Iapetus is one of the largest moons of Saturn, known for its unique two-tone coloration. One side is very dark, while the other is bright and icy, creating a striking contrast. This moon is about 1,471 kilometers (914 miles) wide and has a distinctive equatorial ridge that makes it look like a giant walnut. Discovered in 1671 by the astronomer Gian Domenico Cassini, Iapetus has intrigued scientists for centuries. Its unusual features suggest a complex history, possibly involving the accumulation of material from other celestial bodies. Studying Iapetus helps us understand more about the formation and evolution of moons in our solar system.