for National Geographic News
Scientists have speculated for years that Titan, Saturn's largest moon, may give clues to what Earth's chemistry was like before life formed on Earth.
They have also wondered what lies under the moon's thick cloud coverperhaps large lakes and rivers filled by methane rain?
Now, thanks to the Cassini spacecraft and the Huygens probe, they're getting some answers.
Analysis of the first flybys of Titan reveals that this second largest moon in the solar system (larger even than the planet Mercury) is perhaps even more mysterious than scientists previously believed: Titan is an icy planet-like rock, where it rains methane and where perhaps ice volcanoes exude frozen "cryomagma."
NASA's Cassini first flew past Titan in October last year, providing close-up radar images of the moon's cloud- shrouded surface.
On January 14 the European Space Agency's Huygens probe (which was deployed from from the Cassini oribiter) landed successfully on Titan. (Read the story and see the first photo.)
Since then scientists have been crunching the data gathered during the first flybys and the Huygens landing. Their findings are published today in a special issue of the journal Science.
"We realized that Titan is a very complex place, really a planet in its own right that happens to be in orbit around another planet," said Candice Hansen, a Cassini Scientist at NASA's California Institute of Technology-based Jet Propulsion Laboratory (JPL). "From a complexity point of view, it's as interesting as the Earth."
The nitrogen and methane in Titan's atmosphere combine into long chains of hydrocarbons. For nearly two decades scientists had theorized that these hydrocarbons would condense and rain onto Titan's surface, perhaps creating methane lakes or liquid-filled craters.
Cassini has altered such theories. "We haven't seen liquid lakes, and we've been looking," Hansen said. "We're now thinking that regions of liquid will be fairly confined if we find them at all."
A new hypothesis likens Titan's rain cycle to that of a frigid Arizona, where occasional methane precipitation carves riverbeds that are dry during most of the year.
SOURCES AND RELATED WEB SITES