The first pictures of Saturn's moon Titan returned by NASA's Cassini spacecraft after its initial flyby were not nearly as good as researchers had hoped, but they were good enough to overturn several theories about the moon, scientists said Saturday.
The Jet Propulsion Laboratory team's efforts to peer through the dense, smoggy haze that surrounds Saturn's largest moon revealed only fuzzy details of the surface, and those details left team members puzzled.
The images did not show the large bodies of liquid on the surface that astronomers had expected to find. The oceans of liquid methane or ethane that had been predicted would have shown up very brightly in the images obtained so far, said JPL imaging team member Robert West. "If there are oceans, we should have seen them by now," he said.
"That's a little disappointing," added team member Kevin Baines.
Researchers had previously thought, moreover, that the lighter areas on the surface of Titan were water ice and that the darker areas were other materials. But spectroscopic data from Cassini's infrared spectrometer have "turned those theories on their heads," said deputy project scientist Elizabeth Turtle of the University of Arizona. "The story has changed completely in the last 10 hours."
After viewing the preliminary data, she said, the team knows that the dark areas are almost pure water ice, while the brighter areas are mixtures of water ice "and other things," probably hydrocarbons. "This is a truly strange place," she said.
The images do show one very bright area about the size of Arizona over the moon's south pole. The team thinks the area is composed of methane clouds, probably the equivalent of light, fluffy cumulus clouds on Earth, Turtle said.
The team sees evidence that Titan's atmosphere is being swept up into the clouds by a geographical feature such as a mountain, much like humid air is swept up into storm clouds over the San Gabriel Mountains. The team was disappointed, however, to see no traces of lightning in the clouds.
Turtle noted that the images were taken from 200,000 miles away, and that Cassini would get much closer to the moon on many of the 45 flybys yet to come. The spacecraft will also launch the Huygens probe on Christmas Eve to explore Titan. Three weeks later, Huygens will parachute to the surface of the sphere, transmitting data throughout the descent.
At the same news conference, Don Gurnett of the University of Iowa revealed that the spacecraft's passage through the gap between Saturn's F and G rings -- before and after its rocket fired to bring it into orbit around Saturn -- was not quite as hazard-free as the team had once thought.
Gurnett is in charge of the radio and plasma wave instrument on the large boom extending away from Cassini. The instrument is used, among other things, to detect radio signals from Saturn.
Gurnett noted that when particles of ice and rock struck Cassini's main antenna during the passage through the gap, they vaporized, producing a cloud of plasma -- ionized atoms -- that the instrument detected.
The gap, he said, was "a region thought to be devoid of particles. In fact, a huge number of particles hit the spacecraft during both ring crossings." The peak impact rate, he added, was 680 impacts per second, with a total of more than 100,000 impacts during the two brief crossings.