The Dark Side of Iapetus

Hugh Pickens writes "The difference in coloring between Iapetus' leading and trailing hemispheres is striking. NASA's Jet Propulsion Labs has just released a report on a bizarre 'runaway' process that may explain the strange and dramatically two-toned appearance recently revealed in images collected during a close flyby by the Cassini spacecraft. Scientists believe that initially dark material on one side of Iapetus may have come from other moons orbiting Saturn in the opposite direction. Since Iapetus is locked in synchronous rotation about Saturn, as dusty material from the outer moons spiraled in and hit Iapetus head-on, the forward-facing side began to darken. As it absorbed more sunlight, its surface water evaporated, and vapor was transported from the dark side to the white side of Iapetus. Thermal segregation then proceeded in a runaway process as the dark side lost its surface ice and got darker still. Now the leading hemisphere is as dark as a tarred street and the trailing hemisphere resembles freshly fallen snow."

Re:Obi Wan

[tylersoze]

Actually you must be thinking of Mimas: http://en.wikipedia.org/wiki/Mimas_(moon) [wikipedia.org]

2001 References??

[oni]

No references to the book 2001, A Space Odyssey yet? You guys are slipping. In the mid '60s, when A.C. Clarke wrote the book, he asked asked astronomers (mainstream scientists, not UFO nuts) "if you had to pick one object in the solar system that appeared artificial, what would it be?" They all picked Iapetus. At the time, the blurry photos we had from ground-based telescopes could tell us that it was 50% light and 50% dark, but nothing else. It was a big mystery, even after the Voyager flybys. For that reason, Clarke used Iapetus as the sight of the monolith stargate (the movie version used Jupiter).

We're really lucky to live in a time when all these mysteries are solved.