Saturn's F ring looked braided ring to Voyager. The simulation above
shows a massless particle in a 5::3 resonance with a moon (yellow dot)
of a planet (big circle in the center). Particles are drawn once per
orbit of the moon, so the planet and the moon always appear to be in
exactly the same place. The particle, doing roughly 5 orbits per 3
orbits of the moon, dances around. As you can see if you watch it
long enough, the result is a braided ring.
Cassini is orbiting Saturn
and sending back
nice pictures of rings. F
doesn't look very braided anymore. And the waves I see in
this picture only go out to the edge, not back in again.
Reversible processes (like the resonance simulated above) could
produce braided rings, but not these asymmetric waves. The particles
must be interacting.
NASA says the rings are mostly water ice. I suspect there's more:
an atmosphere extending above and below the rings by several tens of
kilometers. Water vapor? Hydrogen? It could be very thin.
Any chunk of ice that gets bumped out of the ring plane by collisions
would get slowed down by the atmosphere in less than a kilometer and
would fall back to the ring plane. The moon-induced waves would be
winds, blowing the ice crystals around. Maybe the rings are similar to our
cirrus clouds.
I'd like to know the temperature of the rings, and whether the
heat mostly comes from the sun or the Saturnian system. If the heat
comes from Saturn, the temperature's stable. If it comes from the
sun, it drops to near absolute zero once every 15 years when the rings
turn on edge, which would be pretty rough on any water vapor atmosphere.
Am I right? Am I wrong? I don't know. I'm an armchair astronomer.
Update (Sept 2005). Turns out I was
right! The rings do have their own atmosphere. (The crowd goes
wild!) It's mostly oxygen. Water gets ionized, the hydrogen gets
flushed away leaving the heavier oxygen. But is this atmosphere
significant to the behavior of the rings? I still don't know about
that.