Cassini Image Explains Iapetus' Two Faces

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.

The new data seems to lend more credence to the already-leading explanation of why the moon looks the way it does. Astronomers hypothesized some time ago that the leading cause for the brightness and reflexiveness on one of its faces was the fact that migrating ice on its surface moved to that location predominately. The other side, the idea had it, was darker because it was covered with dust. The new Cassini batch of pieces of information contains data collected with its cameras, as well as with its heat-mapping scientific instruments, Space reports.

Iapetus was discovered back in 1671 by French-Italian astronomer Giovanni Domenico Cassini, the scientist after whom the current space probe is named. He noticed that the celestial body appeared to be a lot darker on the side that was oriented forward, as it moved through its orbit around Saturn. Conversely, the side that was oriented backwards, away from the orbital course, was the bright, ice-covered one. The images that show details of the two faces of Iapetus were collected back in 2007, by Cassini's Imaging Science Subsystem (ISS) camera.

“ISS images show that both the bright and dark materials on Iapetus' leading side are redder than similar material on the trailing side,” Freie Universitat expert Tilmann Denk says. He is the author of one of two new papers detailing the findings, which appear in the December 10 online issue of the top journal Science. The leading face may be colored in darker tones because it continuously picks up dust emitted by some other Saturnine moons, some believe. “Iapetus is the victim of a runaway feedback loop, operating on a global scale,” Boulder, Colorado-based Southwest Research Institute (SwRI) expert John Spencer adds.