Cassini ends 20-year mission with final plunge into Saturn

Probe's discoveries transformed scientists understanding of the outer solar system.
By Laurel Kornfeld | Sep 16, 2017
NASA's Cassini spacecraft ended its nearly 20-year mission in the early morning of Friday, September 15, with a planned plunge into Saturn's upper atmosphere.

The probe entered Saturn's atmosphere at approximately 6:30 AM EDT at 9.4 degrees north latitude and 53 degrees west longitude just as that region of the planet rotated into daylight.

Its thrusters fired as long as they could to keep the spacecraft stable and the antenna pointing to Earth as Cassini transmitted the last data it collected in real time.

Within about one minute of entering the giant planet's atmosphere, the spacecraft broke apart and burned up.

Mission control lost contact with the probe at 7:55 AM due to the 83-minute time delay its signal took to travel from Saturn to Earth, specifically to NASA's Deep Space Network antenna in Canberra, Australia.

Because Cassini was nearly out of fuel, mission scientists chose to crash it into Saturn. Had they allowed it to run out of fuel, they would have lost control of the spacecraft, risking it landing on potentially habitable moons Enceladus and Titan, where it could contaminate any microbial life existing there or be mistaken for indigenous life by future probes.

Although the spacecraft was sterilized before its 1997 launch, some microbes on it could have survived and posed this threat.

The mission's end was broadcast live online by NASA's Jet Propulsion Laboratory (JPL) from 7-8:30 AM EDT, and a recording of the broadcast is available for public viewing.

At Mission Control, team members hugged one another after the signal was lost and expressed a combination of both grief at the spacecraft's demise and pride in its long list of accomplishments.

"This is the final chapter of an amazing mission, but it's also a new beginning," associate administrator for NASA's Science Mission Directorate Thomas Zurbuchen said.

"Cassini's discovery of ocean worlds at Titan and Enceladus changed everything, shaking our views to the core about surprising places to search for potential life beyond Earth."

After a seven-year journey, Cassini arrived at Saturn in 2004. Early the next year, it dropped the Huygens probe onto the surface of Saturn's largest moon Titan, in the furthest landing on another solar system world.

Before Cassini launched, Saturn's moons were thought to be dead and uninteresting. The spacecraft's discoveries changed that, revealing hydrocarbon lakes on Titan and geysers emerging from the south pole of Enceladus.

Both moons and possibly a third, Dione, are now known to harbor subsurface oceans that could potentially host microbial life.

NASA extended the Cassini mission twice, first for two years and then for seven more.

During Cassini's final moments, all eight of its science instruments continued sending data back to Earth.

Among that data are visible and infrared images of the location where it entered Saturn's atmosphere at a speed of 76,000 miles per hour.

It will take another year for mission team members to process and archive all the data Cassini collected and sent back.

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