All language subtitles for The.Planets.S01E04.Life.Beyond.the.Sun.Saturn.1080p.iP.WEB.DL.AAC2.0.H.264.JtY

Lift off of Messenger
on Nasa's mission to Mercury.

The Void
by Muse

♪ They'll say no-one can see us

♪ That we're estranged and all alone

♪ They believe nothing can reach us

♪ And pull us out of

♪ The boundless gloom

♪ They're wrong

♪ They're wrong. ♪

Beyond the warm worlds
of the inner Solar System...

...beyond the gas giant Jupiter...

...in the freezing regions
far beyond the Sun...

...lies Saturn...

...a planet made unique, thanks to
a nearly 300,000km-wide ring

of frozen water.

Here, trillions of pieces of ice
have been sculpted

by gravitational forces

into some of the Solar System's most
stunning vistas.

Here on Earth, water takes
many forms - oceans and clouds

and rivers, but it's
in its crystalline form, ice,

that it's at its most beautiful.

Here, ice just adorns the landscape,
but in the Outer Solar System,

where Saturn lives,
ice is so abundant that, well,

it's become a building material.

Now, there's no more beautiful
sight in the Solar System than

the ice rings of Saturn.

It's almost as if a god had taken
snowflakes and sprinkled them

over a gravitational field,
so we could see it, but how could

something so intricate be sculpted
out of something so simple?

Well, as is always
the case in science,

the true beauty lies in the story.

Saturn is a planet that
has undergone

some of the most radical
transformations in the Solar System.

A planet that has
seen destruction...

...and creation.

A planet that harbours
hidden worlds...

...where, just perhaps,

there may exist a second home

for life.

Imagine a place with
no surface to stand.

Just an endless atmosphere.

Compared to Earth,
Saturn is so alien

that it's hard to imagine
how it could have grown

from the same ingredients.

But go far enough back in time

and Saturn would appear to be
surprisingly familiar.

Saturn began life as tiny
worlds of rock and ice...

...tumbling chaotically
through space.

Just like Earth, Mars,
Venus and Mercury,

they began to merge
and clump together and grow.

But unlike the planets of the
inner Solar System, Saturn was

forming on the other side of a
boundary we call the Snow Line...

...a place where the Sun is so
distant and it's so cold,

water exists only in its frozen,
solid state.

Out here, trillions of particles
of ice behave just like rock,

providing huge amounts of extra
planetary building material.

Under the force of gravity,

this abundant ice and rock collided
and combined...

...helping the young Saturn
to grow into a giant.

The details of how the planets
formed in the Solar System

is not fully understood. It's
cutting-edge scientific research.

We're talking about events that
happened over 4.5 billion years ago.

But it seems likely that Saturn was
once a world of rock and ice,

perhaps ten or even 20 times the
mass of the Earth.

And it's almost possible, in
your dreams,

to imagine standing on its surface.

But because of its immense mass
and its place in the Solar System,

Saturn didn't remain a rocky,
icy world for long.

As it grew older, Saturn became a
radically different kind of planet.

In the region in which the young
world was forming, there was

more than just ice and rock -
there were large amounts of gas.

And Saturn began to gain
an atmosphere...

...but on a scale unlike anything
we experience here on Earth.

It's not until you see the Earth's
atmosphere from space

that you appreciate
just how thin it really is.

And it's a similar
story for the other worlds

of the inner Solar System.

Despite being relatively thin,

these atmospheres can exert
powerful forces

on the planetary surfaces beneath.

On Earth, you can see the effects
of an atmosphere

with nothing more than a
sealed container.

It's easy to forget that the
atmosphere has a weight.

There's a column of air stretching
up 100km above my head.

That's a lot of molecules,
and it exerts a pressure.

You really see it if you look at
what happens to this bottle.

We've filled it with air from
the top of the mountain,

which is about 3,000 metres.

Now, up there, the atmosphere
is about 25% less dense

than it is down there at sea level.

So, as we descend, the atmospheric
pressure outside

is increasing and the pressure in
here is just what it was

at the top of the mountain. And so
you see, visually,

that force in action. And that is
squashing the bottle.

Physics in action!

