All language subtitles for Solar.System.2024.S01E04.1080p.BluRay.x264-DRCOX_track3_[eng]

(WIND WHISTLES)

If | asked you,
"What is a planet made of?"

then you'd probably say,
"Well, rocks and iron."

And for the planets
of the inner solar system,

like Earth, close to the heat
of the sun, you'd be right.

But if you head out
into the frozen outer reaches

of the solar system,

then even the gases
that make up our atmosphere,

so nitrogen and carbon dioxide
and, of course, water

are all frozen solid.

And the planets and moons
out there,

the mountains and glaciers,

and even the crust
of the worlds themselves,

are made of that -

solid, frozen, pristine ice.

Ice that,
in the extreme conditions

we find beyond Earth,

behaves in ways
we never imagined possible.

As we've explored
the solar system,

our spacecraft have encountered
moons torn apart...

...by great canyons
of shifting ice...

... dwarf planets
where mountains of solid ice

float across the surface...

...worlds where ice appears
to cover one face...

...but leaves the other
entirely alone.

And elsewhere, alien aurora
hang above the clouds,

all thanks to a strange,
newly discovered form of ice.

Even here, on Earth,

the behaviour of something
as simple as ice has had,

we think,
profound consequences.

Because without ice's
counterintuitive behaviour,

life on our planet
may not have survived.

We begin our journey
to the ice worlds

at the freezing edge
of the solar system.

Out here,
the sun Is so far away,

it resembles just another star.

Pluto is so remote

that it was only in July 2015

that we had our first and,
to date, only close encounter.

As it flew by,
the New Horizons spacecraft

sent back
the first close-up images

of this mysterious
frozen world.

It discovered
a great heart-shaped plain

1,000km across

that dominates one face.

Around the edge of this plain,

mountains made of solid ice
tower over Pluto's surface.

And amongst its rugged uplands,

ice was detected in a form

no-one ever expected to see
on Pluto.

Glaciers.

Flowing rivers of ice
on a world so far away,

we expected
nothing would be moving.

That's because
the temperature here

is only 40 degrees Celsius or
so away from absolute zero...

...a temperature
at which nothing should move.

And yet New Horizons
discovered regions of Pluto

that for all the world

look like the frozen reaches
of our planet.

So when you fly here
over the years,

how much does it change?

It changes every day.

- Yeah?
- Yeah.

The shape of the glaciers
change.

It's never the same.

I'm just imagining flying
over Pluto, actually...

(CHUCKLES)

...beCause
it looks remarkably similar.

Really?

- What is the topography like?
- It's like this.

Same topography,
same mountain heights.

LEIGHAN: That's incredible!

PROF COX: The discovery of
Pluto's dynamic icy landscapes

came as a huge shock.

It forced us
to rethink our understanding

of this so-called dwarf planet.

LEIGHAN:
We're coming in for landing,

so I'll just be talking
to the airplane and not you.

PROF COxX: | respect
that choice.

(LEIGHAN LAUGHS)

I've had a lot of landings,
but none quite like this.

In fact, none like this at all.

It's the world's
most beautiful runway!

LEIGHAN: Welcome
to the glacier, you guys!

(PROPELLER SLOWS)

(WIND WHISTLES)

Wow!

You know, when we arrived,

they said,
"Oh, it's zero degrees,"

and | thought, "That's great.
Zero degrees, it's warm."

Fahrenheit.
Zero degrees Fahrenheit.

It's about minus 20 up here.

It's just...

And you got a real sense
actually, coming in,

of...it looks frigid
and frozen,

you know, unmoving, unchanging,

but it's so dynamic.

You can feel it in the wind
as you land.

And then,
you know, you can see...

...you can see the way
that everything flows.

Just look at that glacier.

You can almost feel
or see it moving.

It looks like
a slow-motion river,

and indeed it is moving.

It does flow very, very slowly.

And the reason

this great mass can grind
its way down the valley

is because of the unique
properties of the ice

from which it's made.

That bright-blue ice
certainly looks solid.

Immovable.

It's formed by pressure.

So these snowflakes
are falling down

onto the top of the glacier,
and over time they build up,

and their weight presses down,

increasing the pressure,

and you get that particular
crystalline structure of ice,

which looks transparent
and blue.

But actually, at those
pressures and temperatures,

it's not completely solid.

The crystals are
sort of arranged in planes,

a little bit
like a deck of cards.

