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In 1610, Galileo pointed his telescope at the planet Saturn, then the furthest known

planet, and noticed that it sort of had... ears.

400 years later, a little probe called Cassini

finally looked back at us from behind those ears.

Rings, of course, catching sight of Earth.

A single bright pixel in a dark sky.

But like the responsible child she is, Cassini still phones

home every week to check in with proud but anxious parents.

You know, if there's ever any problems, I worry about her.

And I want to find out that everything is okay, and say, call me and let me know how

things are going, or I'll just sort of look over

everyone's shoulder as we work together to fix it.

Besides breathtaking images of the sparkling rings, there was Saturn itself,

and a bizarre six-sided polar storm with a massive hurricane at its center.

And... the moons.

62 of them, including the most bizarre worlds in our solar system.

Titan, with its choking atmosphere, hiding rivers and lakes of liquid methane.

And Enceladus, its cracked ice surface spewing water.

Telling of oceans below.

Oceans that could mean extraterrestrial life.

And now, Cassini is braced for a grand finale.

A series of dangerous dives between the

innermost ring and Saturn, headed for oblivion.

These are the stories of a lonely blue marble, sending its

intrepid little machines to places no human can yet go.

To the far ends of the solar system and beyond.

She's the coolest, hottest, most complex, and most expensive

probe we've ever sent out there into the wild blue yonder.

Technically, in ancient ancient times, Cassini is

a flagship class NASA ESA ASI robotic spacecraft.

Built and controlled by people from 17 nations.

Before we shot her out to Saturn, all we'd had

were glimpses of the jewel of our solar system.

Glimpses provided by the pioneers that flew past in 1979.

And Voyagers 1 and 2 in 1981.

But Cassini would be the first to get to Saturn.

Saturn and stay and stay and stay.

Slated for a four-year mission, she just will not give up.

And she's still out there, eight years after her expiration date.

And the pictures she's sending back keep bringing scientists to tears.

She's rewritten the textbooks about Saturn, the rings, the moons, Titan.

So many things have changed because of Cassini.

Roll program is in.

And liftoff of the Cassini spacecraft on a billion-mile trek to Saturn.

Her journey started on October 15, 1997, as a Titan 4B Centaur rocket tore

into the night sky, bearing the precious bus-sized probe

and slinging her into a crazy seven-year flight path.

She went pinwheeling through the inner planets, starting with two loops around

Venus and once around Earth two years later.

Then she hurtled through the asteroid belt and hooked up with the Galileo space probe

at Jupiter in 2000 to tag-team the solar system's largest planet for six months.

Finally, in 2004, Cassini started sending back her first detailed pictures of Saturn

as she made her approach, capturing two

massive storms joining to become a single one.

And snapping pictures of two new moons.

Cassini then winged by the bizarre little Phoebe, probably a primordial rock from

the birth of our solar system, snagged by Saturn's immense gravity.

Then on the first day of July, in 2004, came the most nerve-wracking,

nail-biting part of the mission.

Decades of planning, seven years of flying, and it all came down to this.

Firing her main engines to slow down, just enough to be captured by Saturn,

and put safely into orbit.

Since it takes more than an hour to communicate with the craft at that

distance, there was nothing her Earthlings could do if something went wrong.

The slightest miscalculation would have sent Cassini spinning by, taking with her

several billion dollars worth of hopes, and

breaking the hearts of her many human parents.

Light up the rockets.

Here we had to do a 96-minute burn to get Cassini safely into orbit.

And I remember waiting and waiting, and of course, if an

instrument doesn't work quite right, I worry about her.

And part of the burn was when she was behind the planet.

So we had to wait and wait and wait.

The Doppler has landed.

It's going to end up.

Finally that signal came out, and it was just exactly on the plot.

And we all applauded in such tremendous relief.

Okay, we have burn complete here.

Four years for this moment.

Now began a decade of orbits, a tango of discovery,

unlike anything any spacecraft had done before.

Skimming Saturn's moons and rings, and getting

her dance partner ready for its close-up.

Saturn itself was ablaze with storms of unimaginable force.

The place crackled with giant lightning strikes.

A gorgeous aurora at the South Pole, created by its enormous magnetosphere,

and invisible explosions of charged gases through that magnetosphere.

That Cassini made visible.

This magnetic envelope of the planet, and how it breathes continuously,

and how it rotates with the planet.

So we have thousands of movies now, of an environment that to our eyes is invisible.

The rings were even more dazzling than any had imagined.

Stretching across hundreds of thousands of miles.

Yet sometimes, only ten feet thick.

They're made of particles of pure water ice.

Some microscopic.

Some the size of mountains.

We used to think of rings as these individual particles kind of bumping into

each other, and sort of floating around in space.

And we now know that the bulk of Saturn's

main rings, particles actually stick together.

And they form these long, long rings.

Strands that we call wakes.

And that these wakes line up like the rows of a marching band.

They have grooves, if you like, like an old-fashioned record.

Created as wakes of moons which are orbiting.

Some of the moons are in the rings.