It's brilliant, isn't it?

While just a few hundred metres
of atmosphere can crush a bottle...

...if an atmosphere gets big enough,
it can transform an entire planet.

Within just a few million
years of its birth...

...Saturn had grown as large as it
could, from rock and ice alone.

And now, it turned to another
building material -

the hydrogen and helium gas left
over from the formation of the Sun.

This gas would have been
too light for the smaller worlds

of the inner Solar System to hold
on to.

But Saturn's great mass created
gravitational forces

powerful enough to draw it in.

Trillions upon trillions of tonnes
of hydrogen and helium gas

began to envelop the planet.

And as this new atmosphere grew,

it transformed the surface below.

Enormous pressures, created by the
weight of this gas,

heated rock and ice so much...

...they began to glow.

As Saturn matured, the pressure
at the surface rose

to ten million times the
atmospheric pressure on Earth.

Under those kind of pressures,

matter behaves in extremely
strange ways.

The very idea of a surface
becomes meaningless,

and Saturn was transformed from
an icy, rocky world

into a completely different class of
planet - a gas giant.

Saturn was now so big

it could contain nearly
5,000 Earth-size worlds.

But this vast, wild protoplanet

was totally unlike the Saturn
we see today.

To discover how that world emerged,

we had to send spacecraft
to meet it close up.

We have ignition and we have liftoff
of the Titan Centaur

carrying the first of two Voyager
spacecraft to extend Man's senses

farther into the Solar System
than ever before.

Reports coming back indicate those
twin large solid motors

are functioning perfectly, producing
1.2 million pounds of thrust each.

The guidance data coming back shows
that we're right on the money.

It's there!

CHEERING

Voyager 2 has reached Saturn
after four years in space.

It got there just a bit early -
2.7 seconds early, to be exact -

after a flight of a billion
and a quarter miles.

The Voyager probes gave us
our first detailed look at Saturn,

revealing the planet
in exquisite resolution.

There's just an amazing
harvest of pictures.

You know, there's tens of thousands
of photographs of Saturn

and its rings and its moons
taken by the Voyager 2 spacecraft.

For the very first time,

we were able to study Saturn's
vast atmosphere in detail.

Saturn itself is
composed of hydrogen and helium.

And we are seeing an
exotic meteorology here.

Voyager showed, beyond doubt,
that Saturn's upper atmosphere

was made almost entirely of
helium and hydrogen...

...the very same gases so abundant
in the early Solar System.

But this once chaotic gas

was now organised into intricate
weather systems.

And one above all others
took the Voyager team by surprise.

A huge hexagonal
structure in the clouds,

so big it could fit our
entire planet within it

nearly four times over.

The atmosphere of Saturn was
revealing itself to be stranger

and more dynamic than
we could ever have imagined.

Atmospheres are some of the most
spectacular and complex

planetary environments.

- Not many people see the Alps
like this! Seriously!
- It's so great!

I was afraid that you'd just get too
sick or something. It's awesome!

Man! It's fun, man!

HE LAUGHS
This IS fun!

The atmosphere of every planet
takes on its own unique character.

But what powers them
and the weather systems within

depends on where
you are in the Solar System.

Most of the weather on the Earth
is driven by the Sun.

It heats the ground up down there
and that, in turn,

heats the air up close to the
ground, makes it expand,

and that means that the air becomes
less dense and the hot air rises.

That means you get thermals -

energetic movements of air from the
ground into the upper atmosphere.

And that's what we're
exploiting now, to glide.

All this beautiful weather is
driven by the Sun heating the land

and causing air to move around.

So, we're sailing around...

Sailing around in a turbulent,

moving ocean of air.

But travel further
out into the Solar System

and the driving forces within
an atmosphere must change.

Now, there's been weather on Saturn
for over four billion years,

but Saturn is a long
way from the Sun,

and so those weather systems are not
primarily driven by the Sun's heat.

And yet the storms on Saturn
are amongst the most violent

found anywhere in the Solar System.

With sunlight almost 100 times
weaker on Saturn

than it is here on Earth...

...it means something else is helping
drive its weather...

...and the huge, complex forms that
arise in its atmosphere.

