Voyagers pass 25-year mark, en route for interstellar space

The technological risks these missions face are mirrored in last week's apparent breakup of the Contour spacecraft after a rocket motor ignited to send the craft from Earth orbit toward a planned encounter with two comets – Encke in 2003 and Schwassmann-Wachmann 3 in 2006. At press time, mission controllers at the Johns Hopkins University's Applied Physics Laboratory were trying to contact the craft, which fell silent last Thursday.

Coming projects, proposed in the July 11 report, focus on better understanding the solar system's history, currently estimated at 5 billion years and counting. The scientists also hope to trace the history of chemical compounds that were necessary for organic life to emerge, the processes that led at least one planet to harbor life, and the processes that shape planetary systems.

As they draw new plans, researchers are quick to acknowledge their debt to Voyager.

"Much of the impetus for the exploration of the outer solar system has come from the Voyager spacecraft," says Ellis Miner, science manager for the Cassini mission at Cal Tech's Jet Propulsion Laboratory in Pasadena, Calif., and former deputy project scientist for Voyager. "Each Voyager flyby carried definite surprise. Our theories bore little resemblance to what we actually saw."

For example, he says, many researchers expected the satellites of planets such as Jupiter or Saturn to be rather inert objects, like Earth's moon. Instead, they found a volcano erupting on Jupiter's moon Io, the first object beyond Earth to display active vulcanism. Icy Europa tantalized researchers with evidence of cracks on its surface that hinted at an evolving surface.

Meanwhile, Voyager returned images from Jupiter of auroras, like those around Earth's poles. And for the first time, researchers had a supply of photos of Jupiter's Great Red Spot and other cloud features to begin to piece together a detailed picture of the planet's circulation patterns.

Rings – the spectacular halos of dust and rock once thought to be the province of Saturn – were found to be ubiquitous among the giant planets, Dr. Ellis says.

If Voyager represented a scientific gold mine, it also represented a technological tour de force, adds John Casani, who was Voyager's project manager. Technologies developed for the mission – from small plutonium-heated electrical generators to computer-aided systems designed to run without human commands – have found their way onto a growing number of craft.

Perhaps it's this theory-busting, precedent setting nature of Voyager that sets it apart from its more focused descendants.

Veteran space-imaging scientist Porco says Voyager was unlike any mission before or since. "It was far more romantic than anything we'll ever do again. It was a mission of adventure as well as scientific inquiry."

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