And that means
that as gravity is acting,

trying to slide
this whole thing

down the valley.

those planes can slip
and slide over each other,

and that allows
the whole glacier to move.

You can also get liquid water
between the rock and the ice,

and that sort of lubricates
the glacier,

and that allows it
to slip as well.

So although this looks fixed
and immovable,

at the conditions
we find on Earth,

this can almost behave
like a...like a fluid,

sort of sliding very slowly
and deforming down the valley.

Glaciers were the last things
we expected to see on Pluto.

It's so cold here
that we'd expect

the ice crystals
to be too brittle to flow.

Nothing should slip,
nothing should slide.

Yet that's precisely
what these glaciers are doing.

So if they can't be made
of water ice,

what are they made of?

As New Horizons flew
past Pluto,

its detectors picked up
an important clue.

These are images
of Pluto's surface,

and the colours correspond

to different molecules,
different substances

that New Horizons detected
on the surface.

The purple is methane,

the yellow is nitrogen,

and the green is
carbon monoxide.

All these gases are
frozen solid.

Now, the glaciers on Pluto are
primarily made of nitrogen.

Solid nitrogen.

Now, nitrogen is something
that we're all familiar with.

It's this stuff. Our air is
pretty much made of nitrogen.

So our familiar experience
of it is just we can't see it.

But if you cool it down...

(SIZZLING)

...then we can get it pretty
easily to turn into a liquid.

Now, if we carried on
cooling that down,

it would turn into a solid.

Nitrogen freezes
at minus 210 degrees C,

and Pluto's
surface temperature,

at around minus 230 degrees,

ensures that glaciers
remain solid.

But crucially, the nitrogen ice

is just 20 degrees or so
away from its melting point.

That's very similar to the
situation here on this glacier.

The glacier is about...
Well, the air temperature today

is about minus 10,
minus 20 degrees Celsius.

Heat it up by about 20 degrees,
and it'll melt.

So the temperature difference
between the solid nitrogen ice

and the nitrogen gas,

and the solid water ice
and the water,

is about the same.

That means that,

with just a small rise
in temperature,

Pluto's nitrogen ice
should be able to move.

So the discovery
of its glaciers tells us

something remarkable
about Pluto.

This tiny world must have
a little heat at its core,

a faint warming
from radioactive decay,

just enough to gently melt

the bottom
of these rivers of ice,

sending them on their way
down the valley.

| think, for me,
there are two lessons

from the exploration of Pluto.

One is that geology
finds a way,

even so far away
from the sun,

where temperatures are

only 40 degrees or so
above absolute zero,

pretty much the coldest
it can be,

there can still be
active geology,

particularly where something is
close to its freezing point.

In Pluto's case, nitrogen ice.

The second lesson, | think is
perhaps even more profound,

is that nature's imagination
far exceeds our own.

Nobody expected
that they would see

such a beautiful, active world

so far away from the sun,

on the far icy edge
of the solar system.

The similarities between Earth
and Pluto are striking...

...but New Horizons discovered
a wondertul difference.

Pluto's glaciers
flow through mountains

reminiscent of Alaska's
great ranges.

But unlike Mount Denali's
granite spires...

...Pluto's mountains are made
from frozen water.

But you can't imagine something
that big, that high,

being made of water.
That's the thing

- that amazes me.
- That's crazy!

- All water, no...no rock?
- Yeah, pretty much, yeah.

And this leads
to a surreal twist.

Water ice in the mountains
is less dense

than the nitrogen ice
in the glaciers.

So in places,

we've seen mountains floating
on the glaciers,

carried away like icebergs
onto the vast ice plain below.

Pluto, a world sculpted by ice.

Leaving Pluto and heading back
towards the sun's glow,

we enter the realm
of the ice giants...

... vast gaseous worlds...

...where ice storms rage.

And on the innermost
of these planets,

we've discovered a phenomenon
eerily reminiscent of home.

Just above Uranus's ice clouds

hang beautiful,
ethereal aurora...

... found not at the poles
of the planet, as on Earth,

but scattered
across its face...

...even around the equator.

So what's creating
this beautiful, rare display?

The basic physics
of the aurora on Uranus

is the same as the physics
of the aurora on Earth.

So the sun's
constantly emitting

a rain of high-energy
charged particles,

which is called the solar wind.

And when those charged
particles reach the Earth,

most of them are deflected
around the Earth,

harmlessly off into space,
by our magnetic field.

