All language subtitles for Space Volcanoes BBC Horizon 2017 1080p HDTV MVGroup EN Sub_Subtitles01.ENG

The landscapes of Earth have been
shaped by volcanoes.

We've long been in awe of their
destructive beauty.

But only recently have we discovered
that volcanism exists beyond Earth.

The planets and moons of the solar
system have volcanoes that are even

more extraordinary than those
on our home planet.

Rivers of lava once raced across
our moon.

It's an amazing thought that you
could have been standing on Earth

and looked up at the moon, and seen
these massive eruptions happening.

The largest volcano
of the solar system,

three times the height of Everest,
is on Mars.

The most violent volcano
is on a moon of Jupiter.

Huge, icy geysers fountain out into
space from a moon orbiting Saturn.

We have not closed the book on
volcanism across the solar system
by any means.

But what's most remarkable is what
volcanic activity elsewhere in

the solar system has told scientists
about our own planet, Earth.

What the Earth was like
at its birth,

why we have the geology
and the atmosphere we do.

And even how life on Earth, and
possibly elsewhere, originated.

Way back in the ninth century AD,

a band of Vikings discovered
Iceland.

They experienced volcanic eruptions
for the first time.

To explain their devastation,

they evoked the terrible wrath of
gods such as Surtr, the fire giant.

A Viking poet wrote, "In the
beginning, all was cold and grim.

"Then came Surtr
with a crashing noise.

"Bright and burning,
he bore a flaming sword."

A millennium later, and a team of
international scientists has also

travelled to the land of fire
and ice.

This small country has more types of

volcanoes and geological wonders
packed into it

than anywhere else in the world.

For the team, it allows them to
compare the volcanism of Earth with

volcanoes found elsewhere in
the solar system.

You've got these continual cycles of
glaciers and volcanoes.

Absolutely brilliant.

Yeah, you have a really diverse
range of volcanic features here,

and I think it's a good place to see
the importance of volcanism.

For geologist Jim Head,

Iceland is a familiar landscape.

In the 1960s,

he was teaching the Apollo
astronauts all about rocks

before they headed off to the moon.

We took them everywhere we could

that would give them geological
information.

Iceland was clearly one
of those.

And I think it's completely perfect,
actually,

that we are here today in Iceland,
studying the volcanoes that

actually propelled the astronauts to
go to the moon.

Five, four, three, two, one.

The Apollo missions weren't just
about the space race.

They were also the most ambitious
geological field trips of all time.

A key aim was to discover
if volcanoes

had helped create the moon.

And, if so, were any still active?

Before the Apollo programme,

we didn't even know whether the moon
had volcanism.

For example, some people thought it
was a cold moon,

some people thought it was
a warm moon,

which had heating inside
and volcanism.

So this is a big question -
was it even volcanic rock?

2,000 feet, 2,000 feet.

47 degrees. Roger.

These dark-looking plains
of the moon

were particularly tantalising
to scientists.

They're called the seas,
or the maria.

Beautiful view!
Isn't that something?

Magnificent desolation.

To find out exactly what they were,

the first Apollo landing was
to Mare Tranquillitatis,

the Sea of Tranquillity.

OK, ready for me to come out?

All set.

As the astronauts explored the dusty
and rocky surface,

they recognised basalt - the most
common volcanic rock found on Earth.

And lots of it.

When you erupt molten rock on
a moon, liquid rock on the moon,

it actually is one sixth gravity,

so it's much less gravity
than we see on the Earth.

It looks like a collection
of just about

every variety of rock
you could find.

If the lava is coming up from great
depths, given the gravity, etc,

you'll get a lot of lava coming up,

commonly much more than you see
on the Earth,

and so it flows great distances,

and so we have lava flows that go
over 1000 kilometres,

like, incredible, it would go

halfway across the United States,
no problem.

Another mysterious feature
found on the moon

was these winding canyons,
or sinuous rilles.

These channels were up to 400 metres
deep and over 100km long.

Clues as to what created them
can be found back on Earth.

Under the south-west of Iceland are
curious tunnels through solid rock.

They appear almost man-made.

Gro Pedersen is exploring one.

In the depths of the tunnel,

she hopes to find evidence of what
used to flow through it.

You can actually see how the lava
has been running along
the wall here,

and you can see also that it was
very hot in here,

because some of this lava re-melted,

and basically was dribbling down
the wall. You see that here.

