Visit to a Large Planet

By Frederic Golden

A thousand rings round Saturn, icy moons and lakes of liquid nitrogen

"To think that no other person from Earth has ever seen Saturn and its rings so close!" Wilma said. "I wonder what Titan will be like?" "Well," Buck replied, "it won't be long now."

Last week, while earthlings nearly a billion miles away marveled as they monitored its progress, an all-seeing but unmanned spacecraft no larger than a compact car completed the final and most spectacular phase of an epochal journey. Beating Buck Rogers and the faithful Wilma, sci-fi heroes of the pre-Star Trek generation, by five centuries, Voyager 1 brushed past the ringed planet Saturn, second largest member of the sun's family, and provided the best images yet of that strange and wondrous world, a far-off realm in the solar system never before glimpsed with such glittering clarity. Said one scientist watching the incoming tide of images: "We have learned more about the Saturn system in the past week than in the entire span of recorded history."

Voyager 1's performance was the equal of the marvels it found. Commanded only by its own computers, the robot soared past the mysterious moon Titan, approaching to within 4,000 km (2,500 miles) of its shrouded surface. Gathering ever more speed under the tug of Saturnian gravity, it plunged downward toward the outer edge of Saturn's rings, swirling bits of cosmic debris. Reaching a peak velocity of 91,000 km (56,600 miles) per hour, Voyager skirted within 124,240 km (77,200 miles) of the planet's banded cloud tops for its nearest approach to Saturn.

All the while its instruments and television cameras blinked away furiously, almost as if they had a life of their own. So large did Saturn loom in the robot's probing electronic eyes that they could capture only small swatches of the planet's stormy atmosphere. The spacecraft executed its maneuvers with astonishing precision -- near the climax of its long journey it was only 19 km (12 miles) off course. Finally, Voyager climbed upward, once again crossing just outside Saturn's rings. Casting backward glances with its cameras and instruments, it soared above the ecliptic -- the plane formed by the paths of planets orbiting the sun -- and headed out of the solar system to wander aimlessly among the stars.

Before last week's culmination of Voyager's odyssey, a two-day close encounter of the most extraordinary kind, Saturn was relatively unknown. It is a gigantic swirling gaseous ball, mostly hydrogen and helium, that could encompass 815 earths, but even with the best telescopes and the most settled atmospheric conditions, it had never been seen as much more than a fuzzy yellow ringed sphere. Now, in a flash of binary bits across space, it had become a clearly recognizable place under the sun, with its own wonders, surprises and mysteries.

After only the most cursory study of Voyager's flood of data, scientists were staggered by a succession of discoveries. Many involved Saturn's rings, which until the recent finding of similar features around Uranus and Jupiter were thought to be unique. Before Voyager's visit only six Saturnian rings and a few gaps between them were known. Now there seem to be 1,000 rings or so. One of the so-called gaps may contain several dozen ringlets. Titan, the largest moon in the solar system, appears to be wrapped in a dense atmosphere of nitrogen vapors, rather than methane--the best guess before Voyager--and its surface may be awash in a cold sea of liquid nitrogen. Saturn's entourage of other satellites, until now no more than bright gleams in earthly telescopes, also proliferated--by three --to at least 15. Chunks of ice and rock perhaps dating back to the birth of the solar system 4.6 billion years ago, these moons emerged as distinctive and different, showing scars from the millennial pounding of meteorites and possibly comets, as well as cracks from their own version of earthquakes. One pair of little moons travel in the same orbit within the rings of Saturn. They look like broken teeth and may be remains of some relatively recent cosmic carnage: two halves of a larger satellite that split apart in collision with another celestial body.

The nation, indeed the world, seemed ready for a heavenly break in the news, for a chance to contemplate an event above and beyond politics and oil, wars and revolutions. It took nearly 1 1/2 hours for the spacecraft's first data about the moment of closest approach to reach earth. But at planetariums from Washington, B.C., to Portland, Ore., "near encounter" shows attracted overflow crowds. In Edinburg, Texas, students erected their own satellite antenna to hear NASA's special Saturn broadcasts.

Other nations were watching closely. On Japanese television, astronomers and space specialists took turns filling the airwaves with learned commentary on Voyager's progress. In Britain, television stations broadcast a drumbeat of bulletins on the mission. London's Sunday Telegraph hailed the achievement as "the most spectacular piece of space exploration since men stepped foot on the moon."

