Cassini gave us Saturn, but also gave us Earth — as only deep space could reveal: Small. Frail. Lonely. Steeped in darkness. pic.twitter.com/zjF6jNUFyU
— Neil deGrasse Tyson (@neiltyson) September 14, 2017
Here, with some final words on the mission, is Linda Spilker, who has worked on Cassini for a whole Saturn year - that’s 30 years on Earth.
Things never will be quite the same for those of us on the Cassini team now that the spacecraft is no longer flying. But,we take comfort knowing that every time we look up at Saturn in the night sky, part of Cassini will be there, too.
Where do spacecraft go to die? The staff of the US magazine, Science, have done a wonderful job of pulling together the final resting places of 42 spacecraft. Check it out here.
If you want to know how the funding stacks up for a spectacular mission such as Cassini, you can find a highly accessible infographic here.
Nasa has said farewell to its Saturn explorer.
Cassini showed us the beauty of Saturn.
— CassiniSaturn (@CassiniSaturn) September 15, 2017
It revealed the best in us.
Now it's up to us to keep exploring. pic.twitter.com/E4p1jOvFKf
Earth received @CassiniSaturn’s final signal at 7:55am ET. Cassini is now part of the planet it studied. Thanks for the science #GrandFinale pic.twitter.com/YfSTeeqbz1
— NASA (@NASA) September 15, 2017
John Zarnecki, President of the Royal Astronomical Society, worked on the Huygens lander that touched down on Titan. He knew today would be emotional, but one consolation is that the lander is still on Titan’s surface. Who knows how long it will remain there?
The touchdown was a record, the first landing on a body beyond the asteroid belt, and Zarnecki believes the feat will not be bested any time soon. He said:
We are in the Guinness Book of Records and we could be there for a century. I don’t think we’ll land further away in the solar system for a long time.
Cassini declared dead
Earl Maize, Cassini’s project manager, calls an end to the mission and prompts a round of subdued applause from the gathered team, many of whom started on this adventure more than 20 years ago. A tough moment for some of them, but what a mission, what a legacy.
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Signal lost from Cassini
And that, dear readers, is that. After 20 years in space and 13 spent looping around Saturn and its moons, Cassini’s final signals have been received. The spacecraft died on Saturn more than an hour ago, but this is confirmation: the end of its broadcast at 12.55 UK time as it fell into Saturn and became part of the planet.
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The signal will go in seconds.
The latest signals from Cassini show the spacecraft in the atmosphere and its thrusters firing more and more to keep it steady as it plunges.
Jim Green, the director of Nasa’s planetary division, and Mike Watkins, director of JPL, have been sharing their thoughts on the mission.
Green said water jets coming from Enceladus was one of the “pretty spectacular” discoveries made by the mission. He said it was a call from Saturn’s moon to come back, adding:
Once we see an area that has water then we know there’s a possible of it being a habitable environment.
And Nasa has plans to go back to Enceladus, Watkins said:
It’s a bittersweet event for all of us. For me it’s more sweet than bitter because Cassini has been such a fantastic mission.
He added that finding water jets coming from Enceladus was one of the mission’s greatest legacies, a discovery so compelling you had to go back. He said:
We have to go back, we will go back, and fly through the geysers of Enceladus...Ocean worlds look like an incredibly compelling target.
Cassini in numbers
Nasa has been collating numbers for the Cassini mission and it’s fair to say they make for impressive reading:
Commands executed: 2.5million
Saturn orbits completed: 293 at end of mission
Targeted moon flybys: 162
Targeted Titan flybys: 127
Targeted Enceladus flybys: 23
Images taken: 453,048
Oceans discovered: 2 (Titan, Enceladus)
Titan seas and lakes discovered: 3 seas, hundreds of small lakes
Named moons discovered: 6
Science papers published: 3,948
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The final bits from Cassini, having left Saturn, passed Jupiter and crossed the asteroid belt, will be reaching Mars about now. The signal being received by Nasa’s tracking station in Canberra is loud and clear. We expect it to vanish in 20 minutes.
Carolyn Porco, head of the mission’s imaging team, posted her final “Captain’s Log” this morning, after working on the mission for three decades. She writes:
It is doubtful we will soon see a mission as richly suited as Cassini return to this ringed world and shoulder a task as colossal as we have borne over the last 27 years.
To have served on this mission has been to live the rewarding life of an explorer of our time, a surveyor of distant worlds. We wrote our names across the sky. We could not have asked for more.
I sign off now, grateful in knowing that Cassini’s legacy, and ours, will include our mutual roles as authors of a tale that humanity will tell for a very long time to come.
Maize has been talking about the final minute of Cassini’s life. The spacecraft will have used its small thrusters to fight the torques induced by the tenuous atmosphere, which is about as dense as the International Space Station experiences 200 miles above Earth. Cassini has had to deal with wisps of saturn’s atmosphere before, but those previous dips are nothing compared to the forces it experienced today. Maize says:
This time because we’re going in so deep there’s not a chance it can fight the atmosphere.
Earl Maize, Cassini’s program manager, says Nasa had to dispose of the spacecraft properly. There are international treaties that prevent nations from allowing spacecraft to wander aimlessly through space when they run out of fuel when they are close to pristine environments that may harbour life.
Nasa’s Deep Space Network is tracking Cassini’s signals. Earlier in the week, project scientist Linda Spilker told me that the signal may drop and return, drop and return, as Cassini’s antenna wobbles before it finally loses contact completely. And, as Linda put it:
The end will be very quick after that.