Now, the Earth's magnetic field
looks very much like the field

around a bar magnet.

| can show you that
by sprinkling

some iron filings...

...around a bar magnet.

And the iron filings line up
with the magnetic field lines.

When the solar wind hits
this magnetic field,

most regions of the Earth,

is deflected harmlessly
off into space.

But at the poles,

those charged particles can
become trapped.

And then
they can be accelerated

down into the upper atmosphere

and hit molecules
in the atmosphere,

oxygen and nitrogen.

And that can cause those
molecules to emit light,

to glow.

And that's what,
if you're lucky,

you see as the northern
and southern lights.

So somewhere
deep inside our planet

lies the equivalent
of that bar magnet.

And, of course, it does,

in the form of a hot,
molten iron core,

spinning away,
as the Earth rotates...

...creating electrical currents

and the magnetic field
that projects out into space.

But Uranus is different.

The aurora are not found
at the poles,

and we don't think

it has a molten iron
or metallic core

to support
those electrical currents.

And so the fact that Uranus
does have aurora,

and therefore some kind of
magnetic field,

is a tremendous mystery.

But we do have theories
that allow us

to piece together
what might be going on.

Imagine diving
beyond the clouds of Uranus,

beyond the slushy ice layer
that flows around the planet...

(RUMBLING)

..and keep going
towards the core.

We enter a region
where the pressure approaches

several million times
that of Earth's atmosphere...

...and where it's almost as hot
as the sun's surface.

Rather than molten rock
or metal,

like we find
inside our own planet,

we instead find
yet more frozen water...

..In a bizarre form of matter
known as superionic ice.

Normal water ice has
a crystal structure like this.

So the reds are oxygen atoms,
the whites are hydrogens,

and you can see
that they're bonded together

into this regular
crystal lattice.

Within the lattice,

nothing that could carry
an electrical current can flow,

so a magnetic field
can't be created.

And this...

..1S the crystal structure
of superionic ice.

The oxygens are still there,

bonded together into a crystal,

but now
there are hydrogen nuclei -

electrically charged protons

that can move freely
through the crystal lattice.

That means that this is
an electrical conductor.

It's this movement
of the protons

that could be contributing
to Uranus's magnetic field.

If so, then the superionic ice
is, at least in part,

driving the planet's
mysterious aurora.

Now, this story is still
far from fully understood.

For a long time, this strange
form of ice was only a theory.

But then a team

pointed one of the world's
most powerful lasers

at a droplet of water

and recreated the conditions
that are present

deep down inside Uranus,

and, just for a moment,

caught a glimpse
of superionic ice.

Uranus,
a world illuminated by ice.

On the journey
between ice worlds,

we edge ever closer
towards the sun,

for an encounter
with one of the most

thoroughly explored
planetary systems of them all.

Saturn's rings are constructed
of countless crystals,

ranging in size
from just a few microns

to vast boulders...

..and all of them made almost
entirely from frozen water.

The rings are joined
in their orbit

by at least 146 moons.

And out towards
the edge of the system,

NASA's Cassini probe made

one of its most surprising
discoveries.

The moon lapetus resembles
a walnut,

with a mountain ridge
around its middle.

But that's not
its strangest feature.

Back in the 17th century,

only about 60 years or so,
actually,

after the invention
of the telescope,

Giovanni Cassini
discovered lapetus.

But he immediately noticed
something strange

about the moon as he watched it
orbit the planet,

because
he could see the moon

on one side of the planet,

but then on the other side,
he couldn't.

Now, being sensible -

because he was a scientist,
after all! -

he said, "Well, it's not
somehow disappearing.

"There must be
another explanation."

And he guessed that one side
of the moon must be very bright

and the other side
must be very dark.

Now, 300 years later,

we sent a spacecraft to Saturn,
bearing his name...

...and we discovered...

...that he was right.

Cassini sent back proof

that one side of lapetus
is icy white,

whilst the other looks
as if it's been painted black.

So what could be creating

such a sharply defined
monochromatic world?

A tremendous mystery,
but a clue can be found

in looking at the line
between the two hemispheres,

because there are
jet-black regions

on the surface there

that are also
some of the hottest places

in the Saturnian system.

Hot is relative, of course.

It's still
minus 140 degrees Celsius

on the dark side of the moon.

Now, that's about
20 degrees warmer

than the moon's icy face.

