All language subtitles for NOVA.S51E12.Solar.System.Icy.Worlds.1080p.WEB.h264-BAE_track3_[eng]

NARRATOR:
Throughout our Solar System,

we find worlds shaped by ice.

SABINE STANLEY:
These ice worlds

are so unexpected
and surprising.

There is definitely
more ice out there

than we really
expected or anticipated.

NARRATOR:
Today, spacecraft are
bringing us closer than ever...

...to revealing their secrets.

We've got carbon dioxide snow

on Mars.

KELSI SINGER:
On Pluto,

we have these
nitrogen ice glaciers

that no one would have
predicted.

Deep in the planet of Uranus,

you get this extremely dense
black hot ice.

MICHAEL WONG:
The data has truly transformed

the way that
we understand how ice behaves

so far away
in the depths of space.

NARRATOR:
But many questions
remain unanswered.

PETER GAO:
How do these icy worlds
even form?

How did the ice get there?

Is there life there?

NARRATOR:
And of all the worlds

in our Solar System,

ours hits the icy jackpot.

The ice we have
here on Earth is special.

And if it didn't have
its special properties,

life on Earth would not exist

and you wouldn't be here
watching me.

NARRATOR:
Why is our cosmic neighborhood

home to so many different
and exotic ices?

"Solar System: Icy Worlds."

Right now, on "NOVA."

♪ ♪

♪ ♪

NARRATOR:
Out in the dark expanse

of our Solar System,

far beyond Earth and Mars...

...we enter the realm of
the gas giants.

Where average
temperatures of the planets

begin to plummet.

Venture even farther
away from Earth,

and we pass the ice giants.

Here, temperatures
can drop even lower...

...down to
-370 degrees Fahrenheit.

These worlds are made almost
entirely of ice...

...existing in exotic,
seemingly impossible forms.

WONG:
Thanks to planetary exploration,

we have witnessed
different forms of ice

behaving in ways that
we could not have expected.

NARRATOR:
Scientists are just
beginning to uncover

the icy secrets
of our Solar System.

GURNEY:
We really don't know much
about ice worlds

and planetary scientists

are really discovering

new things every day.

NARRATOR:
Discoveries that can
shed light on

the strange ways ice behaves

and how dynamic it can be,

not only in our Solar System,

but on other worlds
in our galaxy, too.

(ice crackling)

NARRATOR:
Over three billion miles
from Earth,

the space probe New Horizons

is traveling far beyond
the rocky planets.

And after more than nine years,

arrives at its destination.

As it passes Pluto,

...the probe gives us a glimpse

of a world made of weird ice.

DURFEY:
Flyby missions

are do or die.

If you don't get those images,

if you don't get that data,

you've flown by

and you're gone now.

VERBISCER:
We only get one shot
because traveling at

31,000 miles an hour,

it's not like
you can do a U-turn.

NARRATOR:
The $780 million high-risk
mission pays dividends,

delivering a mother lode
of data.

(camera shutter clicking)

New Horizons
surprises scientists

with incredible images
of Pluto's surface,

revealing features
they never expected to see.

GAO:
I think when

people first saw
images of Pluto,

they were just blown away.

We're seeing
incredible diversity in

what the surface looks like.

VERBISCER:
I walked into the geology room

and looked at an image on one
of the computer screens,

and I wondered why
someone was looking at

a picture of Antarctica.

And it dawned on me

(chuckling):
gradually, oh, my goodness,

that was not Antarctica,
that was actually

a very close picture of Pluto.

WONG:
There were tons of mysteries
that we needed to unravel.

There were lots of features

that puzzled us.
How could that possibly be,

so far away in the Solar System?

NARRATOR:
The amount of data collected

allows scientists
to map Pluto's surface.

Pluto's most prominent feature

is a great icy plain
around 600 miles across.

And, despite the extreme cold,

there are signs
of movement in the ice;

lines etched into the surface

as if they are churning.

And then,
something even more unexpected.

Glaciers.

Flowing rivers of ice

on a world so cold...

...it seems
nothing should be moving.

Pluto is a wintery puzzle,

with icy landscapes as dramatic
as anything seen on Earth.

How is
all this dynamism possible

on a world so far from the sun?

♪ ♪

Pluto, a place right on the
edge of the Solar System,

looks remarkably similar to

some frozen landscapes on Earth,

like this glacier in Alaska.

