Voyager 2 expected to solve some of Saturn's riddles

Saturn's mysteries are legion, but space scientists here expect to unravel at least a few of them in the coming week. Last November, America's supersophisticated space probe, Voyager 1, loped within 80,000 miles of the planet, the second largest in the solar system, and gave mankind its closest look to date at the spectacular rings and superficially bland face that Saturn presents to the solar system. The television pictures and scientific data beamed back the 950 million miles to Earth by Voyager 1 multilied Saturn's mysteries.

Now a twin spacecraft, Voyager 2, is speeding across the interplanetary void and closing in on the giant gaseous sphere. Planetary scientists here at the Jet Propulsion Laboratory have had nine months to analyze and puzzle over the earlier pictures and data on Saturn. They have programmed the instruments in the second spacecraft to concentrate on gathering clues to the various riddles which the planet presents. Teh scientists will be aided by substantially sharper TV cameras on the second spacecraft than those on its twin. Also, its path will carry it much closer to the planet -- within 63,000 miles -- and the rings will be better illuminated than on the previous flyby.

As a result, "We anticipate an even better look at Saturn," summarized Ed Stone, a voyager project scientist. In a preliminary press briefing he summarized the outstanding puzzles of Saturn and how scientists hope Voyager 2's electronic eyes and ears will shed light on them.

the rings, of course, are Saturn's most dramatic feature and its biggest puzzle. They were perplexing enough before the first Voyager cameras profiled them. If a scale model were made from the thinnest airmail paper, the rings would be about 30 feet wide with an outer diameter of 135 feet, and almost perfectly flat.

The best scientific explanation for how such a fragile structure could be stable enough to exist for millions of years involved Saturn's numerous moons. Somehow, scientists theorized, the gravitational forces of these moons trapped the ring material, keeping it from falling in toward the plant or spiraling out into space. But the first Voyager shocked scientists with pictures of incredible complexity. Instead of a smooth surface with a few major divisions as they appear from Earth, the pictures showed the rings to be made up of thousands of ringlets. Not only are there thousands of these smaller divisions, but a number of them are complex in themselves. Some are braided in a complicated fashion, while others are eccentric. Also, the appearance of radial features, quickly nicknamed "spokes," were totally unexpected.

After months of study, scientists have come up with two basic explanations for the baffling array of ringlets, Dr. Stone reports. One theory holds that they are not actually separate rings, but waves superimposed on the ring material, ice-covered debris that averages 1 to 10 meters (3.3 to 33 feet) in diameter. The second theory requires the existence of a large number of "moonlets" up to 10 kilometers (62 miles) across which would, by their gravitational influence, tend to clear the finer material out their orbits and concentrate it into bands.

To scrutinize the ring structure, Voyager 2 will be measuring the light of the star Delta Scorpii a thousand times a second as it passes behind the rings. The spacecraft's cameras will also be photographing the gaps between ringlets, trying to locate moonlets.

The so-called spokes represent a deeper mystery. "We know they are clouds of fine material that appear and disappear, but there is no satisfactory explanation for their origin that I know of," Dr. Stone says.

One suggestion is that these strange clouds are levitated above the ring plane because they somehow build up a charge of static electricity. How they would become electrically charged is unclear, but the spacecraft is going to snap an edge-on picture of the rings to look for elevated clouds. Also, Voyager 1 detected radio noise characteristic of electric discharges, and Voyager 2 is going to attempt to pinpoint its source.

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