All language subtitles for Oceans of the Solar System BBC Horizon 2016 1080p EN_Subtitles01.ENG

The oceans define the earth.

They're crucial to life.

In fact, without the oceans, there
would be no life.

We once thought they were unique to
our planet.

But we were wrong.

We've recently discovered oceans all
over our solar system

and they're very similar to our own.

Imagine this at the bottom
of Enceladus' Ocean.

Now scientists are going on an epic
journey in search of new life

in places that never seemed
possible.

Life has got this amazing ability
to, you know, just keep surprising
us.

I want to get data back from a probe
and be able to say,

"It's life, Jim,
but not as we know it."

NASA are even planning to dive to
the depths of a strange,

distant ocean, with a remarkable
submarine.

That first picture...
Are you kidding?

That first picture on the surface
of a sea, on another planet

in our solar system
changes the world.

The hunt for oceans in space marks
the dawn of a new era

in the search for alien life.

Nearly two centuries ago, Charles
Darwin set out on a journey

across the world's oceans to uncover
the secrets of life.

What he came to understand was that
the answer to the mystery

of where we came from lay beneath
the hull of his ship, the Beagle.

As he filled his notebooks with
beautiful sketches of the birds

and animals he came across, he began
to formulate an idea that

life might have actually started in
water.

Darwin's important for the whole
story of the evolution of life

and natural selection,
where we all came from,

how life ultimately started,
as well.

A lot of that goes back to Darwin.

He had ideas, not very well
publicised ideas, not

in the Origin Of Species, but on how
life started in a small, warm pond.

So Darwin had put his finger
on the importance of water

in the origin and evolution of life
very early on.

Water is so essential that it's
dictated where scientists

look in the search for life
in our solar system.

Life needs water. You look at all
life forms on earth.

The one requirement they all have in
common is water.

An ocean may be a good place to
incubate life and,

not surprisingly, an ocean has got
what life needs to survive.

Everywhere where we look on earth,
whether it's frozen

or boiling hot, wherever we find
water, we find life.

Water is our working fluid.

You're mostly made up of water,
I'm mostly made up of water.

The search criteria were simple -
to find life,

first find a liquid ocean.

Only beyond earth,
there didn't appear to be
any in our solar system.

There used to be the idea of the
Goldilocks Zone,

where everything was "just right"
for water to be in the liquid

state on the surface of a planet and
earth was slap-bang in it.

Venus was too close to the sun,

too hot really for liquid water on
the surface.

Mars, thought to be a little
bit too far away.

But is finding liquid water and life
on Mars impossible?

We've been sending evermore complex

and sophisticated spacecraft
to the Red Planet for decades

and we now know more about it than
we ever did.

Unfortunately, all the scientific
evidence gathered so far

points to Mars being dry, cold and
seemingly lifeless.

But has it always been?

It's a question that's intrigued
scientists

and astronomers, like Geronimo
Villanueva, for years.

Ironically, the search for evidence
of an ancient Martian ocean

is being conducted from one of
the driest places on earth -

the Atacama Desert in Chile.

So there is a strong relationship
between Mars and Atacama,

because Mars is a very dry place

and Atacama is one of the driest
places on the planet.

Actually, the relative humidity
measured by Curiosity Rover on Mars

is practically the same as we are
right now, here on this desert.

Fittingly, it's that lack of water
that makes the Atacama

the perfect place to build one of
the biggest

telescopes in the world,

because water in the atmosphere here
would

drastically limit the telescope's
ability to find water anywhere else.

Water and many other things like
organics are what we're

looking for, so we come to a place
which is devoid of those things,

like a desert, so we don't get
the contamination from those

things when we observe through
the atmosphere.

So when you come to a place like
this,

you're trying to look through the
water in our own atmosphere.

What's immediately obvious to anyone
with even an ordinary telescope,

is that there IS water on Mars.

But today, it's frozen
solid at the poles.