By studying the cloud tops of
Saturn, and its great storm systems,

we can now infer a great deal

about the strange world that
lies beneath...

...and the energy source that helps
power this planet.

Below the upper atmosphere,

great clouds of water grow.

Lightning 10,000 times more powerful
than on Earth illuminates the sky.

This lightning transforms methane
gas into huge clouds of soot.

Deeper still, the pressures grow
so great

that these chunks of soot

are likely transformed
into diamonds.

But even these diamonds will
succumb to the pressures of Saturn,

eventually liquefying.

It's not until 40,000km down

that the major source of
Saturn's energy is revealed.

Here, pressures are so intense,
gases behave like liquid metal.

Molten helium falls
like rain through hydrogen...

...and releases incredible
amounts of heat.

And we think that this is
the extraordinary heat source

that has been helping to drive
Saturn's weather.

Within just a few hundred million
years of its birth,

Saturn had lived a life of drama.

Now, it remained largely
unchanged for billions of years,

although still very different
from the planet we know today.

But in time, this great size

would lead to one more
iconic transformation.

Saturn is a planet
defined by its rings.

You get a child to draw a planet,
and quite a lot of the time,

they'll draw something that
looks like Saturn.

Close up, they are almost impossibly
delicate and intricate.

They're made up of trillions of
ice crystals, most of them

no bigger than snowflakes,
but some of them as large as houses.

Now, if you look through
a telescope,

they're highly reflective.

They reflect sunlight back just
as powerfully as the planet itself.

But that raises
an interesting question,

because the Solar System
is full of dust.

Any ice crystals that hang around

for any amount of time
will get dirty,

and so they won't reflect sunlight
back, they won't be as bright.

So, the question is, why then
are Saturn's rings so reflective?

The answer came from one
of the most audacious

and successful missions
to the Outer Solar System.

Five, four, three, two, one...

...and liftoff of the
Cassini spacecraft

on a billion-mile trek to Saturn.

We have cleared the tower. T plus
20 seconds. All systems are go.

The Cassini probe was designed
to study Saturn and its moons

and rings up close, to shed
new light on their origins.

All systems continuing to be go.

But whereas the Voyager probes spent
only days at Saturn as they sped by,

Cassini was built
to enter Saturnian orbit...

Solid rocket boosters have
been jettisoned.

Velocity 4,378 miles per hour.

...and explore the system for years.

Many times more massive than
Voyager, Cassini had to take

a different route to enter
orbit around Saturn.

To conserve fuel,
it flew by multiple planets,

slingshotting past them
to pick up speed

and change direction over
the course of seven years.

As Cassini finally
approached its target,

it was travelling at almost
100,000 kilometres per hour

and had to slow itself
with exquisite precision.

INDISTINCT RADIO COMMUNICATION

CHEERING AND APPLAUSE

After its
3.5 billion-kilometre journey,

Cassini was now able to see
Saturn's rings like never before.

What's more, during its long stay
at Saturn,

Cassini would be able to take
physical samples

for the very first time.

By measuring the way that the dust
from the Solar System falls

onto the rings, Cassini
made a startling discovery.

If the rings have been around Saturn
for billions of years,

they should have been darkened
and dimmed by the dust.

But they are pristine and bright.

And the reason is
because they are young.

Nearly 4.5 billion years
younger than Saturn itself.

The mystery of the origin of the
rings is an active area of research.

And the evidence that Cassini
delivered hints that the solution

lies not with the planet itself,

but with the world's
tracked in orbit around it -

Saturn's moons.

Saturn has 62 large moons
and countless smaller ones -

we're still discovering them.

So it's like a
mini solar system in itself.

And those moons range in size
from planetary-size objects,

like Titan, to small,
irregular-shaped lumps of rock.

And there's so much diversity
in size and form

and surface features, that the whole
system is like a history book.

And if we learn to read it
then we see that Saturn

has had a very violent
and changeable past.

Look at this, this is Mimas, which
is often called the Death Star moon

for obvious reasons.

It has this huge impact crater,
which tells you that once, long ago,

there was a very violent impact

that almost - but not quite -
destroyed the moon.

And this is Iapetus.

