Scientist says goodbye after mission of a lifetime

Linda PASADENA,

Spilker checks the clock: 12:04 p.m. As the NASA scientist sits in this crowded conference room on the Caltech campus, the aging Saturn orbiter Cassini is flying past the moon Titan for a final time. The maneuver on Monday will give Cassini the gravitational tug needed to sling it straight into Saturn’s atmosphere, where it will vaporize amid roiling clouds of dust and gas.

There’s no turning back now. Spilker’s life’s work is officially doomed.

That is the nature of being a planetary scientist. No mission lasts forever. Every spacecraft eventually runs out of fuel. Spilker knew this when she joined the Cassini team half a lifetime ago. Later, as head scientist, she was part of the group that devised the mission’s “grand finale,” which has sent Cassini on dizzying dives between Saturn and its rings and ends Friday with the fatal plunge.

“I’m trying to be stoic,” Spilker says. The mission could have been prolonged by moving the probe into a safer, more distant orbit. But that isn’t Spilker’s style — or Cassini’s. After 13 years at Saturn, it seemed only fitting to send the spacecraft out “in a blaze of glory,” the scientist says. Use that last bit of fuel to see what no one has seen before. Leave behind one more discovery for scientists to puzzle over after it’s gone.

Spilker stands, and raises a plastic cocktail glass of sparkling apple juice (Caltech doesn’t allow alcohol in school buildings) to a room of fellow scientists who have come to feel like family.

“Titan has given Cassini that last push — a goodbye kiss. Its fate is sealed,” she announces. “A toast to a great spacecraft, a great mission.”

The assembled researchers lift their glasses of juice and chorus their appreciation. A few are close to tears. After Cassini disintegrates, this team will be disbanded, and NASA’s view of Saturn will go dark. For the moment, the space agency has no plans to return to the ringed planet.

But Spilker and a young protege have submitted a proposal for a new mission to the Saturnian system, which would investigate one of Cassini’s most significant finds: jets of water on the moon Enceladus that could contain traces of alien life.

This isn’t a funeral, Spilker constantly reminds her colleagues — and herself. It’s more like a graduation: “Both an end and a beginning.”

She holds onto this idea as the mission’s final minutes tick away. Cassini’s work isn’t over. It’s just turning into something new.

Cassini wasn’t built to be a life-finding mission. When it launched 20 years ago, such a goal seemed unimaginable. The molecular “taster” that the team downsized to save money wasn’t powerful enough to test for the long carbon chains that could be considered biological.

And with each passing year, Cassini was using up its fuel. If it stayed in orbit too long, NASA engineers would lose the ability to control the spacecraft. A passing moon or gravitational quirk might knock it off course and send it crashing into Enceladus, where it could contaminate the pristine — and perhaps inhabited? — landscape.

So the “grand finale” was set in motion. Cassini began its dives through the rings in April, each precipitous plunge bringing the craft closer to Saturn’s storm clouds.

Meanwhile, Cassini’s human handlers prepared themselves for the end.

But this is not really the end. With fellow Cassini scientist Morgan Cable, Spilker has developed a proposal to return to Enceladus and seek signs of life.

“I’ve come full circle now,” Spilker says. “Working on another new mission.”

She and Cable will find out in December whether they get to move forward with their proposal. But even in the best-case scenario, it’s unlikely Spilker will see the idea to fruition. At 62, she’s contemplating retirement. If and when the Enceladus mission gets the go-ahead, Spilker will hand control to her younger counterpart. Cable is 35, the same age as Spilker when the Cassini mission was officially approved.

Like generations of astronomers before, Cable seeks from Saturn the answers to humankind’s biggest and oldest questions: Why are we here? Are we alone? “Deep down, I think I always hoped that life exists out there somewhere, and I really hope that we find it in our lifetime,” she says. “It’s just a matter of continuing to look, being persistent. Following the clues that missions like Cassini leave for us.”