And we think that this
difference is just enough

to move ice around the moon

in a very particular way.

The sunlight falls
on that dark surface,

as lapetus rather languidly
rotates, actually,

about once every 79 Earth days,
and it heats it up.

The water molecules rise up,
drift over to the light side,

and then condense,

and fall onto the surface,

making it brighter
and brighter and brighter,

sort of like
what's happening here.

So, out there
in the Pacific Ocean,

the water is turning
into water vapour,

drifting over the cold land,
and falling as snow,

making the whole surface
bright.

On the dark side of lapetus,
ice is warmed

and creates a thin atmosphere
of water vapour.

And where this vapour meets

the colder,
white side of the moon,

it freezes to the surface
again,

resembling fresh snow...

...Maintaining the bright
icy white of this hemisphere.

But a mystery remains,

because lapetus is
an ice moon...

...SO What is the dark material
covering its other face?

In 2009, the Spitzer
infrared space telescope

discovered this.

This is another ring
around Saturn,

but it's enormous.

It's one of the largest
structures in the solar system.

This is about
12 million kilometres across.

Later observations
from NASA's WISE telescope

suggest
that the disc may extend

a further 20 million kilometres
out into space.

At this vast scale,

Saturn and its more familiar
icy rings are barely visible.

It might seem strange
that no-one had seen

one of the largest structures
in the solar system until 2009.

The reason is that that ring
is very dark and very diffuse.

If you were transported
into the ring,

you could look around,

and you wouldn't know
you were in it.

Spitzer saw it

because Spitzer is
an infrared telescope,

and so it detected
not visible light,

but infrared light.

The glow, the heat
emanating from the ring.

The giant outer ring is
therefore very different

to Saturn's ice rings.

So what is it made of,
and where did it come from?

Phoebe is another
of Saturn's outer moons,

and each time a passing
asteroid gets too close...

..the resulting impact throws
dark material out into space.

Over billions of years,

numerous impacts have resulted
in the dust from Phoebe

spreading around Saturn,
forming its vast dark ring.

lapetus passes through the ring
as it orbits,

and so that dark material
from the ring gets deposited

on the surface of lapetus.

This is a really slow process.

Material falls onto lapetus

and increases
the size of that dark layer

by about 4/100ths
of a millimetre

every million years.

It's not a bad analogy, this,
actually.

Some of those sort of
dust particles in the ring

are about this size,

about the size
of...of pepper grains.

Some are bigger,

a few centimetres across
or something,

but it is pretty much
stuff like this.

And yet a puzzle remains.

Why half black and half white?

lapetus spins on its axis
once every 79 days

and orbits around Saturn
once every 79 days.

It's what's called
spin-orbit locked.

It's like our moon.

So it always leads
with one hemisphere,

as it orbits around Saturn
and passes through the ring.

lapetus, then, is a fluke
of nature that exists

thanks to the interaction
of two moons

within a dark ring,

right at the edge
of Saturn's domain.

A world painted by ice.

As we return
ever closer to the sun,

ice becomes
increasingly rare.

Jupiter has 95 known moons...

.. Including
three large ice worlds.

And one of these
is a promising target

in our search
for life beyond Earth.

In 2022, NASA's Juno spacecraft
flew by Europa...

..and photographed a world

crisscrossed
with mysterious red lines.

Grand canyons...

...some 100 metres deep
and tens of kilometres wide...

..In places
coated in a red substance

that may be a newly discovered
compound of salt and water.

Juno is the latest NASA mission
to fly by Europa

and take detailed photographs

of its peculiar,
fractured surface.

The canyons on Europa are

quite unlike anything
seen on Earth...

...Or, Indeed, anywhere
in the entire solar system.

The markings are geometric.

They form lines that crisscross
over the surface,

though what can be causing
that pattern?

Europa's surface features are
an active area of research,

taking NASA scientists
to the frozen reaches

of our own planet
in search of answers.

This is an image of a region
on Europa's surface

called Phaidra Linea.

And you see this feature,

it almost looks like
the Grand Canyon on Earth.

It's actually
about 50km across.

A clue to what this is
can be seen...

If you look at the top line
and the bottom line,

and just in your mind's eye,
just draw these together,

you'll see that
they knit together perfectly.

So this looks like
the crust has just spread.

Now, there's only one
other place in the solar system

where we see features
like this,

and it's here, on Earth.

It's caused by plate tectonics.

