A billion miles from home.
Running low on fuel.
Almost out of time.
We're putting down a fully functioning spacecraft.
After 13 years orbiting Saturn, the spacecraft Cassini
is about to plunge to a fiery death, becoming part of the
very planet it's been exploring.
And at Nasa's Jet Propulsion Laboratory, the entire mission
team has gathered from across the globe to say goodbye to a great
explorer, and to celebrate an extraordinary mission.
Cassini was not so much of a mission as a way of
life.
I've spent 20 years of my life on this.
27 years I've worked on the project.
What we found was spectacular.
It was like a Jules Verne adventure come true.
Cassini sent back dramatic visions of strange new worlds.
Nothing of what we had imagined came close to
the reality.
It revealed methane lakes, electric dunes, buried
oceans.
That Moon has an ocean in it that could harbour life.
It's the end of a mission that has not only
unveiled the beauty and probed the mysteries of Saturn,
but has changed our view of the solar system forever.
Playback is starting to run.
Systems lead, mission planning.
Go ahead, mission planning.
Spacecraft has just crossed 30 degrees north
latitude, attitude is 6,000 miles.
The dead of night, Friday the 15th of September.
In the control room of Nasa's Jet Propulsion Laboratory,
the flight director and her team of engineers
are presiding over the
death of a spacecraft that they have nurtured for nearly three decades.
In less than an hour, they will watch as Cassini sends its final transmission.
It's sad.
It was 27 years of the investment of many lives into this.
Nearby, at the California Institute of Technology,
is the vast family of scientists from around the world who run the 12
instruments on Cassini, measuring everything
from infrared to radar, magnetic fields, and cosmic dust.
It's a big family, indeed.
This is one of the aspects of this mission
that I will miss more.
In some ways, I just want it to be over now.
You know, you're sort of waiting for it
to end and it's really weird.
Very mixed emotions at the moment.
Really strange.
All have played a vital role in exploring Saturn.
But it's Cassini's skills with a camera that
have been truly inspirational.
Head of the camera team and guardian of
the Cassini image gallery is Carolyn Porco.
Carolyn has been responsible for designing the camera
systems, deciding when, where, and which pictures to take, and
delivering and processing hundreds of thousands
of images of Saturn, its rings, and moons.
This is one of my favourites.
The reason why I love it is because because we're seeing the
rings edge on and you just really can tell how thin they are.
You can get the sense of three dimensionality, because we see the
dark shadowing.
It so beckons for you to go there.
And this is the famous hexagon, OK?
This is the feature that drives everybody crazy
because they don't expect to see something
that is straight sided in an atmosphere.
It is nothing more than a jet stream like our jet stream, OK?
Really, you can relax.
This is not the end of the world.
Back at the rings, I mean, have you ever, ever
seen anything just so magnificently regular and beautiful?
With its two on-board cameras, Cassini has
unveiled the Saturn system as a strange, mysterious, and unique
place.
Saturn just captivates people because it looks so supernatural.
It engenders the immediate feeling that
it can't possibly be real.
But we're lucky to have it.
I think we're dead lucky to have Saturn.
I'm glad I grew up in a solar system that had
a planet like Saturn.
But taking and downloading such amazing pictures,
when your camera is a billion miles away, through the bleak void of
outer space, is no mean feat.
In charge of remotely managing the spacecraft from Nasa's Jet
Propulsion Laboratory is Julie Webster.
You know scientists and engineers are true nerds, and you'll
see a lot of nerd stuff.
Julie is Cassini's chief engineer.
She's been caring for the intrepid explorer
since before it left home, and uses a scale
model of the spacecraft to
demonstrate its capabilities.
This is a quarter sized model, so this is
a quarter sized me.
I'd like to be this weight, not this height.
So you start at the top.
This is a four metre antenna.
It was also designed for radar, so this is the composite
infrared spectrophotometer.
This is the ultraviolet spectrophotometer.
This is the VIMS, visual and infrared, and these
are the imaging cameras, the narrow angle and wide
angle, that are used for the actual photos that you see.
So this is the ion and neutral mass spectrometer
that is the most important data that we're going to get in the last few
hours.
And here's part of the magnetometer instrument, and here's
the other half of the magnetometer instrument.
The trick is...
The reason you want to put it out on a
boom is you do not want to measure the magnetic field of the
spacecraft.
You want to measure the magnetic field of Saturn, or
whatever you're at at the time.
Let's see.
That's the nuclear battery.