It's a very large moon,
almost planetary-size.

It's about 1,500 kilometres across.

And half of it is white,
and half of it is dark.

Iapetus also has another
distinctive feature,

which is this ridge all the way
around the equator, and you can see

the scale of it
from this photograph.

And this is clearly visible.

It's one of the highest mountain
ranges in the Solar System,

20km from peak to the ground below.

And it's thought that this formed
because a ring that was once

around the moon, just like Saturn's
rings, collapsed onto its surface.

As Cassini continued its journey,

it revealed in detail multiple moons

made almost entirely of ice.

And many of them had taken
on extraordinary forms

in and around the rings.

As Cassini analysed the ice moons
in ever greater detail,

it became apparent that many of them

were made of exactly the same
material as the rings themselves.

The rings and moons
were profoundly linked.

But for all the
moons that Cassini saw,

it now seemed likely
that one was missing.

When dinosaurs roamed the Earth,

we now suspect Saturn had a moon
in orbit that no longer exists.

A moon perhaps 400km across

and formed almost entirely of ice.

But this world was doomed.

It found itself orbiting too close

to resist the immense forces
of Saturn's gravity.

WAVES ROAR

Gravity is the sculptor
of the Saturnian system

but also the instigator
of change within it.

We tend to think of gravity as a
force that pulls things together,

but it can also act
to rip things apart.

Think of the tides here on Earth,
they're caused by the difference

in gravitational pull of the moon

from one side of the Earth
to the other.

And that difference, which can be
quite subtle, is also powerful,

it can move entire oceans.

It's called tidal gravity.

But the Earth also has a
tidal effect on the moon,

and because the Earth is an
entire planet,

that effect is much more powerful.

The pull of the Earth is enough
to deform the moon's surface.

The effect was particularly strong
4.5 billion years ago

when the moon was
nearly 17 times closer.

Back then, the pull from the Earth
caused a tide of solid rock

to rise and fall.

If the moon had been any nearer
it would have crossed what we call

the Roche limit, a place where tidal
gravitational forces are so strong,

moons can get ripped apart.

WAVES ROAR

The Romans named the planet Saturn
after their god of time and harvest.

And in one of the more gruesome
tales from classical mythology,

Saturn actually ate his newborn
babies in order to prevent them

from taking his power.

What's sort of interesting is, that
what we've learned from Cassini

is that, at least metaphorically
speaking, they weren't far wrong.

Just beyond Saturn's atmosphere,
our leading theory suggests

an icy moon must have approached
close to, or even just inside,

the planet's Roche limit.

As Saturn's immense tidal
gravitational forces

acted across the moon,
it began to rupture.

Saturn began to devour its child.

Up to 15,000 trillion tonnes of ice

broke apart in orbit around Saturn.

Because of the speeds the ice
fragments were travelling,

it's likely that in just a few days
they spread out

to encircle the great giant.

Saturn's iconic ring had been born.

Today, the giant ring has evolved.

Saturn's powerful gravitational
field has helped

keep its near perfect
circular shape.

But collisions within
have caused it to flatten out.

Now this debris forms
a disc wider than Jupiter,

yet, on average,
just ten metres thick.

Within, moon-sized chunks
of ice orbit the structure

clearing great voids.

Turning one ring...

...into many.

In places, moons have pulled
particles of ice upwards

to create strange peaks
over 2km high.

And in just the right conditions,

they cast spectacular shadows
across the rings.

This once tiny world
of rock and ice...

...that has undergone so many
great transformations...

...has today become
the Solar System's jewel.

Cassini had deepened our
understanding of the origin

and evolution of Saturn.

But its mission was far from over.

Because just beyond the rings
it discovered another treasure.

A place that may hold answers
to some of our deepest questions

about the possibility of life
in the Solar System and beyond.

Over a billion kilometres
from the warmth of the sun,

just on the outer edge
of Saturn's rings,

lies the icy moon Enceladus.

Enceladus is quite a small moon -

it's only about the size
of Iceland, actually.

But that does not make it dull.

It is the most reflective
object in the solar system -

over 90% of the light
that hits it bounces back,

and that's because its surface
is covered in pure ice.

