Sunday, October 30, 2005

Saturn's moon being discovered

Previous passes of Saturn's moon Titan by the orbiting Cassini spacecraft have shown tantalizing signs of riverbeds carved by rain, but the only direct observation came last year as the Huygens probe descended to the moon's surface.

During a flyby slated for early Friday, scientists hope to learn enough to prove what lies beneath Titan's hazy skies.

Cassini's radar instruments will be aimed at the Huygen's landing site, giving researchers their first opportunity to compare the visual images with what the features look like in radar.

By extrapolating that data to other radar studies, the team hopes to verify that other locations on Titan have been marked by rainfall.

"The last data we got are really suggestive that there are these channels that you expect to have been formed by rain," said Candice Hansen-Koharcheck, a planetary scientist and the Cassini science team manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "If we can prove that, it would be really cool."

During Cassini's last pass by Titan, only a fraction of the radar studies were recovered due to problems with a tape recorder onboard the spacecraft, as well as a communications glitch with NASA's Deep Space Network.

Even so, scientists found what they believe to be shorelines and channels marking the southern polar region of Titan.

Several factors affect how scientists interpret the radar imagery, such as how much light is reflected from the ground, the magnetic and electric properties of the atmosphere and whether the surface is rock, ice or slush.

During Friday's pass, scientists for the first time will be able to compare the radar images with what optical instruments on Huygens found.

"This pass is really pretty important because it's going to provide us with a ground-truth," said Hansen-Koharcheck.

Only one other pass by the Hugens landing site is planned during Cassini's prime mission. The spacecraft has been orbiting Saturn and studying its moons and rings since July 2004.
So far, the Cassini science team has used the spacecraft's radar instrument during three previous flybys of the planet's largest moon, Titan, the only moon in the solar system that has a thick atmosphere.

With its thick brew of organic matter, Titan is believed to resemble primordial Earth.
The earlier radar passes showed a variety of geologic features including impact craters, wind-blown deposits, channels and signs of ice volcano eruptions.

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