LEIGHAN FALLEY:
Glacier Two for the
Root Canal, acknowledge.

(man speaks indistinctly
over radio)

FALLEY:
Okay, floor above two.

Hang on.

Never a dull moment around here.

Well, isn't this amazing?

Incredible views.
Yes.

NARRATOR:
This landscape might look
frozen solid,

but it is one of the most

geologically active
areas on Earth.

SINGER:
In the time that
you've been flying here,

have you seen a lot of
changes in the glacier?

Absolutely.
Are you kidding me?

(chuckling):
Yes. I've seen
immense changes.

SINGER:
Some aspects of what
we're looking at

that really reminded me
of Pluto,

there's the kind of flow lines

in the glacier

indicating
the direction of flow.

Oh, Pluto
has flow lines?

Yes, they are
moving downhill,

similar to
these glaciers.

FALLEY:
We're coming in for landing.

NARRATOR:
Understanding these
glacial features

can help scientists understand

how Pluto's glaciers flow.

(plane powering down)

FALLEY:
Welcome to the glacier,
you guys.

SINGER:
Wow.
(Falley laughs)

So beautiful.
FALLEY:
Oh...

FALLEY:
One of the greatest ranges
on the continent.

(laughs)

Is the glacier under here?

Yes, we're
probably

on top of about
700 to 1,500 feet

of glacier ice underneath us.

CARLY HOWETT:
If you ever experience visiting
or seeing a glacier,

you might think that
they're completely stationary.

But actually, if you were to

stand there for long enough,

you would see that they move.

HAKEEM OLUSEYI:
Glaciers form on Earth

when snow does not melt

season after season,
and it packs down,

and the weight of that snow
compresses it into ice.

And as more and more builds up

and it gets heavier and heavier,

it begins to flow.

NARRATOR:
These huge glacial
ice features in Alaska

have formed in this exact way.

SINGER:
This is an incredible landscape.

It really reminds me
of what it would be like to

stand on Pluto.

And it's 15 degrees Fahrenheit,

and we're in this
totally frozen landscape,

and on Pluto, it's even colder.

It's -390 degrees Fahrenheit.

How can these glaciers
be flowing

when it's so cold
on the surface of Pluto?

♪ ♪

NARRATOR:
Water ice is frozen
as solid as rock here,

so it doesn't flow in the same
way as glaciers on Earth.

And yet, these glaciers
look like they are flowing.

We even see two glaciers that
appear to flow into each other,

combining to form a mega glacier

that flows onto
the ice plains below.

GURNEY:
So, at Pluto,
we see these glaciers

that are flowing,
but it's way too cold

for there to be flowing water,

so what are they
actually made of?

So, it might be
surprising to hear

that the definition of ice

really depends
on who you're talking to.

If you're talking to people

on Earth doing
their everyday things,

then ice is just
the solid form of water.

But if you're talking
to a planetary scientist,

then ice is a way to describe
a group of materials.

It's water, but it's also
ammonia and methane,

things that are made up
of a lot of carbon,

hydrogen, oxygen,
nitrogen mixed in.

NARRATOR:
On Earth,
these are usually found

as a liquid or a gas,

but in the Solar System,

they can be frozen into ices.

OLUSEYI:
From afar, we can tell
what the composition

of Pluto's surface is.

But once we got there,
what we didn't expect

is the configuration
of those materials.

♪ ♪

NARRATOR:
A clue to the composition
of the glaciers

is Pluto's surface temperature
of -390 degrees Fahrenheit.

That's pretty close to
the melting point of nitrogen,

at around
-350 degrees Fahrenheit.

Similarly, on Earth,

the melting point of water ice
is 32 degrees Fahrenheit,

not far from the average surface
temperature of 59 degrees.

HOWETT:
For a glacier to move,
it has to be made of an ice

that's not too far away
from its melting temperature,

'cause at the bottom,
what you need is-is

the ice to melt
just a little bit

so that the glacier
is able to flow,

and on Earth, water does that--

the water ice isn't that far
from its melting temperature--

but on Pluto, it's so cold,
that's not the case

for water ice, but it is
the case for nitrogen ice.

Take a breath in.

(inhales)

The air that is in your lungs

includes nitrogen,

and it's a gas for us,

it's the air that we breathe.

