Original subtitles

(dramatic music)

It's the truly beautiful, majestic planet.

Saturn just makes us gasp at its beauty.

The Saturnian system is an absolute wonderland.

Saturn, second largest of the planets,

nearly 800 times the volume of Earth, a true gas giant,

adorned by and adored for its mysterious, captivating rings.

The study of Saturn's rings has inspired

great theoretical musings for centuries.

Almost 300,000 kilometers in diameter,

the ring system is just 20 meters thick.

The rings capture the imagination

to the point you have to understand where they came from

and what do they mean?

To try and answer these questions,

humans designed, built, and launched

some of the most advanced spacecraft ever conceived.

It was and is the largest outerplanetary spacecraft

that's ever been built.

This is a massive piece of machinery.

This is the story of the exploration of Saturn,

its rings and moons, told by those who dared to do it,

a place that turns out to be much more

than just a celestial beauty spot.

The building blocks of life could form

in the interiors of these icy bodies.

The kind of conditions we see

are probably present on tens of billions

of environments across the Milky Way.

Saturn could hold the key

to understanding our true place in the universe.

It's definitely the most

interesting place in the solar system.

(title resonates)

To the naked eye, the night sky

is filled with points of light.

Zoom into almost all of them and they remain just that:

shining points in a dark universe.

But one celestial object revealed

to an Italian polymath that it was special.

Galileo wasn't the inventor of the telescope,

but he was one of the first people to use it

for astronomical observations.

It was 1610 when Galileo first observed the Saturn system.

His drawing showed what were described

as ears or jug handles either side of the planet.

So Saturn's my face, it appeared that there

were these weird globes.

And so he thought well, these might be moons

but stuck one on each side of the planet Saturn.

He didn't know Newtonian mechanics, it hadn't been invented.

He didn't know that moons have to go

all away around a planet.

When he went back to look at Saturn

a couple of years later,

he noticed that those features had gone.

(spirited music)

Galileo even suggested that Saturn had eaten

his own children as in the ancient Greek myth,

and that's why the moons had disappeared.

Galileo lived in Italy, but he was aware

of other major figures in his time,

including Constantijn Huygens from the Netherlands,

and in fact it was Huygens' son, Christiaan Huygens,

who eventually solved the puzzle

that was posed by the disappearing handles of Saturn.

Christiaan Huygens turned his telescope towards Saturn.

As technology develops, optics developed,

and he was able to see more.

And what he saw meant that he was able

to come up with this radical idea

that Saturn was surrounded by a ring system,

and he was able to link back to what Galileo saw

because if the ring system was tilted

at an angle to our view from Earth,

it means that sometimes you'll see the rings tilted

and you'll see them sort of almost face-on,

and other times when the planet has moved,

they'll be edge-on.

So at particular times, we'd look at the rings edge-on

and they completely disappear.

In fact even today when Hubble,

the best optical telescope we have, looked at Saturn

across through the ring plane, the rings disappeared.

But not only that, Christiaan Huygens

made another amazing discovery:

that Saturn has a moon and it turns out

that this moon is a really curious place,

and is perhaps even more curious

than the rings of Saturn itself.

After the discovery by Huygens of Saturn's first moon,

Giovanni Domenico Cassini discovered

four more in the next decades,

and moons continued to be discovered

over the next few hundred years.

Mimas.

Enceladus.

Hyperion.

However, from the first there were

big questions posed by Saturn's rings.

What were the rings made of?

How did they arise?

What's the origin of the rings of Saturn?

And why does Saturn have rings and not the other planets?

The only way to answer that question

is to actually get up close, we need to go to Saturn.

But getting to planets in the outer solar system

obviously requires a huge amount of fuel,

but a large amount of fuel means

you have an expensive mission

because you're trying to launch a lot of mass into space

and you need more fuel to be able to do that.

So you start to think about, well,

what are the other ways that you

can accelerate your spacecraft

without requiring lots of fuel?

And one technique that's used

is what's called a gravitational assist.

(monitor beeping)

(inquisitive music)

As a spacecraft passes a planet

that is itself moving around the sun,

it would get dragged along

and accelerated by the planets during the encounter,

gaining extra speed like a skateboarder

briefly holding onto a passing car.

What's more, a huge opportunity suddenly presented itself.

