... Then there can be a repulsion force to explain why moons don't form... but it seems this is not accepted by the mainstream science).

[hermanntrude]

I read somewhere that they're considered to be unstable, and are condensing to form moons as we speak, but they're just doing it very slowly indeed so we think of the rings as permanant.

[insane_alien]

the rings don't form moons because they are constantly tugged at by passing moons. this keeps them nice and dusty. you might want to look up roche limit for how this works.

[swansont]

Also, I think, the tidal forces from the planet will have an effect.

[insane_alien]

hence the roche limit.

[swansont]

How did I miss that? Hmmm. Need more caffeine.

[CaptainPanic]

Thanks for the responses!

 

The Roche limit as defined on wikipedia (for those who are also interested, but not familiar with the topic, like me)...

[math]d = R\left( 2\;\frac {\rho_M} {\rho_m} \right)^{\frac{1}{3}}[/math]

where R is the radius of the primary, ρM is the density of the primary, and ρm is the density of the satellite. - [wikipedia]

 

So you're saying that every particle in orbit around Saturn is one single piece of rock (or whatever material those rings are made of)... none of them are formed by clusters of material, because the rings are within the Roche limit of Saturn? (Single pieces of rock can then withstand the tidal forces... the molecular/crystal bonds of the material itself hold it together).

 

Sounds like if you ever go there with a spacecraft, you should make sure everything is tied down with some strong tape, or the tidal forces will make it move out of its cupboard...

[insane_alien]

well, when you start forming clups they are going to be VERY loosly held together. even a slight force would be enough to move them appart. the tidal forces will do this. it is different for a homogenous body which the roche limit is usually applied to because there are other bnding forces involved.

[Dark matter]

Doesn't it also have to do with the rings being in motion around Saturn?

[antimatter]

Wouldn't it be like an accretion disk, and it would just form a star, the Roche limit doesn't seem to apply to this that much.