I actually sat inside this part during
the build, so when I close my eyes and think of Cassini, I actually see
the wiring inside the spacecraft and the things
switching on and off, and
when it goes in, that's what I'm going to see in my mind is the
aluminium melting on the structure.
I just never thought it would happen.
And now it is.
So now we're headed back up to the first floor to my office.
Cassini divides its time between gathering
data, which it stores on
its internal memory, and then sending it back home.
A typical day, we're out taking pictures,
collecting data, storing it on the solid-state recorder,
and then we'll turn back to Earth and we'll play it
back for nine hours.
We only have four gigabits of data that we can
load up, and it takes nine plus hours to play that data back.
For nine hours at a time, up to six times a week, Cassini sends its
precious images of Saturn on the billion mile
journey back to Earth.
Our fascination with Saturn stretches back to the very first
images that revealed it as a planet like no other.
It was here at the Paris Observatory that Giovanni
Cassini, after whom the spacecraft is named, first observed the main
division in the rings.
Astronomer Pascal Descamps has set up this
telescope to mimic the view seen by Cassini.
This view may seem blurry and indistinct, but it was a
dramatic improvement from the dot of light seen with the naked eye.
And it was enough to allow Cassini to
spot that the rings were not a solid disc.
And it's the nature of these rings that has driven scientists
ever since.
In the 342 years since Giovanni Cassini's blurry but historic
image, our view has improved dramatically, largely thanks
to spacecraft Cassini.
And there is one image from Cassini that may have
done more than any other to alter our perception
of our own place in the solar system.
This, of course, is something I'll be boasting about
for the rest of my days.
It's something I call the day the Earth smiled.
And it is taken when the sun is behind Saturn.
This, of course, you can't do from the surface of the
Earth.
We're on the other side of Saturn in this picture.
But if you look really close over the shoulder
of Saturn, between the E ring and the G ring,
you can see our own planet Earth, a billion miles in the distance.
We have cleared the tower.
And the Cassini spacecraft is on its way to Saturn.
So what does it take to get a spacecraft the size of a bus
with 12 delicate instruments all the way to Saturn and to keep
operating for 20 years?
And the solid rocket boosters have been jettisoned.
So we'll go into the dark room.
Inside the dark room, the mission support
area is where the whole flight team gathers for critical events
like the final plunge, launch, or orbit insertion.
It took seven years to get to Saturn, a spiralling journey that
involved four gravity assists,
close flybys past planets that boost the speed like a slingshot.
It's a flight path designed by head of navigation Duane Roth.
We had a Titan 4B.
Titan 4B.
So that was to get us away from the Earth,
and it still wasn't quite enough to get
all the way to Saturn, so we
had two Venus flybys, gravity assists, from
each of those, an Earth
gravity assist, and finally we had a Jupiter gravity assist,
and that got us to Saturn.
But credit where credit is due.
We built on Galileo.
Galileo built on gravity assists and every mission has
taken it to a new level.
Once Cassini was approaching Saturn, it had to perform possibly
its most critical manoeuvre of the mission.
A perfectly timed engine burn that would slow it down enough
to be captured in orbit by the giant planet.
Saturn orbit insertion was obviously incredibly nerve-racking.
We spent seven years guiding the spacecraft to get to Saturn
to get it into orbit.
If it hadn't done the orbit insertion, which was a 90
minute burn on the main engine, if we hadn't done that,
we'd have been a Saturn flyby, and gone on out
into space.
During its 13 year stay, Cassini has revealed Saturn is a unique
jewel in the solar system, a gas giant with swirling storms,
a dancing, sprinkling of moons, and
surrounded by bright, but paper-thin rings of ice.
What really gives Saturn its enormous cosmic reach are the rings.
We're not used to seeing this vast sheet of icy debris really
looking so incredibly flat, you are thinking it can't
possibly be natural.
The origin of the rings is still a mystery,
as is the complex gravitational interplay between rings,
moons and planet.
So this is one of those discoveries we made that really
threw us for a loop.
This is the outer edge of the B ring and these, as you can see,
are spiky shadows that are created by these features here
that are sticking up two and a half miles.
Two and a half miles above a sheet of debris that is 30 feet thick.
It is just extraordinary.
It is out of science fiction.
That's what this whole mission has been.
But hidden in the images from Cassini are clues
to the formation of this complex and dynamic system.
And even the birth of a moon from that impossibly thin disk of ice.
Well, we know the rings of Saturn are made of ice.
This is a really solid block of ice here, but this is not the sort
of ice the rings are made of.
Carl Murray is part of the imaging team, trying to work out how rings
make moons and moons make rings.
