"Cassini is going to do something at Saturn we've never done before," says University of Arizona astronomer Carolyn Porco, head of the space probe's imaging team. "It's going to orbit."

Indeed, Cassini is expected to gather data through about 80 orbits of Saturn, over a period of 4 years. (And planners hope the craft will have an "extended mission" that lasts years longer.) The three previous Saturn missions -- Pioneer 11, and Voyagers 1 and 2 -- were quick flybys. The luxury of time, combined with the latest instruments, will give Cassini an unprecedented view of Saturn, its satellites and its rings.

Consider, for instance, the rings. Cassini will orbit the planet at various angles -- and thus see the rings from different directions. "Each direction tells you some other piece of the puzzle," says Jeff Cuzzi, a Saturn ring expert at NASA's Ames Research Center. By contrast, he notes, the Voyager probes were largely limited to viewing the rings "almost edge on."

Observing the rings may provide clues to their origin. The rings are believed to have formed in, as Cuzzi puts it, "a catastrophic event dating back to the age of fish" -- several hundred million years ago, or about one tenth the age of the solar system. But what kind of catastrophe is unknown -- it may have been the destruction of an existing moon, or the capture of a comet or asteroid. "Did something in place get torn apart by an incoming projectile?" asks Cuzzi. "Or did something larger just come a little too close?"

As for the planet itself, Cassini will investigate numerous issues that previous probes only began to explore. One such question: Does Saturn have lightning?

"There certainly will be a desire to look for lightning -- and, if it's found, to determine what causes it and how it's the same or different from Earth lightning," says Ellis Miner, a Cassini science adviser at NASA's Jet Propulsion Laboratory.

Detecting lightning requires long-exposure images of Saturn's dark side. The Voyager missions took a few images of the dark side without finding lightning, notes Miner. But it later became clear that the exposures were not long enough to settle the issue, because of light reflected by the planet's rings.