Atom & Cosmos

Planetary rings count comets Subtle ripples recently discovered in planetary rings, akin to the corrugations of a tin roof, provide a record of collisions with comets or their debris, two new studies suggest. The ripples, identified in the rings of both Jupiter and Saturn, persist even decades after a collision and can reveal how often debris clouds from comets and other small objects smack into planets and how many of these objects exist in the outer solar system.