These sort of things are more like fluffy ice,
so it's really the difference between a snowball and a hailstone.
So this would be like a hailstone but if you kind of break it up,
you start to get more of a flavour for what the ring particles might
actually be made of.
And the fluffy nature of the ice kick-starts the process of clumping.
So if the ice is fluffy, the particles perhaps
are more likely to coalesce, rather than to break up
or to bounce off each other, because there's more surface area
for the particles to stick.
Eventually, gravity can take over.
And a moon can be born.
It's a process that Carl believes could still be going on today.
And there is one image from Cassini that could be showing a moon
at the very moment of birth.
When the image came back, I remember looking at it
and seeing something very odd.
There's something right at the edge of the A ring,
a little kind of bump that's maybe 2,000 kilometres in size,
so it can't possibly be solid, because a moon that size right
in the rings would just totally disrupt the rings,
so maybe this is an example of a moon that has just formed.
When I found the object it was my mother in law's 88th birthday,
and so this is just a purely informal nickname, but her name
is Peggy, so we just decided to call the object Peggy.
If Peggy is indeed a new moon being born, it will eventually fly
the nest and migrate away from the rings, joining its sisters
in flight around Saturn.
And it's the moons of Saturn, rather than the planet itself,
that have offered up many of the most
incredible surprises and mysteries to be solved.
So on Earth, of course, we are in love with our
moon, our single moon.
It has become an object in literature and in poetry and so on.
But Saturn has 62 of them.
They're incredibly diverse, ranging in size from a few hundred
metres to bigger than the planet Mercury.
This moon... This was so much fun.
Iapetus.
Iapetus is the two toned moon.
Half of it is as dark as dark gets, and the other half is bright as snow
due to the fact that it actually is passing through a cloud of debris
that is coming off Phoebe.
And look at this.
It looks like a Dalmatian dog, you know.
And this is another crazy moon.
I mean, good grief.
Saturn should win the award for crazy moons, because this
is Hyperion, and it looks like a sponge.
And this is Mimas, our Death Star moon.
But out of all these moons, the two standouts are Titan
and then Enceladus.
Before Cassini's intrepid voyage, our best view of Titan
was as an orange, foggy blob.
Titan was so mysterious to us before we got there.
At first sight, it may not look like much, but it
appears through the fog, and an astonishing world
is revealed, a world that surprised everyone.
We hadn't let our imaginations go as wild as nature turned out to be.
The revelations about Titan began on December the 24th, 2004,
when Cassini dropped a passenger.
The European-built Huygens probe.
The Huygens deploy, we actually did that on Christmas Eve in here.
It was the last year my father was alive, and this was a really
important thing for him, so he was able to sit up
in the balcony and see his daughter say, you know, "Release the probe."
Huygens was designed as a descent module.
Go through the atmosphere and tell us everything we can
find out about this, this sister to our own atmosphere.
Planetologist Athene Coustenis has been with the mission
since the beginning.
And as Huygens fell through the orange atmosphere,
she was at mission control in Germany alongside
astrobiologist Francois Raulin, waiting anxiously for news
from Huygens to find out if it survived the descent.
We were all in a big room, waiting anxiously and suddenly
on the screen is the first picture.
I remember telling my colleagues, "Please remove this image of Mars,"
this photograph of Mars here.
"We're waiting for Titan."
So I was thinking just for a few seconds that it was a joke
from these guys who just wanted to make us happy.
And then someone said, "It's Titan."
"No... It's Titan!"
We can see the pebbles on the ground.
We can see the surface.
And we knew it was not a joke because we saw
some very round rocks, pebbles, that we don't see on Mars.
And just looking at that, it was clear that there was some
liquids which were flowing here to make...
To be able to round those rocks.
And we're there and the probe is taking images continuously
of the same spot.
The parachute goes right above and so we can see
the shadow of the parachute.
So if there was anything living system, like a penguin,
we could have seen him.
That was the first image they saw, but the best was yet to come.
Huygens was busy gathering valuable data throughout the two
and a half hour descent through the orange gloom.
They were taking images on the way down and the Huygens probe spun
and finally they broke through the clouds and they got
into the clear region of the atmosphere and they could
actually see the surface clearly.
These are actual images taken during the descent,
joined into a seamless film, together with a recording made
by Huygens of the sound of Titan's orange atmosphere.
This was the first time that we were able to land softly
in the outer solar system.
Technologically speaking, it is a great achievement,
but scientifically speaking, it brings us a lot of data.
We have now a new vision of Titan that we didn't get before.
