Taking a peek under Titan's organic haze

Titan's cloudy atmosphere as seen from the Voyager probe's flyby in 1980

(CNN) -- A team of scientists has devised an atmospheric model that helps explain weather patterns on one of Saturn's moons, Titan, a haze-covered sphere that might resemble our planet in its infancy.

The study could offer clues about the processes that sparked terrestrial life, because the moon is the only body in the solar system except ours with a dense atmosphere dominated by nitrogen, according to NASA, which partly funded the research.

"Titan is an interesting world. Its organic haze may be an example of the prebiotic organic chemistry that led to life on Earth," said Christopher McKay, a scientist at NASA's Ames Researcher Center in Moffett Field, California.

In Titan's atmospheric haze, which resembles smog pollution on Earth, methane and nitrogen molecules are believed to change into complex organic structures like hydrocarbons and perhaps amino acids, the building blocks of known life.

"We think similar processes once happened here, and life may have started that way," McKay said.

The shroud around the moon, the second largest in the solar system, has long been a mystery. In Voyager probe and ground-based telescope observations, the haze looks brighter in the hemisphere experiencing summer. It also seems much thicker near the polar caps.

Perhaps the most enigmatic characteristic is an outside haze layer, distinct from inner layers, surrounds the moon like a ghostly shell.

McKay and his colleagues came up with a global circulation model that accounts for some of the quirky climate conditions. According to their model, sunlight warms the haze, which fosters winds that in turn transport the haze.

The tiniest haze particles can move from one pole to another within one Titan season, which lasts four Earth years. The model also explains the presence of the separate haze shell, formed from small particles that are blown to the pole and become detached before they go down into the main haze layers.

Keck Telescope image of Titan

"We found that the main features of Titan's organic haze arise from a strong feedback loop between the haze, the sunlight and the wind. This is a critical new factor in understanding Titan," McKay said.

McKay and colleagues, lead author Pascal Rannou and Frederic Hourdin of France published their report last week in the journal Nature.

Bob Samuelson, a planetary atmosphere specialist at the University of Maryland in College Park, said there was good news and bad news about the Titan weather model.

"I do know that Pascal Rannou did have a global climate model, which gives results for Titan that seem a little bit off," said Samuelson, who published a companion piece to the Titan report in Nature.

For example, he said, "there is a so-called winter polar vortex they don't take into account."

Nevertheless, the new model is certainly an improvement beyond previous attempts, according to Samuelson.

"Their model predicts this haze shell, with essentially a lack of haze for about 50 kilometers or so. That's one thing that they predicted that no one else has and it corresponds roughly with the observations," he said.

No matter the model, the true nature of Titan's hazy weather will remain a mystery for time to come. Perhaps the fog will finally be lifted when Cassini and Huygens, sibling NASA and European Space Agency probes, visit Saturn and Titan in 2004 and 2005.