It's been almost two years since the twin Voyager spacecraft showed the rings of Saturn in all their glory. Despite considerable study since then, planetary scientists studying the rings are still baffled by their incredible complexity.
This was apparent from discussions at the annual meeting of the Division of Planetary Sciences of the American Astronomical Society held here recently.
''People keep proposing theories, but we keep shooting them down,'' explains Larry Esposito of the University of Colorado, one of the scientists analyzing the information on Saturn's rings, radioed back by the Voyagers.
Before these spacecraft reached the ringed planet, the scientists involved worried that it would prove bland and anticlimactic after the paisley-colored Jupiter with its dramatic moons. The expectation was that the rings might sport several dozen bands.
Thus, the experts were totally taken aback when the first pictures that the spacecraft radioed back showed the rings looking for all the world like a giant phonograph record etched with tens of thousands of grooves.
Not only did the Voyagers discover a multitude of ''ringlets,'' but they have shown that the rings are much thinner than imagined.
Although floating weightless in outer space, the rings do not appear to be perfectly flat. Because some of Saturn's moons travel in an orbit that takes them above and below the ring plane, their gravitational pulls appear to crinkle the ring ''a little like a potato chip,'' as one researcher put it.
According to current wisdom, perhaps 75 of the ring system's thousands of features may be due to the gravitational tides of Saturn's moons. That leaves a lot to be explained. An early idea was that the myriad of ''gaplets'' might be areas cleared out by oversized ''moonlets'' perhaps a half mile to a mile in diameter. This was given credence by Voyager 1's discovery of a thin outer ring, designated the ''F ring,'' closely flanked by two small ''shepherding'' satellites whose gravity acted to contain the ring material. However, when Voyager 2's cameras searched the place where more moonlets were considered likely, they drew a blank.
While there are not a large number of features due to moonlets, there are some. Generally, these rings tend to be eccentric, lumpy, and sometimes discontinuous, says Richard Terrile of the Jet Propulsion Laboratory (JPL). He has found several such features in the ring system.
About the only other idea floating around that may explain some of the ring features is a theory based on the nature of collisions between ring particles. It was first proposed by William Ward of JPL and Douglas Lin and Peter Bodenheimer of Lick Observatory.
Unfortunately, the rings don't look much like the theory's prediction, Esposito explains. The researchers have tried to improve their model. While this has helped, its predictions still differ in considerable detail from how the ring material is actually distributed.
Within the planetary science community there is some disagreement on the potential value of deciphering the structure of Saturn's rings. But the scientists who have succumbed to the allure of the rings argue that their studies may shed new light on how objects behave in orbit and may also bear on the question of how the solar system formed.