Yet the Martian landscape looks
strangely as though

it was carved and shaped by liquid
water.

Planets show all this morphology,
geomorphology, driven by water,

a huge amount of water, so the
estimates of how much

was on the planet vary a lot,
because we didn't know.

I mean, we see all this carving,
all these big valleys,

and so how much water was there is a
big question.

Answering that question was pretty
much impossible

until scientists got lucky in 1984
in another desert.

This time in the coldest
place on earth - Antarctica.

Here they found a remarkable
meteorite.

Analysis confirmed it was Martian in
origin and that they had

discovered the key that would unlock
the mystery of Mars's watery past.

So once you identify when in the
history of our solar system,

where it came, then you say, "OK,
this rock is dated there
and it comes from Mars."

So you have a good reference point
in time and in place of that rock.

Careful analysis revealed that this
meteorite was 4.5 billion years old.

The meteorite also carried crucial
chemical information -

an isotopic signature fixed by the
amount of water on Mars

4.5 billion years ago.

On its own, this signature was
worthless, but by measuring

the amount of water on Mars today,
then comparing the signatures

of recent rocks against the ancient
meteorite, all would be revealed.

And that's where the huge telescope
comes in.

It's so powerful it can detect
water molecules on the surface
of the planet.

You can actually see the molecules
in every...

Above a volcano in Mars,
above a valley, you can

actually map those molecules from
here.

It's really astonishing.

Armed with a precise measurement
of the amount of water on Mars
today,

Geronimo was able to make an
astonishing calculation.

We extrapolated back in time and
we inferred that there was almost

seven times more water than there is
right now.

What happened? Mars, topographically
speaking, has very low plains

in the north and a very high
altitude place on the south.

So if you throw water, it will tend
to flow into the lower topography,

which is going to be the
northern plains.

So one of the things we did is,

OK, so, we had this volume of water
and so what do we do with this?

So one trick was we said, OK,
just throw it on the planet

and let's see where it falls.

And they just did, like, you know,
follow the rivers and everything,

and it formed an ocean on the
northern plains of the planet.

4.5 billion years ago,
the Martian ocean

covered 19% of the planet and was as
deep as the Mediterranean.

In fact, NASA's planetary models
reveal a Mars at its warmest,

complete with an earth-like
atmosphere.

If you were in an alien spacecraft
randomly coming to earth,

the chances are better than even
that you're going to land

up in water, so bring a boat.

And it's the same on early Mars,
and that's a fundamental point,

that Mars was a water world.

It would have been better to
characterise it as a water world,

whereas now, of course,
it's a desert world.

But it's that water world
that's interesting.

That's the world that may have had
life

and that's the world we want to
investigate.

It even had waves!

The reduced gravity on Mars
meant that these waves

would have been twice as
tall as those on Earth -

a surfer's paradise,

but, according to Nasa scientists,

most of the time

you'd have to be pretty
tough to catch a Martian wave.

If we think back to early Mars,

we would expect it to be
an Earth-like environment -

if it had water

and a thicker atmosphere,
and was warmer.

The one big difference, I think,

would be that it would be
more like the Arctic Ocean.

It would be an ice-choked,

ice-covered ocean.

So, if you imagine standing
on the north shore of Greenland

looking out at
the ice packs moving,

I think you'd get a good imagination

of what early Mars
might have looked like.

Would the surfers
like it better or less?

It depends really on the wet suit,

because it's going to be
very cold on early Mars,

so you've got great waves,
but you're inside a wet suit
to survive it.

Not very many people
surf in the Arctic Ocean

and this could be
part of the explanation.

It may have been cold.

Mars is much further away
from the sun than the Earth,

but four and a half
billion years ago,

life on Mars would have
been technically possible.

This is the time when Mars
was the most habitable time.

When the planet
was formed, actually,

planet Earth and Mars
were similar in some aspects.

It had a thicker atmosphere,

maybe there was a big ocean there,

so habitability of the
two planets were similar

and, interestingly, the time
that we think this ocean was there

was a time that life
started in our planet.

