Visit to a Large Planet

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Other moons examined by Voyager 1 were far less shy in revealing themselves. Tiny Mimas is dominated on one side by a large crater that stares out like the ominous billboard eye in The Great Gatsby. Had the object that caused the crater been much larger, its impact might have shattered Mimas. Its other side is heavily pockmarked with small craters, indicating that it is a relatively old celestial body. Yet Mimas' companion Enceladus displays a less dramatic topography. Scientists speculate that some mysterious heat source, perhaps created by gravitational stresses, has softened its icy surface and smoothed out cracks and craters.

The surface of Tethys, a middle-size Saturnian moon, is cut by a strange, sinuous trench, perhaps the result of a sharp blow delivered on the opposite side of its globe, which is dappled with craters and highlands. Dione resembles the earth's moon, marked by all sorts of craters, big and little, features that look like our moon's "seas," and ice flows, rills and highlands. Iapetus, one of the most curious of Saturn's moons—one hemisphere is five or six times as bright as the other —was seen only from a vast distance.

Perhaps the most stunning new spacescape was presented by Rhea, named after Saturn's mythological wife-sister. Voyager 1 approached so close, less than 72,000 km (45,000 miles) away, that Rhea's features showed with crystalline sharpness. It too looked like the earth's moon, but its craters are so densely packed that U.S. Geological Survey Planetary Geologist Larry Soderblom called them "shoulder-to-shoulder craters, falling on top of each other."

Last week's surprises were only the beginning. NASA scientists expect their lode of data to yield discoveries for months to come. The advanced computer-enhancement techniques developed at J.P.L. for processing color photographs permit researchers to mute or intensify colors to help bring out the faintest details. It was during a photographic fine-tuning session, while he was rerunning fairly distant views of Saturn on the TV screen, that J.P.L. Scientist Stewart Collins, working with David Carlson, a visiting student from Drexel University, discovered the planet's 13th and 14th moons.

As Voyager 1 sped off last week, casting over-the-shoulder cinematic looks back at Saturn, the incredible machine was headed for one last major assignment before going into deep space, where, after its power runs out, it will drift forever in silence. By measuring the flow of solar particles, Voyager will seek to determine where the sun's influence ends and that of the stars begins —in short, to establish the exact outer boundary of our solar system. Still, as exciting as such quests may seem, they come at a time of dwindling Government interest in space exploration.

The only planetary probe now on the drawing boards at J.P.L. is Project Galileo, a scheme to place in orbit around Jupiter a semipermanent observatory. Scheduled for launch in 1984, Galileo is likely to be delayed. Its launch vehicle is the space shuttle. But that much troubled enterprise, plagued by engine problems and difficulties with its crucial heat-shielding, may not make its first orbital test flight before next summer.

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