After taking time out to watch the special coverage of the flyby on public television, President Carter telephoned his congratulations to the NASA team for their space spectacular. He also had some cheering news for the men and women of Caltech's Jet Propulsion Laboratory, in the foothills near Pasadena, who designed the spacecraft and control its mission. They fear that U.S. ambitions in interplanetary space may be rapidly dwindling, but the President announced the inclusion of $40 million in start-up funding in the fiscal 1982 budget for VOIR. That is an acronym for the Venus Orbiting Imaging Radar mission, a new project that had been eagerly sought by J.P.L., along with an unmanned probe to intercept Halley's comet when it returns in 1986. So far the U.S. has refused to authorize the tantalizing mission to the comet. Said J.P.L. Director Bruce Murray after the President's announcement: "We can use the money."

Praise for his lab was well deserved. By any measure, Voyager 1 is a superb technological achievement. It is a stunning example of a machine's ability to be programmed to operate on its own, without human "joy-sticking," as the NASA people put it, from folks on the ground. Voyager 1 is even capable of making its own repairs and correcting navigational errors by itself.

With the reconnaissance of Saturn, the U.S. has completed a close-up inspection of all the planets visible to the ancients, before the advent of the telescope. During this past decade, robot spacecraft provided the first look at the parched, cratered surface of Mercury, the sun's nearest planet. With cameras and radar they inspected cloud-shrouded Venus, a hot, almost hellish sphere with a surface temperature of about 480DEG C (900DEG F) and a crushingly thick atmosphere of carbon dioxide. From both overhead and on the ground they surveyed Mars, finally laying to rest the myth that canals exist on the Red Planet. Two Viking landers even sampled the Martian soil in hopes of detecting biological activity. (Edgar Rice Burroughs notwithstanding, they found not a trace of life.) Reaching farther into space, unmanned envoys from earth approached mighty Jupiter, largest of the planets. Back came stunning color portraits of that multihued sphere and close-ups of the Jovian moons, including tiny lo, which was caught in the act of surprising volcanic eruptions. Says Astronomer Carl Sagan: "I can't imagine anyone remaining blase in the face of such accomplishments."

Voyager 1's three years of space exploration were the result of more than ten years of preparation. The original idea grew out of a rare astronomical event that would occur in the late 1970s. Once every 175 years during their slow travels around the sun, the large outer planets --Jupiter, Saturn, Uranus and Neptune --line up almost like a column of toy soldiers. Using their gravitational pull, scientists calculated, a spacecraft could, literally, hop from one planet to another, eventually flying past all of them. In late 1970 NASA officials, still basking in the glow of the moon landings, decided to take advantage of the unusual planetary configuration by staging what became known as the Grand Tour, a visit to all these planets, if possible by the end of the 1980s.

The scheme required electronic components of such durability that they could survive in the cold, hostile environment of space for the mission's entire twelve-year duration. Because it would have to range so far from the sun that the solar system's great central fire would be no more than a faint glow in the darkness of space, the ship could not be solar powered. The answer: a miniature nuclear power plant that converted the heat produced by the radioactive decay of plutonium directly into electricity. Most challenging of all, the spacecraft had to be able to react to emergencies without human help. If its small directional-control rockets accidentally began firing in the vicinity of Uranus, for example, a warning signal, traveling at the speed of light, would take about three hours to reach earth 3 billion km (2 billion miles) away. By that time the ship might have exhausted its precious fuel, wrecking the mission. To avert such a breakdown, J.P.L. began designing on-board computer systems that could check out spacecraft functions and, if necessary, command corrections entirely on their own.

Scientists found the journey to the outer reaches of the solar system the most exciting kind of exploration. But the Grand Tour soon lost the war of the budgetary worlds to more favored space agency projects, notably the still delayed space shuttle. In 1972 the Grand Tour was, as Voyager Project Manager Raymond Heacock puts it in NASA jargon, "rescoped"; what had started out as a plan to survey all the major outer planets was reduced to less costly inspection of just two: Jupiter and Saturn. The initial work was not all wasted, however. Much of the proposed Grand Tour hardware went into Voyager, including the long-lived components, the nuclear power pack and the array of self-correcting computers. In addition, so much functional overlap was built into the ship that if there was a failure in one component, another would often be available to perform its duties.

Voyager reached Saturn with ten different scientific instruments functioning, ranging from cosmic-ray detectors and magnetometers (for measuring the strength of magnetic fields in space) to infrared and ultraviolet spectrometers (used for remote temperature readings and the search for key chemicals). Only one instrument, the photopolarimeter, had failed. By beaming radio signals through planetary clouds and atmospheres, the spacecraft can also use its radio transmitters for scientific investigation. The effect of particles on radio signals, for example, provides clues to such things as the density and makeup of an atmosphere.