It was discovered that the outer planets

would actually align in a way

that they hadn't since Thomas Jefferson had been president.

So we realized that you could fly past Jupiter,

get a kick, go to Saturn, get a kick,

go to Uranus, get a kick, go on to Neptune.

This gravity assist trajectory was called The Grand Tour.

And if we were gonna go and do this,

take advantage of this alignment,

we'd better get going and launch that spacecraft soon.

NASA quickly responded to the opportunity

by preparing some pathfinding spacecraft,

one that would go to Jupiter

and one that could use a gravity assist

from Jupiter to go on to Saturn.

And that was called Pioneer 11.

(spacecraft beeping)

(flames roaring)

The primary purpose of those Pioneers

was really to pave the way for later spacecraft.

And that mission was called Voyager.

(upbeat music)

And the Voyager mission had two components,

Voyager 1 and Voyager 2.

Each of them would get a gravity assist

from Jupiter to go on to Saturn.

But that's then where the missions deviated,

because Voyager 1 was given an extra special task.

It was to go and visit the moon

that Christiaan Huygens had discovered in 1655, Titan.

Titan would become almost

as important a destination as Saturn itself.

Titan is a really intriguing moon.

This is a massive moon,

probably not worthy of the word moon.

This is a body which is bigger than Mercury,

so it's a big moon.

Its mass is lower than that of Mercury,

but in terms of size, it's bigger than our smallest planet.

As we've been looking around the solar system,

many people have been fixated on Mars

as the place beyond the Earth most likely to hold life,

but there's another place in the solar system

which is probably just as exciting,

and for some people even more so, and that's Titan.

The atmosphere of Titan was hinted at a century ago

and confirmed in the 1940s.

It's the only satellite in the solar system

with a dense atmosphere.

In fact, its atmosphere is actually

denser than our atmosphere here on Earth.

Titan is the most interesting moon

in the solar system, hands-down.

But getting to Titan

meant a change of direction,

curtailing the exploration of the outer plants.

So Voyager 1 going off to visit Titan

meant that it was no longer able

to slingshot on to visit Uranus and Neptune.

If Voyager 1 had not been able

to achieve that objective for whatever reason,

Voyager 2 was going to be diverted to do that job

at the expense of going on to Uranus and Neptune.

(upbeat music)

But that's how they felt about Titan, the importance.

7-4-6-S-1-9.

15 seconds.

When Pioneer 11 eventually arrived at Saturn

six years after flying by Jupiter,

it was an immense, exciting moment.

Five, four, three, two, one.

We made it! (people cheering)

Hooray!

(intriguing music)

The rings of Saturn were big and beautiful in our pictures

and we stood in awe at the closeup views.

My task was to see if we might discover any new rings,

and amazingly, I watched the first images

appear on the television screen

and there was clearly a new ring of Saturn.

The rings of Saturn had originally

been named A, B, and C, in order

from the outermost known ring to the innermost,

but in the 20th century, we began to discover

new rings which were then assigned alphabetically

in the order of discovery, first the D Ring,

then the E Ring, so the next available letter was F,

and so I named that ring Ring F of Saturn.

(tense music)

Pioneer 11 passed Titan by quite a large distance,

couple hundred thousand miles away.

And really all it told us about Titan

was that it was very, very cold,

too cold for life as we know it to exist.

But actually we needed to go back

and look at this thing in much more detail.

Fortunately, two more spacecraft

were already on their way.

4-7-4-7-4-6-U-S-4-9.

The Pioneers had told us it was safe,

it's okay, we can go there.

(triumphant music)

So just a year later, Voyager 1,

equipped with better instruments and better cameras

was preparing to take a look at Saturn and its rings.

The encounter was an amazingly thrilling

and rapid experience,

all happened within a matter of a few days,

and even before you could explain

some of the new phenomena we saw,

Voyager was off on its way out of the solar system.

(people cheering) (people applauding)

Many people referred to that flood of data,

the camera pictures and other observations,

as like drinking from a fire hose.

The estimate is.

(people chattering)

(people cheering) (people applauding)

Do you guys have any questions?

After the Voyager flybys, we knew there were

thousands of rings, and it's that moment

that we stopped naming them with letters.

It was just impossible, exceeded the alphabet.

We saw waves propagating through the rings,

we saw the edges of the rings wiggling.