On Earth, it's the internal
heat of the planet

as it forces its way
through the crust

which Is the driving force
of plate tectonics.

| mean, no-one expected to see
behaviour like this on a moon.

On Europa, it's not molten rock

that's driving its plates
apart.

Density measurements
of the moon suggest

that beneath
the thick icy crust

lies a different liquid,

a global subsurface ocean
of water.

Up to 150km deep,

it may contain
two or three times

all the water
in Earth's oceans combined.

So how can
all that liquid water exist

just below the surface
of this frigid ice moon?

The answer lies with
two other moons of Jupiter,

with lo and Ganymede.

So here's Jupiter,

and then lo goes around
four times...

...as Europa goes around
two times,

and Ganymede, farthest out,
goes around once.

It's called
an orbital resonance.

Four orbits, to two orbits,
to one orbit.

That means that these three
moons line up periodically

and give each other
a gravitational kick,

which means that the orbits
don't stay as nice circles.

They're all ellipses.

And that means
that tidal effects,

just like the tides
here on Earth,

stretch and squash the moons,
and heat them up.

Now, the effect is strongest
for lo,

because that's closest
to the giant planet,

and so that turns lo into,
essentially, one giant volcano.

For Europa, further out,
that heat melts the ice.

But the energy
that goes into Europa

from this eccentric, elliptical
orbit around Jupiter,

um, sort of trickles
into the moon.

So it really isn't enough
on its own

to produce
the very active geology

that we see on the surface.

We estimate the surface ice
on Europa is

somewhere
between 10 and 25km thick.

So whilst the tidal forces
are enough

for the subsurface ocean
to remain liquid,

they're not enough
to split apart all this ice.

So to drive the high-energy
geological processes

we see on the surface
of Europa,

then there must be some kind of
energy storage

in the moon itself.

So I've got two camping stoves
here.

These two pans are filled
with water,

and it's at the same
temperature - zero degrees.

The only difference is
that this water has ice in it,

and this has no ice in it -

the only difference
when we start the stoves.

This is a thermal camera here
cos, you know,

| wouldn't travel without one.

So it will tell us
the temperature

of the water is rising.

Eight, nine degrees already.

Whereas this one
is still zero degrees,

even though we're putting
all the energy into it.

Here, look!

(CHUCKLES EXCITEDLY)

You see that?

So why?

Well, this is a model of ice.

You can see the water molecules
here and here and here.

And they're bonded together
by these longer bonds,

which are called
hydrogen bonds.

They're the thing that hold
the crystal lattice in place.

And they're pretty strong.

So to melt the ice,

you've got to break
all these bonds.

You've got to put
a lot of energy into it.

So all the energy
from this camping stove

at the moment is going
into breaking bonds in the ice.

It's not going into
making all the molecules

move around faster,
which is what temperature is.

So this one is getting hotter
and hotter and hotter.

Nothing is happening
to this one.

Now, these have been cooking
away now, and I'll show you,

| have confidence.

| have confidence in physics.

| believe in it.

| would not put my hand
in there.

| can see it'd be
a stupid idea. But there...

There you go. Physics works.

It's actually freezing.

Now reverse that idea,
reverse that argument.

What happens, then,
when | freeze water,

when | turn it
from a liquid to a solid?

| get all that energy
back out again,

huge amounts of energy,
as the bonds form.

And this is what we think
may be happening on Europa.

The subsurface ocean is warmed
by tidal forces from Jupiter

and its moons...

... Storing energy.

Then,
thanks to its elliptical orbit,

as Europa periodically cools,
the ice begins to freeze...

... releasing the stored energy.

The volume of the icy crust
grows as it freezes...

.. Increasing the pressure...

.. Until the entire canyon
is cleaved apart...

..and briny water
from the ocean below surges up

through the cracks...

...where, bathed in Jupiter's
intense radiation...

.../t turns red.

You're actually very familiar
with this process.

If your pipes burst
in your house

because they freeze,

where does the energy come from
to burst the pipes?

It comes from water
freezing into ice.

Europa is far more dynamic
than we'd imagined.

And it's this dynamism

that makes it
a tantalising target...

...1N our search for life
under the ice.

At its simplest,
life needs three things.

Water, energy,

and the right
chemical ingredients.

Europa has the first two
in abundance...

...but the chemistry for life
is missing.

But fortunately,
Europa is not alone.

