Here's why NASA had to crash Cassini !

The international Cassini mission to Saturn went up in flames.

It was the best, safest end to the years-long mission.

Cassini has provided scientists with crucial data about Saturn and its moons.

NASA has let one of its most valuable space exploration missions go up in smoke.

On Friday morning, the craft that has been exploring Saturn's system plunged into the planet's atmosphere and almost immediately disintegrated. More than $3 billion worth of technology and decades of work just dissolved into flames.

But it really was the best way to end the mission.

"It's a bittersweet, but fond, farewell to a mission that leaves behind an incredible wealth of discoveries that have changed our view of Saturn and our solar system, and will continue to shape future missions and research," said a statement from Michael Watkins, director of NASA's Jet Propulsion Laboratory in Pasadena, California, which oversees the Cassini mission.

Since it first entered Saturn's orbit in 2004, the spacecraft Cassini's operators have been able to steer its course as it explores Saturn's atmosphere.

The mission's planners knew Cassini would eventually run so low on fuel it would be impossible to control the ship.

Once this happened, there were a number of options. For example, the team could have launched Cassini into a stable orbit pattern around Saturn. But it was impossible to resist the lure of the data they could get from Cassini's Grand Finale — the series of dives between Saturn and its rings.

Had they left the spacecraft in orbit, or parked it on one of Saturn's moons, they could have risked crashing into one of the moons around Saturn that could be home to life.

Cassini has explored two of the ringed planet's moons in particular — Titan and Enceladus.

Both are a part of a growing group of "ocean worlds" that contain vast bodies of water. Jupiter's moon Europa is another example.

Enceladus has been of special interest. Though only about 300 miles wide, the moon appears to have many of the necessary characteristics for sustaining life.

International treaties require that space exploration missions avoid contaminating worlds that might be habitable or have life on them. Scientists were particularly concerned a collision with Enceladus could be harmful to the moon.

That, along with the lure of the Grand Finale, determined Cassini's final course.

The mission has given scientists a trove of new information on the mysterious system and has whetted their appetite for new missions in the future.

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

NASA project scientist Linda Spilker told CNBC in an interview that she is proposing another mission back to the Saturn system to take the samples necessary to determine whether Enceladus actually does have life in its vast underground ocean.

"It would be great to get to that," she said. "That would be incredible."