A ring could be maintained between two moons,

one outside the ring and one inside the ring.

And that's the beauty of this idea of moonlets

that are sitting within the rings,

shepherding the gravitational motion

of the particles within it.

(intriguing music) (people chattering)

Maybe it's a scientific prerequisite

to start with a simple idea,

but we had imagined the rings were ancient,

unchanging, and completely uniform,

and this picture of the rings was completely shattered.

The rings were changing in time, changing in space,

they're dynamically changing with waves

lapping across the rings, so this idea of symmetry,

of constant persistence of the rings,

all were immediately questioned.

(people chattering)

(inquisitive music)

But what was the origin of the rings?

Where did they come from?

When an object gets closer to the planet

it gets stretched out, and so a basketball might look

more like an American football under this stress.

The question is, can that stress

be withstood by the object?

For most competent objects, including humans,

we can withstand that stress.

For objects that are piles of rubble or dust

or are big, say larger than 50 or 100 kilometers,

they cannot withstand that force.

If a large moon had once strayed

too close to Saturn, this destructive force

would've been enough to tear it into tiny pieces.

So Saturn once had a moon,

say an object about the size of Titan,

if it were dragged in toward the planet by friction,

first the ice would shatter

and then later the core, which is made of metal,

would shatter or might even end up inside the planet,

and the pieces of ice formed a ring around Saturn.

And now the mission

turned to the prize that was worth

missing out Neptune and Uranus: Titan.

(tense music)

The scientific community and the public

watched with great interest as Voyager 1

made the first flyby of Titan.

What Voyager 1 encountered was still this mysterious veil.

There was an organic haze that encircled the surface

and you couldn't see the surface as a result.

That atmosphere is simultaneously

the bane of my research because it blocks the surface,

but it's also the reason why Titan is so interesting.

All of those hazes that mean that you and I

can't actually see the surface

with light that our eyes can see,

make Titan this organic chemistry wonderland.

One of the other things we figured out was that there was

methane present in the atmosphere of Titan.

Now this is important because

both pressure and temperature measurements

that Voyager 1 took indicated that

it gets incredibly close to the triple point of methane.

This opened the really, really tantalizing possibility

for lakes and oceans on the surface.

Some people think if we look in these methane lakes,

perhaps we'll find a different way of organizing matter,

a different way of organizing life.

(monkey calls)

Titan was still hiding all its mysteries from us,

so that laid down the gauntlet of the challenge.

We must now go to the surface of Titan.

Fortunately, Voyager 1 made

excellent observations of Titan,

so thankfully Voyager 2 was allowed

to go on to the next planet, Uranus, and then to Neptune.

(triumphant music)

The Uranian rings had been discovered

from the ground om 1977,

Voyager itself discovered the ring of Jupiter in 1979,

and while we were on our way to the planet Uranus,

the rings of Neptune were also discovered.

So by the time the Voyager mission had completed,

we knew that all of the giant planets had rings,

just the opposite of what the question had been

before those missions of why only Saturn has rings,

but leaving us with deeper questions about Saturn's rings.

What were they made of?

How old were they?

And why are Saturn's rings so particularly different,

so big and so bright compared to

the narrower, less massive, darker rings

of Jupiter, Uranus, and Neptune?

The rapid flybys that Voyager provided were insufficient

to answer these questions in more detail,

but then those failings could be addressed

by a mission that went into orbit around Saturn

and stayed for many years.

(people chattering)

We already knew that the value of orbiting a system

and the amount of understanding you can gain

by being there for a long period of time

is so amazing that the next step

was clearly gonna be an orbital mission.

And if we're going to send another mission to Saturn

that stays there, it should have a part of it

that lands on the surface of Titan.

Planning began in 1982

for a mission that will be more ambitious and advanced

than anything that had gone before,

a mission called Cassini Huygens.

The spacecraft was about the size of a school bus.

If you saw it when they were putting it together,

it was pretty impressive, you just looked up.

It was a monster.

It was and is the largest outerplanetary spacecraft

that's ever been built, and may,

in my lifetime, ever be built.

Pressures are excellent.

T plus 20 seconds.

The mission was a collaboration

with the European Space Agency,

who designed and built a lander called Huygens.

And this was the vehicle to take us

down through the clouds, down to the surface of Titan.