On Pluto, it's so cold
that that's solid.

(plane engine whirring)

NARRATOR:
And it's this solid nitrogen

that creates
Pluto's flowing glaciers

that are so similar
to Earth's water glaciers.

WONG:
The same physical forces
are responsible

for carving the landscapes
that we see here on Earth

and on Pluto.

It's just using
different building blocks.

GAO:
I think Pluto
has definitely taught us

that the Solar System
is a giant laboratory

where different elements
can be put together

in all kinds
of interesting ways.

♪ ♪

NARRATOR:
When New Horizons
leaves Pluto behind,

it turns back

and takes one last photograph,

revealing Pluto's
breathtaking atmosphere,

rich in the nitrogen
that condenses on the surface

to create its glaciers.

VERBISCER:
What we've seen

in the outer Solar System
from the New Horizons spacecraft

at Pluto and beyond
has been revolutionary,

showing us diversity in ice that
we don't have here on Earth.

NARRATOR:
Pluto offers a tantalizing clue

that very distant
and cold worlds

may be as active
and dynamic as Earth.

♪ ♪

Closer to the sun,

as we enter the realm
of the ice giants,

ice appears
in even more bizarre forms

behaving in unpredictable ways.

It is found
not only on the surface

but also deep inside planets.

Neptune, made up of around 80%
frozen icy material,

has giant ice storms
raging across it.

Another billion miles closer
to the sun...

...is Neptune's icy twin.

♪ ♪

Uranus is an enormous planet
of icy storms.

GURNEY:
When I first saw images
of Uranus,

I thought they were
absolutely beautiful.

Blue, almost ocean-colored.

NARRATOR:
It has a feature

that has puzzled scientists
for decades:

its vast, shimmering auroras.

STANLEY:
The aurora on Uranus
are mysterious

because flashes of light
suddenly appear

all over the planetary surface,

and you don't know
why they're happening there.

NARRATOR:
Their location is puzzling
because, on Earth,

auroras are confined
to the poles.

STANLEY:
Aurora on Earth happen

when high energy particles
from the Sun

gets funneled along
magnetic field lines

on the Earth
towards the polar regions

and there they run
into atmospheric particles,

and that causes
the atmospheric particles

to shine light.

WONG:
Earth's magnetic field
is created

by the churning motion
of the liquid iron

in Earth's outer core.

Because iron
is electrically conducting,

when it moves, it naturally
generates a magnetic field.

NARRATOR:
Magnetic fields create auroras,

but on Uranus,
this poses a mystery.

GURNEY:
We know Uranus doesn't have

this flowing metallic core
that Earth has,

but it still has, uh,
a magnetic field.

So, how is that magnetic field
being generated?

NARRATOR:
A clue could lie

in Uranus's icy composition.

(thunder rumbles)

GURNEY:
If you sent a spacecraft
to Uranus,

you would go through
the atmosphere

and, uh, you would see, uh,
all of this, uh, gas,

uh, because it's a gas giant.

OLUSEYI:
It's a turbulent,
high-speed wind,

gaseous environment,

and descend inward,

you go from gases to liquids.

GURNEY:
It would just get
gradually more dense, um,

as the pressure increases.

And then, when you get
sufficiently deep enough,

now you enter the ice world
in the interior of Uranus.

♪ ♪

(thunder crackling)

GAO:
The pressures and temperatures

in the interior of Uranus
are extreme.

We're looking at pressures
three million times that

of the surface pressure
of Earth,

and temperatures
reaching 9,000 Fahrenheit.

NARRATOR:
Surprisingly,
even at these extremely high

pressures and temperatures,
water can become ice,

but not in the form
we're familiar with on Earth.

GURNEY:
Deep in the planet of Uranus,

you get this
extremely dense, uh,

black, hot ice
called "superionic ice."

NARRATOR:
At extreme pressures
and temperatures

hotter than the sun's surface,

water is crushed
into a solid form.

Superionic ice sounds like
it comes from

a science fiction novel.

It's really strange,
and you just wouldn't expect

that it would exist
in real life.

NARRATOR:
This strange ice
is unlike anything

we find naturally on Earth.

BERDIS:
Here on Earth,

we see all different types
of ice.

We see sleet,

we see snow, we see ice cubes.

