Do the thousands of bands seen by Cassini around Saturn move outward, like ripples from a drop?Whats the rate?

Question

While watching water the thought came to mind...or are the bands stable radially?

Answer 1

I would expect tidal forces to slow the particles and move them to a higher orbit. This is the case with larger bodies, like our moon.

I don't think anyone has measured the rate, but we can make a good guess. Since the ring particles and our moon are in a vacuum, they should move at the same rate. That is, one would expect the tidal forces to have more effect on a larger object, and less on a smaller object, which cancels out the difference in the masses. (Perhaps you recall the famous experiment on the moon where the dropped a feather and a hammer during Apollo 15).

If we accept this, we can use the measured rate that the moon is moving away from the earth (3cm/year) and assume that the ring particles are moving at the same rate.

This is off the cuff, and unchecked, but seems a reasonable place to start.

Answer 2

Hi. Each diameter has its own rotation rate but there does seem to be a 'ripple' after the rings rotate back into sunlight. May be caused by electrostatic forces I read. I see no reason why the movement has to be confined to a particular orbit. (It may move radially, to your point.) Good question!

From the web "The spokes are thought to be the shadows of smaller particles levitating a few tens of meters above the rings due to electrostatic forces (the ``cling'' on fabrics fresh out of a dryer)."