Some of those moons are outside the rings.

And these waves give an interesting texture.

They break apart and they reform.

So there's this beautiful cosmic dance going on inside the rings.

For the next eight months, Cassini whirled back and

forth across an unimaginably beautiful space scape.

Then Cassini started arcing toward Titan, Saturn's largest

moon, and the one that had long held scientists spellbound.

All these years, Cassini had carried a hitchhiker with her.

A little lander called Huygens, that was set to become

the first probe to land on a moon other than our own.

Because Titan had an atmosphere.

And atmospheres have implications.

This orbiter would carry a probe that would actually

parachute down into the atmosphere of Titan.

And we would have cameras, we'd have instruments to measure the temperature,

pressure, composition, and then land for the first time on an icy moon.

Titan has a really dense atmosphere.

A denser atmosphere than here on Earth.

Nitrogen-like here on Earth.

But methane, natural gas, which is being converted into

complex organic molecules by sunlight and radiation.

And the chemistry that's occurring in Titan's atmosphere today may resemble what

Earth was like before life evolved and created the oxygen we all breathe.

We want to understand when you have organic materials sitting on the surface

of a moon for millions or perhaps billions of years, what's in there?

On Christmas Eve, 2004, Cassini cut the apron strings on the little Huygens craft,

the brainchild of the European Space Agency.

Three weeks later, scientists around the world held their collective breaths as the

little craft dropped toward Titan's surface.

You could almost imagine if you're riding along with

the probe, you go slam into the atmosphere of Titan.

A giant parachute pops up and now the heat shift and the

windshield falls away and your instruments are dangling there.

You're basically sort of sensing and smelling and measuring the atmosphere

around you and your cameras are looking around to the sides and looking down.

We just saw more and more haze and fog and haze and haze until finally the probe

broke through that haze and we got to see the surface of Titan for the first time.

The surface of Titan was strangely familiar and utterly bizarre at the same time.

The little craft seemed to have landed on the equivalent of a

mud flat or shoreline with little ice pebbles scattered around.

But on the negative 350 degree surface of

Titan, these pebbles were made of methane ice.

The nearby lake, a lake of methane.

And then Cassini went into orbit around Titan and revealed with his radar system

that there indeed are lakes of liquid natural

gas and other molecules on the surface of Titan.

They evaporate just like here on Earth, create clouds of methane which rain back

on the surface, creating rivers of liquid natural gas and lakes.

Like water on Earth, that rain had cut channels and gullies in the Moon's surface.

But there were dry formations here too, including dunes that

stretched for miles and miles, reaching 100 meters high.

And 3,000 meter mountains, suggesting tectonic

forces at work here, similar to those on Earth.

That methane, that gas that's in your stove, plays the same

role on Titan that liquid water plays here on the Earth.

You could have methane as a gas and form clouds.

You could have methane rain that falls on the surface, and that's what created huge

seas about the size of the Great Lakes on the Earth.

Could there perhaps be some very interesting life in the lakes on Titan?

After the long-anticipated excitement of Titan, Cassini

headed for a close look at a tiny moon called Enceladus.

No one thought this shimmering little ball of ice, barely 300 miles across,

could rival Titan scientifically.

But they were wrong.

Its sparkling surface is ridged and cracked,

and seemingly scraped along its southern pole.

Here, these strange blue cracks, dubbed tiger stripes, 75 miles long and

hundreds of feet deep, resemble fault lines on Earth.

The cracks were about to get stranger and far more thrilling.

Cassini's thermal sensors picked up heat coming out of the

ice ball, 200 degrees warmer than the rest of the planet.

Enceladus is a small ice ball, but it's a crazy world in orbit around Saturn.

It's the widest object in the solar system when we flew by it, and yet it has a lot

of geologic activity evident on its surface, so something was happening there.

Pirouetting to take a look back at the cracks silhouetted against the sun,

Cassini captured giant jets of water, spewing hundreds

of miles out into space from the tiger stripes.

They shoot out at 1,200 miles per hour.

Vaporizing and then freezing.

It was a stunning moment.

It has this tidal forcing that's squeezed on it, kept the ocean a liquid,

and what happens that's so neat at Enceladus is that there are actually four

fractures at the South Pole and jets of this water and

ice come squirting out into space, and we had no idea.

Back on Earth, Cassini's stunned controllers quickly reprogram the probe to

fly right through the jets, collecting particles.

And what they found was even more stunning.

Organic molecules, the basic building blocks of life.

Because the geyser's erupting, and they could guide the spacecraft very

close, they could actually fly through it and look to see if there's water there,

and there is water, and looking for the chemistry that's there.

Enceladus is really special.

It's giving us free samples.

And so Cassini has multiple times flown through.

You can imagine it sniffing the gas and getting coated with these icy particles,

and some of them come in in our sample, and we know their composition.

To our surprise, we found out that in looking at the particles, the ocean was salty.

And it was salty and had a very similar pH to our own ocean here on the Earth.

Here on Earth, wherever there's liquid water, whether it's deep in the ocean and

very hot, or in rocky places or in ice, there's microbial life.

