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NASA Gets Close Look at Saturn's Tiny Moon

June 10, 2004|Thomas H. Maugh II | Times Staff Writer

The first pictures taken of Saturn's moon Phoebe since 1981 were unveiled by NASA on Wednesday, and they showed a tiny moon that appears scarred with tall sunlit peaks and deep shadowy craters.

The images beamed to Earth by NASA's Cassini spacecraft were about twice as good as those taken by Voyager 23 years ago, said imaging team member Torrence Johnson.

But they are merely appetizers for what team members believe will be spectacular views of Phoebe captured when the craft flies within about 1,240 miles of the moon's surface Friday.

The current images were taken from distances ranging from 1.6 million to 2.5 million miles.

Cassini will streak by Phoebe at 1:46 p.m. PDT on Friday as it closes in on entering Saturn's orbit, scheduled for June 30.

The craft will spend four years circling Saturn and studying the planet, its rings and moons.

It also will release a probe, Huygens, that will crash into the surface of Titan, one of the most intriguing of Saturn's 31 moons.

The close encounter Friday, however, will be the craft's only chance to study Phoebe. At 8 million miles from Saturn, Phoebe is nearly four times as distant as the next nearest major satellite, Iapetus.

"A later encounter is simply not feasible," said mission planner David Seal of NASA's Jet Propulsion Laboratory in Pasadena.

In addition to pictures, Cassini will collect a variety of spectroscopic data about the moon in an effort to understand the composition of what many astronomers believe to be an interloper in the Saturnian system.

Only 136.7 miles across -- about one-fifteenth the diameter of Earth's moon -- Phoebe orbits Saturn in the opposite direction from the planet's other satellites. That orbital rotation and the darkness of Phoebe's surface led many planetary scientists to think it was originally an asteroid that was caught in Saturn's orbit.

If that is the case, said mission scientist Bonnie Buratti, "it might hold clues about the early formation of our solar system."

Phoebe rotates on its axis every nine hours and 16 minutes and completes a full orbit of Saturn in about 18 months. Previous ground-based observations have shown that there is water ice on its surface.

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