Voyager's most useful instruments may be two high-resolution television cameras, one with a wide-angle lens, the other telephoto. The cameras can be pointed in virtually any direction--up, down, to the side, even backward. Their optics are so precise that the cameras can spot features only five miles across from a distance of a million miles. To produce color images, the cameras make successive scans through red, green and blue filters. Transmitted back to earth as three separate sets of signals, the pictures are reassembled by computer from the digital data and combined on color film.

As Voyager 1 soared past Saturn, its eyes constantly twisted and turned, switching their attention back and forth from Saturn itself to its satellites and rings. As a consequence, the scientists watching the television monitors inside J.P.L.'s Building 264 found the images more often than not cropping up on target exactly in the center of their screens. The secret of this wizardry lies in the lobes of Voyager's electronic brains. Hours before last week's near encounter, the computer memory banks of Voyager 1 were "sequenced" with a series of explicit instructions radioed from earth. So precisely did Voyager 1 carry out these orders that none of its multitude of observations arrived more than 46 seconds off schedule.

Though Voyager 1 was launched from Cape Canaveral, Fla., in 1977, two weeks after an identical twin, Voyager 2, it followed a less curved trajectory and reached Saturn nine months ahead of the other ship. Voyager 2 is not scheduled to pass Saturn until next August. Because it is taking such a different trajectory, Voyager 2 will be able to study some of the moons that had to be bypassed during last week's encounter. It will also be able to sail on to Uranus in 1986 and Neptune in 1989. Thus, if the spacecraft's instruments are still functioning, J.P.L. scientists and engineers may eventually achieve a Grand Tour after all.

Even if those ambitions are not realized, Voyager 1's conquest of Saturn is already providing an unexpectedly rich scientific payoff from the $500 million program. Almost as soon as the spacecraft began closing on the Saturnian system, the pace of discovery accelerated dramatically. As early as last August, Voyager 1's cameras picked up a red spot in Saturn's southern hemisphere. Another one soon showed in the northern hemisphere. Though these features remind scientists of Jupiter's Great Red Spot, a great whirling storm that has lasted for at least three centuries, Saturn's spots are smaller, perhaps only 12,000 km (7,500 miles) in diameter. Saturn's atmosphere seems at least as violent as Jupiter's. NASA scientists estimate winds at upwards of 1,300 km (800 miles) per hour.

Saturn's rings also yielded puzzling new findings. Barely had Voyager 1's cameras zeroed in on these thin, elegant discs than scientists spotted two new moons no more than 600 km (370 miles) across at the edge of the ring system. They were designated 513 and S-14, because they are the 13th and 14th to be discovered. 513 circles Saturn just outside the so-called Fring, which is about 80,000 km (50,000 miles) from the planet's cloud tops --the gaseous sphere has no real surface. 514 revolves just inside that ring. Like dogs herding sheep along a narrow road, the outer moon seems to be keeping ring particles from flying off into space, while the inner moon stops them from falling toward Saturn--as one scientist put it, "controlling an unruly flock."

In pre-Voyager days, astronomers counted no more than about half a dozen rings, all presumed to be composed of icy debris, including snowballs the size of Volkswagens. Though the rings stretched tens of thousands of miles out from the planet, they seemed to be only one or two miles thick. The existence of the Fring, inferred from sketchy data provided by Pioneer 11, a more primitive spacecraft, was hardly more than a suspicion before Voyager 1. But as the spacecraft's cameras scanned Saturn in ever greater detail, there was an explosive increase in the number of rings visible. Even before the craft passed below the ring plane, the scientists talked of some 90 or so rings. Four days later, when Voyager had started scanning from the underside of the rings, the total rose to at least 500 and perhaps a thousand. The existence of one apparently new ring was deduced in a novel way: from the shadow it cast on the moonlet halves occupying the same orbit.

