51x15 - Solar System: Icy Worlds

[bunniefuu]

Throughout our Solar System,

we find worlds shaped by ice.

These ice worlds

are so unexpected
and surprising.

There is definitely
more ice out there

than we really
expected or anticipated.

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

to revealing their secrets.

We've got carbon dioxide snow

on Mars.

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.

The
data has truly transformed

the way that we
understand how ice behaves

so far away in the
depths of space.

But many
questions remain unanswered.

How do
these icy worlds even form?

How did the ice get there?

Is there life there?

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.

Why is
our cosmic neighborhood

home to so many
different and exotic ices?

Icy Worlds."

Right now, on "NOVA."

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.

Thanks to
planetary exploration,

we have witnessed
different forms of ice

behaving in ways that we
could not have expected.

Scientists
are just beginning to uncover

the icy secrets of
our Solar System.

We really don't
know much about ice worlds

and planetary scientists

are really discovering

new things every day.

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.

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.

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.

We only get
one shot because traveling at



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

The $780 million
high-risk mission pays dividends,

delivering a
mother lode of data.

New Horizons
surprises scientists

with incredible images
of Pluto's surface,

revealing features they
never expected to see.

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.

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

Gradually,
my goodness,

that was not Antarctica,
that was actually

a very close picture of Pluto.

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?

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.

Glacier Two
for the Root Canal, acknowledge.

Okay, floor above two.

Hang on.

Never a dull moment around here.

Well, isn't this amazing?

Incredible views. Yes.

This landscape
might look frozen solid,

but it is one of the most

geologically active
areas on Earth.

In the time that
you've been flying here,

have you seen a lot of
changes in the glacier?

Absolutely. Are you kidding me?

Yes. I've
seen immense changes.

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.

Pluto has flow lines?

Yes, they are moving downhill,

similar to these glaciers.

We're
coming in for landing.

Understanding
these glacial features

can help scientists understand

how Pluto's glaciers flow.

Welcome to
the glacier, you guys.

Wow.

One of the greatest
ranges on the continent.

Is the glacier under here?

Yes, we're probably

on top of about


of glacier ice underneath us.

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.

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.

These huge
glacial ice features in Alaska

have formed in this exact way.

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?

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.

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.

On Earth,
these are usually found

as a liquid or a gas,

but in the Solar System,

they can be frozen into ices.

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.

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.

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.

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.

And
it's this solid nitrogen

that creates Pluto's
flowing glaciers

that are so similar to
Earth's water glaciers.

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.

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.

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.

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.

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


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.

When I first
saw images of Uranus,

I thought they were
absolutely beautiful.

Blue, almost ocean-colored.

It has a feature

that has puzzled
scientists for decades:

its vast, shimmering auroras.

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.

Their location
is puzzling because, on Earth,

auroras are
confined to the poles.

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.

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.

Magnetic
fields create auroras,

but on Uranus, this
poses a mystery.

We know
Uranus doesn't have

this flowing metallic
core that Earth has,

but it still has, a magnetic field.

So, how is that magnetic
field being generated?

A clue could lie

in Uranus's icy composition.

If you sent
a spacecraft to Uranus,

you would go through
the atmosphere

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

because it's a gas giant.

It's a
turbulent, high-speed wind,

gaseous environment,

and descend inward,

you go from gases to liquids.

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.

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.

Surprisingly,
even at these extremely high

pressures and temperatures,
water can become ice,

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

Deep in
the planet of Uranus,

you get this
extremely dense,

black, hot ice called
"superionic ice."

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.

This strange
ice is unlike anything

we find naturally on Earth.

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 ba*ls
are the oxygen

and the white is
the hydrogen; H2O,

two hydrogens for every oxygen.

There are around



found in the Solar System.

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

when the temperature's
really, really high

and the pressure's really high.

And
it's these conditions

deep inside Uranus
that, in theory,

could allow this mysterious
superionic ice to exist.

Superionic
ice is still very new.

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

But in 2018,

scientists announced
they'd made superionic ice.

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.

This unique property

may solve the mystery
of Uranus's auroras.

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.

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.

Precisely
the kind of magnetic fields

that could help generate
Uranus's auroras.

