All language subtitles for NOVA.S51E11.Solar.System.Volcano.Worlds.1080p.WEB.h264-BAE_track3_[eng]

NARRATOR:
When we look beyond Earth,

we discover dynamic worlds.

KATHERINE DE KLEER:
As we're exploring
the solar system,

we are finding

remarkably diverse

and ferociously active worlds.

CLARA SOUSA-SILVA:
Where lava flows,
where volcanoes erupt,

where rumblings beneath
crack the surface.

NARRATOR:
From giant, dead volcanoes

on the planet next door...

JAMES DOTTIN:
It's absolutely mind-boggling

that there are volcanoes
that can get that big

that it can tip a planet.
That's absolutely crazy.

NARRATOR:
...to active ice-cold eruptions

on frozen moons.

PAUL BYRNE:
Where everything's frozen over,

we see volcanic eruptions
blasting out into space,

and that's a real surprise.

NARRATOR:
These explosive worlds

could even provide a clue

to one of the biggest questions
of them all.

JEN GUPTA:
Studying volcanoes
in the solar system

is incredibly important.

It can help answer that question
of where you and I came from

and even how life first began.

NARRATOR:
But ultimately,
volcanoes, fiery or frozen,

reveal the incredible activity
that lies within.

When I think of a volcano,

I think of awesomeness and...

how can I get a ticket
to go there?

NARRATOR:
How can there be so many

different kinds of eruptions
across our solar system?

And what might
Earth's volcanoes tell us

about the possibilities
of life elsewhere?

"Solar System: Volcano Worlds."

Right now, on "NOVA."

♪ ♪

NARRATOR:
Humans have only set foot

on one world beyond our own.

On the moon,
we found a barren landscape,

appearing unchanged
for more than a billion years.

Its surface, scarred
with craters and dark patches.

This was activity that occurred
early on in the moon's history.

The moon now, there isn't much
going on there.

NARRATOR:
Our moon is an inactive world,

frozen in time.

In stark contrast with Earth.

Which seethes with activity
beneath the surface.

Who doesn't love a volcano?
I mean, hot stuff

jumping out
of the ground at you.

It would be really exciting.

OLUSEYI:
I've seen erupting volcanoes,

and I just love active geology.

It just tells me
that the planet is alive,

not literally, but figuratively.

NARRATOR:
And when we look beyond
Earth and its moon,

out into our solar system,

other dynamic worlds like ours
do exist.

As we're exploring
the solar system,

both with telescopes
and with spacecraft,

we are finding
remarkably diverse

and ferociously active worlds
throughout the solar system.

NARRATOR:
Many hold clues
to our own planet's story.

JASON HOFGARTNER:
Looking at volcanoes
elsewhere in the solar system,

we see that Earth has a special
type of volcanic activity,

and so, by understanding
other volcanoes,

we might understand how Earth

had eruptions in the past
or in the future.

NARRATOR:
And since many scientists
think volcanic activity

might have played a major role

in the origins of life
on Earth...

...other active worlds
in our solar system

are especially intriguing.

SOUSA-SILVA:
We know that
there's a relationship

between volcanism and life,

but we don't know where it ends
and where it begins,

and that's why
we need to keep exploring.

♪ ♪

NARRATOR:
The largest volcanoes

discovered
in the solar system so far

are right next door.

Mars is one of the most
explored and photographed

of all the planets beyond Earth.

We've captured its stark beauty.

From ice frosted dunes

to canyons
just over six miles deep.

And many of the most
detailed images

have come from
the Mars Reconnaissance Orbiter.

Launched in 2005,

it is still orbiting
the planet today.

JORGE NÚÑEZ:
It carries instruments,
high-resolution instruments,

that allows us
to view and explore

the surface of Mars
in such detail

that we could map out

things the size of a desk
on the surface.

OLUSEYI:
It's the length of a school bus

with these two big solar panels
to power it,

and as it's going
about its business,

it's sent back
more data to Earth

than any mission ever.

NARRATOR:
These images show in
greater detail than ever before

giant volcanoes

that dwarf anything
seen on Earth.

One so wide...

