Next week, a fireball streaking through the skies of Saturn will herald the end of an era: the demise of NASA’s venerable Cassini spacecraft.
In 2004, Cassini began exploring the Saturn system. For more than 13 years, it has swivelled, flipped, and flown around the ringed planet and its many moons, executing millions of commands and beaming back more than 450,000 images.
While it’s tempting to wish that Cassini could become a permanent inhabitant of the system even after running out of fuel, the probe’s final scientific mission will be to destroy itself by plunging into Saturn’s atmosphere.
“I feel like the end of mission is rushing toward me much faster than I had expected,” says project scientist Linda Spilker. “On that final day, I will feel a mixture of sadness and tremendous pride in all that she has accomplished.”
On September 11, a gravitational nudge from the large moon Titan will set Cassini on a collision course with Saturn. Around 1 p.m. PT on September 14, Cassini will take its last picture. From then on, it will be in continuous contact with Earth as it makes its last journey inward.
Around 3:30 a.m. on September 15, it will begin its plunge through the planet’s cloud tops. As atmospheric friction increases, the spacecraft will slow down, heat up, and start to tumble.
Eventually it will ignite, looking for all the world like a meteorite streaking through the Saturnian sky. Even in its final moments, Cassini will be adjusting itself to face Earth and send data home for as long as it can.
Scientists expect to receive their last signal from Cassini around 4:55 a.m. That last gasp will be like a whisper from the dead: The spacecraft will have been gone for 83 minutes by the time the signal travels from Saturn to a radio dish in Australia.
And then, for the foreseeable future, the Saturn system will be silent.
In this stunning animation, watch NASA's Cassini spacecraft begin the last chapter of its 20-year mission to Saturn.
By coincidence, Cassini will burn up just one month short of the 20th anniversary of its launch. It left Cape Canaveral, Florida, on October 15, 1997, and arrived at Saturn on July 1, 2004. The spacecraft immediately began stunning scientists back home with its views of the iconic planet and its clutch of more than 60 moons.
Early on, Cassini dropped the Huygens lander onto hazy, orange Titan. The second largest moon in the solar system, Titan is shrouded in a thick nitrogen atmosphere that hides its oily lakes and seas from view. Now, thanks to Cassini, we know that Titan is among the best places to look for life beyond Earth.
Not long after, Cassini spotted enormous geysers erupting from fissures at the south pole of tiny Enceladus, an icy moon harbouring a hidden, global ocean. Like Titan, Enceladus is now considered one of the most likely places to find alien life in the solar system.
These two moons are the reason Cassini can’t stay in orbit around Saturn forever.
The spacecraft’s fuel reserves are dry, and leaving it looping around the Saturn system with no way of controlling it risks an unplanned crash into one of these tantalising worlds. But even knowing that destroying Cassini is the best thing for science, plenty of mission members are mourning the end of the beloved probe.
“I loved the fact that every morning I could go to my computer and have a quick look at the latest images downloaded from the spacecraft,” says Carl Murray of Queen Mary University of London. “It was almost like having your own webcam keeping an eye on conditions at the other side of the solar system!”
As the spacecraft’s demise has drawn closer, social media platforms are filling with laments—including the perpetual screaming of a Twitter account that just can’t handle the probe’s impending doom.
It speaks for all of us:
NOOOOOOOO...................................................................................................................................— Cassini Noooo (@CassiniNooo) 6 September 2017
Header Image: In August 2009, NASA’s Cassini spacecraft became the first robotic emissary from Earth to witness an equinox at Saturn, when the sun was shining directly on the giant planet’s equator. PHOTOGRAPH BY NASA, JPL, CASSINI