With data in from the Cassini probe's flyby of Saturn's Iapetus moon last month, scientists are now making progress in understanding the little satellite's unique features.
The moon's division into very clear black and white patches has puzzled researchers for years. Now evidence seems to support what they're calling a "runaway" heating process, in which ice from the warmer black areas is transferred as vaporized water to the light regions.
Researchers still aren't sure where the dark material that covers the side facing forward in the moon's orbit comes from. However, they speculate that it could be dust thrown off from other Saturn moons orbiting farther out, and in an opposite direction to Iapetus.
Once the dark material falls to the surface of Iapetus, it is enough to absorb enough sunlight to warm the underlying ice up to the balmy temperature of minus 230 degrees Fahrenheit, or just enough for the slow release of water vapor. That water vapor then condenses at a cold spot, such as the moon's poles, or lower-latitude areas facing away from the direction of orbit.
Over time, the darker areas get darker as the proportion of dust to ice there rises, and the bright areas get brighter as they in turn collect more ice. This is enough to ensure a strict demarcation between the areas, with the surface showing only strong black and white, rather than gray patches,
Cassini scientists say.
Scientists are also developing theories about the odd equatorial ridge that runs much, but not all the way around the moon, giving the body a unique walnut-like shape.
The new images have shown that it is unlikely to be material from rings that collapsed onto the Iapetus' surface. With very old craters evident, they've also ruled out the possibility of it being a young formation, and now believe it to have been created by tectonic forces, perhaps similar to mountain ranges on Earth.
Cassini is on the Trail of a Runaway Mystery [NASA press release]
(Image one: A false-color mosaic of Iapetus, showing the bright trailing hemisphere. Credit: NASA/JPL/Space Science Institute. Image two: Craters in the dark side of Iapetus. Credit: NASA/JPL/Space Science Institute)
