01x04 - Ice Worlds

[bunniefuu]

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.

Subtitles: [font color="#039af9"]FΛSSTΞCH[/font]
For [font color="#ffd700"]Addic7ed.com[/font]

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.

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


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


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


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



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!

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.

Oh, yeah.

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

- but there you go.
- 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.