Saturn's rings appear eternal, a perfect and unchanging symbol of cosmic order. Yet the truth is far more dynamic and fleeting. The rings are startlingly young, formed somewhere between one hundred and four hundred million years ago. This means the dinosaurs walked the Earth under a sky where Saturn hung bare and unadorned. The iconic structure we recognize today was born when an icy moon wandered too close and was torn apart by tidal forces at the Roche limit, its shattered remains settling into an extraordinarily flat disk of orbiting ice.

But this magnificent structure is not permanent. It is slowly vanishing. Ultraviolet light from the Sun charges individual ice grains, making them responsive to Saturn's magnetic field. Guided inward along invisible field lines, tons of ring material plunge into the planet's atmosphere every second in a ...