The nuclear-powered robot was launched in 1997 to deeply study Saturn and its mysterious collection of moons. Cassini arrived in 2004, dropped off a lander on one moon, and has orbited Saturn and beamed back data and images to Earth ever since.
Scientists would love to keep the US$3.26 billion mission going, but their robot has gotten too low on propellant to safely control.
Extending the mission would risk crashing Cassini - which is contaminated with trace amounts of earthly bacteria - into Enceladus or Titan. These two moons of Saturn hide oceans of water and may be habitable to or even host alien life.
Instead of chucking the probe into deep space, like the twin Voyager spacecraft, NASA decided to destroy Cassini by sending it on a months-long death spiral into Saturn.
This daring manoeuvre - what NASA calls "the Grand Finale" - gave Cassini 22 unprecedented dives between Saturn and its gossamer-thin rings.
As NASA prepares to lose one of its most storied space probes, many space enthusiasts are wondering whether Cassini's final moments will be visible from Earth, 930 million miles away.
Business Insider posed that question to Linda Spilker, a Cassini project scientist and a planetary scientist at NASA JPL. Her answer: "It's gonna be tough, but I'm hopeful."
Why it will be so difficult to see Cassini burn up
When Cassini plunges into Saturn's outer atmosphere at about 76,000 mph, it should produce bursts of light. But that will be tough to see from Earth for a few reasons.
First, the brightest parts of those bursts will be in ultraviolet - the same wavelength of light that can cause sunburn. Because Earth's ozone layer soaks up gobs of ultraviolet light, however, any UV flashes will appear dramatically dimmed to anyone watching from the ground.
Another challenge is that Cassini's two nexuses of control - NASA and the European Space Agency - won't "see" the event in the dark of night, making the signal all the much dimmer as western telescopes fight twilight.
"There are really no big assets that we could be to bear either in the United States or in Europe to look," Spilker told Business Insider. "It's going to be five in the morning here, and of course even later in the day in Europe."
Because of those factors, Spilker said this moment in space history won't be like seeing the Shoemaker-Levy 9 comet wallop Jupiter in 1994.
"Those objects were so much bigger and so much more massive than Cassini, and a lot of those strikes were on the night side. We've got sort of the double-whammy of a little tiny spacecraft that's really not that massive hitting on basically the day side of Saturn," Spilker said. "So it's unlikely, but it's definitely worth looking."
Space is the ideal place to record Cassini's fiery death, since the sun and Earth's atmosphere wouldn't be in the way. So, the Cassini mission asked NASA to use the Hubble Space Telescope to stare down Saturn for signs of a flash.
This could have worked, but Spilker said a recent discovery at Saturn led to a poor "luck of the draw" with Hubble.
During Cassini's last handful of dives between Saturn and its rings, the probe revealed that the planet's outer atmosphere extends farther than previously thought.
Ploughing through those sparse gases gradually slowed down Cassini - and this, in turn, bumped up the probe's time of death by about 15 to 20 minutes, Spilker said.
"It's really just in the last few weeks that we've started to get a better handle on what that time of impact would be," Spilker said.
When NASA studied this new timing, it realised Cassini would burn up while Hubble is flying over Earth's South Atlantic anomaly - a chink in the armour of our planet's protective shield where radiation levels and electric currents spike.
"We were trying to get some time on Hubble, but it looks like … the instrument we want to use will have to be turned off when we're flying across that region," Spilker said. "You don't want to have currents flowing at high voltage. You worry about damage to your instruments, so the best thing you can do is turn off high voltage."
She added: "I was sad to lose Hubble, because above [Earth's] atmosphere looking in the ultraviolet, that was a good chance. And it just didn't work."
Southern astronomers to the rescue?
But Spilker thinks all hope is not lost.
She said there's a chance that professional, ground-based telescopes in the southern hemisphere - perhaps those in Australia or Taiwan - might be sensitive enough and in the right place to record Cassini's death.
She also said there's a large community of space fans with powerful telescopes and refined techniques sprinkled across the globe that could help.
"There's still some really great, really capable amateur ground astronomers, in particular, that have returned some beautiful images of Saturn," Spilker said, reiterating that it will be a "tough one" to capture.
"Maybe the last of the fuel tank will suddenly brighten and we'll be able to see that. I think it's definitely worth looking," she said. "We might be surprised."
This article was originally published by Business Insider.
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