Iapetus

Iapetus, outermost of Saturn’s major regular moons, extraordinary because of its great contrast in surface brightness. It was discovered by the Italian-born French astronomer Gian Domenico Cassini in 1671 and named for one of the Titans of Greek mythology. Iapetus has a radius of 718 km (446 miles) and orbits Saturn once every 79.3 Earth days at a distance of 3,561,300 km (2,212,900 miles). Its bulk density of 1.0 grams per cubic cm implies that...