But there's still much to learn.

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.

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.

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.

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.

Icy mini-moons
sweep through the rings.

Creating what look
like grooves in a record.

Cassini
gave us that view.

They're absolutely astounding.

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

just really, really lovely.

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?

A clue can be
found in the temperature differences

between the white and
black halves of the moon.

The darker
side is a warmer region.

The temperatures are
hotter on the darker side

than on the bright side.

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.

Which also happens on Earth

where scientists are
studying its effects.

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.

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.

This dark glacial till

has what scientists
call a low albedo.

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.

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?

Did the dark material

come from inside of Iapetus

or did it come from
someplace else?

The smoking g*n
was discovered by complete accident.

So, in


another moon of
Saturn called Phoebe,

which orbits Saturn much
further away than Iapetus does.

Phoebe
is in an unusual orbit

because it goes backwards
with respect to the other moons

in its direction around Saturn.

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.

The Spitzer Space
Telescope used infrared light,

or heat signatures, to detect

what's normally
hidden from view.

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.

We got our images,

and they were
extremely interesting.

Phoebe
rides within a colossal ring

about ten million miles across,

wrapped around Saturn.

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.

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.

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.

How
Iapetus orbits Saturn

is key to solving the mystery

of why it has these
black and white halves.

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.

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.

The ice vaporizes
from the darker, warmer side

and refreezes onto
the colder, lighter side.

And so,
this means over time,

the dark side becomes darker,

the light side becomes lighter.

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.

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.

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.

The Juno
mission is to investigate the origin

and evolution of
the gas giant Jupiter,

the largest planet
in our Solar System.

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.

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.

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.

And that's not
all that makes Europa different.

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

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.

These
lines are vast ice cracks,

some of which are 15 miles wide,

with a dark red floor.

What could be creating

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

The canyons on
Europa are so significant

that NASA's planning a mission

to go to Europa to explore them.

And in preparation,

scientists are exploring
similar environments on Earth,

like these icy
terrains in Alaska.

I think many
of the most important questions

in planetary science
can be addressed

by going to worlds like Europa.

NASA scientist
Sam Howell is studying

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

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.

Europa's
surface features indicate

they are a result
of tectonic activity.

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.

So far, this kind

of global tectonic activity has
only been observed on Earth.

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.

On Earth, the
rocky crust is broken into plates.

They move as softer rock
beneath flows very slowly

over geologic time.

Europa does not
have molten rock like Earth does,

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

A vast
body of liquid water

that exists underneath
its icy surface.

There is more water

in Europa's subsurface

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

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?

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."

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.

And as the temperature
of the ocean changes,

the ice shell thickens and
thins and expands and contracts.

The mechanics
of which can be seen on Earth.

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.

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.

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.

Suggesting
a tantalizing possibility.

This crisscrossing system
of salty canyons means

we might find life in the ocean

underneath Europa's icy shell.

Life as we know
it needs three basic things:

water,

a source of energy, and
also, essential elements.

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.

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.

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.

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.

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.

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.

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.

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.

Sometimes,
icy rocks are ejected

from the frigid outer
regions of the Solar System

and pulled towards the sun.

These are known as comets.

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.

As comets
cross this invisible ice line,

their ice starts
turning into gas.

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.

Inside
the ice line, ice is rare,

but there are places
where it can hang on.

Mars is within the
ice line of the Solar System,

but it still has
ice in it and on it.

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.

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.

The images
show dark fans on the surface

meaning something must have
risen into the air above them.

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.

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.

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.

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.

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.

And depending
on which way the wind

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

Because
of Mars's combination

of atmospheric pressure
and temperature...

the carbon dioxide
turns from ice to gas

without passing
through the liquid phase.

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.

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.

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.

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.

This property of
water ice has enormous consequences

for life on Earth,

the only place life is
known to exist to date.

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.

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.

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.

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.

Across
our Solar System,

scientists have found worlds

shaped by ice,

made of a diversity
of substances

behaving in unbelievable ways.

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

Each one has something
we haven't seen before.

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?

We may
not have all the answers,

but we now know that
ice plays a critical role

in our story.

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.