By the time many of us knew that NASA’s Cassini-Huygens was headed for Saturn, it had already slipped the bonds of Earth’s gravitational well. With no impulse engines, no warp drive, and only chemical propellant to send it on its way, it spent six years, eight months and sixteen days to reach its destination. The tantalizing ringed world, just within reach of our earliest optical telescopes, was to become the probe’s home for the next seven years. Today, the plucky spacecraft has come to end of its remarkable journey of exploration. With its fuel all but gone, NASA mission control has decided that it would be better to plunge the $4 billion spacecraft into the surface of the giant planet itself, rather than run the risk of it accidentally colliding with a potentially habitable moon. In particular, this means Enceladus, with its sub-surface global ocean, but also the frozen smog-ball Titan, with its intriguing pre-biotic chemistry.
Beginning in 2010, Cassini began a seven-year mission extension in which it completed many moon flybys while observing seasonal changes on Saturn and Titan. The plan for this phase of the mission was to expend all of the spacecraft’s propellant while exploring Saturn, ending with a plunge into the planet’s atmosphere.
In April 2017, Cassini was placed on an impact course that unfolded over five months of daring dives — a series of 22 orbits that each pass between the planet and its rings. Called the Grand Finale, this final phase of the mission has brought unparalleled observations of the planet and its rings from closer than ever before.
On Sept. 15, 2017, the spacecraft made its final approach to the giant planet Saturn. But this encounter was like no other. This time, Cassini dove into the planet’s atmosphere, sending science data for as long as its small thrusters could keep the spacecraft’s antenna pointed at Earth. Cassini burned up and disintegrate like a meteor, becoming part of Saturn itself.
To its very end, Cassini was a mission of thrilling exploration. Launched on Oct. 15, 1997, the mission entered orbit around Saturn on June 30, 2004 (PDT), carrying the European Huygens probe. After its four-year prime mission, Cassini’s tour was extended twice. Its key discoveries have included the global ocean with indications of hydrothermal activity within Enceladus, and liquid methane seas on Titan.
And although the spacecraft may be gone after the finale, its enormous collection of data about Saturn – the giant planet itself, its magnetosphere, rings and moons — will continue to yield new discoveries for decades.
Here are a few highlights of Cassini’s last orbit. The probe sent back an astonishing 396,000 images, give or take. Most aren’t interesting in their unfiltered, unanalyzed state, and only have meaning in context of thousands of other photographs.
For more information, visit the NASA page on Cassini’s final plunge into the upper atmosphere of Saturn.
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