...it would cover
the length of Nevada.

And one so tall...

...it reaches over twice
the height of Mount Everest.

It's the largest volcano
in the solar system.

Lava once flowed
from these giants,

spilling across the land
in all directions.

So much molten rock

that the combined mass

tipped the planet over
on its axis

by about 20 degrees.

How did these monsters
get so big?

A hint comes from studying
active volcanoes

here on Earth.

OLUSEYI:
If you want to understand
volcanism on Earth,

or if you just want

to understand Earth at all,

you need to start with
plate tectonics.

NARRATOR:
Earth's crust is made up
of seven large plates

and several smaller ones,

which interact with each other
at their boundaries.

AISHA MORRIS:
And they interact
in multiple different ways.

They can be smashing
into each other,

pulling apart from each other,

or grinding against each other
as they move around.

DOTTIN:
So at plate boundaries,

what happens is that

you end up with
rock instabilities

and, ultimately,
the rock melts.

NARRATOR:
Creating the conditions

that have formed the majority
of volcanoes on Earth.

But it's the volcanoes that
don't form at plate boundaries

that tell us the most
about Martian volcanoes.

GUPTA:
On Earth, we also have volcanoes

in the middle of a plate,
not just the boundary.

These are called
hotspot volcanoes,

and Hawaii is a
great example of this.

are typically created
by a plume,

like a bubble of hot magma

welling up directly
from the interior,

hitting the bottom of the plate
and bursting through.

NARRATOR:
Hawaii is a chain
of hotspot volcanoes,

created by a tectonic plate

moving across
a single plume of magma,

erupting onto the surface

forming a line of islands.

Like on Earth,

Mars has hotspot volcanoes,

but with one major difference,

no plate tectonics.

On Mars, instead of the plate
moving over the plume

and making a chain of volcanoes,

you get the plume stationary,
with respect to the ground,

and that means,

over millions or even
billions of years,

Mars has been able
to build up volcanoes

that dwarf anything
that we see on Earth.

NARRATOR:
But all of those
monster volcanoes have quieted.

Still and cold
for millions of years.

Why?

To find the answer,

scientists look deep within,

tracing the source of heat
that drives volcanism

on rocky planets like ours.

Four and a half
billion years ago,

with the rest
of the solar system,

the Earth formed
from the collapse

of a cloud of gas and dust

being smashed together

under the force
of its own gravity.

NARRATOR:
Much of the energy
that went into these collisions

turned into heat,
trapped inside Earth.

Added to that is heat
from radioactive elements

inside the planet, like uranium.

So over time,

these elements actually decay

into lighter elements

and as they do so,

they are constantly warming
and heating our planet

from the inside.

When you stop
and think about it,

it really just is incredible
that all of this heat

that is powering volcanoes
here on Earth

can be traced back four
and a half billion years ago

to the formation of the Earth.

♪ ♪

NARRATOR:
Mars shares
Earth's origin story.

It formed in the same way...

...at the same time...

...capturing enough heat
to drive volcanism

on a staggering scale.

But now the volcanoes are
cold and silent.

Where did all that heat go?

A clue exists
within this volcanic landscape.

In Mars's northern hemisphere
lies the Marte Vallis area...

...where cliffs are built

from an intricate array
of pillars.

Arranged in uniform patterns,

these structures are made
of solidified lava.

Similar structures also exist
here on Earth...

...and they can help
unravel the mystery

behind why Mars's volcanoes
are now silent.

PAUL BYRNE:
We see columnar jointing

in lots of places on Earth.

There's a particularly
beautiful example

in the Studlagil Canyon
in Iceland.

NARRATOR:
Hot lava once flowed here.

As it cooled,
it did something extraordinary.

PAUL BYRNE:
As that lava's cooling down,

it's shrinking,
it's contracting.

And as the lava pulls apart
from itself, as it contracts,

it makes these fractures

and these fractures form
this very regular,

even pattern.

NARRATOR:
Exactly what conditions cause

these unusual structures
to form is complex.

But they do reveal

one of the most fundamental
laws of nature.

DOTTIN:
The simplest explanation

for the second law
of thermodynamics

is that heat flows
from hot to cold.

