Cassini's final mission: Crashing into Saturn - CNET

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It won't be happening until next year, but now is the time to start saying goodbye to Cassini. Last week, the countdown clock for the Satu probe's final plunge was installed and started. In a year's time, the mission will commence.

Cassini launched in 1997 and entered Satu's orbit in 2004, and has spent the years since collecting more information on the ringed planet than ever before. By its first aiversary in 2014, it had sent back over 500 GB of data, which contributed to over 3,000 scientific papers. It discovered seven new moons and invaluable information about its rings, an active laboratory demonstrating how moons and planets form.

It revealed that beautiful Titan has rain, rivers, lakes and seas and a nitrogen-rich atmosphere similar to what Earth might have had, and studied the eerie radio-wave pattes, revealing that they are not related to Satu's ier rotation (although what they are related to remains yet to be discovered). And it showed us Satu's magnificent polar hexagon.

The final mission is, fittingly, called the Grand Finale, and there's a lot more involved than simply falling down. As the probe gets closer and closer to Satu, it will have an unprecedented opportunity to study its minutiae, as detailed by NASA's Linda Spilker at the European Geosciences Union General Assembly last week.

First, Cassini is going to conduct a series of orbits just outside Satu's outermost F ring, repeatedly circling the poles for a final look at that hexagon. During this phase of the mission, it will also probe the plume of moon Enceladus' active geysers, and perform 12 close fly-bys of glittering Titan.

When this phase is complete, Cassini will swoop in close, starting a series of 22 daring orbits between Satu and its iermost D ring, from April 2017. Cassini will be closer than any spacecraft has ever been to Satu, just 64,000 kilometres (40,000 miles) from its centre (Satu has an equatorial diameter of 75,000 miles).

From this vantage point, Cassini will be able to make detailed maps of Satu's gravity and magnetic fields, which will reveal a lot about the planet's inteal structure, and hopefully help figure out how fast the interior is rotating under all that gas. It will also be able to examine much more closely Satu's rings, sampling the icy ring particles being pulled into the planet's atmosphere.

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And, of course, we'll get to see all sorts of wonderful, detailed, up-close photos of Satu's rings and clouds.

And when all this is said and done, On September 15, 2017, Cassini will plunge past Satu's atmosphere, through its clouds and fog, for a crash landing on the surface far below, collecting and sending data right up until its final minutes.

Don't cry for Cassini, though. Its mission has already been extended twice, far exceeding its four-year expectation, and its ruing out of fuel. Leaving it in unfueled orbit around the planet risks crashing into Enceladus or Titan, the potentially life-sustaining liquid water on which could be contaminated by microbes that could still be living on Cassini, even after 20 years.

And its swansong will be a thing of wonder: a treasure trove of data that will (hopefully) keep Satu scientists busy for years to come.