Making a Second Pass at Saturn

By Frederic Golden

Another Voyager approaches the mysterious belted planet

There is not perhaps another object in the heavens that presents us with such a variety of extraordinary phenomena as the planet Saturn ...

--Sir William Herschel, 1805

In an era when astronomers talk about objects as strange and remote as quasars, about cosmic enigmas like black holes and the faint radio noises that may be an echo of the creation, an ordinary planet, even the second largest in the sun's family, hardly seems likely to awe or surprise. Yet, remarkably, Saturn still has that power, as the Voyager 1 spacecraft so dramatically showed last November. Swooping within 78,000 miles of the luminous ringed sphere, the little robot sent back a collection of full-color images as dazzling as any ever received from deep space.

That portfolio included close-up views of the gaseous planet's stormy clouds, where equatorial winds rage at 1,100 m.p.h. It provided the first real look at the myriad small, icy worlds that are the planet's moons. But its most remarkable pictures were those of Saturn's rings. Formed out of rocky, icy fragments ranging in size from dust particles to boulders as big as apartment buildings, they totaled more than 1,000 in all. Astonishingly, some rings were twisted into what looked like braids of hair. Others contained patterns that resembled spokes of a wheel. Some even whirled around Saturn in eccentric paths like grooves of a record that had slipped its spindle.

Such phenomena seemed to defy the revered laws of classical physics. But scientists are about to get a chance to unravel these mysteries--and perhaps more. At precisely 11:25 p.m. E.D.T. next Tuesday, Aug. 25, a second spacecraft, Voyager 2, will finally reach Saturn after a four-year, 1.4 billion-mile flight. Ducking behind the planet (as seen from earth), it will skim to within 63,000 miles of the planet's cloud tops. Then Voyager 2 will plunge through the plane of Saturn's rings, brushing precariously close to that rocky debris. All the while, its cameras and instruments will be working furiously to take advantage of every precious second of the encounter.

Most of the observations will be aimed at answering questions raised by the earlier flight, with special emphasis on the rings. During one 13 1/2-hr. period, for instance, Voyager 2's cameras will be taking pictures every 3.2 min. The movie-like sequence should not only show the formation and disintegration of the spokes during each rotation but also help explain what forces are acting on them. One theory: the spokes are in fact composed of dustlike particles lifted out of the thin ring plane by electrostatic forces perhaps created by the faint light of the distant sun.

Still another experiment involves Voyager 2's photopolarimeter, a light-measuring device that failed on the first flight.. As the spacecraft approaches the planet, the instrument will be aimed through the rings at Delta Scorpii, a far-off star. By measuring disruptions (or blinking) of the starlight caused by the intervening ring material, the scientists should get the most precise data yet on the number of rings, their density and width and the size of the stuff they are made of.

Voyager 2 will also turn its eyes on Saturn's moons, now known to number at least 17. It will focus especially on the larger ones, bearing mythological names, which were missed or only glimpsed from afar last time. One of special interest is Enceladus, which somehow no longer shows any scars from the primordial bombardment that all of Saturn's major moons must have undergone early in the solar system's history. Voyager will also look at lapetus, which is curiously darker on one side than the other, and outermost Phoebe, a fickle satellite that rotates counter to all the other moons, will also be photographed.

Voyager 2's primary radio receiver broke down early in the four-year flight, but the inevitable NASA back-up has been working flawlessly ever since. Yet even if that system should fail, the space-traveling robot's memory carries enough instructions from controllers at Pasadena's Jet Propulsion Lab for another four years of automatic operations. It will surely need that electronic brainpower. Unlike Voyager 1, now headed directly out of the solar system, Voyager 2 will get a slingshot-like gravitational assist from Saturn that will send it hurtling past Uranus, the seventh planet from the sun, by Jan. 24, 1986. There Voyager 2 will get another boost directing it toward a rendezvous with Neptune, the eighth from the sun, on Aug. 24, 1989. If its nuclear-powered instruments are still working, earthlings will get their first close views of these distant planets.

When Voyager 2 passes Uranus, what will it find? Speculations by a scientist at the University of California's Lawrence Livermore Laboratory raise an intriguing possibility.

Theoretical Physicist Marvin Ross notes that both Uranus and Neptune are large, layered spheres with atmospheres of hydrogen and helium, and presumably a hard, rocky inner core. But between the gases and the core is an ocean, incongruously known as an "ice layer," made of water, ammonia and methane. At a depth of nearly 6,000 miles, this sea of liquid is subject to enormous pressures, at least 200,000 times that of the earth's atmosphere at sea level; and its temperatures probably start at 2,500DEG F.

To find out what happens to materials under such extreme conditions, Lawrence Livermore researchers have been firing high-velocity projectiles into small samples of water, ammonia and methane, creating shock waves. The water and ammonia compressed, as expected. But the methane broke apart into its components, hydrogen and carbon. The question is: What form would the carbon take within the actual planet? One possibility: diamonds; so many, in fact, says Ross, that they might equal 15% of the total mass of the planet, enough sparklers to carpet the earth. Ross is quick to add, though, that since the gems are so deeply buried, the South Africans have nothing to fear. .. yet.

--By Frederic Golden. Reported by James Schefter/Pasadena

With reporting by James Schefter

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