It's a lava tube and, long ago, lava
was surging through these tunnels.

One of the very exciting things
people found on the moon

was these sinuous rilles and,

of course, before people actually
had been on the moon,

they were thought to potentially
be water eroded.

But then people have gone
to the moon,

and it has been studied much more
and we've found out that these

sinuous rilles were always connected
with the maria,

the moon lava that we have up there.

Perhaps these sinuous rilles
were once enclosed lava tubes.

So one of the things that
you see here, obviously,

is that we have what we call
skylights,

so the roof has collapsed.

If all of the roof collapses,
you will end up with a valley,

like something you see on the moon.

But you can also see the tubes on
the moon by a string of skylights,

just as we see here, one hole after
the other, and you just follow them,

you trace them down and you can see
that these are within lava flows.

But when did these eruptions
take place?

And why did they eventually stop?

The answer would come in small bags
of volcanic rocks

brought home by the astronauts.

On Earth, they could be
accurately dated.

So when the moon rocks were brought
back, it's, like, unbelievable.

OK, this we can tell,
four-billion-year-old rocks.

These are the keys to the
understanding of the solar system.

Like other planetary bodies
made of rock,

the moon was a mass of hot molten
magma as it was forming.

It's an amazing thought that you
could have been standing on Earth

and looked up at the moon and seen
these massive eruptions happening.

But all the time, it was cooling -

being relatively small,
a quarter the diameter of the Earth,

the moon cooled down quickly.

By three billion years ago,

almost all the lava and interior
magma had solidified

into one big lump of cold rock.

No more volcanoes.

But you see the remnants of it.

I mean, when you look at the sky
and you look at the moon,

you see the evidence
of the volcanism,

because you see the dark areas,
the basalt,

which has filled in the craters.

Understanding how the moon lost
its volcanoes

helps explain why Earth remains
so active.

Being larger allowed the Earth to
retain much of its original heat.

And so today, our planet is
a dynamic and ever-changing world,

rather than a dead one.

So, the discovery on the moon
of lava flows

gave us pause to think
about how this worked

on other planetary bodies.

How does volcanism work on Mars?

So, the lunar exploration
really opened up

a field of, really,
planetary volcanology.

Exploring our neighbour, Mars,

also reveals secrets about
Earth's geology.

When probes first reached
the red planet,

one feature stood out
above swirling sandstorms.

The volcano Olympus Mons.

Olympus Mons is enormous,
it's about 25km high.

On Earth, you would be looking at
something ridiculously high.

Most commercial aircraft fly
10-15 kilometres.

So you're looking at something
that is towering way above

what commercial aircraft might fly.

Its base covers an area
the size of France.

It's three times the height
of Mount Everest.

Making it the largest volcano ever
discovered in the solar system.

Finding out how it grew to be
so colossal

tells scientists more about
the volcanoes of Earth.

That's why three of the team have
come together to study this volcano.

Icelanders call it Skjaldbreidur,
which means "broad shield",

as side on, it's reminiscent of
a Viking shield.

Although small in stature,
it's of great significance.

This shield volcano
is the one over...

about which all the other volcanoes
of this type are called,

in the solar system
and on the Earth.

So this is the first one,
in many senses,

the first one to be named
the shield.

It's only 1,000 metres high,

a 25th the height of Olympus Mons,

but crucially, it's the same type
of shield volcano.

At the summit is the crater.

Wow, now you can see the crater.

Yeah. Fantastic. Wow!

That's very nice.

I mean, you could even have come
skiing up here. Oh, wow. Yeah.

Then we can imagine, like,
a lava lake.

Yeah, just round the top.

Yeah. Dribbling over where
we are now. Yeah.

Around the rim
are mysteriously-shaped rocks.

They look almost like
fossilised snakes.

Yet they give a hint how this type
of volcano forms,

and what gives it
the distinctive shield shape.

This is a type of lava
we call entrail,

and it's a bit like the entrails
from the inside of a human body

or any animal body.

They're characteristically
quite thin.

I mean, you can see from the shape
of my hand,

it's a couple of hand widths.

Shield volcanoes comprise lavas
that are very runny,

because the shapes of them,

this broad shield shape, tells us
it has to have been.

And we have the evidence in front of
our eyes of these small tubes,

these entrails running down
the sides of the volcano,

telling us that indeed,
it had to be very runny.

