Ever since the NASA/ESA Cassini spacecraft started orbiting the gas giant Saturn, in 2004, experts have noticed something very peculiar about one of its moons, called Iapetus. The celestial body appeared to have two faces. On one, it was very bright, as viewed with the probe's cameras, whereas the second was a lot darker. Astronomers have had a hard time explaining the difference, but now new data from Cassini has helped them clear out the mystery, and come up with an explanation for the moon's two faces. 

Interesting ... and a cool pic, too.