(dramatic music)

The Huygens probe was actually

designed to be able to float in liquid

as well as land on a solid surface

because we didn't know at the time whether it was going to

land in a liquid or on a solid surface.

So we designed the mission to cope

with as many characteristics as possible.

No one's ever tried to measure the depths of an ocean

and how hard a rock is

depending on which one you're gonna land on.

We knew from Hubble images that there

probably wasn't a global ocean,

but whether there were other liquids was still not known.

Huygens' team had to prepare for that

but also a very hard landing, or maybe you can imagine

a very squish surface full of organic goop.

(liquid gurgling)

20 seconds and counting.

This is Titan Launch Control.

Without any doubt, the most risky element

of any space mission is the launch.

T minus 15 seconds.

It was a nighttime launch, so you had to get on the bus

something like two in the morning or something to go out,

and we did that, and we went out to the launch site,

and the first opportunity, the launch was scrubbed.

And so we did the same thing again two days later.

T minus 10.

When you've put eight years of your life

into designing and building and testing something

which is going to go into space--

Nine, eight, seven.

And then seeing on the top of a rocket

that's being vibrated on its way to Saturn,

it is quite a feeling.

One.

(explosion booms) (dramatic music)

When it did go off, it created a huge amount of light,

(flames crackling)

and then the rocket went behind the cloud.

When it went behind that cloud, it was very impressive.

The whole cloud lit up.

We all thought oh goodness, has something gone wrong?

United Station, our fly ring data.

And then the nose cone came out

and you were getting all, phew.

(inquisitive music)

(people chattering)

Wait, do I come?

Go ahead Aswar, come.

One of the things you have to do

when you arrive at a big planetary body

is slam the brakes on pretty quick.

You need to slow yourself down and get yourself into orbit.

You typically do this by going

very close to the planet to slow you down,

so you get captured by the gravitational pull of Saturn.

It was an incredibly complex sequence

that we had basically worked on for two years.

Even after Pioneer and Voyager, we didn't know enough

about the possible dangers of the Saturn system.

And because the Cassini spacecraft was moving

at about 10 miles per second,

even hitting a grain of sand or a chunk of ice

could be deadly to the spacecraft,

and so we took a number of ways to remove that risk,

(dramatic music)

and the best was to turn so that

the spacecraft antennae was facing forward.

The high-gain antennae, which is a thing

which communicates back to Earth,

was actually protecting it from

potentially being hit by dust particles,

so it couldn't be in communication with Earth at that time.

This was an incredibly nervous

and dangerous maneuver to do given the unknowns.

Once Cassini had crossed

the plane of Saturn's rings,

the spacecraft had to reorient itself again.

The thrusters had to be turned

so that they would point in the direction of motion

to be able to capture it into orbit.

During the 90 minutes

that Cassini's engines were firing,

the spacecraft was completely shielded from Earth.

At its closest approach, the spacecraft

was just 20,000 kilometers from the cloud tops of Saturn.

All the mission controllers on Earth could do was wait.

We all held our breath waiting for the signal to return.

But then we got a signal which was dead-on.

The doppler has landed.

And we knew at that moment we had

successfully gone into orbit, and there was a huge cheer.

(people cheering) (people applauding)

It was really a fist pump moment.

People were jumping up and hugging.

(people cheering) (people applauding)

I was watching it in the middle of the night

via the internet, and I must've went into a huge cheer

which woke everybody else up in the house.

When the burn was completed,

we knew we were in orbit, so we turned away from the Earth

and photographed the dark side of the rings

and then after we come back through

the ring plane crossing again,

we turn back to the Earth to start play back that data,

and those images I'll never forget them.

We've had much prettier images but my gosh,

to see the ripples and the structure in those rings,

it was absolutely, like I said, I'll never forget it.

(triumphant music)

It's one of those moments you'll take to your grave.

Cassini Huygens had arrived

at the Saturnian system, an enormous gas giant

with 82 moons at present count,

orbiting on the outside and within

the hundreds of rings of varying shades and colors.

We could now truly start to appreciate

the awesome beauty and complexity of this planetary system.

(gentle music)

From a mission engineer's point of view,

the rings are a hazard. (laughs)

But once we've discovered that the environment's safe,

then we can start to open up the stops a little bit

to allow more activity.