But if we zoom in
under a microscope,

we see that they are all

this very similar

hexagon pattern.

This is water ice
as we know it on the Earth.

It's called "ice Ih,"

and the H stands
for this hexagonal shape

that you can see
in the structure.

Here, the red balls
are the oxygen

and the white
is the hydrogen; H2O,

two hydrogens for every oxygen.

STANLEY:
There are around

20 different types of water ice

found in the Solar System.

The other types that we don't
find here on Earth, uh, can form

when the temperature's
really, really high

and the pressure's really high.

NARRATOR:
And it's these conditions

deep inside Uranus
that, in theory,

could allow this mysterious
superionic ice to exist.

GURNEY:
Superionic ice
is still very new.

It took us a long time to figure
out, uh, that it even existed.

NARRATOR:
But in 2018,

scientists announced
they'd made superionic ice.

MILLOT:
We did the experiment,

and then we look
at all the evidence,

and we have to say,
"Well, it's true."

It's crazy, it's weird,
it's strange,

but it's there.

At super-high temperatures
and pressures,

ice forms
a very different structure.

What you're looking at here
are oxygen atoms, shown in red,

now connected with one another,

and the hydrogen atoms,
in white, have broken free.

♪ ♪

NARRATOR:
This unique property

may solve the mystery
of Uranus's auroras.

OLUSEYI:
Inside of superionic ice,

what's happened is that

the hydrogen atoms have broken
free, and now they're free

to flow around
within the material,

and they are the conductors
of electricity.

WONG:
It's like something
out of science fiction where

the hydrogen atoms
are flowing like water,

conducting electricity,
and potentially responsible

for the wacky magnetic fields
that we see on Uranus.

NARRATOR:
Precisely the kind of
magnetic fields

that could help generate
Uranus's auroras.

But there's still much to learn.

GURNEY:
We don't fully know
what's going on inside Uranus.

We're only just beginning
looking at these icy worlds.

We're really at the tip
of the iceberg. (chuckles)

NARRATOR:
And since these ice giants,
Uranus and Neptune,

hold vast amounts of water,

this bizarre hot black
superionic ice

may turn out to be
the most common form of water

in our Solar System.

As we get closer to the Sun,

ice begins to look
more familiar.

Almost a billion miles
from Uranus

lies Saturn.

Adorned with its
famous icy rings.

Saturn's rings are truly
the jewel of the Solar System.

The first time anyone sees them
through a telescope,

you can't believe your eyes.

NARRATOR:
But we never realized
the true beauty of them

until NASA's Cassini spacecraft
went to visit.

The photographs
and data sent back

were spectacular.

OLUSEYI:
Saturn's rings

turned out to be made up
primarily of water ice

that range in sizes from like

smaller than a millimeter
to larger than an automobile.

NARRATOR:
Icy mini-moons
sweep through the rings.

Creating what look like
grooves in a record.

HOWETT:
Cassini gave us that view.

They're absolutely astounding.

To see the ripples in them,
the gaps in them,

just really, really lovely.

NARRATOR:
The rings are joined
in their orbits

by over 140 moons.

And Cassini
saw something intriguing

on one of the moons
farthest from Saturn.

Iapetus is one of
the oddest looking moons

in the Solar System.

It resembles a walnut

with a mountain ridge
around its middle.

But that's not
its strangest feature.

In 2007,

Cassini sent back
pictures of Iapetus.

One side icy white,

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

Iapetus is one of the
weirdest looking moons

in the Solar System.

It looks like it has two halves.

One really bright side
and one really dark side.

We would expect the moons

in the Saturn system

to have formed with roughly
the same brightnesses.

The darkest materials on Iapetus

are 20 times darker
than the brightest materials.

How can such a bizarre
yin-yang moon exist?

NARRATOR:
A clue can be found
in the temperature differences

between the white and black
halves of the moon.

VERBISCER:
The darker side
is a warmer region.

The temperatures are hotter
on the darker side

than on the bright side.

NARRATOR:
The dark side's
daytime temperature

can be up to
54 degrees Fahrenheit hotter

than the bright side.

This temperature difference

between the black
and white surfaces

creates a peculiar
feedback loop.

(helicopter rotor blades
whirring)

Which also happens on Earth

where scientists
are studying its effects.

WONG:
So right behind me,
we've got this dark glacial till

right next to bright white snow

created through
the erosion

of the majestic mountains
around me.

