Everything's Organic on Titan

Peering through the thick atmospheric haze that surrounds Saturn's giant moon Titan, the Cassini spacecraft has uncovered a geological wonderland, suggesting a world of organic lakes, melted water and ammonia volcanoes, and sticky polymer surfaces.

During the craft's close-up flyby last week, numerous spectrometers, radar, and microwave instruments scanned a rectangle covering about 1% of Titan's surface. Early results from the instruments showed that organic molecules most likely blanket Titan's surface.

"The picture emerging is that Titan is really covered in organics," said Ralph Lorenz, a member of the Cassini mission radar imaging team at the University of Arizona, Tucson.

Titan's largely nitrogen atmosphere contains methane, which, when broken apart by sunlight, can recombine to form other molecules such as ethane, propane, and acetylene. These would fall to the surface as solids or liquids, "but how much is liquid or solid is still unclear. That's going to take a lot of work to tease out," said Jonathan I. Lunine, another Cassini team member at the University of Arizona.

Some of these surface deposits could be sticky or flaky. For example, frozen acetylene is a nondescript white material, but it readily polymerizes to form substances that could look metallic or black.

Images show bright rough areas that look similar to basaltic flows seen on Venus or Earth. But flows on Titan would not be caused by molten rock. Rather, upwellings would likely spring from melted water ice in its interior.

Fine bright features that stretch across dark areas may be cracks in a thin solid layer, like an eggshell. And mysterious streaks on the surface could be caused by wind.

"We now have strong evidence for active atmospheric processes--winds moving solids or liquids around," Lunine said.

A dark, cat-shaped area that may be a large lake has been dubbed "SiSi, the Halloween cat" (after the daughter of one of the team members), by Charles Elachi, director of the Jet Propulsion Laboratory, which manages the Cassini mission for NASA.