Sun light caused mysterious blemishes on Iapetus

From the NewScientist online magazine

Blame the Sun for the mysterious dark blemishes on Saturn's moon Iapetus. New photos from the Cassini spacecraft reveal the splotches are mainly found on the sunward-facing slopes of craters and mountains, suggesting a runaway heating process is tainting portions of the moon. Cassini's imaging team members found that there are sharp-edged dark spots all over the surface, even on the moon's bright trailing hemisphere. Careful analysis revealed that these isolated spots are preferentially located on the sunward facing slopes of craters. That suggests that as the slopes get slightly warmer, ice there starts to evaporate. That exposes more dark stuff in the ice, which is then ready to retain even more solar heat.

thanks to Shaun Saunders for the update

Cassini Is On The Trail Of A Runaway Mystery

From Sciencedaily.com

NASA scientists are on the trail of Iapetus' mysterious dark side, which seems to be home to a bizarre "runaway" process that is transporting vaporized water ice from the dark areas to the white areas of the Saturnian moon. This "thermal segregation" model may explain many details of the moon's strange and dramatically two-toned appearance, which have been revealed exquisitely in images collected during a recent close flyby of Iapetus by NASA's Cassini spacecraft. Infrared observations from the flyby confirm that the dark material is warm enough (approximately minus 230 degrees Fahrenheit or 127 Kelvin) for very slow release of water vapor from water ice, and this process is probably a major factor in determining the distinct brightness boundaries.

Saturn's Iapetus showing strange mottled features

NASA's Cassini spacecraft flew within 1000 kilometres of the moon on 10 September, it saw much some complicated patterns on the surface of the moon Iapetus. Previous to this flyby, Iapetus was thought to have the strange feature of one bright side and one dark side. Not just from lighting, but composed of different materials on each side. Now the Cassini probe shows that the strange features are even more complex. Iapetus has a landscape unlike anything else in the solar system: sharp-edged islands of dark material within pale regions, and patches of white ice on the dark mountainsides. The coating of dark material is a puzzle. "We think it's thin, probably no more than a few metres, because we see an impact that's not very big but has punched through to show the bright material beneath," says Carolyn Porco. ( head of the Cassini imaging team at the Space Science Institute in Boulder, Colorado, US.) "But that's about all we know right now." She suspects that the dark stuff was swept up from space by the leading hemisphere of Iapetus. "Where that material came from is still a mystery," Porco told New Scientist. "Maybe from a moon further out, maybe a pre-existing body that got disrupted?"

Thanks to Shaun A. Saunders for the post
(Image: NASA/JPL/Space Science Institute)

Cassini Delivers Up-Close Images of Saturn Moon

NASA's Cassini probe performed its closest pass to Saturn's odd little Iapetus moon on September 10th , and the first, unprocessed pictures have begun showing up online.

There are many more stunning pictures online, click the article title or this link for more of the story and more pics!

Thanks to Shaun A. Saunders for the post