Cassini space craft to bid adieu, directed on a crash course with Saturn with University of Iowa instrument on board

'It's just been a dream mission to work on'

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IOWA CITY — Life could exist on Saturn’s Enceladus moon, an icy “ocean world” hiding salt water beneath its crust. It also could exist on Titan, another of Saturn’s moons — the largest.

Those remarkable possibilities is why Friday marks the disintegrated demise of the 20-year Cassini space mission — which has carried a research instrument from the University of Iowa.

“I think after Voyager, Cassini is perhaps the next most successful and fruitful mission that NASA has flown,” said Bill Kurth, a UI research scientist and lead investigator on the instrument. “Everybody has their favorite. But there’s been virtually no problems with the mission. The space craft has performed flawlessly. It’s just been a dream mission to work on.”

Shortly before 7 a.m. Iowa time Friday, that dream will end.

Cassini will accelerate at about 67,100 mph into the ringed planet’s atmosphere, burning up along the way and disintegrating from lab into legend.

Its calculated destruction is necessary because Cassini — 20 years after its launch, 13 years after entering Saturn’s orbit and nine years beyond its original four-year mission — finally is out of fuel. If it were to instead float into space on an empty tank, it could inadvertently smash into one of the moons, transferring any “bugs from Earth” that might have survived the epic voyage.

“If a couple decades from now we fly a lander with the ability to detect the presence of life or elements of life, and we found some, there always would be the question of whether that life came from Cassini,” Kurth said. “The desire is to make sure that doesn’t happen.”

Kurth, who also was involved in the Voyager mission and serves as lead co-investigator on the Juno mission to Jupiter, became involved in Cassini several years ago after UI professor and famed astrophysicist Don Gurnett passed the baton.

The UI instrument on board, called Radio and Plasma Wave Science, enabled the spacecraft to — among other things — study radio emissions generated near Saturn.

“Those are basically produced by the same process that creates the auroras on Saturn,” Kurth said. “Saturn has Northern and Southern lights — just like on earth.’

Behind its study of Saturn’s radio waves and auroras was the hope of comparison with Earth’s phenomena, Kurth said.

“Earlier in the mission, we actually flew Cassini directly through the source region for these radio waves for the first time, and that represented the first time we were able to fly a space craft through a radio source region — other than at Earth,” he said.

The UI instrument, as with the entire Cassini mission, has surpassed expectations. By staying in orbit longer than initially planned — thanks to gravitational assists from a massive moon allowing the space craft to save fuel — Cassini and the UI instrument investigated thunderstorms on Saturn, some lasting months.

Even in its death, Cassini will pursue its research charge, according to Kurth, who’ll be observing from the California Institute of Technology campus in Pasadena, with other mission players.

“We’ve spent a fair amount of effort designing what the spacecraft will do during the last few hours of the mission,” he said. “We wanted to get as much as we could while the spacecraft could still transmit data to the earth.”

Kurth and his counterparts have designed “observing schemes” enabling observations to come immediately back to Earth for as long as the spacecraft can direct its antennae toward its stations. And although the window of opportunity could close quickly, Kurth said, scientists are hoping to glean groundbreaking information about Saturn’s ionosphere and upper atmosphere.

“This is the closest we’ll get to the planet,” he said. “The measurements that both the Iowa instrument makes and other instruments on the spacecraft can make as we go in will be some of the most important ones of the mission, I think.”

l Comments: (319) 339-3158; vanessa.miller@thegazette.com

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