This fast-flowing lava creates

the gentle slopes of all
shield volcanoes,

including the largest one of all,
on Mars.

But while shield volcanoes
on Iceland

have just one crater at the summit,

Olympus Mons has six
overlapping craters.

That's the key. We actually can use
what we see in Iceland to say,

what we see in Mars is similar,
but also different.

It has to be much, much longer lived
with multiple phases of eruptions

to produce these multiple summit
craters we see on Olympus Mons.

When this behemoth erupted,
Mars shuddered.

Rivers of lava swept down the
massive flanks of the volcano.

But Earth is twice the size of Mars,

so why don't we have volcanoes
as enormous as Olympus Mons?

It's all to do with plate tectonics.

Earth is made up of
seven huge plates

drifting above a sea of magma.

The circulation of magma recycles
rocks and gases,

bringing them to the surface
and then back down again.

Iceland is the perfect place to
witness plate tectonics in action.

This rift is where the North
American plate, to the left,

divides from its Eurasian cousin,
to the right.

The rift is widening rapidly,
at over two centimetres a year.

We've got the best evidence of plate
tectonics we can find here.

You can see the tension of the
plates moving apart from each other.

Yeah, this is the only planet that
we know that's got plate tectonics.

Mars, like all other planets we know
of, has no active plate tectonics.

The entire crust of Mars remains
locked in place,

with repercussions
for its volcanoes.

Any upwelling magma
continually breaks through

at one fixed location.

On Mars, it's just centred,
the same spot, for so long,

building up a huge volcano.

So it's a very focused eruption
of magma for billions of years.

And what happens is you just end up
with a huge volcano,

the biggest in the solar system.

While Mars is no longer
volcanically active,

it does share an important feature
with Earth - the polar ice caps.

The story of these ice caps

has been revealed
through unusually shaped volcanoes.

They have steep sides and a flat top
like a table.

Scientists now believe they might
have been formed when volcanoes

exploded through an ancient
ice sheet.

To understand how ice can change
the behaviour of lava,

scientists are carrying out
an extreme experiment.

For this, Ingo Sonder and Tracy
Gregg need to make their own lava...

..out of 50kg of
basalt rock.

We're turning it to its lava state,

and the students have built
a little ramp

that the lava will pour down
and pool at the end.

And at the end of this lava stream,
there will be a little pond of ice.

So the lava's going to flow
over the ice.

We know this has happened on Earth.

We think it's happened on Mars
in the past.

So we'll see what happens.

The electrical furnace is running
at 80,000 watts.

By now, the molten rock
is over 1,200 degrees Celsius.

It's ready for the big pour.

Look where it hits
the ice, it's boiling!

Because the ice is melting
and it's flashing to steam.

And it's creating all those bubbles
there on the lava.

Whoa! And now, this is what
happens...

..when the lava melts the ice
and there's enough water,

we're getting some little
steam explosions.

Right, there's no more lava
coming out of the furnace.

But underneath that black crust,
it's still liquid,

it's slowly flowing down.

And you can see where
it's ponded over the ice,

there's some heaving going on
as gas is trying to escape.

The experiment lets Tracy identify

key features as molten rock
interacts with ice.

When the lava hit the ice, a couple
of things happened really fast.

The lava started to bubble,

as the ice melted
and then flashed to steam.

And then, as more melt occurred,

there were actually puddles of water

that started to boil
and spatter just like

on your stove, right,
the water spattering.

Where the ice wasn't, we have
nice, neat, organised flows,

folds in the lava.

And right where the ice starts,

we get these bigger bubbles
on the surface.

Look, that one's broken open,
you can see inside.

That's the kind of thing
we could look for on Mars.

Right? To see if there was any
lava-ice interactions on Mars.

Can you hear it?

As the lava cools, it contracts,

and it makes little pops
like breakfast cereal.

Pop, pop.

Yep.

That's amazing.

The artificial volcano confirms that

lava behaves very differently
when it meets ice.

But what happens
out in the real world?

One of the most distinctive types of
volcano in Iceland is called a tuya.

The team believe they can help
explain the mountains

with a similar shape on Mars.

Wherever we see volcanoes
that look like this,

on Iceland we know that the ice
has been there,

and if we see the same sorts
of volcanoes on Mars,

we've got a good idea or a very good
idea that there was ice present.

There are two polar ice caps
on Mars today.

But millions of years ago,

they were far more extensive.

