Original subtitles

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.