Original subtitles

(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.