So it certainly suggests microbial life could have evolved on Enceladus because it

has all the properties that the Earth had when life began here.

And so if we go back with more sophisticated instruments, perhaps with

the free samples, we could answer that question.

Enceladus held another shocker for the scientists.

Most of the water spewed out of its south pole falls back onto the planet's surface.

You could imagine standing on Enceladus, putting out your hand,

and there'd be this gentle snow coming down all around you.

But the fastest moving particles break away from the moon.

But the very tiniest particles, things that are smaller than the diameter

of a human hair, they escape from Enceladus's gravity

and they go on to form a ring called the E-ring.

The indefatigable probe wrapped her original four-year mission in 2008.

During the next two years, Cassini zipped

past Titan 26 times and Enceladus seven times.

Dione, Rhea, and Helene each got a single royal wave from the probe.

It would be years later, in 2013, that Cassini flew behind the ring and

looked back at Earth, our home planet, a single pixel in the vast solar system.

And there was no slowing her down as she made whirling visits to moon after moon,

ring after ring, before she began a series of adjustments to take on one final

spectacular mission, one that NASA, with the

help of the public, dubbed the Grand Finale.

This is prop.

I read you five minutes.

Be ready.

System straight science.

We have X-band carrier signal detection.

The start of Cassini's final orbits began on April 23, 2017.

In many ways, even after 20 years in space, this

seemed like a brand new mission for the probe.

The first of these daring orbits took her high above Saturn's North Pole,

flying just outside its narrow F-ring.

And through the water-rich plume of Saturn's moon Enceladus.

Then, in an attempt to squeeze even more great science, scientists figured out how

to alter the craft's trajectory, bringing it dangerously

closer to the planet than it's ever been before.

They found that if we fly by Titan in just the right way, we can actually jump from

just outside the rings all the way across the planet.

We can cross the rings and dive through a gap in between

the innermost ring and the top of the atmosphere.

Now this gap is only a thousand miles wide.

A task so bold and risky that it could only be

undertaken at the end of its long and storied journey.

Today is a potentially very historic day for Cassini.

It may be the last main engine rocket firing of the

entire mission after about 180 burns over our 20 years.

Being in charge of the propulsion system, it's with a tinge of sadness, I think,

that we may never use that rocket engine again.

Of course, the Cassini mission is all about the science and tonight we commence

the F ring orbits, actually orbiting for the first

time between the rings themselves and the planet.

Very exciting.

Cassini plunged past Saturn every six days as our cameras

provided the first ever ultra-close images of Saturn's clouds.

A gorgeous aurora at the South Pole, created by its enormous magnetosphere...

and rings.

Cassini took this series of photographs over a one-hour time frame just before

turning the saucer-shaped antenna towards the direction of its trajectory,

protecting the craft crossing Saturn's rings.

And you feel like you're there and you can reach out and touch the rings.

And then that space between the rings and the planet, measuring the particles and

fields and plasma, what's going on in that region?

These final dives were used to reveal the mass of the

rings, which gave scientists an idea of their age.

Early findings suggest that they may perhaps be just 100 million years old,

much younger than the 4.6 billion year old planet they surround.

Cassini is revealing Saturn from the inside out, with our gravity and magnetic

field measurements, we get to see inside the planet.

How deep do the winds go?

How is the magnetic field generated?

What's the length of Saturn's day?

As Cassini began to run out of fuel, making it unnavigable and unresponsive to

trajectory commands, its team back home had to take into account

the possibility of life existing on one of Saturn's moons.

They could have parked it in an orbit around the planet nearly indefinitely.

But that would have involved an unacceptable risk.

The probe could eventually get snagged in the gravity well of Titan or Enceladus,

where extraterrestrial life may be getting a foothold.

It's possible that despite all this time and space, and the extreme conditions she

has faced, little Cassini could have hardy Earth microbes clinging to her.

So, to protect these worlds, for planetary protection, we

decided to end the mission by going into Saturn's atmosphere.

September 15, 2017, marked the end of Cassini's bittersweet grand finale.

NASA controllers plunged the craft into the maelstrom of the gas giant.

She continued to send back data until the very last second.

We want to know as we get deeper and deeper into Saturn's atmosphere,

what's it made of and what's there.

So we'll be gathered, I'm sure, with our Cassini

family watching that tiny signal on the screen.

And then as the atmosphere gets too dense, it will

just turn her away, and then the end will come quickly.

She'll be torn apart, a giant fireball going through in Saturn's atmosphere.

And if

you think about it, as she disintegrates and

melts, her molecules will become part of Saturn.

A very wonderful ending for this spacecraft.

She studied Saturn, and her end is going to be with Saturn.

She isn't just, you know, bits of metal and wires and things.

She's really the hopes and dreams of all of the scientists

and engineers and all of the people who put her together.

And so when I go and look at the night sky and I see Saturn, I'll see Cassini,

because she'll be there.

NASA Jet Propulsion Laboratory, California Institute of Technology