Although Saturn's moon Iapetus was first discovered by Giovanni Cassini in 1671, it wasn't until 2007 that we earthlings got a close-up look at the patches of mountains on Iapetus' surface.

Picking up where the spacecraft Voyager 2 left off in 1981, Cassini made one flyby of Iapetus, snapping photos of the dual-toned moon. The mountainous regions in this photo are located in the transition between the mountains' lighter- and darker-colored hemispheres.

Just last year, researchers offered a hypothesis to explain why one side of the moon is conspicuously darker than the other. They say dust particles may be flying off another moon, Phoebe, and are smacking into Iapetus's leading edge "like bugs on a windshield."