Idiosyncratic Iapetus

Saturnian moon puts a time stamp on the outer solar system

Iapetus, the third-largest and second-farthest-out of Saturn’s satellites, is the weirdest moon in the solar system. One half of it is as bright as snow, the other as black as charcoal. Neither spherical nor ellipsoidal, as most moons are, Iapetus looks like a walnut, with a bulging waistline and squashed poles.