NASA killed Cassini to avoid contaminating Saturn's moons

Spacecraft's 13 years in orbit have produced suggestions of potentially habitable worlds

Posted: September 15, 2017
Last Updated: September 16, 2017

For 13 years Cassini has explored Saturn, its rings and moons. The spacecraft's Grand Finale is to burn up in the planet's atmosphere, avoiding the risk of contaminating a moon that could have forms of life. (NASA/JPL/Space Science Institute)

NASA scientists killed the hard-working Cassini spacecraft to avoid contaminating Saturn's moons with Earth microbes because they may have the potential to support life.

On Friday at 7:55 a.m. ET, the world said goodbye to Cassini after 20 years in space and 13 years orbiting Saturn and its moons, providing incredibly detailed, high-resolution photos of what many consider the jewel of our solar system.


Though Cassini's life was extended twice with new missions, the spacecraft had a limited fuel supply. So NASA announced in April that it would carry out one final mission, dubbed The Grand Finale.

Scientists and engineers altered the orbit of the spacecraft to run into Saturn, where it would safely burn up in its atmosphere.

Cassini provided stunning images of picturesque Saturn, including this true-colour image of its rings. (NASA)

Cassini's fate arose directly from its success in shedding a light on the possibility of life on other worlds. 

On Wednesday, NASA's planetary science division director Jim Green spoke about Enceladus, a small, icy moon, spewing organic material that likely originates from a subsurface ocean.

"What we thought was an icy ball, when we observed the southern hemisphere, and geysers of water spewing out into the Saturn system, it amazed us," he told reporters.


"And it began changing the way we view the habitability or potential habitability of moons in the outer part of our solar system."

Allowing Cassini to run out of fuel would leave NASA no way to control the spacecraft. One day it could crash into Enceladus or even Titan, Saturn's largest moon, which is also being studied for potential habitability.

This illustration depicts the final steps to Cassini's dive into Saturn. (NASA/JPL-Caltech)

While there is no guarantee that there is microbial life on any of these moons, there is a chance of contaminating their surface with Earth microbes. 

"Now because of the importance of Enceladus that Cassini has shown us, and of Titan, another potential world that could be habitable for life, perhaps not like we know it, but perhaps completely different than ours, we had to make decisions on how to dispose of the spacecraft," Green said.

"And that led us, inevitably, to the plan of taking Cassini and plunging into Saturn."

On the plus side, Cassini's Grande Finale has given us unprecedented views of the planet's north pole as well as its intricate ring system. For the first time in its mission, the spacecraft flew between the planet and the rings. 


'We might find in fact a higher probability than I'm willing to admit right now that life exists in the interior of Enceladus.' — Larry Soderblom, Cassini scientist

And, with its success and valuable insight into the potential habitability of other worlds, it's likely there could be new missions.

Missions have been suggested to explore Enceladus, including its interior and the subsurface liquid body, Larry Soderblom, an interdisciplinary scientist on the Cassini mission, told CBC News.

"We might find in fact a higher probability than I'm willing to admit right now that life exists in the interior of Enceladus."

This false-colour mosaic, made from infrared data collected by Cassini, reveals differences in the composition of surface materials around hydrocarbon lakes on Titan. (NASA/JPL-Caltech/University of Arizona/University of Idaho)

While astronomers and planetary enthusiasts may miss the data and photos gathered by Saturn, NASA's Juno spacecraft is also orbiting Jupiter. And there are plans for the Europa Clipper, which will conduct flybys of another icy, potentially habitable moon, Europa.

If there is a chance for life to be found in the Saturn system, NASA is eager to protect it. 

"Because of planetary protection and our desire to go back to Enceladus and go back to Titan and go back to the Saturn system, we must protect those bodies for future exploration," Green said.


Nicole Mortillaro
Senior reporter, science

Based in Toronto, Nicole covers all things science for CBC News. As an amateur astronomer, Nicole can be found looking up at the night sky appreciating the marvels of our universe. She is the editor of the Journal of the Royal Astronomical Society of Canada and the author of several books. In 2021, she won the Kavli Science Journalism Award from the American Association for the Advancement of Science for a Quirks and Quarks audio special on the history and future of Black people in science. You can send her story ideas at