Astronomy
The Dynamics of Planetary Ring Systems: Shepherding and Resonances
Quick fact
Saturn's F ring, a thin, braided ribbon, is kept so narrow by two tiny shepherd moons, Prometheus and Pandora, that they were discovered by studying the ring's structure before being seen directly.
Why this is interesting
Saturn's dazzling rings aren't just frozen ice; they are alive with carved edges, narrow ribbons, and mysterious gaps. But what invisible hand trims them?