Rings caused by a 5::3 resonance

July 8, 2004

Saturn's F ring looked braided ring to Voyager. The applet 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.