Secrets Of The Rings

WHAT CASSINI DISCOVERED WHEN IT GOT TO SATURN--AND THE WONDERS IT MAY UNCOVER IN THE MISSION TO COME

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It would be hard, indeed. The Cassini-Huygens mission will now begin an extended tour of the glittering Saturnian system with its seven rings, 31 moons and untold cosmic secrets. By any measure, this is the most sophisticated planetary probe NASA has ever flown. About the size of a small bus, the Cassini orbiter is more than 22 ft. tall and weighs more than 6 tons when fueled. An engineering marvel, it is packed with a dozen scientific instruments and powered by a miniature nuclear generator. Carried on its side like a high-tech papoose is the Huygens lander, a 9-ft., 700-lb. wok-shaped probe that this winter will plunge through the atmosphere of Saturn's mysterious moon Titan, aiming for the most remote landing any human-made machine has ever achieved on another celestial body.

The payoff--for space scientists and curious civilians--could be staggering. Three other planets in the solar system--Jupiter, Uranus and Neptune--have rings, but they are faint and thready things, nothing like the magnificently complex cosmic jewelry that decorates Saturn. Seven of the other nine planets have moons, but none that perform the gravitational dances among themselves and within the rings that Saturn's do. And no planet has a moon anything like Titan, a world with much of the preorganic chemistry that Earth had 4.5 billion years ago--offering scientists a one-of-a-kind window into our vanished past.

The Saturnian system is, in a very real sense, the solar system writ small. And while other spacecraft have glimpsed it before--Pioneer 11 in 1979, Voyagers 1 and 2 in 1980 and 1981--they were mere flybys, quick hits by ships snapping a few pictures before whizzing off into deeper space. Cassini-Huygens--named after 17th century astronomers Jean Dominique Cassini and Christiaan Huygens--is there to stay.

"It really is like coming back to the promised land," says Torrence Johnson, a veteran of Voyager and a member of the Cassini imaging team.

The centerpiece of the Saturnian system is, of course, the planet itself, and plans call for it to get a going-over that it has never had before. The second largest of the solar system's four gas giants, Saturn--like its big brother Jupiter--is sometimes described as a starlike body with a chemistry of hydrogen and helium but without sufficient mass to light a nuclear furnace. That doesn't mean, however, that Saturn isn't roaring with activity.

By far the planet's most dramatic feature is its hellish weather. Winds blow around the Saturnian equator at 1,100 m.p.h.--five to 10 times the speed of the most powerful winds on Earth. Giant hurricanes tear through the planet's atmosphere, often two or more storms at a time, which then meet up before dying out. Displays of light similar to Earth's aurora borealis illuminate Saturn's skies, thanks to charged particles falling in from its moons. And where the auroras aren't flashing, lightning may be striking.

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