And we started seeing channels carved through the hills and we have
this very dark area in the middle that eventually we
identified as a dry lake.
Nothing of what we had imagined came close to the reality.
Long after Huygens was tasting the atmosphere and taking
snaps of the surface, Cassini continued to
explore Titan far above.
We went by Titan over 125 times.
Each flyby needs to be incredibly precise, and to prepare for them,
Julie has a simulation of Cassini and the universe around it.
Hello.
The integrated test laboratory.
This stuff is 25 years old.
It was built in the early '90s.
State-of-the-art at the time.
All of these racks here and all of the racks over here are how
we simulate the universe.
Cassini is in there.
Those are the star cameras and the computers are back in the back.
That's real flight equipment.
A real-time absolute time.
She uses the mock-up to anticipate every eventuality
and rehearse every minute.
We must have run 10,000 simulations.
When you fly spacecraft, you have to learn how to fly them.
So the first two or three years were the most difficult,
because you're kind of learning how...
What makes the personality of the spacecraft.
Cassini was originally intended to orbit Saturn for just four years.
But the mission has been so successful, it's
been extended twice.
Right in here, some of this was in the Equinox
mission 2007, 2008.
By the end of the mission, it will have done a total of 293 orbits,
covering every corner of the system.
So it should be right at the beginning again?
So you're going to hit 1044, you're in the last 20 minutes.
Careful planning and endless simulations by Julie and her team
have kept Cassini in full working order even after 20 years in space.
Engineers are somewhat superstitious in that we believe
that if we practice it, if we practice the worst-case
scenario, it won't happen.
I didn't change anything.
There's engineers and there's scientists,
and we are the engineers.
So scientists like to constantly be surprised, right?
They like new data.
They like to say, "Oh, I don't know what this means."
I don't know... That can't.
"There's something new."
Engineers do not like to be surprised.
And Cassini didn't disappoint the scientists.
It delivered plenty of mystery and surprise.
One particular puzzle is that they were expecting to find
large bodies of liquid methane on Titan's surface that
would feed the atmosphere.
But after four years, not a drop.
And then it got even more perplexing
when the radar team on Cassini returned evidence of dunes.
I mean, talk about wild and unexpected.
These are dune fields which are enormous.
They are several kilometres apart.
They are 100 metres high.
And they go on and on for hundreds of kilometres and in all of these
dark areas that you see, it's covered with dunes.
At first sight, these dunes look remarkably like the very largest
dunes found on Earth.
But a more careful investigation reveals some very
crucial differences.
So one of the biggest mysteries in terms of Titan dune science
is that they appear to be oriented in the wrong direction.
The sand on Titan's dunes doesn't blow in the prevailing wind.
And the dunes seem to be resistant to all but the very
strongest of storms.
Joshua Mendez Harper and George McDonald have been
trying to work out what's so special about Titan's sand.
One idea is that these dunes are cohesive or sticky,
that the grains that make up these dunes somehow keep together.
The question is, OK, if these dunes are sticky,
what's causing them to be sticky?
The answer seems to lie in the difference between Earth
sand and Titan sand.
So Earth sand like you find on this beach is mainly
bits of ground up rock, ground up seashells.
That's broken down by a process of erosion.
And our Earth sand is free-flowing.
If you want to make it sticky, you need to add water
to help it clump together.
But on Titan, the sand comes not from rocks or shellfish,
but from Titan's exotic atmosphere.
Ultimately, it must be coming from the hydrogen and carbon
that is stored in the atmosphere, so you're
basically making sand from something that is raining out
from the atmosphere.
Titan sand is thought to be made of hydrocarbons,
similar in make-up to plastic.
In their experiments, Josh and George compared Earth sand,
which flows freely, with polystyrene beads, standing in for Titan sand.
And if your sand is made from something similar
to polystyrene beads, it can easily build up
a charge of static electricity,
which makes it sticky.
So on Titan, when these winds blow, these hydrocarbon grain particles
rub against each other and charge frictionally, and so when you do
that, things tend to clump together.
The forces are strong.
It does provide that stickiness.
Which, as well as making Titan the best place in the solar system
to build sand castles, makes Titan's dunes so strong,
stable, and resistant to all but the biggest storms.
Titan was proving more mysterious than anyone imagined.
And the search was still on for the elusive surface liquid.
One day, nearly five years after man landed,
one of Cassini's instruments spotted something shining through the haze.
That is basically the sun glinting off the sea of Kraken Mare.
Doesn't that just make you want to go on vacation around
the shores of Kraken Mare?
