Iapetus 

Iapetus was discovered by Giovanni Cassini in 1671 and is well known by its mysterious dark material that covers the surface on the leading side. Its trailing side is bright. The dark material could probably come from the inside or caught from space. However the true reason remains unknown. One theory suggests that the material could come from Phoebe, in which meteor mpacts could send dust into space that Iapetus sweeps up with its gravitational field. Another theory suggests that the material is of internal origin because much of it is concentrated in the crater floors. Whatever the reason, this mystery will continue to puzzle scientists until further studies are conducted.

Physical Data Key Mass Mass Mass Mass compared to that of Earth. Radius Radius Radius Radius compared to that of Earth. Mean Density Average Density. Distance Distance to the planet's center. Magnitude The brightness of a star or object.

Orbital Data Key Rotational Period Number of days to make one complete rotation. Orbital Period Number of days to obital the planet. Mean Orbital Velocity Average obital speed. Orbital Eccentricity Eccentricity. Orbital Inclination The tilt of the moon or planet. Escape Escape Velocity. Albedo Visual geometric albedo.