Saturn’s giant surprise

Saturn’s main ring system is a familiar image, but it’s only part of the story. Most Solar System rings lie within a few radii of their planet, where gravitational accelerations inhibit satellite formation. Saturn’s faint E ring is an exception, made up of sheets of dust that extend out to about 10 planetary radii. Beyond that, Spitzer Space Telescope observations of Saturn’s most distant moon Phoebe reveal an enormous and previously unknown saturnian ring, extending from at least 128 to 207 planetary radii. The ring’s vertical thickness of 40 planetary radii matches the up-and-down motion of Phoebe along its orbit, and the ring may be composed of material ejected from Phoebe. These ring particles appear to span the saturnian system from the main rings to the edges of interplanetary space.