WASHINGTON – Saturn has not disappointed. The Cassini spacecraft has found new mysteries at the ringed planet and Titan, its largest moon, leaving scientists eager to see what else the craft will uncover during a mission in Saturn’s neighborhood expected to last at least four years.

Cassini’s first views of Titan were blurry and did not reveal the seas or lakes of methane that some scientists had expected. But Carolyn Porco, the head of the Cassini imaging team, said that should not be too surprising, given the environment. “There is a thick, hazy atmosphere,” Porco said. “We know that it is impeding the transmission of light.”

Photographs taken in visible light do show shadowy features, including round markings hinting at impact craters and lines that could be cracks that opened as the icy moon cooled down. But Porco, who grew up in the Bronx and graduated from Stony Brook University, said there is not enough topographical detail to make any definitive statements. “We really don’t know,” she said. The smallest surface features detected are about 6 miles wide.

The Titan images were taken by Cassini at a range of about 210,000 miles on July 2. Porco said the imaging team hopes to see more detailed features on Titan when Cassini passes within about 750 miles of the moon on Oct. 26, the first of 45 planned encounters with Titan through May 2008.

The October flyby and subsequent encounters promise much more than the first images, said Jonathan Lunine, a planetary scientist at the University of Arizona and Cassini team member.

Astronomer Tobias Owen, a team member from the University of Hawaii and an expert on Titan, said the blurriness of the initial photos may be more than an artifact of Titan’s murky atmosphere. Icy surfaces on Titan may be eroded by flows of liquid hydrocarbons.

Owen said, wearing everything down “like a melted ice cream sundae.” Another instrument produced images of Titan in near-infrared wavelengths. Those views also were somewhat murky, revealing a varied surface with darker regions that scientists say could be relatively pure water ice.

and brighter areas that could be rich in hydrocarbons such as methane.

The spectrometer also showed a circular feature in the north that may be a crater and a bright cloud of methane particles near the south pole. The persistence of the cloud suggests it could be composed of particles larger than those typical of the haze that surrounds Titan, scientists say.

As the spacecraft draws closer to Titan, the Cassini team will be able to use radar to penetrate the cloud cover and produce a map of surface features.

But the most anticipated chance to learn some of the moon’s secrets should come in January, when the European-built Huygens probe – now attached to Cassini and scheduled for release on Christmas Eve – plummets through Titan’s nitrogen-rich atmosphere. The 705-pound probe, with a camera and other instruments aboard, will parachute to a crash landing at about 15 mph. The probe could land on a solid surface or in a cold lake of liquid hydrocarbons, scientists say. It is expected to operate no more than 30 minutes.

Scientists believe Titan may be a deep-frozen preserve for some of the same organic chemicals that gave rise to life on Earth. Titan is too cold, about minus 290 degrees Fahrenheit at the surface, to allow any sort of life, scientists say. But studying its chemistry may provide clues on how Earth may have looked 4 billion years ago before biological activity arose.

Meanwhile, back at Saturn, Cassini has gathered new information about the planet’s shimmering rings that is still being mulled by scientists. The spacecraft passed through the plane of the rings twice as it entered orbit around Saturn on July 1.

An instrument called the Ultraviolet Imaging Spectrograph took the best ultraviolet views to date of the planet’s main rings, which are lettered A through F in order of their discovery. One image shows that the broad A ring has a dense outer region made of ice particles and a “dirty” interior made of possibly smaller particles.

“There are different theories on how the rings might get “dirty,’ ” said Roger Clark, a Cassini team member from the U.S. Geological Survey office in Denver. Dirt-laced regions of the rings could have been formed by the disintegration of small moonlets, scientists say, or constant bombardment by micrometeoroids.

The spacecraft also found more dark particles than particles of ice in the gap, called the Cassini division, between the A and B rings. Clark said the region may be dirtier than expected because a constant influx of meteoritic dust would have more impact in a region with little material to start.

While it has many encounters ahead with Saturn’s moons, Cassini already has made its closest approach to the rings. It revealed a complex, icy world in which sheets of ring particles are herded by the gravity of nearby moons, which also can twist the rings into braids and produce scalloped ring edges.

The early pictures have left scientists eager for more. “Everybody can see how marvelous the images are,” said Porco. “We have a lot of work ahead of us and a lot of discoveries ahead. That’s what scientists like to do.”



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AP-NY-07-23-04 0615EDT



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