Heh, nope!

There are no large moons orbiting inside the Roche Limit of either Saturn or Jupiter. In fact, Saturn's ring system actually extends past the Roche Limits.

Note here that the Roche Limit is also a factor of mass. The tiny bodies orbiting very close to the planets are not massive enough to be torn apart by the unequal gravity.

By your questions, I think you are starting to get this! Consider for a minute what the Roche Limit actually postulates. In essence, it says that a body over a certain mass and under a certain tenstile strength(like steel has a higher tenstile strength than rock) which approaches too close to another massive body is affected by the gravity of the massive body unequally. The point closest to the massive body feels the gravity more than the point farthest away. As a result of shear, when the inequality gets high enough, the object can be torn apart.

In Io's case, it is close enough to the Roche Limits that it feels that unequal pull of gravity to the point that it is nearly pulled apart. The stress this causes makes the moon flex, and this flexing creates heat. Now add to that the fact that it also is flexed by the gravity of Europa every 2nd orbit (the 2:1 resonance I mentioned earlier) and you can see it is being flexed alot.

You can reproduce this effect somewhat, using a handball. Take the handball and squeeze it for a few minutes, and you will notice it heats up. Same process.

This should also make it obvious what the effect of the moons spin is. As the moon spins, the "bulge" created by the unequal gravity moves. In Io's case, the amount of heat generated has apparently melted it from a point only a few kilometers below the lithosphere right to the core. The lithosphere remains solid due to the coldness of space, causing heat to build up more and more within the melted core.

The heat has to go somewhere--so melted material from the core pushes through the weakest points of the lithosphere it can find and viola, volcano.
Remember here that stuff which is heated expands. It will continue to expand until it is stopped (like by say, the lithosphere) however as it is heated more it keeps trying to expand until finally something has to give. In Io's case, the lithosphere cracks.

Can you see how this would also make a difference on a smaller body? Less room to expand = more pressure.

Cheers!

__________________
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