email a friend iconprinter friendly iconVoyage to Saturn
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Saturn began in the disk-shaped cloud of dust and gas that swirled around the newborn sun 4.6 billion years ago. Bit by bit, particles stuck together until gravity could take over, drawing material into ever larger lumps of iron and rock. One of them, perhaps several times the mass of Earth, was the seed that grew into Saturn.

Over time, the gravity of this rocky core attracted great clouds of hydrogen gas. The gas settled around the core, and the planet's mass rapidly grew. Pressures mounted, squeezing the innermost layer of hydrogen so hard that scientists believe it turned into a liquid metal—a superb electrical conductor. Currents surging through the metallic hydrogen generate Saturn's immense magnetic field.

More than four billion years later the core still retains heat from its formation, which stirs massive updrafts in the planet's deep atmosphere. They whip up supersonic winds, among the fastest in the solar system at up to a thousand miles an hour, and drive vast weather systems. "We see storms, lightning, zones of clouds, and strange wavelike features in the atmosphere," says Kevin Baines of NASA's Jet Propulsion Laboratory. In images from Cassini's infrared camera, the heat rising from deep in the atmosphere sets the planet aglow. "We're seeing backlit clouds," Baines says. "We can watch the weather day and night. It's a revelation."

Only at the very top of Saturn's atmosphere, capped by a yellowish layer of haze, does the turmoil subside. Here, on calmer clouds, the distant sun inscribes shifting patterns of shadows cast by Saturn's vast system of rings.

From edge to edge, the main rings span some 165,000 miles, over two-thirds the distance from Earth to the moon. Yet the thickness of these bands of icy rubble averages only 150 feet. "Think of a sheet of paper spread over ten football fields," says Cuzzi, who studies the rings.

No one knows how the rings formed, although some scientists speculate that Saturn's gravity tore apart an icy moon or a comet, strewing debris that provided the raw material. Whatever their source, the rings are recent, cosmically speaking. If they had existed for the life of the solar system, Cuzzi says, their subtle pinks, yellows, and tans—the result of dust buildup—would have darkened. But they offer a model for something ancient: the disk of particles orbiting the young sun and its interplay with the newborn planets.

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