Cassini is no longer with us, but the last packets of information, or ghost bits, the spacecraft beamed home on its death plunge will be reaching Jupiter about now. Next stop, the asteroid belt!
But it was Enceladus that really caught scientists’ attention. Before the Cassini mission, astronomers considered Enceladus, a tiny ice moon only 500km wide, as inactive and uninteresting. But on a flyby, Cassini detected something remarkable: plumes of salty water spraying from the moon’s south pole. More flybys confirmed the geysers and spotted simple organics in the fluid. Researchers now believe the jets of water come from a global, subsurface ocean of liquid water where hydrothermal vents warm the seafloor.
Cassini was a rare thing among space adventures: a mission to a planet where the moons were the stars. In 2005, Cassini dropped the Huygens lander onto Titan, its largest moon. It was the first landing on another planet’s moon, and the first touchdown on a body beyond the asteroid belt. Titan turned out to be an extraordinary world, a place where hydrocarbon clouds floated in an orange sky and rained methane down into rivers, lakes and seas.
On touchdown, scientists first thought Titan had a thin, brittle crust over softer material beneath. But on closer inspection, Huygens had simply set down on a pebble and then settled on more forgiving ground.
My colleagues have put together a stunning gallery of images taken by Cassini as it looped around Saturn. In the 13 years it spent in the Saturn system, Cassini circled the planet 293 times, including its final orbit that ended with its destruction this morning.
Saturn is the most distant planet that can be seen from Earth with the naked eye. If you can spot the planet in the sky tonight, know that Cassini has now become part of it.
Look up tonight & see Saturn in the sky. Tomorrow, our spacecraft will be part of the planet it studied for so long. https://t.co/tcEez0OfeG pic.twitter.com/SDGb6V34zo
— CassiniSaturn (@CassiniSaturn) September 15, 2017
The last signals sent from Cassini will now be on their way to Earth, zooming past Jupiter and Mars at the speed of light. Very roughly, those last bits of data, containing information on Saturn’s atmosphere, will pass Jupiter around noon UK time, Mars at about 12.30pm and arrive at Earth just before 1pm UK. Those signals will be picked up by Nasa’s tracking station in Canberra, Australia, and from there relayed on to mission control at the Jet Propulsion Lab in California.
Cassini vaporised at Saturn
More than one billion kilometres away, the Cassini spacecraft has more than likely already begun to tumble and so lost its ability to point its antenna back to Earth. If it’s still in one piece, it won’t be for long. If it hasn’t been burnt to a cinder yet, it will be soon.
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Scientists and engineers, some of whom have worked on the project since its conception in the 1980s, are at Nasa’s Jet Propulsion Lab in California to wave goodbye to the spacecraft that taught them so much about Saturn and its moons.
Earlier this week, I spoke with Linda Spilker, Cassini’s project scientist at Nasa’s Jet Propulsion Lab. She started work in the project in the 1980s, a time of big hair and shoulder pads and, of course, Rick Astley. Linda told me:
It’s going to be tough to say goodbye, but I’m very proud of all Cassini has accomplished and to have been part of the mission from the very beginning. It’ll be a mixture of sadness and pride and joy at having worked on the mission and saying goodbye to my Cassini family.
The Cassini-Huygens mission captured Saturn, the most distant planet visible from Earth with the naked eye, in exquisite detail. Arriving in 2004, after flybys of Venus and Jupiter, Cassini found Saturn to be circled by millions of rings that have their own active lives: material clumps together into muddy snowballs, while tiny moonlets clear space in the rings, creating shapes that resemble propellers thousands of kilometres long. Nasa even named them after early aviators. The largest is the Bleriot propeller, after Louis Bleriot, the French engineer who in 1909 became the first person to fly across the English channel.
At Saturn, Cassini has only minutes left before it burns up in the atmosphere. We expect the spacecraft to become a meteor in Saturn’s sky at about 11.30am UK time, but confirmation will not come until nearer 1pm UK time.
Why Cassini must crash into Saturn
Cassini was steered onto a collision course with Saturn to ensure it did not run out of fuel and drift aimlessly through space, potentially endangering the pristine environments of Saturn’s moons which, at last count, numbered 62. As the mission found to scientists’ surprise, these moons may be the most promising places in the solar system to find life beyond Earth.
On Friday morning, Cassini was heading for Saturn at 111,000 kilometres per hour. For as long as it can, it will use tiny onboard thrusters to keep itself steady and its antenna pointed to Earth. But even before Cassini hits Saturn’s clouds, the tenuous atmosphere will cause the spacecraft to tumble and communication will be lost. Moments later, Cassini will be torn apart and burn to a cinder as atmospheric friction takes its toll.
Saturn is a gas giant and so has no discernible surface. The tiny pieces of Cassini that survive its fireball entry into Saturn’s clouds will fall towards the centre of the planet, through increasing temperatures and pressures, until they melt and ultimately become diluted within the planet itself.
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And so the time has come. Two decades after the Cassini spacecraft blasted into space with its Huygens lander from Cape Canaveral in Florida, the probe will say its final farewell and ditch into the clouds of Saturn.
The spacecraft is expected to burn up in Saturn’s atmosphere moments after 11.30am UK time on Friday, but at one billion kilometres away, it will take 83 minutes for Nasa engineers to receive confirmation of Cassini’s demise.
Join us as we follow Cassini on its death dive into Saturn.
