cassini_scitues_040622As the Cassini-Huygens mission prepares to go into orbit around Saturn, project scientists are eager to begin an eye-opening look at the planet and its environment.
During its planned four-year mission, Cassini should give astronomers their closest glimpse of Saturn's rings, probe the gas giant's interior and magnetosphere, as well as swing by seven of the 31 known moons circling the planet.
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 | Cassini snapped this image of Saturn on May 21, 2004 as it approaches the ringed planet. Researchers hope the spacecraft will be able to determine the exact composition of the planet's multicolored bands. CREDIT: NASA/JPL/Space Science Institute. Click to enlarge.
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| This image taken by Cassini shows where the spacecraft will cross Saturn's ring plane(marked as an X) as it enters orbit around the planet. Also visible are several of Saturn's moons, which have been labeled. CREDIT:NASA/JPL/Space Science Institute. Click to enlarge.
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"Cassini-Huygens is the most sophisticated mission ever launched to the planets," said Orlando Figueroa, director of solar system exploration division at NASA. "It represents for Saturn what the Galileo [probe] did for Jupiter."
Studying how Saturn's rings and moons formed, for example, could give researchers insight into how planets form around stars.
"In a sense Saturn is almost like a miniature solar system," Linda Spilker, deputy project scientist for Cassini, said in a telephone interview.
Saturn up close
Cassini will swing around the planet 76 times, probing it with 12 science instruments designed to peer through at least the upper layers of its atmosphere.
The orbiter should answer some questions about the composition of Saturn's atmosphere and its internal structure and dynamics, said Charles Elachi, team leader for Cassini's radar instrument and director of NASA's Jet Propulsion Laboratory. The spacecraft should help scientists determine whether, deep down, the planet has a metallic, rocky core, he added.
"We think the core is made of liquid hydrogen and helium," Spilker said, adding that inside that core could be a rocky center. Scientists don't know exactly how giant planets are born, so determining the core composition would improve models of planet formation.
Cassini also carries tools to study cosmic dust around Saturn, as well as the planet's auroras and its odd magnetic field. One interesting puzzle, Spilker said, is that the planet's rotation axis and its magnetic field axis appear to be closely aligned.
Rings and moons
Saturn has a wealth of rings and at least 31 moons, which Cassini researchers expect their spacecraft to study in great detail during its voyage.
First up are the rings, which Cassini will pass through twice at the end of this month during a 96-minute engine burn to enter orbit around the planet.
"We will never be as close to the rings as that first pass," Elachi said in a press briefing earlier this month.
Scientists do not know exactly when or how the rings formed.
Studying the rings at different wavelengths with Cassini instruments should tell scientists about their composition. Researchers are also eager for the spacecraft's images of some of the more unusual aspects to ring structure, such as braided and kinked structures, as well as the tiny shepherding moons that sweep through the rings, clearing out gaps and herding particles into nearby swaths.
"We're trying to understand how the rings are evolving," said Spilker, who is also a ring specialist. "To me, that will be the most exciting time."
Cassini's flight profile will carry it on 52 close passes by several of Saturn's moons, including Enceladus, Dione, Tethys and the Mimas, the innermost of the planet's major satellites.
A close flyby of the moon Phoebe has already returned stunning images and a wealth of data.
"I suspect there are more moons there than we know off," Spilker said, adding that Cassini will be instrumental in finding additional satellites around Saturn. Other scientists have also speculated that the rings likely harbor small, unknown moons. In fact, it may be difficult to decide at what size a ring particle should be called a moon.
Cassini will also swing by Titan, Saturn's largest moon, 45 times to conduct scientific studies as well as to snag an orbital boost from its gravity.
Planet-like Titan
One of highlights of the Cassini-Huygens mission is the Huygens probe's visit to Titan, the only planetary satellite in the solar system to boast its own atmosphere.
"If it had formed anywhere other than around Saturn, it would be a planet in its own right," Spilker said.
Built by the European Space Agency (ESA), the piggybacked probe should plunge through Titan's nitrogen-methane atmosphere in early 2005, and relay data during a two-hour parachute trip through the moon's sky.
"We're going to measure the atmosphere and winds, and lightning may be detected," explained Jean-Pierre Lebreton, ESA Huygens probe project manager. "And there's a small microphone to record Titan sounds."
Huygens should spend about two hours drifting down to Titan's surface, where mission scientists said its camera could find a hard surface, or methane rivers, lakes or oceans. Titan could also support a prebiotic environment, serving as a sort of example of what Earth may have been like before biology evolved here.
"I do not expect to see any creatures on [Titan's] surface, but if they're there we'll see them," Elachi said.
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