It's the Robots' Turn, by Jove!

Surprises from a second look at Jupiter and its moons

Of late, NASA has had little to gloat about. While Skylab showered down on Australia and the surrounding sea last week, the space shuttle was still in Florida, months behind launch schedule. Meanwhile, high above the earth, two orbiting Soviet cosmonauts headed toward a new record (140 days) for living in space. Normally, all this would have cast a pall over this week's celebrations of the tenth anniversary of the first lunar landing. But beleaguered space agency officials could take pride in one spectacular performance: that of their wide-ranging robots, which are scattered over much of the solar system and are turning 1979 into the year of the planets.

Last winter Venus was explored by two Pioneer spacecraft: one a radar-equipped orbiter still spewing data, the other a multiple probe that dropped five instrument packages into the Venusian atmosphere. Among the findings: the neighboring planet has an extraordinary five-layered cloud cover, is riddled by continuous lightning bolts and scarred by a rift valley and mountain peak more grandiose than any on earth, and has totally unexpected abundances of primordial neon and argon. Their presence suggests new ideas about the nature of the great cloud of gases and dust from which the sun and planets were born.

In March another unmanned space craft called Voyager 1, traveling still farther afield, sped past giant Jupiter and its moons. From half a billion miles away, the computer-controlled robot radioed starlingly clear color pictures of the banded Jlanet and its satellites, including briliantly hued closeups of the stormy Jovian Great Red Spot that would not look out of place in a gallery of modern art. It also sent back new data about Jupiter's Jovian radiation fields and found a "hot spot" of plasma, whose temperatures reach 300 million to 400 million degrees C. It even discovered a thin ring of debris around Jupiter, making it the third planet in the solar system (after Saturn and Uranus) known to have such a feature.

Last week another automatic spacecraft named Voyager 2 picked up where its twin left off. Programmed by controllers at Caltech's Jet Propulsion Laboratory in Pasadena to fill in gaps left by the first flyby, Voyager 2 did its closest reconnoitering of the larger Jovian moons on its approach to Jupiter rather than on its way beyond it, as Voyager 1 had done. That gave scientists at J.P.L. a totally different perspective on these little worlds.

The latest flood of information from these Jovian satellites would have thoroughly awed the great Italian Scientist Galileo, who discovered them 369 years ago. Moving at speeds approaching 45,000 m.p.h., the 1,800-lb. spacecraft swept by Callisto, the oldest, outermost and apparently smoothest of the Galilean moons.

Then it moved on to Ganymede, photographing a tortured, cratered sphere whose cracked and faulted icy crust may indicate moonquakes. It took a closer look at Europa, which revealed an intricate lattice work of veinlike lines that may represent shallow fissures in an icy sea. Finally, Voyager 2 shifted its electronic gaze to lo, the innermost and most spectacular of the Galilean moons. Four months ago, Voyager 1 had spotted eight volcanoes in the midst of eruption, the first time such activity was observed other than on earth. Last week its successor photographed six of the same eruptions, suggesting to the U.S. Geological Survey's Laurence Soderblom that they may "last for several years."

As the robot swept around Jupiter itself, coming within 404,000 miles of the cloud tops, the J.P.L. controllers fired Voyager 2's small thruster engines for 76 minutes, a "slow burn" that changed its speed slightly. Thus, after sailing by its next target, Saturn, in August 1981, Voyager 2 will continue on to Uranus, more than 1.6 billion miles from earth. It will reach Uranus 4 1/2 years later, in January 1986. Leaving Jupiter, Voyager took an edge-on look at the planet's ring, which emerged on J.P.L. TV screens as a glow-'ng white neon-like boomerang.

So sure were the scientists of the success of the mission that they were already Bopping champagne corks before the actual flyby. "Here's to Saturn," toasted Jniversity of Arizona Planetary Scientist Bradford A. Smith. Added Physicist Torrance Johnson: "And on to Uranus."

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