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Zeca
2004-Aug-15, 05:26 PM
Why are Saturn rings so flat? Why are they at equator's plane?
I have a theory but I'd like to know your theory first.

Thanks,

Ut
2004-Aug-15, 05:30 PM
Well, presumably the objects that were torn apart to form the rings were already orbiting in the equatorial plane. Tidal forces nudge satellites into the equatorial plane, and if they cross the Roche limit they're torn apart. The bits that are left over continue to get pushed into the equatorial plane until the rings are flat.

Zeca
2004-Aug-15, 06:15 PM
Well, presumably the objects that were torn apart to form the rings were already orbiting in the equatorial plane. Tidal forces nudge satellites into the equatorial plane, and if they cross the Roche limit they're torn apart. The bits that are left over continue to get pushed into the equatorial plane until the rings are flat.

It is a possibility but what about all inner satellites of Saturn, they are all at the same equatorial plane with less than 1% of inclination...

I think the main reason for the rings to be so flat and at equatorial plane is the pole flateness of Saturn itself. Saturn polar diameter is 90% of it's equatorial diameter. Any satellites or dust particle of rings at low orbit suffer a diferential gavitational pull of the equatorial Saturn bulge. So all objects at low orbit will sonner or later be confined to equatorial plane orbit.

Okay?

Ut
2004-Aug-15, 07:26 PM
It is a possibility but what about all inner satellites of Saturn, they are all at the same equatorial plane with less than 1% of inclination...

What about them?


I think the main reason for the rings to be so flat and at equatorial plane is the pole flateness of Saturn itself. Saturn polar diameter is 90% of it's equatorial diameter. Any satellites or dust particle of rings at low orbit suffer a diferential gavitational pull of the equatorial Saturn bulge. So all objects at low orbit will sonner or later be confined to equatorial plane orbit.

You seem to be saying pretty much the same thing I did.

It has to do with momentum transfer. If Saturn weren't spinning, it wouldn't have the same kind of effect on its satellites (though, it also wouldn't have the buldge). The satellites are in the same orbital plane for the same reason the planets are: Angular momentum must be conserved.

Zeca
2004-Aug-15, 07:35 PM
You seem to be saying pretty much the same thing I did.

It has to do with momentum transfer. If Saturn weren't spinning, it wouldn't have the same kind of effect on its satellites (though, it also wouldn't have the buldge). The satellites are in the same orbital plane for the same reason the planets are: Angular momentum must be conserved.

Yes, angular momentum must be conserved, but you think all the satellites and rings were born at this very equatorial orbital plane? About captured satellites?
What I mean is that if you try to put a satellite at any inclined low orbital plane it will migrate to the equatorial plane within few decades, no more than centuries.

Eros
2004-Aug-16, 12:28 AM
A flat disc is the lowest energy formation for a spinning object. That's why despite approximations every spherical object that spins is slightly squished at the poles and bulged at there equator. I would imagine that over time all these pieces would just collect up in the flat disc since this is the most stable place for them to be.

Look at the planets? ok so there is some change in inclination but its not like we have a planet going around at 90degrees to us and all the planets exibit direct motion... with Uranus the only exception - it sort of roles around

Ut
2004-Aug-16, 12:43 AM
You seem to be saying pretty much the same thing I did.

It has to do with momentum transfer. If Saturn weren't spinning, it wouldn't have the same kind of effect on its satellites (though, it also wouldn't have the buldge). The satellites are in the same orbital plane for the same reason the planets are: Angular momentum must be conserved.

Yes, angular momentum must be conserved, but you think all the satellites and rings were born at this very equatorial orbital plane? About captured satellites?
What I mean is that if you try to put a satellite at any inclined low orbital plane it will migrate to the equatorial plane within few decades, no more than centuries.

I'm interested in your ideas, and would like to subscribe to your newsletter.

Padawan
2004-Aug-16, 09:49 AM
A flat disc is the lowest energy formation for a spinning object. That's why despite approximations every spherical object that spins is slightly squished at the poles and bulged at there equator. I would imagine that over time all these pieces would just collect up in the flat disc since this is the most stable place for them to be.


i'd hate to go off topic here, but i'd like to ask a question: If that above is true, then the discs around black holes should also be flat, right?

Zeca
2004-Aug-16, 04:35 PM
A flat disc is the lowest energy formation for a spinning object. That's why despite approximations every spherical object that spins is slightly squished at the poles and bulged at there equator. I would imagine that over time all these pieces would just collect up in the flat disc since this is the most stable place for them to be.


i'd hate to go off topic here, but i'd like to ask a question: If that above is true, then the discs around black holes should also be flat, right?

If that was true yes but that is not true. The shape of a spinning planet (and somehow fluid planet) is a point of equlibrium of forces: the gravitational pull of the planet itself and the inertia. If the planet doesnt spin it would be a perfect sphere. Imagine if you freeze Saturn to the actual shape and stop its spin, what do you get? A planet with a huge moutain crest around all equator line and a depression at poles. If you defrost this still Saturn there will be a flow from equator to poles but if Saturn is spinning there will not be this flow, the inertia keep the equatorial bulge.

stu
2004-Aug-23, 02:00 AM
We were taught in intro astronomy that it was because as the rings evolve, any random motions in the vertical direction of particles would be cancelled out by impacts between particles.

Also, this topic was addressed here in the past (I don't remember where or when), and someone said that it was also because of the ellipticity of the planet itself -- that the extra mass around the equator helps to draw the ring particles there. This is along the lines of what Zeca said.

beskeptical
2004-Aug-23, 02:45 AM
I like your site, stu.

I've been meaning to find out and now here's a thread so I can ask. Just how thick are the rings? They look awful thin and I was curious about them.

stu
2004-Aug-23, 03:53 AM
I like your site, stu.

I've been meaning to find out and now here's a thread so I can ask. Just how thick are the rings? They look awful thin and I was curious about them.

Thanks. :D

According to NASA, the rings are about 5-30 m thick, except for the G and E ring, which are 10^5 and 10^7 m thick, respectively. [source: http://nssdc.gsfc.nasa.gov/planetary/factsheet/satringfact.html ]

Kaptain K
2004-Aug-23, 01:10 PM
As stu said, any moonlet in the rings that is in an inclined orbit will, sooner or later, collide with another moonlet. This tends to lower the inclination of its orbit. Differential gravity from the equatorial bulge also tends to keep them all in the equatotial plane.

beskeptical
2004-Aug-25, 08:28 AM
I like your site, stu.

I've been meaning to find out and now here's a thread so I can ask. Just how thick are the rings? They look awful thin and I was curious about them.

Thanks. :D

According to NASA, the rings are about 5-30 m thick, except for the G and E ring, which are 10^5 and 10^7 m thick, respectively. [source: http://nssdc.gsfc.nasa.gov/planetary/factsheet/satringfact.html ]Wow, the thin ones are really thin, 5 meters!