Mapping the tuyas on Mars reveals

the coverage and depth
of the ancient ice sheets.

That's amazing, that you can
actually say something about

ice thickness in the past
on a different planet,

after the ice has gone.

Which may have been three and a half
billion years ago, as well.

Yeah. It's similar processes on
different planets but it's yielding

valuable information. It's telling
us about what most planets...

how they were evolving and what was
happening at the time.

Today, Mars and our own moon are
cold and desolate planetary bodies.

Geologically inert.

While Earth has retained
active volcanoes.

To understand how we got here,

we need to find out what Earth
was like four billion years ago.

And scientists think they've found
the perfect place to look,

a moon far out in the solar system.

Ashley Davies is a top
planetary volcanologist.

He's fascinated by a moon of Jupiter
called Io.

One of the most important images
that's ever been collected by any

spacecraft was obtained
by Voyager at Io.

The image revealed this crescent
rising above Io's surface,

no-one knew quite what this was.

Could it be another moon behind Io,
or some artefact in the image?

And then it was realised that this
was actually a huge volcanic plume

rising up from Io's surface.

For me, this was

an image that I think shaped
the rest of my life,

because from this point...

I was a schoolboy and I realised
this was a huge step in an unknown

direction for astronomy
and planetary science.

And in a way, this actually put me
on the path through school and into

scientific research,
and finally brought me here to study

this absolutely astonishing
little world.

We now know that crammed into Io,
the same size as our moon,

are over 400 active volcanoes.

Compare this to just 60
on the whole of Earth.

The most powerful eruption
was seen at a volcano called Surtr,

which is actually named after
an Icelandic giant.

A fissure opened up and a huge
volume of lava literally gushed out

of the ground to form large lava
fountains kilometres high.

It must have been an absolutely
incredible sight to see

if you were there to witness it,
but not from too close by.

When Surtr roars,

it sends plumes of lava and ash
over 500km into space.

Io proved for the first time

that Earth wasn't alone in having
active volcanoes.

And, perhaps more importantly,

Io offered a clue
as to the conditions

that existed as the Earth formed.

But first, scientists needed
to discover

where the heat driving Io's
volcanism came from.

The reason why Io is so active

is it's caught in this gravitational
tug-of-war between Jupiter, Io,

Europa and Ganymede,

and this pumps a lot of energy
into the system.

What happens to a squash ball
is just like Io,

as it's pulled between gigantic
Jupiter and her other moons.

A thermal camera reveals the
temperature of the squash ball

as the rallies progress.

We hit the ball against the wall
and it heated up.

And it heated up because
it was being compressed,

twisted and turned.

And Io is very much like that.

With Io, it's being twisted and
turned and squeezed by gravitational

forces, and the gravitational forces

cause a lot of interior heating and
the heating manifests at the surface

as huge volcanoes.

Io heats up so much
that it might erupt

an extremely rare and hot form
of lava called ultramafic.

Ultramafic lava was abundant
4.5 billion years ago,

when the Earth formed,

but no longer.

To discover this primitive lava
on Io

would offer scientists a window
on the past.

Volcanologist Rosaly Lopes
does her research in Hawaii.

We're studying volcanoes on Hawaii
not because of Hawaii itself,

but because Hawaiian volcanoes
are such a good analogue,

or a mirror if you like, for
volcanoes on Jupiter's moon, Io.

And it's really understanding
the volcanoes on Io

that we are after.

Hawaii has more active volcanoes
than anywhere on Earth.

In fact, the islands are a chain
of shield volcanoes,

built up from the ocean floor.

Rosaly looks for the most active
lava flows.

It's challenging, it's beautiful.

I think a volcano in activity

is just the most beautiful thing
that anyone can see.

Io is like Dante's Inferno, it's
absolutely volcanoes everywhere.

Sulphur everywhere,
hot lavas everywhere,

it is a volcanologist's paradise,

but it would be absolute hell
if you were actually there.

Rosaly will measure the cooling rate
of the lava here in Hawaii,

and then apply it to the volcanoes
of Io.

In this way she hopes to find out if

Io has the especially hot
ultramafic lava.

The team use a thermal camera.

These should be nice images.
Very nice, very nice.

And then just really hot
in the middle,

where that's cooling so fast.

That's beautiful, just spectacular.

The hottest lava is the moment
it emerges.

If Jenny manages to break through
the surface,

you are going to see the hot lava
spilling out.