It's also crisscrossed by crevasses

like this one you see
in this glacier,

but on a much grander scale.

The largest,
known as the tiger stripes,

are over 100km long.

But for all its surface beauty,

it's what's going on below the ice

that makes Enceladus so special.

What we found beneath Enceladus's
shell of ice must rank

as one of the greatest discoveries
in 21st-century space exploration.

But it was a discovery
that had been hiding in plain sight.

This is a photograph taken
by Voyager 1 of Enceladus in 1980.

Now, nobody noticed anything
remarkable about it at the time,

but this image has been enhanced,
and now you can see

this sort of misty blob
off one side of the moon.

Now, that is fascinating.

It means something is rising
up from inside Enceladus.

Now, when Cassini got back there
24 years later,

it saw the same thing,

but this time in much more detail.

As Cassini approached Enceladus,

the anomaly revealed itself.

Giant plumes of water vapour and
ice were erupting from its surface.

Over 200kg of material
was being released every second.

But this material
was not lost to space.

It seemed to be feeding one
of Saturn's outside rings,

helping to replenish it.

And these discoveries
inspired an audacious risk.

Piloted from over a
billion kilometres away,

Cassini was guided
dangerously close to the plumes.

The craft passed within just 48km

of the surface of Enceladus.

And Cassini was able
to touch the plumes.

What we discovered, thanks to a
series of these flybys,

was breathtaking.

The ice in the plumes was actually
frozen particles of salty water.

We had found a subsurface ocean
leaking into space.

Far, far from the sun,

Enceladus was harbouring
an ocean of liquid water.

And it was there because of Saturn.

Enceladus orbits Saturn
in an elliptical orbit,

which means the gravitational forces
across the moon

are constantly changing.

It's maintained in this orbit by
the pull of another larger moon -

Dione.

These ever shifting
gravitational forces

stretch and squeeze its heart,

warming and melting its
icy interior.

But Cassini's data had
one more surprise in store.

As the plumes of water ice were
analysed in ever greater detail,

we discovered complex
organic compounds

and silica particles
that could only have come

from hot hydrothermal vents.

In the frozen outer reaches
of the Solar System

we had found a warm, watery oasis.

WATER GUSHES

Cassini has given us a glimpse
beneath the ice of Enceladus,

and it is fascinating, genuinely,
in a scientific sense, because many

biologists believe that hydrothermal
vents like those

that are almost certainly present on
the floor of Enceladus's ocean

were the cradle of life on Earth.

All the ingredients are present -

there's hot water in touch
with ice and minerals.

That's a reactive
cauldron of chemistry.

There are reactive gases - methane.

Cassini found molecular hydrogen
in the plumes,

and that was one of the food sources
of primitive organisms on Earth.

So there really is a possibility
that there is life

in orbit around Saturn today.

The prospect of life on Enceladus
is exciting.

But if it's there, it's likely
to be only the simplest

and most primitive of organisms.

WATER ROARS

And given how violent and changeable
Saturn's past has been,

this world of ice and liquid water

may only have arisen
relatively recently.

Now, we don't know how long

Enceladus has been geologically
active, how long its had an ocean.

If it was only tens of millions or
even hundreds of millions of years,

that may not have been enough
time for life to get going.

But if there is life there
then we can glimpse its future,

because there are still hydrothermal
vent systems present on Earth today,

and life doesn't just
survive there, it thrives.

Often found in the deep oceans along
fault lines in the Earth's crust,

hydrothermal vents are some
of the richest and most complex

ecosystems on Earth.

Feeding off the abundant bacteria
that breed there,

these habitats support a multitude
of strange and complex organisms.

Whilst creatures like this will
never exist on Enceladus,

billions of years from now,
it is just possible

that this distant world may
become home to its own

unique forms of life.

But for Cassini, the brave new world
under the ice of Enceladus

was a bittersweet discovery.

13 years after it arrived at Saturn,

Cassini's fuel
finally began to run dry.

NASA couldn't risk letting
this probe crash land on Enceladus

and contaminate
a potential habitat for life.

-
- Systems, ACS One.

We've just had transition
to high-rate mode.

And so the decision was made to send
Cassini on one final journey.