We knew that we'd have long, consecutive pieces of data

to test our theories, but we didn't realize

that because we could orbit Saturn hundreds of time,

the same aspect could be seen over multiple times

by all the 12 instruments,

and that hit us in the head sometimes.

Oh, this is something unexpected that's happening.

It's very easy to think of the system as isolated parts,

especially when you're working with a spacecraft mission

and you target this feature

and then you target the satellite.

Any speculation, any idea we had had from the years

between Voyager and Cassini, could now be tested.

And as for the origins of the rings and moons,

the Cassini team made a further discovery.

(dramatic music)

As we have seen quite clearly,

Saturn's rings are made out of ice,

which is the fragments of shattered icy moons.

But the alternate is also true.

Cassini showed us that the pieces of the ring

are sticking together to make new moons.

So the rings are collecting in places to make moons,

and the moons are being shattered to make new rings.

So this is sort of a cosmic recycling of material.

So not only are the rings of Saturn

most likely made of moons, but they also make new moons.

One of the best measurements that Cassini made

was to measure the total mass of the rings.

This determines how long this recycling process could go on.

The amount of pollution, the amount of meteoric dust,

the combination of those two facts

say that the rings are about 100 million years old.

This can be extended, perhaps, to a billion years or two,

but the current one is the rings

that the dinosaurs would've seen.

(dinosaur roars)

(gentle music)

(intriguing music)

If we were to look closely,

many of the ring particles would appear fluffy to your hand.

They're fairy castle structures sort of like snow.

You would see a range in particle sizes

continually colliding, but at a relatively low velocity,

maybe a millimeter a second,

which is gentle enough that the surfaces

might be slightly compressed.

But occasionally, particles will hit each other

at a much higher velocity, which will knock off

a spray of small particles of snow and ice

which eventually are recaptured by other clumps,

so the equilibrium, the balance between these two processes,

leads to a distribution of sizes from dust to mountains,

and each of the objects being like a pile of rubble

with a coating of snow on the top.

(inquisitive music)

After six months in orbit,

Cassini was scheduled to deploy the Huygens lander

on December the 25th, 2004.

We had Christmas dinner at my home

and had a lot of the European and American contingent

because we were all spending Christmas at JPL.

My whole family was here.

I made them come to JPL and they watched

as we released the probe that night.

(people chattering)

(people cheering) (people applauding)

A few days later we turned around

to take a picture of where the probe was supposed to be.

It's a little speck and it's not very exciting,

but it was a genuine confirmation

it was exactly where we thought it was going to be.

Because what happens with a probe

is essentially when you release it,

you've turned on a little three-week egg timer.

(dramatic music) (timer ticking)

Your worst nightmare is silence.

That's happened too many times to people in space missions

and it's just a punch in the gut.

But three weeks later, right on schedule,

we get the signal back.

When we arrive at Titan,

we're traveling at incredible speeds,

and what you gotta do is go from ballistic,

incredibly fast speeds at the top of the atmosphere

to zero speed at the bottom

of the atmosphere on the surface,

and this is pretty hard to do.

There are several elements in order

to get yourself down to the surface.

The first is a heat shield.

Titan has a huge atmosphere,

and Huygens was just screaming in.

And if we were to send the probe

in without protection, it will burn immediately.

So you have the sacrificial heat shield

in front of the probe, so the fireball that's created

as the probe slows down doesn't destroy the lander itself.

And in the case of Huygens,

the heat shield was made of many of those tile.

While the heat shield

was slowing the probe down,

Huygens experienced a deceleration of 15G.

Once it had got to an altitude of 170 kilometers

and was only traveling at a mere 400 meters per second,

Huygens deployed the first of its three parachutes.

The drogue parachute stabilized the probe

and pulled off the back cover,

which deployed the main parachute,

at which point the spent heat shield was discarded.

(clock ticking)

But Titan's atmosphere is so thick

that if we kept that parachute on,

the batteries would've run out before it got to the surface.

It was gonna go a little slowly.

So it actually deployed that parachute

and then dropped the last chute

which allowed it to descend at a more reasonable pace.

You get horizontal winds coming across

and swinging the probe about,

so as it descends through the atmosphere

it's not perfectly still, it's swinging like a pendulum.

The images from descent show channels on the surface

and there was no doubt, there were no questions,

it was obvious what we were seeing.