Oh, there we go. So that's the heart
of the lava flow.

The thermal camera reveals
how quickly

the lava cools here on Earth.

Even on the hottest parts,
it was only about 910 Celsius.

The melting temperature of this rock
is about 1,200 Celsius,

so that tells you that even in those
red hot parts, the lava has cooled,

you know, more than a couple
of hundred Celsius,

so lava cools very, very fast.

Rosaly suspects this also happens
on Io.

Space probes to Io have revealed
that the surface hot spots

are 1,200 degrees.

When we get measurements of
the temperatures on Io,

we know that those temperatures
likely have cooled

by at least a couple of
hundred degrees Celsius.

It means the temperature of the lava
just below the surface of Io

must be around 1,400 degrees.

Lava this hot is strong evidence
it's ultramafic.

An exciting finding,

as it means Io could hold
the secrets of the Earth's past.

Io is a model of the early Earth,

because the lavas on Io may be
of the ultramafic type,

and those are lavas
that are very hot,

very primitive and they erupted
on Earth billions of years ago.

The more we research Io,

the more we find out what the Earth
was like as it was forming -

the type of lava flows,
the form of volcanism,

the tremendous density of volcanoes.

By studying Io,

we look at volcanism on a scale that
has not happened on Earth

for billions of years.

So, Io reveals what
primitive Earth was like...

..Dante's volcanic Inferno.

Volcanoes have played a key role

in the evolution of planets
in another way -

by creating their atmosphere.

And the best way of looking at that

is the most extreme example of all -
Venus.

The planet Venus
is a very hot climate.

The atmosphere is dense

and its primary constituent
is carbon dioxide.

It has the densest atmosphere
anywhere in the solar system.

And one of the hottest.

This extreme atmosphere was almost
certainly created by volcanism.

It pumps out these gases.

But the thick atmosphere

also hid what was happening on
the planet's surface.

So, we really didn't have much of
an idea of what was beneath those

clouds, and it was a bit of
guesswork.

You know, you send the probes down,
are they going to survive,

what's the atmospheric pressure
going to be, how hot is
it going to be?

So when the first probes went down
onto the surface,

they didn't last very long.

But a new generation of probes,
armed with radar,

eventually peered through
the veil of Venus

to reveal an astonishing
landscape.

More volcanic cones and craters

than any other planet
of the solar system.

When they eventually got

the correct sort of radar going
through the clouds

and seeing what was going on,
then it got really exciting.

Then we thought, "This is a planet
with a lot of volcanoes on it,

"and even more fascinating,

"volcanoes unlike any we see
on the Earth."

These volcanoes are unique to Venus.

Some are 65km across,

surrounded by cliffs
over 1000 metres high.

Almost perfectly circular,
they're known as pancake domes.

The pancake domes were very much
a mystery.

What we saw on the surface of Venus
were just large, basically pancakes,

stuck on top of these flat plains.

It was just,
"What are these things?"

They are so untypical of what else
we saw on Venus,

and that's when people started
thinking, "Well, the sort of
lava flows on Earth,

"where we actually have
these same features,

"and these lava flows we have
in places like Iceland."

What could pancake domes tell us
about volcanism on Earth?

These are the extraordinary lava
flows at Torfajokull in Iceland.

They end in cliffs,

similar to the pancake domes,
but on a smaller scale.

It's like walking across
a mossy Venus, isn't it?

Dave and Ian have come here
to discover

more about the lava
that created these landscapes.

One of the things I want to do
quite soon

is to find a nice piece of this
lovely lava to hit with my hammer,

so we can have a good look
at what's inside it.

I'm going to hit this bit here, OK?

It makes a lovely noise as well,
doesn't it?

It does indeed.
And a nice smell, actually.

I love the smell of rhyolite
in the afternoon!

So, you can see lots of little white
crystals actually aligned in that

particular direction.

These only line up when you've got
something that's very,

very sticky, and forcing crystals

to actually line up in
the one direction.

And in this case, I know these
crystals tell me

this rock is very high in silica.

Silica thickens the lava, and Dave
and Ian believe this was what

created the pancake domes of Venus.

It behaves differently
from thin lava.

The most common type of lava we have
in the solar system is basalt,

and the entire surface of the moon
and the entire surface of Mars

is covered in basalt.

I'm going to illustrate that
by using oil.