Orbiting close by,

lo has the missing ingredients
we believe necessary for life

in abundance...

...erupting into space

in enormous quantities
around Jupiter.

Here's where the story gets
even more wonderful,

because the volcanoes of lo

are constantly producing
chemicals,

materials, that rain down

onto the frozen surface
of Europa,

but if it wasn't
for the geology,

then they'd be separated
for ever from the ocean below

by 10 or 20km of ice.

But that active geology

creating the plate
tectonic-like behaviour

can bring those materials,

those chemicals,
into the ocean,

and then we have
all the conditions

we think are necessary
for the origin of life.

So Europa's dynamic surface

may form part of
an extraordinary ecosystem...

..one that stretches
from one moon to another,

and work is already under way
to send robotic probes

into that distant icy ocean.

It would be
a profound discovery

to find life on Europa,

but it would also be profound
if we didn't,

because everything we think
we know

about the origin of life,

all the ingredients
that are necessary,

seem to be present on Europa,

so if we go there
and send a cryobot

into the oceans of Europa
and find nothing at all,

then it may be far more likely

that we are alone for...

...millions or even billions
of lightyears

in every direction.

Europa, a world
completely encased in ice,

couldn't exist
much closer to the sun...

... because
just a little closer in

lies the solar system's
ice line.

Cross it, and temperatures
become too warm

for ice to stay frozen
for long.

When comets fall inwards
towards the sun,

some of the ice they carry
is transformed

into water vapour...

.. forming tails
that streak through space

for hundreds of kilometres.

Inside the ice line, then,
ice Is rare.

But there are places where
it can hold on at the margins.

Most of the ice on the surface
of Mars Is held at the poles.

Here, NASA's
Mars Reconnaissance Orbiter

has captured
these extraordinary images

of a strange phenomenon

that takes place
on the southern ice cap.

Dark spiderlike formations
that we think are being formed

as the seasons turn.

During the winter,
it gets so cold on Mars

that the carbon dioxide

in its thin atmosphere
freezes...

...creating crystals of dry ice
that fall as snow on the pole.

Snowfall on Mars is
nothing like snowfall on Earth.

Every winter, between
three and four trillion tonnes

of carbon dioxide freezes out
onto the surface.

That's about 15% of the entire
Martian atmosphere.

And then, in the springtime,
everything changes.

As the sun returns
in the spring,

the ground is warmed...

..and the frozen
carbon dioxide vaporises

in an instant,

from solid to gas.

Geysers of gas that lift dark
Martian dust high into the air.

And it's this dust,
as it settles,

that's causing
the fanlike spidery marks

that we've seen from orbit.

From Mars, it's just
a short hop to our own world...

..and Earth too has permanent
ice caps at its poles.

But there the similarity ends.

If an alien astronomer got
a powerful telescope

and pointed it
at our solar system,

they would immediately see
there's something interesting

and very rare about
the third planet from the sun,

about Earth,

because they'd see
a place like this,

a place with...with mountains
covered in snow,

and flowing rivers
and clouds and rain.

It's a place where water exists
in all three of its phases -

solid, liquid and gas -
at the same time.

And that's extremely unusual.

Let me show you what | mean.

So I'm going to draw

what's called a phase diagram
for water.

It has pressure there

and temperature along here.

The Earth sits
at one atmosphere pressure,

so atmospheric pressure...
there.

And it sits at around zero
degrees Celsius, give or take.

So the Earth exists somewhere
in this region here.

I'm going to draw a line.

I'll tell you what it is
after I've drawn it.

So these two lines mark out

the region of pressure
and temperature

where water can be
either a solid,

a liquid or a gas, or vapour.

And the Earth is here.

Little tiny range,
where you can have solid,

liquid and vapour.

Mars sits
somewhere around here.

So that means that on Mars,

water can either be frozen
as a solid,

or it can be a vapour,

but it can never be a liquid

cos the atmospheric pressure
is too low.

Pluto sits around here,
minus 230 degrees,

where water can only be
a solid,

frozen hard as steel,

building the mountains
of Pluto.

On the other hand,

Uranus sits somewhere
over here,

at, what, millions of times
atmospheric pressure

and extremely high
temperatures.

And there, we get

these strange structures
of ice, the superionic ice.

So Earth sits in a very narrow
range of temperature

and pressure, where water can
exist in all three phases.

And that's what makes the Earth
unique,

certainly in our solar system,

and perhaps for hundreds
or even thousands

of light years beyond.