And it was just so spectacular to see something

and know what it was on the surface of Titan

and for it to be river channels.

(introspective music)

It then landed on the surface

and it started transmitting back to Cassini,

which was way up overhead.

The spacecraft, meanwhile, is flying over the top

and pointing at the point on

the surface of Titan where the probe is.

And eventually the spacecraft goes over the horizon.

The batteries were still going

even after we lost sight of it.

The spacecraft turned back

and started to play the data back.

Imaging guys turned around an image

of the surface very, very quickly.

(keyboard keys clacking)

And it flickered up on the screen.

And everybody looks up and goes,

"What's going on here?"

It was almost like it was fake.

To see something like that on a moon

in the outer solar system, it was just spectacular.

It still gives me goosebumps to think about

all of that working so well.

Seeing something that no human in history

had ever seen before, it was truly awe-inspiring.

It was a moment I will never, ever forget.

It was sitting on this flat lake bed

and the things that appeared as rocks in the background

were actually pebbles of ice that had been frozen.

Titan is an icy satellite.

Its bedrock is made of water ice.

But when we look at the surface of Titan

with the spectrometer, it's actually really hard

to find any pure water ice spectral signatures,

and I think that the key there

is all these atmospheric products

that are continually falling out across the surface.

Titan's atmosphere is actually

mostly nitrogen like Earth's atmosphere,

but it's cold in the outer solar system,

and the next most common constituent in the atmosphere

is methane, and methane in Titan's atmosphere

plays a role very much like water on Earth.

So the methane in the atmosphere

can condense to form clouds,

it can actually rain out onto the surface,

it can run across the surface in rivers,

form lakes and seas, and there may even be

methane aquifers in the subsurface as well.

So it really does have a complete hydrological cycle

where methane plays the role that water does on Earth.

Carl Sagan and his research partners, Khare and Thompson,

gave us a really interesting insight

by doing experiments where they mixed

nitrogen with methane and then provided

some free energy source, some light or some particles

(light booms)

to break them apart or to ionize them,

and it led to this incredible organic chemistry

that was beyond the wildest dreams,

created this stuff in the laboratory the called tholins.

The methane dissociates at the top of the atmosphere,

recombines to form very complex molecules,

and all of that material falls out onto the surface.

How long that process has been going on

is still not well understood,

but if Titan has had an atmosphere like it has today

for the entirety of the solar system,

that's going to produce a volume of sediments

that means that Titan's crust is not just water ice

but also has a bunch of organic sediments

that have been built up over time.

All of these organic materials have been

sitting around littering the surface of this moon

where there's the opportunity, potentially,

for them to have mixed with liquid water.

If you react water with these precursor molecules,

what's been demonstrated is these tholins

that have been studied in a lab can form amino acids.

And the universe provides us that mechanism

when impacts hit the surface of Titan,

(object whooshes) (impact booms)

because every impact has enough kinetic energy

to melt some of the crust.

The bigger your impacter, the more kinetic energy

you impart, and so the more melt you can generate.

And then based on how much melt you generate,

you have this pool of liquid in the near subsurface

that's going to cool slowly over time,

and based on the sizes of impact craters

that we've seen on Titan,

this can be anywhere from hundreds

to tens of thousands of years.

So we know that Titan has all the ingredients

necessary for life as we know it,

and it's been doing these chemistry experiments

for hundreds of millions of years.

You also have the opportunity for organic material

to mix with a different solvent

in the form of liquid methane,

and so perhaps there are other prebiotic systems on Titan

that have progressed that are completely alien

to the water-based biology we have on Earth.

It's hard to conceive how a methane-based

form of life would work, but nature has repeatedly

surprised us as demonstrated by all the findings

of the Cassini mission, so I'm not willing to rule out

the possibility of life in the liquid methane lakes.

I'm personally skeptical that we would find that.

There are some difficulties with that.

So for example long-chained carbon molecules,

organic molecules, tend not to dissolve very well

in liquid methane, they'll precipitate out.

So you could imagine an inverted structure almost

where because cells are a mixture

of insoluble and soluble parts,

it's possible it could work the other way around,

and I find it much more difficult

to conceive how that could work.

Certainly it would be very exotic

and at present we have no indications

in any of the current measurements

from the Cassini or Huygens part of the mission

that there's anything bizarre

that we might need to attribute to the activity of life.