It spreads out where it wants to go,

beautiful little fingers coming down
thin and fast.

However, in some parts of the Earth
and these pancake domes on Venus,

which is very exciting, we have this
much thicker lava flow and I'm going

to illustrate that with treacle,
and let's see how that goes.

Beautiful.

See how slow and how thick it is?

That's exactly what we expect to see

when we have these thicker
lava flows

that are much richer in silica.

The forward edge is very thick

because everything
is getting compressed

and squeezed forward
at that forward edge.

If this was a real lava flow,

you would actually see blocks
falling off the front of it.

On this sort of surface
that's sloping,

you will see something that looks
a little elongate,

as we can see here. But if you pour
it onto a perfectly flat surface,

you will get, basically, a pancake,
a circular pancake.

It's utterly fascinating,

because until recently,
I thought these planets

were very, very boring,
just had basalt,

but having found this particular
type of rock on Venus,

it excites me personally,

because I've been working on them
for 30 years.

But are any volcanoes on Venus
still active?

Some exciting circumstantial
evidence has recently
been discovered.

They found that Venus had hot spots
within it that occurred over quite

a short time interval, and this was
the first evidence we had of perhaps

something active on Venus.

This image of the planet's surface
was taken on June 22nd 2008.

The hottest parts
are yellow and red.

And the same area,
just two days later.

The best explanation of these new
hot spots is erupting lava.

We're also seeing unexplained spikes
of sulphur in the atmosphere,

which are probably related
to these bursts of hot activity

appearing on the surface.

That really is quite exciting,
to actually see these.

It's these active volcanoes

that create the dense atmosphere
of Venus.

But why haven't all the volcanoes of
Earth led to a similar dense

and hostile atmosphere
on our own planet?

Claire Cousins is an astrobiologist.

She's been coming to Iceland
for ten years,

as this is the ideal place
to find out

how volcanoes can help support life.

Claire and her colleagues

are tapping into the gases
of a volcanic vent.

Oh, that's interesting.
That looks good, that looks good.

Nice.

So what kind of volcanic gases do
we typically get from these systems?

It's about 2% CO2, carbon dioxide.

About 1% H2S, hydrogen sulphide,

and all of the other gases
are in trace amounts.

Many of these gases
are highly toxic.

So, we wear these gas masks while
we're sampling these volcanic gases

because they're what we call
acidic gases,

so they're things like carbon
dioxide or hydrogen sulphide,

and they're basically gases that we
just don't want to be breathing in.

They're really poisonous.

But surprisingly, the most abundant
gas is actually water vapour -

97% at this site.

Across the entire Earth, all these
gases have a global effect.

Volcanoes, they're not just
destructive processes.

In the long-term, especially,
they produce a huge amount

of essential ingredients for life,
basically.

Particularly water vapour,

we're just surrounded at the moment
by all this

volcanic gas and the vast majority
of it is water.

Earth's early atmosphere and oceans
were created by volcanism,

pumping water and gas
into the primeval sky.

But because the tectonic plates
of the Earth

dragged so much of this water

and gases back inside the planet...

..the right amount of atmosphere
remained up above

for life to evolve.

Through this whole process,

volcanoes actually deliver
to the surface

of the planet many fundamental
ingredients required by life.

In contrast, Venus,
without plate tectonics,

pumped ever more gases
into her atmosphere.

Over time, this dense atmosphere
created a hell planet.

All life that we know of needs heat,

liquid water, and an energy-rich
foodstuff.

On Earth, volcanoes provide
all three.

If they can do this for life here,

volcanoes might support life
beyond Earth.

At a volcanic hot spot in Iceland,

Claire is searching for unusual
life forms that can survive here.

Our perspective of what's extreme
is incredibly human-centric.

We think that living at,
you know, 20 Celsius

in an oxygen-rich atmosphere is,

that's what we like,

and we see anything that's different
to that as, you know, extreme.

But in reality,

that's just what we've evolved
to live in,

and microbes that live in these

very hot or very acidic
environments,

they've evolved to live here

and they wouldn't actually grow
in our conditions.

Mars had very similar environments
where volcanism met ice.

This makes it a good candidate for
evidence of extraterrestrial life.

Iceland acts as a useful parallel,

and here Claire tests the water
for sulphur,

which certain bacteria can feed on.

The intensity of the blue tells you

how much sulphide is dissolved in
the water.

How much food there is
for the microbes to eat.

