NASA's Cassini spacecraft, originally sanctioned for a four-year mission when it arrived at Saturn, has just celebrated its tenth year of discoveries and observations of the ringed planet and its moon system.

Three extensions of that original term have kept the spacecraft busy as it circles through and around the gas giant planet's cosmic arrangement of moons and rings.

With the European Space Agency's Huygens probe aboard, Cassini arrived at Saturn on June 30, 2004, set for that scheduled four-year science assignment, but has had its mission prolonged and is still impressing with the quality and quantity of its scientific observations, NASA scientists said.

"Having a healthy, long-lived spacecraft at Saturn has afforded us a precious opportunity," said Linda Spilker, Cassini project scientist at the space agency's Jet Propulsion Laboratory in Pasadena, Calif. "By having a decade there with Cassini, we have been privileged to witness never-before-seen events that are changing our understanding of how planetary systems form and what conditions might lead to habitats for life."

Some of Cassini's accomplishments during its tenure at Saturn include sending the Huygens probe to make the first touchdown on a moon orbiting in the outer solar system, namely Titan; revealing that moon to be an Earth-like body with river, lakes, seas and rain; sending back images of spouting plumes of ice on the moon Enceladus, suggesting the moon possesses an underground ocean; and discovering giant hurricanes whirling around Saturn's north and south poles.

"It's incredibly difficult to sum up 10 extraordinary years of discovery in a short list, but it's an interesting exercise to think about what the mission will be best remembered for many years in the future," Spilker said.

Designed by scientists and engineers from the start to be durable, Cassini has had a mostly trouble-free 10 years at Saturn.

As to how much longer the spacecraft can continue to operate, that's down to the amount of propellant it has left in its fuel tanks because the longevity of its mission to date has been due largely to efficient and skillful piloting by Cassini's operations and navigation teams, NASA said.

"Our team has done a fantastic job optimizing trajectories to save propellant, and we've learned to operate the spacecraft to get the most out of it that we possibly can," said Earl Maize, JPL Cassini project manager. "We're proud to celebrate a decade of exploring Saturn, and we look forward to many discoveries still to come."

Those discoveries may not end until 2017 when Cassini will intentionally be sent plunging into Saturn's atmosphere, bringing its mission to a close, NASA said.

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