Phoebe is the outermost satellite of Saturn. It is a dull and generic rock with a retrograde orbit, low albedo, and a diameter of only 220 kilometers. Despite this, it is easily the second most interesting moon in the Solar System.

The first most interesting moon in the Solar System is Mimas. Mimas, which also orbits Saturn, is interesting because it is not a moon at all, despite its rocky, cratered exterior and lack of internal activity. It is an alien exploration craft.

When human beings finally arrive in Saturn orbit, they will discover on the surface of Mimas the mummified and space-suited remains of a being a full ten meters long. They will refer to this being only as the Entity. He, she, or it will be found in an attitude of extreme despair. That fact, and the seeming lack of any accompanying technology, will be one of the enduring mysteries of the Age of Space. Unless, of course, somebody thinks to perform a thorough and careful survey.

Phoebe is where the Entity lost his keys.