Kraken Mare, the first alien sea ever discovered.
And Cassini soon found a host of seas and lakes
at Titan's North Pole.
I mean, this could be Earth.
Finally Cassini had found the surface liquid that
everyone was expecting.
In many ways, this lake is much like what we would find
on Titan, but in other ways, it is very different.
First of all, on Titan, the liquid is not water.
It's liquid methane, because the temperatures are so cold
that methane cannot be a gas.
It's a liquid.
The sky would not be blue.
It would be kind of a deep orange.
There's a lot of haze in the atmosphere.
We might be able to gaze through the haze and see Saturn off
in the distance with its rings.
Planetary scientist Jani Radebaugh is looking at the parallels
between the two worlds.
The mountains surrounding this lake are made of rock, but on Titan,
even though the mountains would look very similar, they wouldn't be quite
as tall, but they would be heavily eroded, they would have river
channels, and they are made of water ice.
And on Titan, ice is so cold that it is a solid rock.
Just as the Earth has a liquid cycle, where water changes
from clouds to rain, to rivers, lakes, and seas,
so Titan has one too, with methane taking the place of water.
This methane actually follows exactly the same cycle
that water has on Earth, evaporating from the oceans,
getting into the atmosphere, making clouds, clouds of methane
on Titan, falling through the atmosphere in the form of rain,
rain of methane on Titan.
But all of this is exactly the same processes we have on Earth,
but with completely different materials.
And with surface liquid, you find places with special significance.
The meeting point between solid, gas, and liquid.
A beach.
We're thinking more and more about the importance of beaches
as a possible cradle for life on the Earth.
What's so vital about the beach is you have this space
where there is liquid interacting with solid materials,
important building blocks, and the atmosphere.
All three of those things can exist, coexist, on a beach.
Those things together basically enable the right kind of chemistry,
the right chemical conditions, that may lead to life.
Tons of larvae.
Stinky!
Life on Titan's beaches is extremely unlikely.
But it offers a window into some early pre-life
processes on our own planet.
So all those processes which were present here
on the early Earth are here on Titan, and since we
have no way to go back
to what was going on on the Earth four million years ago,
we have here a place where we can study those processes right now.
Cassini had one more secret to reveal about Titan,
a secret buried deep inside.
Mission scientists had conceived an experiment that would allow them
to probe the interior of the moon.
Our main goal is the determination of what is inside Saturn's moons.
To determine what's inside requires measurements which are indirect.
Unable to look directly inside Titan, Luciano less has
to make do with the tools available.
What he has is a fast spacecraft moving past a colossal object.
Cassini is flying according to the laws of celestial
mechanics, pulled by gravity.
The tool is essentially track the spacecraft,
see how it moves, how it accelerates, and measure
it very accurately.
The principal, in a sense, is very similar to that
of the speed camera.
46 kilometre per hour.
On Cassini, we are doing pretty much the same, however
it is done much more accurately because Cassini cooperates.
Luciano's cosmic speed gun uses signals that go all the way
to Cassini and back again.
What he's looking for are tiny changes in Cassini's speed,
brought about by fluctuations in the gravitational pull
of whatever it's flying past.
The speed measurements are so precise that Luciano is able
to work out the internal structure of a moon.
In the case of Titan, he found that the gravity
field changes depending where it is on its orbit.
Were Titan completely solid, Cassini wouldn't measure any change,
but Cassini did measure a change, and therefore the only
possible conclusion was that under the icy shell,
there must be a liquid water ocean.
Cassini and Huygens together lifted the veil of orange fog and revealed
Titan's treasure trove of secrets, a moon strangely Earthlike
and yet otherworldly.
But it was another moon that would offer up the most
profound discoveries.
The tiny ice moon Enceladus.
Cassini's revelations about Enceladus blew everyone away.
They emerged initially from an unexpected source,
from Cassini's sixth sense, its ability to sense
magnetic fields.
The magnetometer is an instrument run from London's Imperial College
by Michelle Dougherty.
This large boom here, which is 11 metres in length
on the main spacecraft, is where we put our instrument.
The prime role of the magnetometer is to measure the magnetic field
generated by Saturn to help probe the inner workings of the gas giant.
OK, so we're going to go into the Cassini room.
It has all of our data processing computers
in there and there's a direct link to JPL.
It's the way in which they send us our data.
For 20 years, data has been flowing from Cassini's magnetometer
a billion miles away via the Jet Propulsion Laboratory
into this small room in London.
Coming in the back is the direct link to JPL.
