Phoebe is Saturn’s largest moon with a retrograde orbit.
A retrograde orbit carries a moon around its planet in the direction opposite to Saturn’s rotation and the motion of most major Saturnian moons. Phoebe’s orbit is also moderately eccentric and highly inclined, marking it as an irregular satellite in Saturn’s Norse group.
Phoebe was discovered photographically in 1899 by William Henry Pickering, making it the first natural satellite found through photography. NASA’s Cassini spacecraft flew past Phoebe in 2004 and revealed a dark, heavily cratered world about 213 kilometers across. Its unusual orbit and dark surface support the idea that Phoebe may be a captured object, possibly a former Centaur from the outer Solar System.
A common mix-up is Hyperion: it has a slightly larger radius than Phoebe, but Phoebe is more massive and is the largest retrograde moon of Saturn. Phoebe also gives its name to Saturn’s enormous, faint retrograde Phoebe ring.