Iapetus. Referred to as "Japetus" in the novel 2001:A Space Odyssey where it was a described as a cosmic heliograph flashing at Earth for 300 years. The second monolith, or star gate, was located at the centre of the white hemisphere.
When the Voyager 1 and 2 spacecraft flew by Saturn in 1980 and 1981, they were able to pay only fleeting attention to Titan, the second largest moon in the solar system (larger even than the planet Mercury) and the only solar system moon with an appreciable atmosphere. These images are from subsequent Titan flybys in 2005 and 2006. - Image credit: NASA / JPL / University of Arizona