December 17, 2004 4:51 AM PST
Tantalizing clues in pictures of Saturn's moons
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Photographs taken during a flyby of the Cassini space probe this week may clarify and even overturn longheld assumptions about the surfaces of these satellites, according to researchers at the American Geophysical Union conference taking place in San Francisco this week.
Bright streaks on the surface of Dione, a heavily cratered moon with little atmosphere, have long been believed to be ice, noted Carolyn Porco, imaging team leader for the Cassini project from the Space Science Institute in Boulder, Colo.
Images captured this week, however, appear to indicate that the bright streaks are cliffs. They may have been created by ice, though not a lot of ice remains in the area.
"This wispy terrain is really a fracture," Porco said. "For 25 years, we've had it on the brain that Dione has thick ice deposits, and it turns out it doesn't."
Meanwhile, the "ocean" on Titan may not be. Instead of a liquid body of water, the dark mass seen on the surface of the Titan may be a viscous fluid flowing onto the white "coastline," Parco said. Then again, the viscous fluid could be flowing down from a higher altitude, like a glacier, onto the white mass.
Right now, researchers only have two-dimensional images. Often, scientists look at the images and analogize it to information they know about on Earth, such as island chains or coastlines, she said. Stronger conclusions may be possible with the availability later of images that are more precise, or stereoscopic images that include shadows or information on altitude.
Kevin Baines, a Cassini science team member, said that the images captured this week for the first time revealed clouds in Titan's atmosphere that weren't clustered around the poles. (Images of polar clouds were produced in October.) Observing nonpolar clouds can help determine weather patterns on Titan, he said. So far, one surprising observation seen in the images is that there isn't as much methane, or as many clouds, in Titan's atmosphere as previously expected.
Separately, astronomers at the University of Southern California studying data from Cassini released on Thursday new information about Saturn's E ring. A massive eruption of atomic oxygen from Saturn's outer rings may be an indication that the planet's distant E ring is eroding so fast that it could disappear within 100 million years, the researchers said in a statement. Spectrograph data indicates that about 275 million pounds of oxygen was abruptly released in a short period of time.
The Cassini probe will release the Huygens projectile on Dec. 24. Huygens will then descend through Titan's atmosphere on Jan. 14.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.
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