So if you were to go outside
on a cold day

with a hot cup of coffee,
eventually,

that hot cup of coffee will be
the same temperature

as your outdoor surroundings.

NARRATOR:
More than 65 feet tall,

these columns show
this very principle in action.

BYRNE:
So we can think of how, say,
columnar joints form

through that lens of energy
flowing from hot to cold.

When the lava flow is
flowing over the surface,

in the case of Earth, at least,

it's much hotter than both
the ground and the air.

NARRATOR:
As the lava cools,

its heat rises
into the atmosphere

and then out into space,

slowly cooling
the entire planet.

♪ ♪

TRIPATHI:
The beautiful truth
about physics

is that the laws are the same
everywhere.

So the laws of thermodynamics
work on Earth,

they work on Mars,
they work beyond.

NARRATOR:
The physics may be the same:

volcanoes driven
by ancient internal heat

moving towards equilibrium

with the coldness
of outer space.

But one key difference

caused a big change
in how quickly

Mars lost its heat.

OLUSEYI:
If we look at these two balls

as an example for Earth--
the baseball--

and Mars-- the golf ball--

then they're different sizes.

So as the object gets bigger,

the volume grows faster
than the surface area grows.

In spite of having a volume
that's only 15% of the Earth,

Mars's surface area is,
actually, bigger proportionally.

It's got about 28%

of the surface area
of the Earth.

You can think of it this way.

If I make a big pot of coffee,
it's gonna stay warm for hours.

If I pour some of that coffee
into a mug,

it'll cool down much faster
because there's less of it,

but there's more surface area.

And these differences
have resulted

in so much of what we see today,

including the geologic
and volcanic history

on the two worlds.

♪ ♪

NARRATOR:
Earth and Mars started out

with similar materials:
heat and volcanic activity.

But while Mars's heat
and its volcanism ebbed away,

Earth's volcanoes continue
erupting to this day.

And many scientists believe
that on Earth,

volcanism on the ocean floor
played a role

in life's beginnings.

So with such similar
origin stories...

...could there once have been
life on Mars?

NÚÑEZ:
Mars is like Earth's cousin.

And so very early
in their history as they formed,

they had this volcanic activity,
and we found evidence

that Mars had liquid water
on its surface.

It had a thicker atmosphere.

And around the same time

that we know that life emerged
here on Earth,

there was liquid water
on the surface of Mars

and it had conditions
very similar to early Earth.

NARRATOR:
Today the Perseverance rover,
on Mars since 2021,

is creating packages of rock
samples with the intention

that a later mission will
one day return them to Earth.

Could they contain evidence
of Martian life?

DOTTIN:
So generally, in these rock
samples from Mars,

we're looking for signatures

that there was life
on the planet.

But it would be
absolutely amazing

if we actually found cells
or something similar

in these rocks that indicated

that there is life
on Mars today.

NARRATOR:
For now, any secrets of life
on Mars remain a mystery.

But what Mars does demonstrate

is the smaller the planet,
the more quickly it loses heat.

Still, there is a rule breaker:

a world even smaller than Mars

that is somehow the most
ferociously active body

in the solar system.

Leaving the quiet
volcanoes of Mars behind...

...passing through
the asteroid belt,

the cold rubble left over

from the formation
of the planets...

...we reach the first
of the gas giants.

Twice the mass of all
the other planets combined,

Jupiter is circled
by more than 80 moons.

Some are icy.

Like the frozen expanses
of Ganymede.

And Europa.

But then, there is Io.

About the size of our moon,

Io orbits closer to Jupiter
than any other moon of its size.

Since 2016,

the space probe Juno
has been our eyes

on Jupiter and its moons.

With an elongated orbit,

it has made regular
flybys past Io...

...witnessing violent eruptions,

which shoot out
columns of gas and dust

that reach far out into space...

...and send rivers of lava
pouring across the landscape...

...creating a surface
dotted with lakes of lava.

Io is a volcanic powerhouse,

defying all expectations.

DE KLEER:
Considering how small Io is,

the heat sources
like we have on Earth,

the heat of formation
and the radioactive decay,

those should be, essentially,
completely gone on Io by now.

