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Why NASA's Cassini spacecraft has to die at Saturn

Cassini will soon destroy itself in Saturn's atmosphere, but its dramatic death plunge is all for the good of science.

This NASA artist's illustration shows Cassini between Saturn and its rings.

At the ripe old age of 19, NASA's Cassini spacecraft will die next month. That would be young for a human, but it's old for a space probe. 

Cassini launched on Oct. 15, 1997 on a very specific mission to study Saturn, its rings and its moons. On Sept. 15, it will plunge into Saturn's atmosphere. But why do we have to say goodbye? The answer involves fuel and the potential for contamination of some of Saturn's most intriguing moons.

Cassini is running low on rocket fuel. NASA needs that fuel in order to steer the spacecraft. Cassini can't be left to float unmoored out in space due to the remote possibility it could accidentally crash into Saturn's moons Titan or Enceladus. 

Cassini's studies have shown the two moons might have the ingredients to support life. NASA doesn't want to contaminate either one with Earth microbes that could have hitched a ride on Cassini. So Cassini pretty much sealed its own fate with the data it sent back. 

It took Cassini seven years to reach Saturn and it has spent 13 years traveling around the ringed planet's neighborhood. Thanks to Cassini, we know there's a snowman shape on Enceladus and what an aurora looks like on Saturn.

The spacecraft is deep into its grand finale phase, which includes daring dives between the planet and its rings and a dip into Saturn's outermost atmosphere.

Now playing: Watch this: Cassini creeps closer to crashing into Saturn

Cassini has had a great run and it will continue to collect and send back data up until it is destroyed. The spacecraft has given us an intimate view of a very fascinating alien planet. It feels like a old, long-distance friend who is constantly in touch. It's hard to see it go, but Cassini's legacy of discovery will live on.

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