A journey that would take it

into the atmosphere
of Saturn itself.

A journey from which
it would never return.

-
- And we
are in the atmosphere.

Radio signal still holding.

30 seconds.

STEAM HISSES

-
- Just heard the
signal from the spacecraft is gone

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

The planet that had borne witness
to some of the greatest dramas

in the history of the Solar System
was now consuming the craft

that had told its
extraordinary story.

Cassini and Saturn had now become
inseparable companions.

We journeyed out to Saturn
to experience and explore

this great beauty.

But in the end we were rewarded
with insights closer to home.

Cassini and her team of scientists
and engineers

should be counted amongst
our greatest of explorers.

The mission had all
the ingredients -

a vessel and a crew drawn
by the prospects of beauty

and new knowledge across an
uncharted ocean to an alien world.

And, as is so often the case
in exploration,

the real treasure was found
in the unexpected shadows.

In this case,
in the shadow of the rings,

where we found this tiny
world, Enceladus,

that may harbour life
and provide us with reassurance

that we are not alone
in the universe.

See? The beauty is in the story.

Would it matter really
if we found life on Enceladus?

It would only be microbes after all.

Yes, it would matter.

We are at a time in our history,
I think, where we need reassurance

or perhaps a reminder that
there is beauty and knowledge

and perhaps even life and meaning
beyond our shores.

We will, I'm sure, go back
to Saturn and its moons,

explore deeper, stay longer,

and maybe one day
even visit ourselves.

We don't know what we'll discover

but we can be sure that the story
has only just begun.

Cassini has been one of the most
successful probes ever flown.

But constructing a machine
that could survive 13 years

in the outer Solar System was a huge
challenge for everyone involved.

T plus 20 seconds.

Even when they were proposing
Cassini, I thought,

"No, no, this is never
going to happen."

It's, like, maybe too ambitious
or something.

It's difficult to put a number
on how many people

were involved in Cassini.

Tens of thousands, I would say.

This is a very, very complex effort.

There's over ten miles of wiring,

and you have to check out
every wire.

So it took us two and a half years
to put the thing together.

All of us spent a lot of effort
to get to that moment,

so there's a lot of emotion
attached to it.

And then you see it launch

and you know that it's on a journey
to a very, very distant place...

...and so you feel like
you're going too.

When Cassini first began to send
close-up pictures back to Earth...

...it was a special moment
for the whole team.

I was sitting in what they call
the Blue Room

being interviewed while they were
beaming for the first time,

and then one of these pictures
came on and I just went,

"Wow, look at that!"

That was really the jumping
out of the chair moment for me.

And it was just the first day.

What we were seeing was the highest
resolution that had ever been seen.

I saw phenomena that I'd only seen

in, kind of, computer
simulations before

and now I was seeing it
for the first time

and realising all this was real.

And we were seeing details
in the rings

that were shocking... shocking.

We just lacked the imagination
that it would require

to predict what it would look like.

For me, when that great
backlit picture came out,

that's when it hit for me.

"Oh, my God, we've done something
really unique and wonderful."

It was like, "This is going to be...
This is going to be huge."

Over Cassini's 13 years at Saturn...

...it explored the planet's
incredible storms.

The formation of its rings.

And discovered the oceans
of Enceladus.

But Cassini's greatest insights
may be yet to come.

There's such a wealth
of information in the data.

I think we've just skimmed
the top of the data.

I think people will continue to make
discoveries from Cassini data

for another 30 to 40 years.

The data Cassini collected
in its final moments

is already changing our
understanding of the planet.

It has revealed the rings
are disappearing.

As much as 10,000 kilograms
of material

is falling into the planet
each second.

It now seems likely that just
100 million years from now,

Saturn's great rings
will be no more.

Cassini has shown us that
we have been uniquely fortunate

to behold this great beauty.

We head into the darkness.

To the ice giants -
Uranus and Neptune.

And beyond,

to a world 4.5 billion kilometres
from the sun.

Pluto.

Journey through our Solar System
with the Open University,

and discover more about its planets
and moons.

Explore this and more with our
academic experts.

Go to...

...and follow the links to
The Open University.