As more pictures came in, Saturn's many-splendored rings began looking more and more like grooves in a celestial gold record. Even the Cassini division, a dark area first noticed three centuries ago and once thought to be the only gap in an otherwise solid surface, suddenly showed rings within it. At least two other rings were spotted slightly off center, like wobbly wheels on an old car, a curious and as yet inexplicable quirk. To complicate matters, near the outer edge of Saturn's phonograph disc, the Fring shows sinewy strands of material that look as if they had been twisted into braiding. Equally perplexing, spokes seem to form in some regions of the rings as the material whirls out from the planet's shadow. Such aggregations of particles--apparently very tiny ones, judging from the way they reflect sunlight--should be quickly ripped apart, like a spoonful of sugar being stirred in a cup of coffee. Yet somehow the spokes survive for hours at a time, almost as if they were intentionally setting out to destroy scientific theories about the rings. Says University of Arizona Astronomer Bradford Smith, chief of Voyager's photo-interpretation team: "Those spokes are giving us nightmares!"

The golden planet's previously known major moons, all of them named for mythological figures remotely linked with Saturn, the Roman god of agriculture, also presented surprises and mysteries. Though Titan's thick cloud cover disappointingly permitted not even a glance at the satellite's surface, infrared probing yielded chilly temperatures that may drop to -183DEG C (300DEG F) near the surface. Those readings, along with data from other instruments, could not be explained by the thick concentrations of methane that earth observers had expected. Instead, scientists now conclude, the atmosphere is dominated by nitrogen, with only a smattering of methane (less than 1%) along with such hydrocarbons as propane, ethylene, ethane and acetylene, and topped by a Los Angeles-type photochemical smog. These conditions remind scientists of what is known about the condition of earth more than 3 billion years ago, but of an early earth locked in a deep freeze. Despite the presence of more complex organic compounds, like hydrogen cyanide, Titan now appears to be too cold for the life-building processes that some scientists hoped might be occurring there.

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.

The shuttle's problems are also a source of grief to planners of another major scientific effort: the placing in orbit around earth of a ten-ton, 96-in. space telescope. Scanning the heavens above the obscuring atmosphere, and radioing back its findings, the robot telescope could greatly extend astronomy's observable universe, allowing stargazers to see farther and deeper into space. The telescope might even be able to pick out the faint traces of planets orbiting nearby stars.

Until now, says J.P.L.'s Murray, the U.S. has been the unquestioned leader in such activities. Interplanetary space, he notes, has been virtually "an American lake." But he and others fear that with the dearth of new programs, the U.S. could lose ground--especially in relation to the U.S.S.R., which space experts, like military men, are concerned about. Although the Soviets have not fared well in their unmanned explorations, except for landings on Venus, they are surpassing the U.S. in manned space projects. By launching men into orbit every few months, they have accumulated nearly twice as many man-hours in earth orbit as the U.S. Warns Senator Harrison Schmitt, a geologist and former astronaut soon to become chairman of the Senate's space subcommittee: "The Russians are ahead on the knowledge of how people can perform in space, and they are ahead on will and purpose."

Both he and Murray are pressing Ronald Reagan's incoming Administration to pay more attention to space. In an attempt to convince Washington that there is a large popular constituency for space programs, Murray has joined with Sagan in forming a new lobbying effort, called the Planetary Society, that will seek to promote--as "the ultimate adventure" --exploration of the solar system, the search for planets and attempts to communicate with extraterrestrial life.

Pressure for a greater role in space is also coming from the military. Fearing Soviet strides in the development of killer satellites and other threatening products of space technology, the Pentagon is looking for new ways to meet this challenge. One tactic has been to tap the resources of such places as J.P.L. Says Pentagon Research and Engineering Chief William Perry: "The Russians regularly build more tanks and planes than we do. The only option open to us is exploiting our technological advantages. An area of tremendous advantage is space."

It is peaceful exploration that most excites scientists. Sorties into the unknown are often dismissed as wasteful, especially in a time of economic trouble. Yet space exploration has already paid for itself many times over. Many technological developments--miniature electronics, microwave ovens, live TV broadcasts via satellite--can be traced to NASA-sponsored research. More benefits will surely follow as NASA expands the understanding of earth's solar system. The technology used in Voyager 1's independent intelligence could be adapted to robots that might replace divers in the dangerous work of deep-sea oil drilling. Learning about climate and conditions on distant worlds may instruct mankind in how to take better care of this fragile planet. But aside from such practical spinoffs, the exploration of space is in the very grandest of human traditions, profoundly stirring for its own sake. Carl Sagan says it well: "The exploratory instinct is deeply built into us and possibly an important part of the success of ourselves as a species." With the performance of Voyager 1, that instinct is thriving.

By Frederick Golden Reported by Jerry Hannifin and Joseph J. Kane/ Los Angeles

With reporting by Jerry Hannifin, Joseph J. Kane

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