But the only way to find out is to go and look,

and so you have with Titan this wonderful possibility

that we might find life as we know it

or we might find life as we don't know it.

In any case, just going to look around

will be a fantastic thing to do,

so what's not to like, really?

But as exciting as Titan was,

there were even more intriguing discoveries to be made.

When Cassini was approaching Saturn for the first time

at the end of 2003, our experiment,

the ultraviolet imagining spectrograph,

was systematically scanning

back and forth on the planet Saturn,

and we were amazed to discover

that the system was filled with molecules of oxygen,

and the oxygen was completely unexpected

and we mapped this out and we noticed

that the peak in the distribution

was just a distance four times Saturn's radius

from the center of the system.

We knew that the moon Enceladus

was orbiting just at that distance.

Enceladus is a tiny moon

just 500 kilometers in diameter

with a surface area slightly larger than Texas.

It coexists with one of Saturn's

fainter rings, the E Ring.

The E Ring is just a ring

of icy grains in the micron range.

It was tenuous enough ring that we could

fly through it and examine it.

We had these tentative ideas that maybe

there was a connection between the E Ring and Enceladus

because they were pretty co-located,

but we didn't really have any understanding

of how they were playing together.

Enceladus originally was on the itinerary,

but only marginally so.

It was another very interesting Saturn moon,

small, very shiny, very white, very bright,

but other than that too small to be interesting.

(dramatic music)

And it was in the first close flyby

that the magnetometer team detected

something interesting that they didn't expect.

The magnetic field instrument observed

that the magnetic field lines didn't quite

come down to the moon the way they should.

This significant deflection in the magnetic field

was extremely unexpected.

The magnetometer team said

it looks like it has an atmosphere.

Well, anybody that knows anything about moons

says that's too tiny, can't have an atmosphere,

it's way too small to hold onto anything.

A moon as small as Enceladus

has a tiny gravitational field,

far too week to hold onto an atmosphere.

What's more, the atmosphere that was there

didn't seem to be evenly spread out.

If you flew by the south pole

it looked like there was an atmosphere,

but if you flew by at the equator

you didn't see anything at all.

But then we went back again and again

and explored with more instruments

and then took some images,

and all of the sudden realized

that not only it had an atmosphere,

it was an icy atmosphere,

but it had these plumes coming out of the southern pole.

And here's water geysers on a tiny moon.

(intriguing music)

And that water that was coming out of

what we've later found out to be an interior ocean

was what was forming the E Ring.

We were able to measure the amount

of water in those plumes exactly enough

to explain the ring of oxygen around Saturn

that we had seen before that approach.

What an amazing development that the geysers

on the moon Enceladus are continually erupting

water molecules broken down by the sun

to form atoms of oxygen that we could see

even millions of miles away from the planet Saturn.

And as we flew through these plumes

coming out of the south pole, some of that plume material

was captured by the instrument.

And we used that to learn more

about the interior ocean chemistry.

Not only did it contain water vapor,

but it had traces of ammonia, methane, H2, CO2,

and then there was a whole host

of organic compounds that we could also see.

The experiment that we did here at Colorado

is very similar to that.

We didn't actually fly through the plume

but we watched a star set through the plume.

And now we can put all that information together

to get a picture of the shape of the eruption

and also the material that's being

erupted from inside of Enceladus,

and amazingly enough that material

has the basic building blocks of life.

We've been dominated as biologists

with a fixation on the idea that all life on Earth

is powered ultimately by the sun.

Any formation of life going on on Enceladus

is going to be happening beneath the icy crust

and the oceans underneath where we see

the same kind of hydrothermal vent systems

releasing hydrogen gas into the oceans there,

which we know for a fact would've

been present on the early Earth,

and they don't strictly require the sun.

We think based on the types of molecules

and other chemicals we're finding in the plume

that this process called serpentinization is happening.

Serpentinization is a geological process.

It's a fancy way of saying how

liquid water can react with rocks,

and serpentinization is thought to be

really important for supporting microorganisms

and the base of an ecosystem outside of these

hydrothermal vents because it makes abundant hydrogen,

and hydrogen is sort of like rocket fuel

for a microorganism, it's a great way

to have a food that can be burned to provide energy.