It's the reason we're behind closed doors.
If the door's left open for more than a minute,
an alarm goes off at JPL.
Early in 2005, a stream of data arrived to these cables that
would radically change the entire mission.
In 2005, there were three planned flybys of Enceladus.
The first flyby took place on the 17th of February,
and it was a distant flyby, 1,000 kilometres above the surface.
For the magnetometer team, this was a prospect no more exciting
than any routine day's worth of data.
So how's that?
It took me 24 hours to look at the data.
I didn't expect to see anything.
But hidden in the graphs was the tiniest of glitches.
You can see, there's a little pimple in the data just over there,
an anomalous signature.
When I first looked at the data, I thought, "I know the spacecraft"
is moving really quickly.
Maybe we haven't got the trajectory right.
"Maybe that's why we're seeing this funny signature on the data."
This strange signature seemed to suggest that something
on or near Enceladus was somehow blocking the magnetic
field of Saturn.
It's almost as if Enceladus is acting as a much bigger obstacle
than its physical size.
One of the ways you can do that is if you've got an atmosphere.
The other thing we noticed is there was a lot of noise
in the data on either side, and what we were able to do
is calculate what ions were generating those waves,
and it was water group ions.
It seemed to suggest that there was some kind
of atmosphere around the moon.
An atmosphere of water that no one had anticipated being there.
A second flyby a month later confirmed the results.
One of the reasons we waited for the second flyby
is it was really weird to see that there was potentially
an atmosphere on the first flight, because Enceladus is small,
so the implication was there was something generating the atmosphere,
so this was a real surprise.
That's why I so wary about saying anything until we'd
had the second flyby.
Just to make sure.
Because, you know, you don't want to make a fool of yourself.
Michelle and her team decided it was time to alert
the rest of the mission.
We knew for us to be able to have a chance of really seeing
what was going on on Enceladus, we needed to get close.
And so we made the decision that I would go out to JPL and try
and persuade the project to take us really close.
And so, armed with her anomalies, Michelle made
the journey to Pasadena.
I went out to JPL.
I went to get a coffee, because I was jet-lagged to hell.
And I was standing in the coffee line, and the man in the line
in front of me, Jerry Jones, was responsible for essentially
driving the spacecraft.
He said to me, "What are you doing here?"
And I told him what we'd seen, and I said I wanted to try
and get us really close, and he smiled at me and he said,
"I've always wanted to go closer to a planetary body
than anybody else."
So I thought, OK, Jerry was onside.
So I went into the meeting feeling slightly more confident.
It took a lot of discussion.
Not everyone was supportive.
Some of the teams would then lose some data
because some of the planned
observations of Enceladus would have to change, but the project talked
about it and they then decided we would go much closer
on the third flyby.
The principal investigator of the magnetometer, God bless her,
she went into action and convinced the project to take the spacecraft
close to the South Pole so we could all get a better look.
And I must confess, I didn't sleep for two or three nights
before that close flyby, because if we hadn't seen anything,
no one would ever have believed anything I said again.
So... But what we found was spectacular.
When Cassini returned to Enceladus in July 2005,
it passed just over 100 miles from the moon.
What it saw thrilled everyone.
We finally got to see the South pole of Enceladus, and here it is.
It's crisscrossed by these major fractures.
Nicknamed the tiger stripes, Cassini found that these fractures
were radiating heat.
Heat?
I mean, who expected the South Pole of Enceladus to be hot?
And what we found was instead of the atmosphere covering
the entire surface, it was just focused at the South Pole.
And that's not all.
Pouring out of the tiger stripes were giant geyser-like jets,
spewing water vapour and ice particles from the cracks
in the ice crust.
This image made me nearly fall off my chair because here we see
dozens of jets, big and small, coming off the south polar region.
Whoa!
That's spectacular.
That was amazing.
And think, on Enceladus, it goes 700 kilometres into space.
And the discovery of the plumes has revealed the origin
of Saturn's outermost ring, a ghostly ring called the E ring.
Something like maybe 200 kilograms per second of predominantly water
ice is thrown out into space.
Some probably comes down as snow, so it probably snows on Enceladus,
but a lot of it actually escapes, and so what it does is form a ring
and that's the E ring.
This is where a moon makes its ring.
The question was where was the water coming from?
Luciano less soon commandeered Cassini to do some gravity flybys,
so he could get his cosmic speed gun out and look inside Enceladus.
We have been able to determine that there is a large
water pocket or sea, deep sea, under the South
pole of Enceladus.
It's about the size of Lake Superior in North America.
