Saturn's secret should 'boggle' scientists for years

By , Natural science editor of The Christian Science Monitor

As Voyager 1 leaves the Saturn system and heads for the depths of outer space , some of the world's greatest planetary scientists already are scurrying around to each other asking, "Amazing, bizarre, what does it all mean?"

Dramatic pictures of Saturn's rings and tantalizing glimpses of its moons have given scientists a hatful of surprises and puzzles that will keep them busy analyzing and theorizing for years.

Titan was only mildly disappointing in that its thick clouds never did allow a look at its surface. However, data taken at infrared (heat) and radio frequencies are reported to be excellent. They will reveal many details of the structure of Titan, the largest moon in the solar system, and of its atmosphere. Already they have revealed that Titan's atmosphere is composed largely of nitrogen and as least as thick as Earth's atmosphere. Indeed, its surface pressure may be anywhere from one to three times that of Earth. Among other organic chemicals, hydrogen cyanide has been discovered. This is a precusor of the kinds of chemicals involved in organic life, although no one expects life itself to be found on Titan.

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A number of Saturn's other moons also have been seen in some detail. Impact craters, extensive and puzzling surface markings, and other features suggest that the moons have had active evolutionary histories. The wealth of information that has been sent back about them should fill in a chapter in solar system development that has been largely blank, Laurence Soderblom of the US Geological Survey said.

Using words such as "bizarre," Dr. Soderblom said that surface features on these moons, which are rich in water ice, will be interesting to explain. Unlike molten rock, which is lighter than solid rock, water is heavier than ice. Thus, features that look volcanic and would be accounted for as outflows of lava on a rocky moon are hard to explain as outflows of water on an icy moon.

Perhaps, he speculated, the water has been charged with gases to the point that it erupts violently when the surface of such a moon is fractured -- a kind of Seltzer-bottle effect. In any event, Soderblom said, the moons of Saturn are a unique system and widen the range of moon types which now are known.

Meanwhile, it is the awesomely beautiful, challengingly complex ring system that has become the hallmark of this Voyager Saturn mission.

It was amazing enough to discover Nov. 11 that two of the ringlets individ ually were eccentric (not circular) and did not quite join smoothly together as they girdled the planet. Dr. Bradford A. Smith of the University of Arizona, leader of the imaging team, explained that no one had expected such rings or even imagined them to exist. He called them "very surprising indeed."

But then on Nov. 12, as Voyager 1 swung within 124,000 kilometers of Saturn's cloudtops, he announced with a mixture of perplexity and amazement that an even more startling phenomenon had appeared. The photos had become detailed enough to show that the narrow "F" ring at the outer fringes of the ring system actually consists of two distinct ringlets. What is more, they appear to cross each other in a loosely braided fashion.

"With the discovery of those eccentric rings yesterday -- not just one, but two eccentric rings -- we thought perhaps we had seen all there was to see," Dr. Smith said. "But in this strange world of Saturn's rings the bizarre has become commonplace. . . . It boggles the mind that it [the braided ring pair] even exists."

The reason for this sense of perplexity lies in the strict order that Saturn's rings represent. The rings consisting of millions of particles believed to be a few centimeters to a few meters in diameter, each orbiting the planet as a separate body. And the rings are believed to have maintained their pattern for billions of years. In spite of disruptive influences such as collisions among themselves or drag and pressure exerted on them by sunlight, which tends to disperse a system of orbiting particles, Saturn's rings are preeminently stable.

Experts in celestial mechanics once thought they could explain this in terms of gravitational interaction between ring particles and some of Saturn's larger moons, an interaction locking the rings in place.

Then, as it became evident that the rings are composed of many ringlets with at least a thousand small satellites interspersed among them, the simple explanation broke down. Especially when two such satellites were found orbiting immediately on either side of the "F" ring, it seemed that these small satellites herded ring particles into a well-defined channel. The whole system -- large satellites, small satellites, and ring particles -- seemed locked together in a complicated web of gravitiational force that was baffling to understand.

Now experts are even more baffled. They have to explain how this interplay of gravitational forces can maintain the rings in an orderly series of bands of orbiting particles and yet allow some bands that do not close on themselves or that appear to braid together.

Imaging team leader Smith observed that the braided rings have probably been around for billions of years "That means that this weird configuration is stable ," he said. Yet it defies understanding in terms of standard celestial mechanics.

However, Smith noted, gravitational interactions are exceedingly complex, to the point where only two-body interactions can be easily handled. Problems involving systems of three-body problems can only be solved for a few special cases. Yet the dynamics of Saturn's rings involved many bodies.

With such a limited ability to grapple with gravitational problems, planetary scientists find themselves unprepared to cope with the reality of Saturn's rings. What they had once thought to be relatively simple now is revealed to have a complexity that is beyond their grasp. That is why the existence of braided rings "boggies the mind." As Smith observed, "Obviously they [the rings] are doing the right thing. We just don't know what the laws are."

Thus, the Voyager 1 data will force planetary scientists to face a tough problem in celestial mechanics -- the so-called many-body problem, which has been conveniently brushed aside in the past. Because this is the kind of challenge scientists love, it is little wonder that the Voyager team is calling the Saturn close encounter a resounding success.

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