Saturn's Rings Still a Mystery
June 28, 2004 -- They've been described as a flamboyant hooped skirt, a jeweled necklace and a band of troops marching in a circle round the planet. Galileo Galilei, who discovered them, called them "ears."
Saturn's rings have inspired countless awe-filled descriptions, but they have also eluded scientific explanation.
A team of researchers from 17 different countries are now pinning their hopes on the six-ton, instrument-loaded Cassini spacecraft to duck into Saturn's orbit, peek into its rings and reveal their secrets. Cassini has already captured close views of Phoebe, Saturn's largest outer moon, and found it is covered by icy patches and very comet-like in nature. Scientists now expect to see greater detail of Saturn, its inner moons and mysterious rings once the craft maneuvers into a gap between two dust rings and enters Saturn's orbit on June 30.
Some of the questions they hope the craft may help them answer are what gives the rings their salmon hue? What's behind their strange waves? How old are they? And how long will they persist in Saturn's orbit?
"It will be like opening up a whole new world," said Linda Spilker, an expert on Saturn's rings and a project scientist for the joint NASA-European Cassini mission. "Things will go from fuzzy blobs to clear worlds."
Understanding what is contained in the rings and how and when they were formed could lead to understanding an even bigger picture — how the solar system formed. The ring of rocks and ice around Saturn represent a solar system in miniature, since scientists believe planets may have formed from similar cosmic debris.
Rings May Be Recent Feature
This is not the first time a spacecraft has visited Saturn's world. In the 1970s and early 1980s, earlier probes made fly-by's of the planet and returned some photos. But none came close in clarity to what Cassini's instruments promise.
"Instead of getting a crude spectrum," said Jeff Cuzzi, a planetary scientist at the NASA Ames Research Center, "We will be able to map the detailed shape of every bump and wiggle in the rings' spectrum."
From a distance, Saturn's rings appear as smooth wisps around the planet, but closer images reveal they're mostly made up of icy chunks of debris ranging in size from dust particles to barn-sized boulders. It's the ice that gives the rings their almost shiny appearance as light glints off their surface.
It's also this shine that has led some scientists like Cuzzi, to suspect the rings may be fairly young — only a few hundred million years old. It's believed the rings sweep up cometary dust as they swirl around Saturn. So the fact that they haven't been dulled may suggest their relatively recent formation.
In fact, early dinosaurs may have roamed the Earth before Saturn got its rings.
"It's a big question we want to address," said Cuzzi. "Some think they may only be 10 percent as old as the solar system."
Although it isn't well known, a number of other planets, including Jupiter, Uranus and Neptune, also have rings. But they are fainter and duller than Saturn's rings and may be older — and dustier.
By analyzing how the collection of debris that makes up Saturn's rings shift and change over time, scientists hope to calculate how long they've been around, how long they may continue their orbit — and how they were formed in the first place. No one is certain what made the rings — they could be pieces of a moon that broke apart or remnants of a shattered comet.
The rings' unusual patterns could also reveal undiscovered tiny moons in Saturn's orbit or space rocks that have plunged through the ring's debris.
Another question looming in the Cassini team's minds is what gives the rings their unusual hue? One theory is the color is created by organic material, perhaps from destroyed reddish moons that were destroyed and then pulverized to form the rings.
To decipher the color in the rings, Cassini will use a camera that can read color through 15 different filters. By analyzing the rings' various shades, Cuzzi says they hope to essentially "fingerprint" what elements are contained in them.
"Different molecules each have different absorption rates in the color spectrum," he said. "You can see the fingerprints of silicate rocks, ice or whatever."
Titanic Quest
Just as Saturn's rings can lend clues about how the solar system may have formed, another target beyond the rings — Saturn's largest moon, Titan — could provide clues to very early conditions on Earth. Right now, scientists know little about the moon, other than it has an atmosphere of mostly nitrogen, contains organic matter, is very cold (nearly 300 degrees below zero) and hosts something that produces methane — perhaps volcanoes.
"Titan could bear a very close resemblance to Earth in very odd respects," said Carolyn Porco, leader of the Cassini Imaging Science team and senior research scientist at the Space Science Institute in Boulder, Colo. "It might tell us something about our own history long ago when there was organic material that later developed into life. It's a thrilling target for us."
The $3.3 billion Cassini is scheduled to slow down and ease into Saturn's orbit on June 30. Some 30 hours later, it should capture its first glimpse of Titan and in January, it will deploy a probe to the mysterious moon's surface.
No doubt the images Cassini sends back over its four years of orbiting will inspire more poetic descriptions of the ringed planet. But hopefully this time they'll also offer explanations.