And we also get microbes which
actually store the sulphur inside

their cells for future use,

like packing a sandwich
into your bag for later.

And they use that sulphur when

they can't find any sulphur
in the environment.

She collects the microorganisms
to study them more closely.

We can read the DNA of these
microorganisms and, you know,

we can identify what they are,

we can see what genes they have,
you know, for certain lifestyles.

Whether they can eat sulphur or not,
for example.

And we can really get a handle on
the microbiology of these sites.

Claire believes that life on Earth
and possibly Mars

could have originated in
a volcanic hot spot just like this.

But Mars is not the only
planetary body

where volcanism is closely linked
to ice.

Linda Spilker is head of the team
that runs the Cassini probe that's

been exploring Saturn and her moons.

Linda is most interested in the moon
called Enceladus.

Enceladus is only about 500km
across,

and that's only about one seventh
the size of our own moon.

And that tiny moon, we think,
should have been frozen solid.

And if you look carefully,

you notice it doesn't look like
our moon at all.

Our moon is covered with craters
and it's dark,

but this is bright, icy white,
and very few craters.

As the Cassini probe
approached Enceladus,

Linda observed something never seen
before on a planetary body.

If you look carefully, you can
actually see individual geysers

coming up and shooting out
into space.

And what a surprise.

Everyone was in awe and amazement
to see this level of activity.

And we knew for the first time,
this wasn't a dead moon.

Enceladus was an active world.

These eruptions are not molten rock.

They are geysers, water and ice,

fountaining over 700km
into space.

It means that liquid water

deep below the surface is being
forced upwards by heat.

The material erupts so high

that it's actually become part
of Saturn's rings.

So, all along, visible evidence
of volcanic activity

was present in the rings of Saturn,

but scientists hadn't even realised.

Coming out of the geysers,

there's water vapour,
there's tiny particles.

If you'd stand near one of
these cracks on Enceladus

and put out your hand,

it would almost be like it
was snowing.

These tiny particles would fall
back down.

And that's why there's no craters.

That these particles go and fill in
with fresh snow, on Enceladus,

fill in all of the craters,

and so, some pieces of Enceladus'
surface are only minutes old.

Covered by these tiny particles,
falling in from space.

So, how are these extraordinary
geysers of ice and water formed?

Again, Iceland provides
a powerful analogy.

This is the Strokkur geyser.

Claire loves to witness
its raw power.

A great natural wonder of the world.

So what we have here,

rather than molten lava coming
out of the ground,

as you typically get
for your regular volcano,

what we have here is actually
just water,

just ground water
which is within the ground.

And it's being heated up
by these magma chambers,

which are actually much further,
deeper underground.

And this water gets superheated

until it just can't stay
underground any more,

and all that steam
and all that energy,

just like in a normal volcano,

will erupt all of that water
to the surface.

Just before the eruption, what we
see is a kind of bubble forming,

where we get this really beautiful,

kind of almost glassy-looking dome
of water,

which is all this superheated water
just coming up to the surface

until it finally erupts.

A thermal camera measures
the heat of the water.

What we can do when we look
at the thermal camera here,

we can get an idea of how
high temperature the system is.

It's about 70 Celsius.

For me, Enceladus is one of the most
exciting places, I think,

in the solar system to go out
and explore. It's...

LOUD WHOOSH

For reasons exactly like that,

it's one of the other places in the
solar system where we actually have

this active hydrothermal activity,
where we have these plumes which are

massive in scale compared to what
we have here.

The geysers of Enceladus
are so powerful,

there must be an ocean of heated
water hidden below the icy surface.

Linda Spilker has ingeniously
found out what's in this ocean.

The Cassini spacecraft, since we can
get so close to Enceladus,

we can literally skim, fly through
the jets and make measurements.

We can measure the gas, we can
measure the particles coming out,

and figure out what they're made of.

And the clues inside those
particles, those composition,

tells us about the ocean underneath.

It is full of salts
and organic compounds.

Some of the key building blocks
of life.

So, we wonder,
could Enceladus also have life

very similar to the life on Earth?

Is it like the same kind of life
we have here on Earth?

Is it something totally different
that we can't imagine?

We've had volcanism on Mars,

we've had volcanism on Enceladus and
its various different geysers.

To find evidence of life
on another planet would be...

It would just be absolutely
ground-breaking

in terms of our understanding

of our place, not just
in the solar system,

but in the universe as well, right?