OLUSEYI:
This little, tiny,
small world of Io,

you'd expect it to be
geologically inactive.

Instead, it's the most

volcanically active body

in our solar system.

That's a surprise.

NARRATOR:
Eruptions continue
day in, day out,

across the entire surface.

A world like no other
in our solar system.

♪ ♪

But similarities can be found

by taking a closer look
beneath the surface

inside volcanoes here on Earth.

Astrophysicist Jen Gupta
is entering a chamber

created by a volcanic eruption

over 4,000 years ago.

GUPTA:
The incredible thing
about this place

is that
as the magma drained away,

it left behind these colors

that we can see here
on the walls,

from elements and minerals

that were dragged up
from the interior of the Earth

during that volcanic eruption.

The one that immediately grabbed
my attention is the yellow.

This is from sulphates
and sulphur,

and these are
the exact same colors

that we see covering
the entire surface of Io.

NARRATOR:
Images of Io are dominated

by its yellow surface,

created by the same sulphates
and sulphur

that line the chamber walls
here in Iceland.

GUPTA:
The scale of this place
is just astonishing,

and to think that
there are chambers like this

under the surface of Io,

filled with molten magma
ready to erupt out.

It's easy to think that Earth,
our home planet,

is completely unique,

but the more we discover
about the solar system,

the more we see
these remarkable similarities,

like having volcanoes on Io.

NARRATOR:
And unlike Mars's
ancient dead volcanoes,

Io's are continually erupting,

creating a thin atmosphere
of volcanic gases.

As Jupiter blocks the sun,

Io passes into its shadow.

Even
with such constant activity,

temperatures plummet,

so low that the thin atmosphere
begins to freeze,

creating an incredible frost.

Made not of water,

but of delicate crystals
of sulphur dioxide.

A few hours later,

they are gone,

evaporating away

as the sun returns.

DOTTIN:
Sulphur is a major component

of volcanic eruptions.

And so it's not surprising

that the surface of Io is

covered with sulphur crystals

because there's so much
volcanic activity

going on there.

NARRATOR:
Io isn't big enough

to have retained heat
from its formation.

So the heat
that drives this much sulphur

to the surface

must be coming
from somewhere else.

DE KLEER:
So, the question is,

why is an object this small

still volcanically active?

Why hasn't it run out
of heat yet?

GUPTA:
The thing about Io

is it doesn't orbit Jupiter
in a circular orbit.

What it does instead is
travel round

in an elliptical orbit
like this.

And it's that elliptical orbit

that's one of the driving forces

behind the level
of volcanic activity

on the moon.

NARRATOR:
Jupiter is the largest planet

in our solar system,

and its gravitational pull
on Io is enormous.

GUPTA:
As Io comes in
towards the planet,

the gravitational pull
of Jupiter is stronger,

causing the very rock on Io

to bulge out
towards its host planet.

Then as Io moves further away,

the bulge shrinks and moves,

causing a tide of rock on Io

that's over 300 feet tall.

That's rock the height
of this chamber

bulging and moving
on that rocky moon.

This is rock
rubbing against rock

in a similar way to
when we rub our hands together,

and they warm up.

It's generating huge amounts

of heat
underneath the surface of Io.

NARRATOR:
A process known as
"tidal heating."

But this bulging movement
generates only some of the heat

that drives
Io's violent volcanoes.

So where is the rest
of the heat coming from?

DOTTIN:
When we think about our moon,

we understand that we only see
one side of the moon,

and this is because

the Earth and the moon
are tidally locked.

NARRATOR:
But as the moon travels

its elliptical path
around Earth,

we actually see it
at slightly different angles.

OLUSEYI:
It's sort of like

if I was to shake my head
and say "no."

Right? You see my face
the entire time,

but because it rocks
back and forth,

you see slightly more of my head

than if I just kept it
pointing right at it.

So, it's like the moon is
looking down on the Earth

and going, "Mm, mm, mm.

Look at those humans."

NARRATOR:
Just like our moon,

Io is tidally locked
to its planet

and has an elliptical orbit.

