Cassini Spacecraft Nears Saturn, Photographs Moon

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"There's no first-time event, and that's what always gets you—when you have first-time events, something comes up you didn't count on. We've scrubbed all those out, and that's why we're confident," Matson said.

Why Saturn?

Scientists are eager to study the Saturnian system in detail, because they believe it will yield answers to fundamental questions about chemistry and physics, planetary formation, and the conditions that give rise to life.

Four years of detailed investigation of the system will allow scientists for the first time to understand how the various components interact with each other—the difference between knowing the individual parts and the essence of the whole, Matson said.

He uses an analogy of a mechanical clock, where one can measure the wheels and various gears but totally miss out on the essence of what they do. "The essence of it is totally bound up in the interaction between the parts," he said.

Saturn and Jupiter's systems of planet, rings, and moons have long been considered physical models of the process of planetary formation and are referred to as miniature solar systems.

"[Studying] these different experiments in planetary formation will help us understand how the process works," said Ralph Lorenz, a planetary scientist at the University of Arizona in Tucson. Lorenz is an expert on Saturn's moon Titan.

Saturn's largest moon, Titan is a major focus of the Cassini-Huygens mission. Its surface, covered in a thick, smoggy haze, has never been studied in detail, but scientists believe that Titan's atmosphere is rich in organic material. This suggests that Titan may be similar to what Earth was like before life evolved.

"The pre-biotic Earth was probably not as reducing and not as cold, but many of the same chemical steps are there—long overprinted and destroyed on Earth but frozen in place for us to study on Titan," Lorenz said.

On December 24 Cassini will release the European Space Agency's Huygens probe. The probe will enter Titan's thick, nitrogen-rich atmosphere on January 14, 2005, deploy a set of parachutes and begin 2.5 hours of intensive scientific observations.

Images and data will be relayed via Cassini to scientists on Earth, providing details of the unknown landscape. What the probe will land on or in is unknown, but Lorenz has his fingers crossed it will splash into a lake of methane or ethane.

According to Matson, "Titan won't have any secrets left when we get through with it."

Mission Controversy

Anti nuclear activists staged several protests against the Cassini-Huygens mission, because at launch it carried about 70 pounds (30 kilograms) of plutonium dioxide to power the spacecraft's electrical system via radioisotope thermoelectric generators, or RTGs.

RTGs rely on heat, which is produced as the plutonium decays.

Activists were concerned that Cassini-Huygens posed an unacceptable risk of exposing billions of people to radioactive material if the spacecraft failed and blew up at launch or burned up in Earth's atmosphere.

Both of the events passed safely, but activists are still concerned about NASA's use of RTGs as well as RHUs, or radioactive heater units.

"I certainly do still feel that launching Cassini was a big mistake," said Russell Hoffman, who maintains the Stop Cassini Web site from Carlsbad, California. "Just because it now appears that the mission might succeed is no reason to change my mind. The statistics have not changed significantly—the failure rates for launches, for example. Indeed, we've suffered a number of spectacular space failures since Cassini was launched."

According to a NASA document on Cassini's power source, extensive testing shows that the use of RTGs is "very safe" even in the event of an accident. Although activists disagree with NASA's assessment, the space agency plans to continue their use.

For more Cassini and space-related news, scroll down

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