NARRATOR:
These dark spots
are not solid rock,

but are dust and dirt
covering the ice.

And there's
a huge, stark contrast

between the brightness
of the snow

and the darkness
of the glacial till.

NARRATOR:
This dark glacial till

has what scientists call
a low albedo.

WONG:
Which means that it absorbs
most of the sunlight

that hits it, heating it up,

and that heat gets transferred
to the surrounding snow,

melting it into liquid water,

causing the dark streaks
that you see

coming down the side
of that cliff.

And a very similar process
happens on Iapetus.

NARRATOR:
With so little light
and heat from the sun,

it's a very slow process.

Over a billion years,

it's estimated the dark regions
can lose around 66 feet of ice

compared to the white side.

As this feedback
mechanism continues,

it keeps the black side black...

...and the white side white.

But a mystery remains.

Where did all the dark material
come from in the first place?

VERBISCER:
Did the dark material

come from inside of Iapetus

or did it come
from someplace else?

NARRATOR:
The smoking gun was discovered
by complete accident.

VERBISCER:
So, in 2005, I was observing

another moon of Saturn
called Phoebe,

which orbits Saturn much
further away than Iapetus does.

SINGER:
Phoebe is in an unusual orbit

because it goes backwards
with respect to the other moons

in its direction around Saturn.

VERBISCER:
If you look at
the Cassini images of Phoebe,

you see that it is a pretty
heavily cratered surface.

So, it's been hit with things
for billions of years,

and material has been excavated

and thrown into the space
around Phoebe.

The question is,
where did all that material go?

Where are all those
dust particles?

So, we got the idea to use
the Spitzer Space Telescope

to try and look for dust

in the region around Phoebe.

NARRATOR:
The Spitzer Space Telescope
used infrared light,

or heat signatures, to detect

what's normally hidden
from view.

SINGER:
If you were able to see

how the Spitzer telescope sees,

it would be like when you put on
night vision goggles,

and all of a sudden,
you're able to see in the dark.

VERBISCER:
We got our images,

and they were
extremely interesting.

NARRATOR:
Phoebe rides within
a colossal ring

about ten million miles across,

wrapped around Saturn.

VERBISCER:
It is the largest ring by far
in the Solar System.

This ring is so big that
a billion Earths

could fit inside
the volume of the ring.

It makes perfect sense
that this ring

should be called the Phoebe ring

because it is associated
so closely with the moon Phoebe.

NARRATOR:
The Phoebe ring
moves around Saturn,

in the same direction
as its moon Phoebe,

backwards from
the other moons and rings.

Each time a passing object
or rocky debris

gets too close to Phoebe...

boom.

The resulting impact

throws dark material
out into space.

SINGER:
Some of this dark material

in this huge ring starts
to fall in towards Saturn,

and Iapetus is basically

running through those particles
in its orbit.

NARRATOR:
How Iapetus orbits Saturn

is key to solving the mystery

of why it has these
black and white halves.

(wind howling)

WONG:
So Iapetus, like our moon
that orbits the Earth,

is tidally locked,
which means one side of Iapetus

always faces Saturn,

the other side always faces
away from Saturn.

Imagine this snowball
is a freshly formed Iapetus,

completely uniform
in its brightness on all sides.

Now, as it orbits around Saturn,
through the Phoebe ring,

it will pick up
dark dust particles

from that ring.

And because it is
tidally locked to Saturn,

the same hemisphere

will keep piling on dust

every time it goes around

for millions and millions
of years,

continuously darkening
this side of Iapetus.

DURFEY:
As soon as the front side

of Iapetus became darkened,

the ice underneath started
heating up more quickly,

so that would become a gas
and migrate around

to the colder,
lighter side of Iapetus.

NARRATOR:
The ice vaporizes
from the darker, warmer side

and refreezes
onto the colder, lighter side.

DURFEY:
And so, this means over time,

the dark side becomes darker,

the light side becomes lighter.

NARRATOR:
It's a slow process,

one dust particle at a time.

But it's the best explanation

of how this peculiar moon

got its self-sustaining,
warm, dark face.

OLUSEYI:
Iapetus just shows us
the potential

of the interconnectedness

between the planetary bodies
of our Solar System.

We think they're isolated,
but nothing's isolated.