Which means
that as Io orbits Jupiter,

it appears to rock back
and forth by around one degree.

But there's one big difference
between our moon and Io.

OLUSEYI:
Jupiter is way more massive
than the Earth,

and Io is similar to the moon,

so the tidal effects
are more extreme.

NARRATOR:
Io's tidal bulge

is continuously pulled
towards Jupiter.

So as Io faces the planet
at slightly different angles

throughout its orbit,

Jupiter not only raises the
rock tide 300 feet up and down,

but also drags that tidal bulge
back and forth

40 miles across Io's surface.

Earth's heat was captured
billions of years ago,

locked inside the planet
at the time of formation.

But on Io, its heat
is constantly replenished

by its elliptical orbit.

NARRATOR:
As Io deforms,

the intense friction generated

by these tidal forces
produces enough heat

to drive Io's spectacularly
violent volcanism.

But could all that heat
have driven out

some common planetary
ingredients, like water?

Io doesn't seem
to have any water today,

and we actually don't
entirely know why that is.

Maybe it was never able
to form with any water,

but maybe it just lost
all of its water over time

because of
this tremendous amount of heat

that's produced in it.

FRANCK MARCHIS:
So, there is no water on Io.

Is there life?
We don't know.

If there is life,
it would be a life

which is very different

to the life
we have on our own planet,

and the only way
for us to find it will be

to go there
and to explore directly.

DE KLEER:
Every time
I point a telescope at Io,

I still have that new excitement

because you don't know
what's going to be happening.

You take an image of Io,

and you're saying,
"Which volcanoes are active?"

And you look at it,
and you can just immediately see

from the picture and identify

which volcanoes are going off
at that time.

NARRATOR:
As scientists learn more,

they are finding the effects

of tidal heating
on an even stranger world.

That same source of heat,

caused by an elliptical orbit,

drives volcanic eruptions
that aren't even hot.

Even farther
from Earth than Jupiter,

across a great gulf of space,

lies the next planet.

Saturn's rings loop for hundreds
of thousands of miles.

And just beyond them,

one of its largest moons
changed everything

we thought we knew
about volcanic activity

this far out
in the solar system.

♪ ♪

With a hard, frozen exterior,

Enceladus' surface
averages a chilly

-330 degrees Fahrenheit.

It's one of the coldest places
in the Saturn system.

An ice world,

where we'd expect everything
to be completely still,

frozen and unchanging.

But in 2005,

NASA's Cassini spacecraft
travelled to the South Pole

and discovered
that stillness shattered.

It captured explosive jets

constantly erupting
from the surface.

♪ ♪

NÚÑEZ:
So, when we first saw
those plumes

coming out of Enceladus,

it was just... mind-boggling

that to see this tiny world

spewing material out,

indicating
that it was geologically active.

Discovering the jets
at Enceladus's south pole

completely changed the way
that we see icy worlds.

It changed the way that we see
small, icy worlds in particular.

NARRATOR:
Giant plumes far bigger
than the moon they erupt from

are an incredible sight.

But how is it possible
to have such powerful eruptions

on a frozen moon?

Our usual experience
of volcanic eruptions

is of molten rock

bursting onto the surface.

But eruptions on Enceladus
are different,

more like what's happening here.

At a geothermal power plant
in Iceland.

A mile below the surface

lies a reservoir
of superheated water.

Drilling down into it
allows steam and water

to erupt out
and generate electricity.

HOWETT:
To be here is amazing!

I spent most of my entire
adult life studying Enceladus,

but I've never heard it,
I've never seen it,

I've never felt it,
and this is one-tenth

of what one of the jets
on Enceladus would be like.

It's astounding.

NARRATOR:
Over 660 pounds of water

erupt from the surface
of Enceladus every second,

creating visible eruptions

that can thrust up to
6,000 miles into space.

It's called cryovolcanism.

"Cryo" from the Greek for cold.

Cryovolcanism
is absolutely volcanism.

When we study the planets,
we learned that,

even though they have different
chemistry or slight differences,

that these processes are common
throughout the planets,

and volcanism is one of them.

