Saturn’s satellite Phoebe was discovered in 1899 by William Henry Pickering; it has been for a century the outermost known satellite of Saturn. It orbits at about 13 million kilometers (or 215 Saturnian radii) from Saturn; its orbit is highly inclined and is retrograde, which suggests that Phoebe was captured, rather than having been formed together with Saturn. It may have originated as a Kuiper Belt Object. Phoebe was first observed by Voyager 2 in 1981 and then extensively explored by the Cassini orbiter. Its diameter is 220 km and its density is 1.6 g/cm3. Phoebe might be the source of a tenuous external Saturnian ring, and might also be responsible for feeding the dark side of Iapetus with dark material.