Since some of the original Cassini pictures were released a couple of years ago, there's been a lot of speculation about Iapetus because of the wierdness of the images coming back. Some are calling it The Great Wall of Iapetus
Now comes news that the mystery of the Great Wall might have been solved. Scientists at JPL are saying that Iapetus might be one of the oldest moons in the solar system, and because of radioactive decay, the moon could have shrunk, forming the ridgeline.
The jury is still out, however. One thing is for certain: the more public speculation and involvement in the story, the more interest there is in NASA and the Cassini mission. Cassini is tasked with another close fly-by of walnut-shaped, Pac-Man-looking Iapetus in September. Let's hope for something that keeps the public interested."