The grand finale everyone was talking about on the internet — no, not “Game of Thrones” — was the final moments of NASA ’s Cassini satellite orbiting Saturn for one last trip.

On Friday, Cassini made a forced descent into Saturn where it officially ended its 13-year mission orbiting the planet to study its moons. The finale was significant because Cassini was the only spacecraft out of four to enter Saturn’s orbit.

Related: Rest in peace, space probe Philae

But why did NASA crash the spacecraft instead of letting it orbit indefinitely? Why is the program ending now after 13 years? When did Cassini make it final transmission to earth? Here are a few things to know about the end of this mission.

Why crash Cassini into Saturn?

Cassini had run out of fuel. And without fuel, NASA can’t control it. So instead of letting the spacecraft orbit around Saturn, operators used its last fumes of fuel to purposely crash it instead of running the risk of letting it hit a moon and potentially contaminate it, according to NASA’s Jet Propulsion Laboratory.

When did Cassini launch and why is it ending now?

On Oct. 15, 1997, a rocket launched the Cassini orbiter and the Huygens moon lander into space where, in 2004, the two separated for their respective missions. Huygens landed on Titan, one of Saturn’s many moons, while Cassini continued a 13-year orbit mission around Saturn.

Cassini’s mission ended because the aircraft is running low on fuel.

https://twitter.com/CassiniSaturn/status/907305542456025088

Why was Cassini’s mission significant?

Cassini was sent to Saturn to study its rings, the makeup of its surface and its hemisphere and to study its moons. In the 13 years flying around the planet, Cassini helped astronauts on Earth discover six moons around Saturn while snapping more than 450,000 images.

The mission helped NASA make a number of major discoveries, including a better glimpse at how planets are formed within Saturn’s rings.

https://twitter.com/CassiniSaturn/status/905512050427908096

What will happen on Friday when Cassini crashes?

On Monday, Cassini began its final orbit around Saturn. By the early morning hours Friday, it was expected to enter its atmosphere and disintegrate.

Cassini’s radio antenna was set to point toward Earth where it would continue to transmit images until it lost its signal. Because it takes a long time for data to travel, Cassini’s final transmission was expected to arrive 83 minutes later.

What are scientists and space aficionados saying about this finale?

Cassini fans have been beside themselves, sharing thoughts and memories with the hashtags #GoodbyeCassini and #GrandFinale.

https://twitter.com/Astropartigirl/status/907333873511546880

https://twitter.com/ShinobiWannabe/status/906342023396913152

https://twitter.com/erikanesvold/status/908003560356532224

Even actor Robert Picardo, who played The Doctor on Star Trek, dedicated a song to Cassini on its final goodbye.

Planetary Society board member Robert Picardo (Star Trek: Voyager) sings a very special goodbye to the Cassini mission at Saturn. Get Robert's monthly space updates delivered stra ...

To follow updates on Cassini’s final moments, go to NASA’s website to get the latest news.

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Email: luis.gomez@sduniontribune.com

Twitter: @RunGomez

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