The hunt for volcanoes elsewhere

continues to produce
amazing breakthroughs.

This is one of the remotest and most
distant parts of the solar system.

Pluto.

After a nine-year odyssey,

the New Horizons probe finally
reached Pluto in July 2015.

What it discovered was astonishing.

The New Horizons spacecraft
that just visited Pluto

found features that have every
indication of being cryovolcanic,

mountains, shield-like mountains,

flows on the surface.

Completely unexpected.

And just an extraordinary discovery

which just shows us how exciting
the game can be.

This is Wright Mons on Pluto.

At 150km across,
and 4km high,

it's believed to be the largest
cryovolcano of the solar system.

It's driven by a similar process of
mountain formation as on Earth,

but instead of molten rock,
it's built up from flowing ice.

In the case of Pluto, it's so cold.

It's not water ice,

it's actually... can be nitrogen ice
that can be there.

Or methane ice.

Other things that can be ice in that
very cold environment of Pluto.

And there are some
tantalising features

that perhaps are cryovolcanoes -
maybe something has flowed out.

You mix a little bit of water and
ammonia together and it can actually

flow on the surface.

A rare event on Earth
called frazil ice

reveals how freezing water
can sometimes behave

in a similar way to lava.

During winter, it's occasionally
observed in Yosemite National Park.

A slowly flowing river of chunks
of ice, given the right conditions,

suddenly freezes solid.

What happens when we see frazil
ice on Earth,

is it is so close to
its freezing point.

That's why it's filled
with ice crystals.

And if it cools down just enough,
just another half a degree Celsius,

a quarter of a degree Celsius,

suddenly all the water that's liquid
between those ice crystals freezes,

and it happens just like that.

And it's entirely possible that that
same process could be happening

on the surface of Pluto.

It's towards the end of
the Iceland expedition,

and the team gather
to discuss their findings.

Key to this is
the fascinating paradox -

volcanoes are a violent
and destructive force,

while also essential to life.

Whenever we find volcanism on Earth,

we find all sorts of kind of
crazy chemistry, really,

which can just support
microbial life, as it is on Earth.

And the real question is whether

these same kinds of processes that
happen on Mars or on Enceladus,

whether those can actually support
microbial life in the same way.

There's a lot of similarities
between this type of environment,

that we've obviously got life in,
we know that.

So this is the type of environment
that would be a great target

to look for on Mars. Yeah.

But volcanoes of the solar system
also give us a window

on what might happen to our own
planet in the future.

What I think is really fascinating,

when you look throughout
the solar system,

is that you have this diversity of
bodies, and each of these bodies,

all of them, or most of them
show volcanism.

And then you see that they have been
developing in different ways,

each of the bodies.

In about a billion years,

it's predicted that the plate
tectonics of Earth could end.

A catastrophe for life here.

Plate tectonics and volcanism
replenish the atmosphere

with what we need, but won't you
just lose the atmosphere

if you stop plate tectonics?

If Earth just literally kind of
grinds to a halt, then, yeah,

eventually the atmosphere will be
stripped away by the solar wind,

it will be just lost
into space and, yeah,

basically I think we'll end up
becoming very much like Mars,

just a very cold and dry,
barren, rocky planet.

Earth as Mars is one option.

But another scenario is possible.

Even if plate tectonics ended,
volcanism might continue unabated,

and our atmosphere would become
thicker and hotter.

It could go the other way
and end up like Venus,

where we have all this carbon
dioxide in the atmosphere,

and, you know, either way, the
options aren't looking that great.

So the interesting thing is

we've got these three planets
next to each other,

and they've all got these incredibly
different scenes at the present day,

that they may be telling us a lot
about the potential futures for

the Earth, as well, and volcanoes
are a big part of that story.

So you can see the higher life forms
on Earth, like human beings,

dying out as the conditions become
much more difficult for them.

Perhaps we'll lose our atmosphere,

perhaps actually we start losing
our water.

It's going to be very difficult for
human beings to adapt to those

conditions, but the microbes
will love them. Yeah.

Microbes will inherit the Earth.

Fortunately, all this is
a billion years from now.

Way back in the ninth century,
Vikings discovered Iceland,

its landscape sculpted by volcanoes.

Today, a new generation of explorers
are looking out into space,

discovering how volcanoes have
shaped not just our planet,

but other extraordinary worlds.