Just like its big sister Titan, Enceladus had joined
the under ocean club, and many more visits were planned.
The closest flyby was within 16 miles of the surface.
By the time we did that one, we were very confident.
So we flew in on thrusters because we didn't know
what Enceladus would do to us.
And then you were getting like one thruster pulse.
In the process of getting good at it, they used
up all the propellant!
They didn't have much choice.
But no, I think they've been very good at it for a long time.
It's just that now some of these flybys are just
exquisitely accurate.
So accurate, and so close, that Cassini was able to taste the spray.
And what it found raised an extraordinary possibility.
Cassini was able to go through the plumes and detected
the presence of organics in the plumes.
If you have plumes, that means you have energy.
So we have liquid water, we have a source of energy,
and we have the organics.
So we have the three ingredients essential for the emergence of life.
This is now one of the places in the solar system where people
think potentially life might have formed in the past or
might be able to form.
We have to go there and look for life next time.
I love this picture.
It's about as much meaning as you can get out of the Cassini
mission because we know that moon has an ocean in it that
could harbour life.
If life evolved in that sealed ocean, then it must have evolved
separately from life on our planet.
It would be a sign of a second Genesis.
I think that all we need to do is find that life has
independently arisen, just one other time.
And that would tell us that it's everywhere.
If it happened a second time, it probably has happened, you know,
a colossal number of times throughout the cosmos
and throughout its history.
But sadly, ironically, it was this greatest discovery
of Cassini's that ultimately sealed its fate.
After 20 years, the great explorer is running out of fuel.
And when the fuel is gone, so too is Nasa's ability
to steer the spacecraft.
We didn't want to lose control of Cassini and have it crash
on the surface of Enceladus.
If this happens, there is a chance that we contaminate the ocean.
If you discovered life there one day, there might be those
doubters who would say yes, but a spacecraft crash landed
and took bacteria there.
And so the mission team decided to use the last drops of fuel to set
Cassini on a final phase that would take it closer
and closer to Saturn.
Before plunging into the planet and being destroyed.
A phase Nasa called the Grand Finale.
Cassini's station is currently looking towards...
In April 2017 many of Cassini's mission scientists gathered
at Nasa's JPL to witness the beginning of the end.
There is a real buzz here of excitement and, you know,
slight nerves as well.
The reason it's so exciting is this is the start
of the end of the mission.
We're running out of fuel and we are going to make sure we go
out with as much great science as we can.
The Grand Finale began with a hair-raising
dive through the gaps
between the rings and the cloud tops of the planet.
It's risky, but with the mission coming to an end, the team
could afford to take risks that would previously have
been unthinkable.
And send the spacecraft exploring closer to Saturn than ever before.
We are actually travelling with the high gain antenna pointing
the direction of travel and that will protect the spacecraft
and most of the instruments from any dust in the rings.
Using the antenna as a shield may help minimise the risk.
But it also meant Cassini couldn't communicate with Earth
during the manoeuvre.
And the mission team had to wait to see if it survived.
We are just waiting for the data...
It was worth the risk.
Because flying inside the rings would allow the team
to explore enduring mysteries, such as the mass and
the age of the rings.
The exact length of Saturn's day and, in its final moments,
the actual composition of the atmosphere.
I can confirm playback is locked and starting to run.
The green spike was the first sign that Cassini survived the dive.
And was now sending data back to Earth.
Oh!
Well, we saw the signal back from Cassini, it's safe
and it's sending data back.
So it's the answer that we wanted.
I'm so relieved.
The Grand Finale consists of 22 of these hair-raising dives
between the rings and the planet, before the final plunge
into Saturn's atmosphere.
We have a bonanza of science ahead of us in the Grand Finale,
we are flying in a place no spacecraft has flown before.
And we're going to get back new science, because we are closer
to Saturn than we have ever been before.
So who knows what surprises might await us in these final orbits.
It could be we will find things right now we can't even imagine.
From this unique vantage point, Cassini has already sent back these
images of the atmosphere.
Taken on the very first dive.
Merged here into a slice of Saturn, taken from closer than ever before.
Analysing images such as these will keep scientists busy for years.
And this.
The first-ever series of images showing the rings
from the inside, looking out.
It's coming in right now.
We are at about two hours before the plunge.
Critically, for those very final moments of the mission,
Julie must ensure that Cassini is able to collect and transmit data
until its dying breath.
So what my team is doing right now is simulating the last four
hours of Cassini's life.
We have cleared off the solid state recorders, we have dumped
down all the pictures.