MARCHIS:
What is surprising

is not only the presence
of the jets,

but their size,
the fact that this is

an extreme cryovolcanism

coming from such a small body.

NARRATOR:
But where does such
an enormous amount of water

come from on a frigid ice moon?

There is a hint.

As Enceladus orbits Saturn,

it wobbles by about 0.12 degrees
on its axis.

A tiny but significant
movement...

...that tells us something
about the moon's interior.

HOWETT:
A simple way to think about

what's happening
inside Enceladus

is to consider what happens
when we rotate two eggs,

one of which is hard-boiled
and the other one isn't.

So, we'll start with this one.

If we spin the egg...

(laughs) Just with eggs,

doesn't seem like
the most obvious solution.

You can see that it...

As it rotates, it's got
a bit of a wobble to it,

and if we rotate it a bit faster
and then stop it,

it'll continue to rotate.

Whereas this one,

we do the same thing.

It rotates more smoothly,

and if we rotate it and stop it,

you can see it stops.

NARRATOR:
The reason the first one wobbles

is because it is raw.

Whereas this one...

...is hard-boiled.

The raw one, of course,
has a liquid in the middle,

and so, even after
you stop the shell,

the liquid continues to rotate,

and that causes
the shell to rotate.

It also caused
that wobbly rotation

that we see all the way along.

Whereas the hard-boiled one
is solid all the way through.

When you stop the shell,
you stop all of it.

It also causes it
to rotate very nicely.

But it's the liquid one,
the raw one,

that's like Enceladus.

NARRATOR:
Enceladus is unlikely
to crack like a raw egg.

But it does wobble like one.

And that tells us that
there is an outer shell of ice,

sitting on top
of a global ocean of water.

But how does that water
manage to erupt

through a shell of around
three miles of solid ice?

QUICK:
When the liquid ocean
is heated from below

by energy from tidal heating,
it expands,

so the liquid wants
to take up more space.

As it seeks
to take up more space,

it pushes up against
the bottom of the ice shell.

NARRATOR:
Once there, another force
comes into action.

Once that water goes
through a crack

and then is exposed to the
vacuum of space,

it's like a suction.

That's what vacuum does.

BYRNE:
The reason water
behaves this way

when it's exposed
to zero pressure

is because
there's nothing acting

to keep
the water together.

So, the water will try
its best to expand

as much as it possibly can.

One force pushes the water up,

and the other force
pulls it out onto the surface,

and that's why we have
these magnificent jets.

NARRATOR:
And they carry with them
the secrets

of what lies beneath the ice.

These plumes contain
traces of silica

and molecular hydrogen

that could've come
from the ocean water

interacting
with hot volcanic rocks.

Suggesting that, in the depths
of Enceladus's ocean,

there may be hydrothermal vents,

towering structures
created by water flowing

into the volcanic rocks
on the seabed.

I think the chances
are pretty high

that there are
hydrothermal vents

at the bottom
of Enceladus' ocean.

Just like Earth's ocean,

Enceladus's ocean sits right
on top of its rocky mantle.

NARRATOR:
And with probable
hydrothermal vents,

an exciting possibility
for life.

NÚÑEZ:
We think that life
could've originated on Earth

in hydrothermal vents.

And these hydrothermal vents

have those ingredients

that are essential for life.

NARRATOR:
And it isn't just
the possibility of heat

that makes Enceladus
a compelling incubator for life.

HOFGARTNER:
There are three key ingredients

to a habitable environment:

liquid water,
chemical nutrients,

and an energy source to use,

and now we know that Enceladus
has all three within its ocean.

QUICK:
A 2023 study showed
that Enceladus's jets

have phosphates in it,

anywhere from 100 to 1,000 times
the amount of phosphates

that we find in Earth's oceans.

Phosphates, we know,
are a key component of DNA,

which is the
building block of life.

NÚÑEZ:
Does that mean
that we found life?

Well, we don't know.

Just because
we found phosphates,

it's-it's a potential
ingredient,

but it's not a slam dunk,

and so, we need to go back
and really explore

in more detail to see

what is the origin
of this phosphate.

