Intimate Glimpses of a Giant

Rendezvous with Jupiter reveals a beautiful, violent world

Seething gases and liquids mask its rocky core. Its frigid atmosphere consists mostly of hydrogen and helium. Great cyclones and hurricanes swirl in its turbulent sky, with brilliant red and orange clouds constantly merging and breaking apart in ever changing patterns. Often the turbulence creates trails of sinuous white vapors thousands of miles long. The awesome, forbiddingly beautiful world is that of Jupiter, a planet so large it could swallow more than 1,300 earths.

Last week, after a journey of 18 months, a tiny visitor from earth streaked precariously close to the giant of the solar system, penetrating deep into Jupiter's powerful magnetic field and coming within 278,000 km (172,400 miles) of the Jovian cloud tops. Back at Caltech's Jet Propulsion Lab, controllers waited breathlessly to see whether the plucky robot would survive that dangerous encounter. But even before Voyager 1 made its closest approach on Monday, the 826 kg (1,820 lb.) unmanned spacecraft sent home a trove of new findings about Jupiter, including evidence that its atmosphere is even more violent than anyone supposed. The craft also provided the most dramatic and detailed pictures yet of long-puzzling Jovian features like the Great Red Spot.

Voyager 1 is not the first unmanned vehicle to make the 400-million-mile journey to Jupiter, but it is easily the most ambitious. Equipped with eleven different instruments, as well as both wide-angle and closeup cameras, it should not only complete a stunning reconnaissance of Jupiter but, by taking advantage of a favorable alignment of the outer planets, will also be able to survey another little-known world. Boosted by Jupiter's strong gravity, Voyager 1 will be catapulted out to Saturn by mid-1980.

Whether or not this technological gambit succeeds, the $400 million project has already provided rich scientific dividends. Even before the drum-shaped spacecraft's first brush with the so-called bow shock region, where the Jovian magnetic field traps the solar wind, Voyager's sensitive instruments picked up a bewildering jet stream of frozen ammonia apparently traveling at 560 km (350 miles) per hour above the planet's clouds. Voyager also discovered a dazzling, doughnut-shaped cloud of electrically charged particles that formed displays similar to the earth's northern lights.

Yet it was Jupiter's stormy weather that caused the greatest excitement. Voyager's electronic eyes spotted dozens of storms across Jupiter's banded face. Most of them measure about 6,000 miles wide, far larger than their earthly counterparts. Largest is the Great Red Spot, a permanent hurricane with a maximum width as much as three times the earth's diameter. University of Arizona Astronomer Bradford A. Smith was both awed and puzzled by these storms: "It's as if each of these things has a life of its own. You can stretch them, deform them and even break them apart, and they still have an inner cohesion that keeps them together."

No visitor to Jupiter could, of course, neglect its moons, especially the four largest, which were discovered by Galileo in 1610. Higher-powered telescopes have since discerned at least 13 natural satellites, but little has been learned about them. Voyager is now lifting that veil.

Its photographs of Callisto, darkest and outermost of the Galilean moons, showed that this gloomy sphere may be at least half water. Ganymede also seems watery, but appears to have an ice crust and possibly a mud core. Remarkably, both moons are dotted with dark spots that some scientists are tentatively calling ice volcanoes--craters that spew ice instead of fire and lava. Still closer to Jupiter, Europa apparently hides a rocky core beneath its bright icy surface.

But the most curious of all these major moons is the innermost, lo (pronounced eye-oh). Roughly the size of the earth's own moon, it has reddish polar caps, a yellowish sodium cloud cover and a strange surface chemistry that may be a consequence of intense radiation bombardment. On its closest approach, Voyager will come within 18,800 km (11,650 miles) of this mysterious moon. Then, as Voyager sweeps away, its instruments will get glimpses of the other Jovian moons, perhaps even a tiny 14th moon, which was spotted several years ago. sb

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