All we are doing is as much real-time data as we can.
Data can only be sent as long as the antenna is pointing
precisely at the earth.
Something that will get increasingly difficult as Cassini starts to be
buffeted by Saturn's atmosphere.
So what we do is we let the spacecraft go until it hits
the two milliradian dead ban and then it fires
a thruster to push it back.
And then we let it drift over to the other side.
So it's called bang-bang controlling.
It doesn't know it's in trouble yet.
Right now they're firing once every, you know, minute or so.
And then as they get into the atmosphere,
they'll start firing more and more and more in the last few minutes.
And what we want to see is we want to see how much
of the atmosphere we can see before we lose the signal.
Before it can't fight the atmosphere any more and it goes off point.
And then at that point it starts to burn up.
It goes from 200 to 2000 degrees in just a matter of seconds.
And then everything will start to melt and disintegrate.
And then it'll go away.
It just will lose the signal and that'll be end of mission.
So pretty much everybody will know at the same time,
the end of mission.
Because we will all see the carrier signal go away.
So after the best part of three decades, it's nearly
time to say goodbye.
My navigation team will be sitting up here.
I will be in Pasadena together with my colleagues.
It will be a pretty emotional moment because I wrote my
proposal to Nasa in 1989.
And back here, radio science is going to be one
of the most critical positions.
Because they'll have the open loop receivers and they'll be
the very last signal.
September 15, I will be in Pasadena.
There will be a big festivity, we say in French.
Everybody will be watching the spacecraft, making sure that
we're getting all the data.
Cassini's going to be getting and transmitting
data to its last breath.
On the 15th of September I'll be at JPL.
This will have a cast of thousands.
Every seat will be taken.
I'm going to cry my eyes out.
I cried when it launched.
I will be out in Pasadena.
I have worked on it from the '90s.
I've spent 20 years of my life on this.
It's really difficult to believe it's all coming to an end.
Because this will be 27 years I've worked on the project.
I'm going to be with everybody else at JPL.
Project manager, I usually like to sit next to Earl.
So Earl will be here.
I'm in the flight director's seat.
And I don't know, I don't know if I'm going to erupt into tears.
Am I going to clap, am I going to feel, job well done.
Oh no, I think, I think there will be a few of us, well most
of us are going to be rather upset.
Flight director, everything is up.
Copy.
Spacecraft has just crossed 10 degrees north latitude.
Altitude 1000 miles.
In its final, fatal kiss, Cassini touched Saturn's atmosphere
and then began to burn up.
We are in the atmosphere.
Becoming part of the very planet it had got to know so well.
At exactly 4:55 and 46 seconds, on Friday the 15th of September,
the signal disappeared.
That would be the end of the spacecraft.
Project manager, off the net.
And Cassini, unquestionably one of our most successful
missions into space, came to a final, spectacular end.
It's a 20 year old friend.
I can't imagine anything topping that.
But we will try for a new mission.
It's always that way, it's like a death in the family.
You know, it is imminent, but when it happens,
it's the finality of it that really is what you're left with.
Cheers, Cassini.
Cassini may be gone, but its revelations will continue.
Results are already starting to emerge from the Grand Finale orbits.
We have found out some things.
We have got some hints of other things from the Grand Finale orbit.
Cassini revealed really a surprising picture, something
that we did not expect, really revolutionary
results I think.
One of the things that we can probably say is that the rings
didn't form together with Saturn.
And we could be a step closer to discovering
the length of Saturn's day, by pinning down the mysterious tilt
of its magnetic field.
If there is a tilt, it is really small.
But we need to find that tilt if we're going to work out how
long a day on Saturn is.
I would think we would probably have a final answer
in three to six months.
It is mission accomplished.
And for us it was a long, long mission.
It was totally appropriate that it was slightly raining
here as we walked out.
Because you know, I think even the earth is crying right now.
That was a great spacecraft, it did exactly what we asked it to do.
All the way to the end.
No surprises.
And the legacy of Cassini looks set to continue,
long into the future.
Scientists will be poring over our images and all the data
from Cassini for, I mean it, 100 years.
We have got this amazing amount of information to pass
on to future generations.
We have only skimmed the surface of what's in that data.
Godspeed.
You know, been a great spacecraft, a great programme.
You know, thank it and release it.
In its dying hours, Cassini left us with these, its final pictures.
And this, its last ever image.
There's a completely different world.
And you end up in just dark corners.
Blind spots, without witnesses. That's where your murder comes from.
A lot of detectives tell you they are seekers of the truth.