Close Encounter with Saturn

Voyager 1 spots two new moons, foresees a heavenly waltz

Every December the ancient Romans indulged in a colossal round of drinking, carousing and tumultuous revelry. The orgiastic festival, perhaps coinciding with the winter planting, was staged to propitiate Saturn, the sickle-wielding deity of agriculture. Now scientists gathered at the Jet Propulsion Laboratory in Pasadena may be tempted to hold their own Saturnalia. Next week, after traveling for more than three years, their robot Voyager 1 spacecraft will achieve its closest encounter with Saturn, providing the most spectacular view yet of the beautifully ringed planet and its system of moons.

After nearly four centuries of telescopic observation, astronomers know Saturn is a giant, rapidly spinning ball of hydrogen and helium, surrounded by rings of icy debris and numerous satellites, including the largest moon in the solar system. Still, many questions remain. What are Saturn's rings made of? Can they be traced back to the solar system's origin 4.6 billion years ago, or did they evolve later from the breakup of passing objects captured by Saturn's gravity?

Equally perplexing, since scientists figure Saturn should have cooled off ages ago, the planet is radiating more heat back into space than it receives from the distant sun. What is the source of this mysterious energy? Perhaps the most tantalizing question concerns Titan, Saturn's largest satellite (even bigger than Mercury) and the only moon in the solar system with a thick atmosphere. Could it harbor organic molecules, the precursors of life?

Voyager 1, weighing a scant 825 kg (1,820 Ibs.) and drawing its electricity from a compact nuclear power pack, is ideally equipped to answer such questions. One of two identical ships en route to Saturn (its twin will reach it next August), the spacecraft carries eleven instruments, including two television cameras. During Voyager's swing by Jupiter in March 1979, these keen eyes sent back stunning closeups of the planet's turbulent atmosphere, detailed views of its moons and even a spectacular shot of a volcanic eruption on the Jovian satellite lo.

Since August the robot has been performing its magic on Saturn. Pictures already transmitted by Voyager show light and dark horizontal bands in Saturn's atmosphere as well as ovals and whirls that are apparently great storms. And Saturn's moons, until recently only flecks of light in earthly telescopes, have become clearly distinguishable little orbs.

The discoveries are coming fast. At a pre-encounter press conference last week, University of Arizona Astronomer Bradford Smith announced two previously undetected moons--Saturn's 13th and 14th known satellites--probably no more than 320 km (200 miles) in diameter and 80,000 km (50,000 miles) above its clouds. The scientists also reported puzzling complexities--apparently less dense regions--in the planet's ring system; the varying speeds of material traveling in different portions of the rings should presumably smooth out such features, but somehow they survive for hours at a time. Finally, the scientists confirmed the existence of three other moons, which had been only tentatively identified from earlier observations. Two of them are traveling in the same orbit and seem to be edging ever closer, but probably will slip by each other in a kind of celestial waltz approximately two years from now.

Voyager 1 will not be around for that spectacle. After sweeping within 4,000 km (2,500 miles) of Titan, the spacecraft will plunge through the plane of Saturn's rings, soar past the moon Tethys, and on Nov. 12 come to within 124,000 km (77,174 miles) of the planet's cloud tops. Whipped by Saturn's gravity, the spacecraft will then swing quickly up and around the planet, photograph other moons, make a film of Saturn's swiftly moving clouds and rings and, finally, head out of the solar system.

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