NARRATOR:
Any mission to Enceladus
is a ways off.

But there is another world
much closer to home

that has more volcanoes
strewn across its surface

than any other planet.

To find it, we have to return

all the way back
into the inner solar system.

Past Mars's ancient peaks...

...and beyond Earth.

...to a mysterious,
cloud-covered planet.

Venus's dense atmosphere
of carbon dioxide

and clouds of sulfuric acid

obscure the surface.

For decades, orbiting probes
have used radar

to peer through the clouds.

Revealing a landscape dominated

by more than 85,000 volcanoes.

But it was hard to see
in the images

if any were recently active,

or if, like Mars,

they were relics of the past.

So why does Venus
have so many volcanoes?

And are they still
erupting today?

To find out, scientists
are studying Iceland,

one of the most volcanically
active places on Earth.

Here they are investigating
recent lava flow activity

to help prepare
for future missions to Venus.

SUE SMREKAR:
I have remained
fascinated by Venus

because it tells us so much
about the Earth.

They really are twin planets

evolving down different paths.

NARRATOR:
Sue Smrekar is leading
the Veritas mission

preparing to launch to Venus
in the next decade.

She uses radar data,

which creates
black-and-white images

that reveal the texture
of the surface.

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SMREKAR:
I try to see things
with my radar eyes,

just imagining
what they look like.

When it's a nice smooth surface,
the radar wave comes down,

and it looks dark.

But these areas
that are super rough,

you'll get
a lot more reflection, so,

in radar, these areas
will be much brighter.

NARRATOR:
Whether new lava flows
like we see on Earth

exist on Venus
was a much debated subject,

as scientists
had no direct evidence

of recent volcanic activity
on Venus.

Until now.

ROBERT HERRICK:
It's really

only been
in the last decade or so

that technology
has made it possible

to be able to zoom in and out

and flip back and forth
between data.

Robert Herrick and his team
reanalyzed images taken

by the Magellan orbiter...

over 30 years ago,

and spotted a volcanic crater

that had doubled in size
over eight months.

Proving that a volcano,

about the size of Mount Everest,

was erupting
from its northern flank.

HERRICK:
When an investigation
actually works out,

and you learn something
important, and you're like,

"Oh, this is... this is cool."

So, yes,
it's a thrill to, you know,

"Wow, I've-I've made my mark
on the field."

I was so excited
when we saw those images

because what that tells us
is that everything

we've been thinking
about Venus is right,

that this world probably
is volcanically active,

and that just makes us hungry
for more.

NARRATOR:
But evidence of one
probable eruption can't reveal

if the rest of Venus's volcanoes
are still active.

And another mystery remains.

Venus could have been
Earth's twin.

It is roughly the same size
and built of the same stuff.

So why are the two planets
so different today?

Understanding where volcanoes
are found may solve this puzzle

and explain
why Venus is now a planet

with such extreme conditions.

SMREKAR:
So, this map shows
the distribution

of volcanoes on the Earth.

And you can see
there's a big line of them

that goes down the coast
of North America

on down to South America,

and their location
is really controlled

to a large degree by the
location of plate boundaries.

NARRATOR:
Most volcanoes
on Earth are found

where two plates meet,
or are pulling apart,

creating lines of volcanoes
along their edges.

But on Venus,
the pattern is very different.

SMREKAR:
So, this is a map
of the volcanism on Venus,

the volcanoes, and you can see

that they are
all over the place.

They don't follow any nice,

uh, tight line of volcanism

the way we saw for Earth.

And, you know, the difference is

that, uh, on Venus,
we don't have plate tectonics.

Venus has
some entirely different system.

NARRATOR:
Not only are
there numerous volcanoes

scattered
across Venus' landscape,

they take on odd forms.

From lines
of flattened volcanic domes

that look like chains
of pancakes...

...to strange volcanoes

whose rutted sides make them
look almost like insects,

clamped to the surface.

Venus is a volcanic zoo,

with a variety of volcanoes,

including some that are unique
in the solar system.

Venus doesn't have
plate tectonics,

but its crust has
uneven thickness,

and so, magma from within

can climb and poke into
the crust and then cool.

