SUMMARY: Cassini made a relatively close flyby of Iapetus on December 31, 2004, and took photographs which show Saturn's third-largest moon in unprecedented detail. Iapetus is best known for its two-toned colour; one hemisphere is dark, while the other is bright. Cassini passed within 123,400 km (76,700 miles) of the moon, which is 10 times closer than Voyager 2. One possiblity for Iapetus' dark side is that it passed through a cloud of organic material which painted one side. Another idea is that the dark material originated from inside Iapetus, and was ejected in a series of volcanic eruptions. Hopefully this, or an upcoming flyby in 2007 will give scientists enough information to understand it better.

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