email a friend iconprinter friendly iconVoyage to Saturn
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Now, after centuries of curiosity and anticipation, scientists are taking a long, close look at Saturn. A metal cylinder 22 feet tall, bristling with scientific instruments and topped by a white saucerlike antenna, Cassini-Huygens was built by NASA, the European Space Agency, and the Italian Space Agency. It rocketed toward Saturn in 1997 and arrived on June 30, 2004, to begin at least four years of exploration.

As it neared the end of its 2.2-billion-mile journey, Cassini had to shed speed so that Saturn's gravity could capture it. The spacecraft fired its engines and dropped to within 13,000 miles of the planet's butterscotch clouds, making a daring passage between the outer rings. "White-knuckle time," Cassini project manager Robert Mitchell recalls.

The rings look crisp and manicured, but they are actually swarms of debris: billions of particles from mite- to mansion-size. A single stray pebble slamming into Cassini as it sped through the rings at over 68,000 miles an hour could have ended the 3.4-billion-dollar mission. Mitchell's team at NASA's Jet Propulsion Laboratory in Pasadena, California, anxiously monitored signals until Cassini, intact, settled into orbit and began to look around.

Exceeded in size only by Jupiter, Saturn could hold more than 700 Earths. Yet the planet, made almost entirely of hydrogen, is lighter than water. Dropped into an ocean big enough to contain its 75,000-mile diameter, it would float, bobbing like a colossal yellow sponge ball. It spins so fast that it bulges to a diameter 7,300 miles greater at the equator than at the poles, so fast that a Saturn day lasts less than 11 hours.

Because Saturn is mostly gas, it has no fixed landmarks to reveal its exact rotation rate. But its dense interior generates a powerful magnetic field that spins with the planet. Over the past two years, Cassini has clocked the field's rotation at 10 hours, 47 minutes, and 6 seconds, although no one is sure the planet itself spins at exactly the same rate. But the field also opens a window into the heart of Saturn.

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