Visit to a Large Planet

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In pre-Voyager days, astronomers counted no more than about half a dozen rings, all presumed to be composed of icy debris, including snowballs the size of Volkswagens. Though the rings stretched tens of thousands of miles out from the planet, they seemed to be only one or two miles thick. The existence of the Fring, inferred from sketchy data provided by Pioneer 11, a more primitive spacecraft, was hardly more than a suspicion before Voyager 1. But as the spacecraft's cameras scanned Saturn in ever greater detail, there was an explosive increase in the number of rings visible. Even before the craft passed below the ring plane, the scientists talked of some 90 or so rings. Four days later, when Voyager had started scanning from the underside of the rings, the total rose to at least 500 and perhaps a thousand. The existence of one apparently new ring was deduced in a novel way: from the shadow it cast on the moonlet halves occupying the same orbit.

As more pictures came in, Saturn's many-splendored rings began looking more and more like grooves in a celestial gold record. Even the Cassini division, a dark area first noticed three centuries ago and once thought to be the only gap in an otherwise solid surface, suddenly showed rings within it. At least two other rings were spotted slightly off center, like wobbly wheels on an old car, a curious and as yet inexplicable quirk. To complicate matters, near the outer edge of Saturn's phonograph disc, the Fring shows sinewy strands of material that look as if they had been twisted into braiding. Equally perplexing, spokes seem to form in some regions of the rings as the material whirls out from the planet's shadow. Such aggregations of particles—apparently very tiny ones, judging from the way they reflect sunlight—should be quickly ripped apart, like a spoonful of sugar being stirred in a cup of coffee. Yet somehow the spokes survive for hours at a time, almost as if they were intentionally setting out to destroy scientific theories about the rings. Says University of Arizona Astronomer Bradford Smith, chief of Voyager's photo-interpretation team: "Those spokes are giving us nightmares!"

The golden planet's previously known major moons, all of them named for mythological figures remotely linked with Saturn, the Roman god of agriculture, also presented surprises and mysteries. Though Titan's thick cloud cover disappointingly permitted not even a glance at the satellite's surface, infrared probing yielded chilly temperatures that may drop to -183° C (300° F) near the surface. Those readings, along with data from other instruments, could not be explained by the thick concentrations of methane that earth observers had expected. Instead, scientists now conclude, the atmosphere is dominated by nitrogen, with only a smattering of methane (less than 1%) along with such hydrocarbons as propane, ethylene, ethane and acetylene, and topped by a Los Angeles-type photochemical smog. These conditions remind scientists of what is known about the condition of earth more than 3 billion years ago, but of an early earth locked in a deep freeze. Despite the presence of more complex organic compounds, like hydrogen cyanide, Titan now appears to be too cold for the life-building processes that some scientists hoped might be occurring there.

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