Saturn's giant moon Titan refused to give up its secrets Friday as the Cassini spacecraft (search) flew by for the first time and peered into its murky atmosphere to try to see its surface.

"It's not as clear as we'd hoped," Cassini imaging team leader Carolyn Porco said as unprocessed images transmitted across 900 million miles of space arrived at NASA's Jet Propulsion Laboratory (search).

Some things were visible to imaging experts, and Porco was certain that some were surface features. She said processing might draw out more from the images.

"We haven't applied our full bag of tricks yet," she said.

Cassini will make many more flybys of Titan and in December will launch a probe that will enter the moon's atmosphere in January.

Titan was Cassini's first encounter since the spacecraft began orbiting Saturn (search) this week for a four-year exploration of the ringed planet and many of its 31 moons.

Cassini transmitted about 21/2 hours of data and images collected as it passed by Titan at a distance of about 200,000 miles.

Titan images recorded in June from millions of miles away appeared to show linear features that could suggest tectonic activity, Porco said.

The frustrating haze is part of what makes Titan interesting to scientists.

"That haze is kind of an organic goo much like the smog that one might see in Los Angeles, composed of hydrocarbons, and not allowing us to see through to the surface," said Linda Spilker, the Cassini deputy project scientist.

Scientists believe Titan could have chemical compounds much like those that existed on Earth billions of years ago before life appeared.

Larger than Mercury or Pluto, Titan has an atmosphere 11/2 times as dense as Earth's, containing organic — meaning carbon-based — compounds. Scientists believe there could be hydrocarbon seas or lakes.

Mission scientists, meanwhile, released initial findings of clues to the composition, origin and lifespans of Saturn's spectacular rings.

The seven major rings, known alphabetically as A through G, are believed to be made of boulders ranging from a few feet across to the size of cars.

But Cassini's detection of a short-lived, unevenly distributed bloom of atomic oxygen in the Saturn system earlier this year suggests the rings may contain larger objects.

After measuring the system with its ultraviolet imaging spectrograph for two weeks beginning Dec. 25, Cassini found the massive amount of extra oxygen when it repeated the process about a month later.

Larry Esposito, a planetary scientist from the University of Colorado, said the event supports a theory that the rings contain objects one to 10 kilometers across. Collisions between such objects would release a large amount of ice, from which atomic oxygen would be stripped by other forces.

The loss would eventually destroy a ring, said Donald Shemansky, co-investigator for the ultraviolet imaging spectrograph.

He calculated that meant the E ring, which is thousands of miles wide, would have a lifespan of 100 million years.

As expected, Cassini's visual and infrared mapping spectrometer found that the rings are mostly very pure ice, but there was also material that Cassini team member Roger Clark called "dirt."

The material's spectrum shape was found to be similar to that of Saturn's battered moon Phoebe, which Cassini visited earlier.

Scientists believe Phoebe is a remnant from an era billions of years ago when the outer solar system was filled with many small objects that ultimately became the building blocks of the giant planets.

The $3.3 billion dollar mission, funded by NASA, the European Space Agency (search) and the Italian Space Agency (search), was launched in 1997. The spacecraft flew 2.2 billion miles on a roundabout route to Saturn.