Iapetus features a high-contrast surface of light and dark. As such, it has been dubbed the yin and yang of the Saturn moons. Iapetus, like Rhea, is thought to be composed of ice and rock.

In 2007 Cassini flew within a few thousand kilometers of Iapetus's surface to take this dramatic picture of the ridge. A movie of the flyby is available at the NASA site devoted to Saturn.