To me, Titan is less exciting than Enceladus

because Enceladus has oceans

with alkaline fluids from hydrothermal vents going into it,

and therefore it's exactly analogous

to how I think life started on Earth.

This says to me that would be a good place to go,

measure those plumes, maybe drill down

and see if there's any form of life there.

So Enceladus may have

just the right conditions for life

to get started far away from the sun,

and the evidence for its mysterious inner workings

can be seen in the enormous, diffuse E Ring.

This is just another case of how the moons make rings,

so by grinding of their surface,

which throws dust into orbit around the planet,

by erupting of geysers, or by shattering them to bits,

the moons are the parents of the rings that we see,

but also the children because the rings in some cases

can collect up to form new moons.

(whimsical music)

Cassini would spend

more than 13 years at the Saturnian system

and completely 294 orbits of the planet,

but eventually its fuel would run out.

Everything has to end, including Cassini.

(melancholic music)

We went through this amazing time

at the end of the mission,

ending up with orbits which went inside Saturn's rings,

but we knew at the end, of course,

that the idea was to actually

burn the spacecraft up in the atmosphere of Saturn,

and that's to avoid it hitting these

astrobiologically feasible places like Enceladus and Titan.

The last thing we would want to do

would be contaminate those with something sent from Earth.

You can go where you've never been before.

You can get science you will never have

any other opportunity of getting,

and you'll keep Enceladus safe.

No brainer. (laughs)

But the emotions were all over the map.

All good things must come to an end, (laughs) right?

Yes, it's sad in a way, but.

The spacecraft was oriented so it could

communicate with the deep space network here on Earth,

but then the other axis was set

so that the spacecraft could get the best measurements

of Saturn's atmosphere as we plunged into it.

We have loss of signal in X-ray band and CR-band.

Total loss of signal at 11:55:46

for the S-band, so that would be the end of the spacecraft.

I don't think any of us were ready.

If you ever had pets, and I've gone through

eight cats and two dogs during

the 23 years I worked on Cassini,

and when you know it's time, it's time,

and it was time to end the spacecraft.

Now I, don't get me wrong,

I'm very sentimental about it, but it wasn't a pet,

it was just an amazing instrument, a robot,

that did some incredible things at our behest.

Signal from the spacecraft is gone

and within the next 45 seconds, so will be the spacecraft.

I hope you're all as deeply proud

of this amazing accomplishment.

Congratulations to you all.

This has been an incredible mission,

an incredible spacecraft,

and you're all an incredible team.

I'm gonna call this the end of mission.

Project manager off the net.

(people applauding)

Cassini was only made possible

by the hard work of hundreds of scientists and engineers

from even before I was born,

so to be able to be there with them

for the end of the mission was supremely humbling

because of the gift that they gave us.

And I cried like a baby (laughs) the whole time.

(inquisitive music)

I've always loved the rings of Saturn.

The Cassini exploration has allowed us

to see them really close up, changing before our eyes.

The idea of oceans beneath the ice

that might support life is far from the old paradigm.

It opens up a whole new idea of how life

might form in solar systems in the cosmos.

If you were to say to me,

"Where would I most want to send a rocket?"

it would be to Enceladus and it would be to look at

the plumes and alkaline hydrothermal vents under the surface

because to me, that's the environment

that's most likely to drive the origin of life.

Finding life on Enceladus

or underneath the surface of Titan

would drastically change our view of the universe

and our place in it, and it's a future test

to search out and find out if those ingredients

have led to the evolution of life on those celestial bodies.

In the summer of 2019,

NASA announced that it had approved a mission

called Dragonfly that would return to the surface of Titan.

Dragonfly is a mission that's going to Titan

to study its prebiotic chemistry.

It's an octocopter.

By being a mobile lander, Dragonfly is going to allow us

to truly discover what the surface of Titan is like.

And it would spend most of its time on the surface

making scientific measurements,

but then we'd be able to fly from place to place

so that we could measure the chemistry

in different environments.

Dragonfly's main goal is to taste the surface of Titan

and tell us what the end product

of all of this fantastic chemistry that Cassini revealed is.

And really understand how far

prebiotic chemistry can progress in an environment we know

has all the key ingredients for life.

Dragonfly is scheduled

to leave Earth for the Saturn system in 2026

and should arrive at Titan in 2034,

55 years after Pioneer 11

gave us our first encounter with Saturn.

(intriguing music)