It's this that allows
a complex ecosystem to exist

on the surface of our planet.

Earth's snow-covered mountains,

great oceans...

...f1Vers...

..and storm clouds
can only exist together,

thanks to the rare
and very narrow

temperature and pressure range
that our planet enjoys.

And that's surely necessary

for complex life
to have emerged on just one

of the solar system's
ice worlds.

But there is one more twist
to our Story of ice -

a strange property
of the everyday ice

with which we are so familiar.

Ice on Earth has
the unusual property

that it floats
on its own liquid.

It's due to that complicated
crystal structure

with all those hydrogen bonds.

Now, there are times
in Earth's history

when the planet
almost froze solid.

But because ice floats,

there was always
a bit of liquid water

at the base of the ocean,

and life could cling on
in that liquid.

That means that there has been
an unbroken chain of life

for 3.8 billion years,
culminating in us.

So next time you stick
a few ice cubes in your drink,

just pause for a second

and give a thought
to the wonder of ice.

The three key ingredients
that you need for life are,

number one, liquid water,

two, a source of energy,

and three, various chemical
elements

that we associate with life.

And we think that Europa has
all of these ingredients.

PROF COX: Juno has deepened
our knowledge of Europa,

but the mission is due to end
in 2025.

While we are yet to find
any evidence of life on Europa,

it's clear that this icy moon
is worth a closer look.

Sam Howell is part
of a NASA team

scoping a hugely ambitious
attempt

to explore the moon
and its subsurface oceans

in search
of that elusive proof.

It's alla guess
until you go swimming in it,

but, um,
we're building this picture up

where we understand

how saltwater and rock
interact on Earth,

and the chemistry
that produces,

which is likely important
to the emergence of life.

How are we gonna prove that?

We're launching
the Europa Clipper mission,

and that will,
in the early 2030s,

arrive at Jupiter
and orbit Jupiter,

surveying the entirety
of the world.

NEW SPEAKER: Europa Clipper is

the first dedicated mission
to Europa.

And, in fact, it's the first
dedicated mission

to any icy moon.

NEW SPEAKER:
Europa Clipper is set to launch

from the Kennedy Space Center
in October 2024.

DR QUICK: And we have a payload

of ten instruments
that are going to work together

to characterise
Europa's icy surface,

its ocean,
what their compositions are,

and to figure out
if Europa has environments

that could support life.

DR HOWETT: Any time
you're anywhere near Jupiter,

it's really dangerous.

These high-energy particles
that are zipping around

can hit your spacecraft
and damage it.

And that's
one of the big challenges

facing Europa Clipper.

PROF COx: And it's not
just the spacecraft

that must survive
Jupiter's onslaught.

DR HOWETT: We know
that this intense radiation,

that's bad for life
as we know it, life as we are,

but maybe life on Europa
doesn't mind it too much.

But what's more likely is
that the thick layers of ice

that are at Europa's surface

shield life
in the subsurface ocean.

DR QUICK: We think that the icy
crust is 18 miles thick,

but Europa Clipper
will tell us more.

DR HOWETT: I'm really excited

about learning
about Europa's plumes.

| think they could be the key

to sampling
the subsurface ocean.

We'll figure out if there are
traces or ideas of life

in those plumes,
and that's something

we're going to be able to do
with this amazing spacecraft.

PROF COX: Clipper will only
ever survey Europa from afar,

but future missions are being
developed that, one day,

may land on the surface
and explore beneath the ice.

There is no ice on this planet

that behaves
like the surface of Europa.

There, the ice is so thick
and so hard

that the upper few miles are
like concrete or rock.

What we really look at are ways
to pack enough heat

into a cylindrical probe

so that it can melt all the way
to that ocean,

but can also carry along
the scientific payload with us

that we want to use to explore.

So is this recording video now?

Yes, absolutely.

Ah... Oh, yeah.

| don't know if you've ever
seen yourself on camera before,

- but there you go!
- (LAUGHS) Hello!

We're just going to deploy it
there,

right into the hole, and...

...good luck.

And then there we go,
we're down in the lake.

We're looking around
the interface

of the ice and water
just beneath us.

DR WONG:
Finding life on Europa would be

extraordinarily profound,

because it's almost guaranteed

that that would be
a separate instance

of an origin of life.

So Europa could teach us
a lot

about how life begins
across the universe.