NARRATOR:
Iapetus is not
the only icy moon affected

by the system it exists within.

Another moon closer to the sun

reveals not only a unique
connection with its neighbor,

but also hints

that something
potentially profound

could lurk beneath its surface.

NASA LAUNCH ANNOUNCER:
T minus five, four,

three, two, one.

Ignition and liftoff

of the Atlas V with Juno
on a trek to Jupiter.

NARRATOR:
The Juno mission is
to investigate the origin

and evolution
of the gas giant Jupiter,

the largest planet
in our Solar System.

LYNNAE QUICK:
The main goal
of the Juno spacecraft

is to study Jupiter.

However,

as it orbits Jupiter,

it's taking
these wonderful images

of Jupiter's largest moons.

NARRATOR:
Ganymede,

the largest moon
in the Solar System.

Io,
the most volcanically active.

And then,
there's the icy moon, Europa,

the odd one out
with the smoothest surface.

It's an ancient moon,
billions of years old,

and yet, mysteriously,

has a young surface,
with few craters.

DURFEY:
We can get

an idea of how old
a planetary surface is

by counting the number
of impact craters.

Europa barely has
any impact craters,

which means that its surface
must be really young.

NARRATOR:
And that's not all
that makes Europa different.

It's criss-crossed by a strange
network of striking red lines.

GONZALEZ:
The surface of Europa

has a lot of interesting cracks
and features to it,

and has lots of lines,

which look almost like a network

of blood vessels in an eye.

♪ ♪

NARRATOR:
These lines are vast ice cracks,

some of which are 15 miles wide,

with a dark red floor.

OLUSEYI:
What could be creating

these criss-crossing lines and
patterns on Europa's surface?

♪ ♪

QUICK:
The canyons
on Europa are so significant

that NASA's planning a mission

to go to Europa
to explore them.

NARRATOR:
And in preparation,

scientists are exploring
similar environments on Earth,

like these icy terrains
in Alaska.

(wind whistling)

SAM HOWELL:
I think many
of the most important questions

in planetary science
can be addressed

by going to worlds like Europa.

NARRATOR:
NASA scientist Sam Howell
is studying

what may be at the heart of
Europa's mysterious appearance.

HOWELL:
What I'm most excited about,

coming from a background

in studying plate tectonics
here on Earth,

we see systems of rigid,

icy plates moving around similar

to the way Earth's plate
tectonics looks on the surface.

But digging in, we expect those
processes to be very different.

NARRATOR:
Europa's surface features
indicate

they are a result
of tectonic activity.

BERDIS:
This is an up-close image

of Europa's surface,
and you can see

this large, dark red band

in the very center of the image.

We know that
this feature is created

due to tectonic activity

because
it appears that the crust

of Europa has pulled apart,

and you've had material flow up
from underneath.

But if we were
to take this feature

and extract it from this image,

both sides of the crust would
fit back together

like a puzzle piece.

We did not expect
to see tectonic activity

on a tiny moon like this,
but there it is.

NARRATOR:
So far, this kind

of global tectonic activity has
only been observed on Earth.

OLUSEYI:
Take a look at Earth,

and you'll see
that South America looks like

it fits right neatly
in there into Africa.

And so, we know
that in the Atlantic,

the seafloor is spreading,

and that's what spread
those two features apart.

NARRATOR:
On Earth, the rocky crust
is broken into plates.

They move as softer rock beneath
flows very slowly

over geologic time.

QUICK:
Europa does not have molten rock
like Earth does,

but what we do believe Europa
has is a subsurface ocean.

NARRATOR:
A vast body of liquid water

that exists
underneath its icy surface.

WONG:
There is more water

in Europa's subsurface

than all of Earth's oceans,
rivers and lakes combined.

NARRATOR:
This massive ocean
sits beneath a layer

of water ice, which could be
up to 15 miles thick in places.

So what force is powerful enough

to crack
Europa's extensive icy shell?

BERDIS:
As Europa and all of the
other large moons orbit Jupiter

and interact with it,

they are all constantly pushing

and pulling
and tugging on each other,

and this process
is called "tidal heating."

NARRATOR:
The tidal heating varies,

depending on how close
or far Europa is from Jupiter

and the other moons,

resulting in temperature changes
in the ocean.

