Science: The Little Spacecraft That Could

Voyager 2 brings cheer during NASA's worst week

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Largely overshadowed by the tragic loss of Challenger, the feats of the indomitable Voyager 2 last week provided the only bright notes during the U.S. space program's darkest hours. As the 1,800-lb. spacecraft sped away from its close encounter with Uranus, it continued its flawless performance, transmitting data and pictures that are gradually stripping away some of the mysteries of the planet. At NASA's Jet Propulsion Laboratory in Pasadena, Calif., nearly 2 billion miles away, William McLaughlin, the Voyager flight- engineering manager, could speak only in superlatives as he reviewed the data. Said he: "I think it is the most successful space mission of all time."

Indeed, having brilliantly explored Jupiter in 1979 and Saturn in 1981, Voyager had already compiled an enviable record. Now the spacecraft was on the verge of duplicating its earlier, spectacular accomplishments. At week's end it had already discovered ten tiny Uranian moons and sent back incredibly detailed photographs of the five larger, previously known satellites. It had photographed the nine known rings and found at least two more. The versatile spacecraft also managed to pry a bewildering volume of information from Uranus itself, despite the fact that the giant planet is shrouded by a thick and opaque blue-green atmosphere.

Scientists at J.P.L. seemed most fascinated by Voyager's close-up views of the five major Uranian moons. By far the most exotic was Miranda, about 300 miles across and the closest of the large moons to the planet. Miranda, Geologist Laurence Soderblom explained, "is a bizarre hybrid," combining at least ten different types of terrain, some similar to the "valleys and layered deposits of Mars . . . the grooved terrain of Ganymede (a moon of Jupiter) and the depression faults of Mercury." The crusts of Miranda and three of the four other major moons, Soderblom said, "have been tectonically shuffled in a cataclysmic fashion," probably by the powerful tug of gravity from Uranus, which has a diameter four times as large as the earth's.

Both Titania and Oberon, each some 1,000 miles in diameter, have huge, distinctive features. Voyager spotted a three-mile-high mountain on Oberon and a valley running all the way across the visible surface of Titania. On the moon Ariel, 730 miles across, three linear patterns seemed to resemble the tracks left by terrestrial glaciers. Only Umbriel, 740 miles in diameter and covered with overlapping meteorite craters but with few other features, seems to have been largely unaffected by Uranian gravity--for reasons scientists cannot explain.

As Voyager swung behind Uranus, it bounced radio waves off the rings and discovered that they are quite different from those of Saturn, which contain an abundance of fine particles. The Uranian rings are made largely of dark "boulders," most of them more than a yard wide, that circle the planet once every eight hours. Many scientists believe they may be the remnants of a large moon that shattered in an ancient cataclysm.

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