This is a picture of two tiny moons of Saturn - Anthe (top left) and Methone (bottom right) - in Saturn's faint G ring. The moons are only a couple of miles across. Those arcs the moons are sitting in are caused by debris from mirco-meteorites hitting the surface of the moons. The cool thing here is that, after countless orbits around Saturn, the debris should form complete rings, as the material spreads out and around. That's what scientists expected to see. But, as I've said many times here before, the closer you look, the weirder it gets.
Apparently the debris forming the arcs is kept in place by gravitational resonances with other moons of Saturn, a concept I must confess I don't fully understand. It has something to do with a set of moons gravitationally interacting with each other (there is a third one, Pallene, in this "family" of moons). Even weirder, the moons aren't always in the center of their arcs, but wander to one side, then the other.
I like the idea of incomplete structures out there. It's easy to see Saturn's rings as stately and unchanging, proof of a stable, predictable clockwork universe. The arcs point to a more accurate picture of things, a solar system that is forever changing and evolving, rearranging itself into ever more complex structures. The moons and their arcs remind me of scaffolding around a building, the girders of a skyscraper under construction, the first few halting paragraphs of a new chapter in an epic narrative.
The photo is from NASA.