QUICK:
And as the temperature
of the ocean changes,

the ice shell thickens and thins
and expands and contracts.

(wind whistling)

NARRATOR:
The mechanics
of which can be seen on Earth.

QUICK:
As water freezes,

it takes up more space
and expands into ice.

It's very similar to if we were
to take a bottle of water

and place it into the freezer.

First, it would expand,

and then we'd notice a large bit
of cracking.

This is what is happening
on Europa.

NARRATOR:
Scaled up to the size of a moon,

these ice expansion cracks
create massive canyons

across Europa.

And as these canyons form,

a key ingredient
from the ocean below surges up

through the cracks,

giving Europa's markings
their distinctive red.

BERDIS:
So the red marks that we see
on Europa's surface--

these cracks and lines--

are salts

that have come up
from below the surface.

♪ ♪

NARRATOR:
Suggesting
a tantalizing possibility.

This crisscrossing system
of salty canyons means

we might find life in the ocean

underneath Europa's icy shell.

SINGER:
Life as we know it
needs three basic things:

water,

a source of energy,
and also, essential elements.

NARRATOR:
Europa has an ocean,

and a source of energy
from tidal movements.

But it's missing
the final key ingredient:

some essential elements.

However, with a little help
from its neighboring moon Io,

these elements can be found
on Europa.

SINGER:
Io

is an extremely
volcanically-active place.

And these volcanoes emit

sulphur
and other sulphur products,

and these make it
all the way onto Europa.

And sulphur is one of those
essential elements that life

on Earth uses.

♪ ♪

BERDIS:
All of the sulphur
that's coming from Io

and landing on Europa's surface

is interacting
with the salts and water

that's coming up from underneath
Europa's icy crust.

NARRATOR:
Chemical reactions
between the sulphur from Io

and the salts on Europa
create essential molecules

needed for life.

And this allows
for this perfect breeding ground

for potential life
to form and evolve.

NARRATOR:
Europa is such a strong
candidate for life

that NASA is already preparing
to explore the moon.

The goal is to study
Europa's surface

in more detail

so that a future mission
can one day land

and explore
beneath its icy crust.

And scientists like Sam
are already testing ideas

for studying
Europa's watery world.

HOWELL:
What we're doing is
we're deploying a robotic probe

into the ice and under it

to explore what this
lake environment is like.

We might have the opportunity

in my own lifetime

to answer a question
that's intrinsic to all of us:

are we alone in our universe?

Are we alone
in our Solar System?

And one of the most exciting
aspects of exploring Europa

is the potential
of someday knowing

whether or not there's life
in our own Solar System.

NARRATOR:
Europa is one
of the last ice moons

that can exist
this close to the sun.

Worlds existing any closer
to the warmth of the sun,

like the rocky worlds
of Mars, Earth, and our moon,

have relatively little ice.

Because they lie inside
what is known as the ice line.

DURFEY:
You can't see the ice line,

but you can see its effects.

When small bodies that are

primarily composed of ice

cross inside of the ice line,

the ice within them
begins to vaporize.

NARRATOR:
Sometimes, icy rocks are ejected

from the frigid outer regions
of the Solar System

and pulled towards the sun.

These are known as comets.

HOWETT:
Comets are basically
dirty snowballs,

mostly water ice
with a little bit of dust,

and as they come
into the inner Solar System,

they get heated up by the sun.

NARRATOR:
As comets cross
this invisible ice line,

their ice
starts turning into gas.

HOWETT:
And that's what forms
these long tails

that we can see
when you look at a comet,

and those tails
stream away from the sun

as the comet
moves in towards it.

NARRATOR:
Inside the ice line,
ice is rare,

but there are places
where it can hang on.

DURFEY:
Mars is within the ice line
of the Solar System,

but it still has ice
in it and on it.

NARRATOR:
It's the end of winter,

and it's been dark
at Mars's south pole

for over 150
Martian days straight.

Mars holds onto
much of its ice at its poles.

The ice sheet here
is not like any on Earth.

Because as winter
turns to spring,

the surface becomes covered
in strange features.

And with the launch of
the Mars Reconnaissance Orbiter

in 2005, we began to see them

like never before.

OLUSEYI:
The Mars Reconnaissance Orbiter

is a satellite
of Mars that takes

photograph after photograph

of Mars's surface,

and so it's able to see
these things come and go

and change with the seasons.

