Friday, January 11, 2013

Iapetus, the Dinosaur Moon



Iapetus is a moon of Saturn with a funny name and a funny geological feature. I always think of it as the "dinosaur moon", because it has a distinct ridge feature on its surface that reminds me of the back of a dinosaur. Orbiting at 2.2 million miles from Saturn's surface, it's farther away from Saturn than Titan is. The surface of Iapetus was imaged by the Cassini mission in 2004, and the images revealed the equatorial ridge, a 6 mile high mountain range. It's a bit unclear how this band of mountains ended up on Iapetus. One theory is that a long time ago, Iapetus had a ring similar to Saturn's ring. As the moon evolved, the ring began to collapse onto the surface, and this ridge is where all the material collected. A second idea is that the ridge formed during a time when Iapetus was spinning on its axis much faster than it does today. Bodies in space, such as the Sun and the Earth, spin on their axis. Because of this, they bulge just a little bit in the middle. So Earth and the Sun are not perfect spheres, but rather balls that are slightly wider at the center. If Iapetus was spinning really fast some time in the past, this ridge might be the result of the moon bulging in in the middle. Astronomers will have to take a closer look at the composition and orbital properties of this moon before they can determine exactly how the ridge formed.

Image Credit: NASA/JPL/Cassini