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jeffcoffin1970
2008-Sep-23, 04:27 PM
Why don't the rings of Saturn coalesce into one moon? I have heard many theories that our moon, and even planets, started out as orbital debris and then coalesced into a single body.

schlaugh
2008-Sep-23, 05:11 PM
You may want to do some searching for the Roche Limit, which describes the tidal forces that can tear an orbiting body into small pieces, such as Saturn's Rings, or why the Earth's moon has managed to hold together. For now. :)

01101001
2008-Sep-23, 05:13 PM
NASA: Frequently Asked Questions About Saturn's Rings (http://www2.jpl.nasa.gov/saturn/faq.html#how)


How did the rings form around Saturn?
There are currently three theories on how the rings formed around Saturn:


The rings are remnants of material of the early solar system that never formed into satellites because they were within the Roche limit.
A medium size moon of Saturn strayed inside the Roche limit and was pulled apart by tidal forces, forming the rings.
The ring material is the remains of a satellite shattered by meteor impacts.


They cannot coalesce, (most) being so close to Saturn.

Wikipedia: Roche limit (http://en.wikipedia.org/wiki/Roche_limit)


The Roche limit (pronounced /ˈroʊʃ/), sometimes referred to as the Roche radius, is the distance within which a celestial body, held together only by its own gravity, will disintegrate due to a second celestial body's tidal forces exceeding the first body's gravitational self-attraction.[1] Inside the Roche limit, orbiting material will tend to disperse and form rings, while outside the limit, material will tend to coalesce.

Fiery Phoenix
2008-Sep-23, 05:49 PM
So, because the rings lie inside the Roche Limit, they don't coalesce. And the opposite is correct. Is that it?

mugaliens
2008-Sep-23, 05:52 PM
Occam's razor, which was used, long ago, to divide Saturn's GREAT MOON into billions of small particles suitable for adorning Jupiter's lovely sister.

schlaugh
2008-Sep-23, 07:35 PM
...And the opposite is correct. Is that it?

Solid bodies can exist inside the Roche Limit if they have adequate tensile strength. The Wikipedia article refers to a couple of moons of Jupiter and Saturn which lie within the limit but remain in one piece.

cjameshuff
2008-Sep-23, 10:09 PM
So, because the rings lie inside the Roche Limit, they don't coalesce. And the opposite is correct. Is that it?

On a small scale, gravity plus the intermolecular forces that make solid objects solid are enough to hold individual particles together and form temporary clumps of material. Larger objects are affected more by tidal forces, and not only do those tidal forces stretch clumps out to the point that particles constantly drift away, collisions with other ring particles constantly break them up.

You may find this interesting:
http://www.colorado.edu/news/releases/2007/484.html

Fiery Phoenix
2008-Sep-24, 01:32 AM
On a small scale, gravity plus the intermolecular forces that make solid objects solid are enough to hold individual particles together and form temporary clumps of material. Larger objects are affected more by tidal forces, and not only do those tidal forces stretch clumps out to the point that particles constantly drift away, collisions with other ring particles constantly break them up.

You may find this interesting:
http://www.colorado.edu/news/releases/2007/484.html

Thank you. I'll check it out tomorrow. Too tired right now.

grant hutchison
2008-Sep-24, 10:50 AM
Solid bodies can exist inside the Roche Limit if they have adequate tensile strength. The Wikipedia article refers to a couple of moons of Jupiter and Saturn which lie within the limit but remain in one piece.A body can stay intact inside the fluid Roche limit without having any tensile strength, and this seems to be what's happening for the known inner satellites: they lie inside the fluid Roche limit, but all are outside the rigid Roche limit, which is the point at which tensile strength becomes important.

The fluid Roche limit assumes that a body will deform like a fluid under tidal forces, producing a couple of tidal bulges. When the bulges get big enough, their effective surface gravity falls to zero, and stuff begins to drift off. But real bodies seem to behave more like "rubble piles": they deform, but rather reluctantly, and the various chunks tend to lock against each other. So the whole thing behaves more like a scree slope than a body of liquid. The tidal deformation is therefore less extreme, and the body manages to survive within the fluid Roche limit, held together by its own gravity and the friction of its component chunks. However, if it is disrupted by an impact, it can't reform.

Grant Hutchison

GOURDHEAD
2008-Sep-24, 06:10 PM
Why is entry number 6 of this thread placed ahead of larger number entries that are dated earlier? I have made entries on other threads that appeared out of sequence in a similar way and wonder whether they were considered in the right context.

mugaliens
2008-Sep-24, 09:29 PM
My view of them all seem to be in sequence...

01101001
2008-Sep-24, 10:28 PM
What's wrong with this chronological order (times PDT):


#3 (permalink) Yesterday, 10:13 AM
#4 (permalink) Yesterday, 10:49 AM
#5 (permalink) Yesterday, 10:52 AM
#6 (permalink) Yesterday, 12:35 PM
#7 (permalink) Yesterday, 03:09 PM
#8 (permalink) Yesterday, 06:32 PM
#9 (permalink) Today, 03:50 AM
#10 (permalink) Today, 11:10 AM

What do you see that's different (with adjustment for timezone)?

ngc3314
2008-Sep-25, 02:23 AM
Solid bodies can exist inside the Roche Limit if they have adequate tensile strength. The Wikipedia article refers to a couple of moons of Jupiter and Saturn which lie within the limit but remain in one piece.

Not to mention yet smaller things like ISS. I show a picture of it in class when talking about the Roche limit, with a large yellow label saying "Not a small body held together by self-gravity".

Sock puppet
2008-Sep-25, 10:30 AM
Not to mention yet smaller things like ISS. I show a picture of it in class when talking about the Roche limit, with a large yellow label saying "Not a small body held together by self-gravity".

I like that. May have to steal it :)

ngc3314
2008-Sep-25, 03:01 PM
I like that. May have to steal it :)

I show it like so:

GOURDHEAD
2008-Oct-01, 01:06 PM
What do you see that's different (with adjustment for timezone)? The anomaly went away---or my hallucination, whichever it were.