NARRATOR:
The images show dark fans
on the surface

meaning something must have
risen into the air above them.

GONZALEZ:
We see these features,

and they will go
in the direction

depending on the wind pattern
of Mars.

So we know that material

is being pushed out
from underneath.

NARRATOR:
This phenomenon seen on Mars

depends on the type of ice that
falls from the Martian skies.

During winter at the South Pole,

more and more snow falls.

But with so little water
in Mars's atmosphere,

this isn't the type of snow
we have on Earth.

This is carbon dioxide snow.

GAO:
Every winter,
three to four trillion tons

of carbon dioxide snow
falls on Mars.

That's so much snow
that the atmospheric pressure

at the surface of Mars
decreases by about a third.

NARRATOR:
The air is literally
freezing to the ground,

forming carbon dioxide ice caps
at the poles.

But in spring, as the warmth
of the sun reaches

the poles again,
something incredible happens.

DURFEY:
As the sun comes over
the horizon,

the carbon dioxide ice
is heated.

This carbon dioxide ice
can turn to gas,

and when it does,
it forms these geysers

that also bring other material
from the subsurface

to the surface.

GONZALEZ:
And depending
on which way the wind

is blowing, it'll form
these nice looking fan features.

NARRATOR:
Because of Mars's combination

of atmospheric pressure
and temperature...

...the carbon dioxide
turns from ice to gas

without passing
through the liquid phase.

WONG:
On Mars, its atmosphere

actually falls onto the surface

and then vaporizes
back into the atmosphere

on an annual basis.

That's absolutely wild

because it's so different from
what's happening here on Earth.

NARRATOR:
These conditions on Mars

have enabled carbon dioxide snow

to create unique features
on its surface.

But the conditions found
on its nearest neighbor,

close enough to see
from Mars with the naked eye,

have allowed for something
extraordinary to form.

And just like Mars,

Earth, too, has ice caps
at its poles.

But the similarities end there.

HOWETT:
Earth's ice is really unique

because we operate in
a very small temperature range

and a very small pressure range
on the surface.

The ice that we experience
is a very small subset

of the total ice
that's in our universe.

NARRATOR:
Earth's temperature
and pressure ranges

allow water to exist
in all three states:

solid, liquid, and gas.

Earth is the only place known
to have floating icebergs

and bodies of water
not completely frozen over.

And frozen water
under Earth's conditions

has an important property.

We might take this for granted,

but the ice
that we have here on Earth

floats because its density

is lower than the water
that it is floating in.

And so, the molecules
of water ice,

as it freezes,
expands out slightly

and moves away from each other

to lower the overall density
of the ice,

and this allows it to float
on top of the water.

NARRATOR:
This property of water ice
has enormous consequences

for life on Earth,

the only place life
is known to exist to date.

BERDIS:
The ice on Earth provides
a form of protection

to any life below the surface

that might need protection from
anything that could harm it.

NARRATOR:
Ice's ability to float

means that,
during Earth's colder periods,

bodies of water didn't freeze
from the bottom up,

instead remaining a liquid

where life may have held on.

(birds and insects chirping)

For around four billion years,

liquid water on Earth

has allowed an unbroken chain

of life to evolve.

Resulting in oceans.

Home to countless species.

And rivers teeming with life.

All made possible
by the unique interplay

between liquid water
and floating ice on Earth.

OLUSEYI:
The next time you find yourself

making a beverage
and you put ice in it,

just take a moment and reflect

on the amazingness of the ice

that made your life possible.

NARRATOR:
Across our Solar System,

scientists have found worlds

shaped by ice,

made of a diversity
of substances

behaving in unbelievable ways.

DURFEY:
There's a massive variety
of ice worlds out there.

Each one has something
we haven't seen before.

NARRATOR:
We are in a golden age
of discovery,

but our knowledge of these
ice worlds is far from complete.

There is so much left to learn
about ice worlds.

Our understanding
is only skin deep.

We want to explore
these worlds because

it really tells us
where we fit into the universe.

Why are we here?
How did we first get here?

NARRATOR:
We may not have all the answers,

but we now know that ice
plays a critical role

in our story.

WONG:
Without the kind of ice
that we have here on Earth,

we might not even be here
to be discussing ice

and all of its wondrous forms.

♪ ♪

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