All language subtitles for Solar.System.S01E04.Ice.Worlds.1080P.WEB-DL.x264-skorpion_track3_[eng]

If I 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, glaciers,

and even the crusts of the world
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 1,000 kilometres 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...

..because it looks remarkably similar.
- Really?

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

Same topography, same mountain
heights.

- That's incredible!

- 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.

- We're coming in for landing,

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

- I respect that choice.

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!

- Welcome to the glacier, you guys.

- Wow!

You know, when we arrived, they said,
"Oh, it's zero degrees."

And I 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've got a real sense actually
coming in, 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 that 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 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 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 solids.

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...

..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 -210 degrees C,

and Pluto's surface temperature, at
around -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 -10,

-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.

I 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, I 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
wonderful 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 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' 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 is 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.

I 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, it's
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...

..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 is 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'
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
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 Iapetus 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 Iapetus.

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 - 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 Iapetus 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?

It's 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 -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 Iapetus 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 Iapetus, 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 Iapetus 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 can 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.

Iapetus passes through the ring as it
orbits,

and so that dark material from the
ring

gets deposited on the surface of
Iapetus.

This is a really slow process.

Material falls onto Iapetus and
increases the size of that

dark layer by about four hundredths 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
a pepper grain.

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?

Iapetus 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.

Iapetus, 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 50 kilometres
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.

I 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
suggests

that beneath the thick icy crust lies
a different liquid,

a global subsurface ocean of water.

Up to 150 kilometres 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 Io and Ganymede.

So here's Jupiter,

and then Io 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 Io,

because that's closest to the giant
planet,

and so that turns Io 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, it
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 25 kilometres 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,

I wouldn't travel without one.

So it will tell us the temperature of
the water is rising.

Eight, nine degrees already.

Whereas this one, it's still zero
degrees,

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

Here, look!

Ha-ha!

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,

I have confidence. I have confidence
in physics.

I believe in it.

I would not put my hand in there.

I 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 I freeze
water,

when I turn it from a liquid to a
solid?

I 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...

..it 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...

..in 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, Io 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 Io 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 forever

from the ocean below by 10 or 20
kilometres 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 spider-like 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 fan-like

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 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 I 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,

-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 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...

..rivers...

..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.

- 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 all a guess until you go
swimming in it,

but we're building this picture up
where we understand

how salt water and rock interact on
Earth, and the chemistry

that produces, which is likely
important to the emergence of life.

- How are we going to 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.

- Europa Clipper is the first
dedicated mission to Europa.

And, in fact, it's the first dedicated
mission to any icy moon.

- Europa Clipper is set to launch

from the Kennedy Space Center in
October 2024.

- 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.

- 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.

- And it's not just the spacecraft

that must survive Jupiter's onslaught.

- 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.

- We think that the icy crust is 18
miles thick,

but Europa Clipper will tell us more.

- I'm really excited about learning
about Europa's plumes.

I 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.

- 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.

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

but there you go.
- Ha-ha! 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.

- 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.

- Next time...

..a powerful force creating oddball
worlds...

..of bizarre shapes...

..and hidden secrets.

These are the Solar System's Strange
Worlds.