NARRATOR:
The inner heat drives
vast lava flows

that can run
for thousands of miles,

and creates far more blemishes
and bubbles

on the surface
than here on Earth.

But the lack of plate tectonics

points to a far more
profound difference

between Earth and Venus.

DOTTIN:
So on Earth,

there have
been times where

there were
volcanic eruptions

that were so large
and so constant

with tons of toxic gases
and greenhouse gases.

NARRATOR:
Venus's greenhouse gases
trapped heat,

increasing the temperature,

but thanks to plate tectonics,

Earth had a way
to balance this effect.

MORRIS:
On Earth,

carbon dioxide is actually

pulled out of the atmosphere

when it rains,

and those molecules interact
with the rocks

and the carbon dioxide gets
deposited in the rocks,

and as the plate tectonics
cycle occurs,

that material gets then
pulled into the subsurface

and removed from the atmosphere.

BYRNE:
When we have

these huge volcanic eruptions

injecting all this CO2

into the atmosphere,

we see substantial
and severe climate change,

at least for a while,

until plate tectonics is able

to regulate things
and get them back under control.

DOTTIN:
So, plate tectonics

is probably one
of the main reasons

why we've been able
to maintain the climate

that we have on our planet.

NARRATOR:
As Venus's volcanoes erupted,

it seems there was no mechanism

to remove those gases
from the atmosphere

back to the interior.

So the planet got hotter
and hotter,

turning it into the hellish
landscape we see today.

Venus shows the importance
of plate tectonics

in helping to control
not just volcanoes,

but the climate, too.

MORRIS:
So, the lesson
that we can learn from Venus

is that on Earth,

the planet is actually able
to stabilize itself

through the process
of plate tectonics,

and we see on Venus what happens

when the planet's not able

to maintain that stability
in the atmosphere.

NARRATOR:
But human activity emits

at least 60 times
more carbon dioxide

than all the volcanoes
on Earth each year,

and plate tectonics
is a slow process.

OLUSEYI:
What we see in Venus's
atmosphere is a cautionary tale

for the situation that Earth
is in at this very moment.

We have a greenhouse effect
taking place

that's warming
our planet.

Venus is a runaway
greenhouse effect

just gone rampant,

and the whole planet is now
a hotbox of it.

NARRATOR:
Scientists don't think

human emissions alone
can send us

to those extremes.

But with Venus,
we have another planet

that's identical in many ways.

And by understanding
why it's so different today,

we can appreciate the unique
habitability of our own planet.

(explosive pop)

SMREKAR:
Venus is kind of a...
like a teenager.

We go back in time to the
early part of Earth's geology

when we study Venus.

So, it's a... it's a really
a fascinating, you know,

look at our...
the evolution of our own planet.

NARRATOR:
Future missions
like the Veritas orbiter

will help explain
the different processes

behind volcanism on Venus.

SMREKAR:
With Veritas, we have just

all kinds of ways
to look for new volcanism.

We can actually see the surface
deforming at the scale of,

you know, an inch or so.

And I think we're just going
to see vastly more flows

that are young and even,

I predict,
happening during our mission.

NARRATOR:
With new insights into Venus,

we can better understand
the role

plate tectonics plays in
balancing our own environment,

creating the conditions
for life to thrive.

One of the revelations
in our exploration

of the solar system is
what we are finding

isn't a collection
of inactive worlds.

HOFGARTNER:
There is a great diversity

of geological activity in
the solar system,

and sometimes nature

makes it occur
in surprising places.

NARRATOR:
From the tiny,
explosive moon of Io...

to the stunning cryovolcanoes
on Enceladus,

they are telling us
so much about Earth.

SOUSA-SILVA:
When we look
at other planets and moons,

we see snippets
of Earth's past and future.

We were once covered
in volcanoes like Io is now,

and in Venus,
we see what happens

when greenhouse gases
get out of control.

NARRATOR:
But they also tell us

just how remarkable Earth is,

for one very special reason.

Amongst all these geologically
active worlds,

it's still pretty amazing
that the only place

where we saw these
active geology become biology

is here on Earth.

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