So, you know, if the conditions
were favourable for life here -

to start life, you know -

what could be the conditions
on the planet Mars?

Sadly, however habitable
that early ocean was,

it didn't last.

Scientists think that the
early Martian atmosphere

was vulnerable to
solar radiation and,

over the course of one
and a half billion years,

it evaporated away

leaving just 13%
frozen at the poles.

But if Martian life was
theoretically possible

in that ocean millions of years ago,

is it possible that anything
could have survived until now?

I think the possibility of
finding life on Mars now

traces directly to the possibility

of finding liquid water on Mars

that's relatively fresh.

And finding water
has been a large part

of the Curiosity rover's mission.

Curiosity has been trundling
around Mars since 2012

and the images it's been sending
back have been stunning.

Sequences, like this blue sunset,

are starting to change our
understanding of the planet,

but it's the pictures from
the Mars reconnaissance orbiter

of a region called the Newton crater

that are helping to shed new light

on the amount of liquid
water left on Mars.

This is a time-lapse sequence

showing streaks on
the crater wall -

apparently growing
and getting darker.

Scientists think that they
might be caused by water.

These small amounts of water -

compared to an ocean on Earth
or even an ocean on early Mars -

they're insignificant.

But as an indicator of
Mars still being active

and still having liquid phases,

and maybe a hint of bigger
and better things elsewhere,

then I think it's very important.

What appears to be happening

is that the moisture in the soil

is evaporating during the
relative warmth of the day

and condensing back at
night when it's colder.

So, Mars still has a heartbeat.

It's a faint one if
we measure its heartbeat

in terms of the presence of water.

At one time, it was huge,

it was an ocean

and now there's just
a faint glimmer of it.

The problem is that these
small amounts of water

are exceptionally salty.

The Curiosity rover has identified,

in the Martian soil,

a salt called calcium perchlorate.

It's this salt that
absorbs the Martian dew

as it condenses onto
the cold surface each day.

The salt also lowers
the water's freezing point,

keeping it a liquid -

even at sub-zero temperatures.

But it also makes these
faint traces of brine

so concentrated

they'd be toxic to
conventional life forms.

So, could they support life on Mars?

There may be clues in the
saltiest parts of the Earth,

like the Bonneville
Salt Flats in Utah.

It's famous for land-speed records,

but it's fascinating
for astrobiologists

because the salty surface here

not only mimics that found on Mars,

it contains life.

Even though this looks dead,

we could probably take some
of these crystals right here

and get bacteria to grow.

I know it seems ridiculous,

but, you know, as a microbiologist

one of the things that

we've come to appreciate is

if there's any liquid water present,

you're typically going to find life.

So, life has got this
amazing ability to, you know,

just keep surprising us.

Unfortunately, Mars is way colder

than the Bonneville Salt Flats.

The average temperature
of minus 50 degrees Celsius

is a huge challenge
for anything living

on the surface of the red planet...

..and it's partly to do
with the angle of its axis.

Earth spins on an
axis of 23 degrees,

which should make
the planet unstable -

but it isn't.

Earth's axis is
stabilised by the moon -

sort of like an outrigger,

a gravitational outrigger
that keeps the Earth stable.

Mars doesn't have a
large moon and so...

And it's also closer to Jupiter.

As a result, its axis
wobbles significantly.

Much, much more than Earth's.

More than double
the wobble of Earth's.

Over 100,000 years,

Mars' tilt wobbles by
as much as ten degrees,

causing huge climate change.

Similar but more extreme

than the Earth's ice ages.

At the peaks of that cycle,

the surface of Mars is briefly
warm enough to support life -

but to survive 100,000 years
of cold between these peaks

would demand a strategy
of extreme hibernation.

But for micro-organisms, this
strategy of living when it's warm

and then sleeping when it's
freezing cold is a good one.

Those organisms can be frozen and
thawed without any damage at all.

Every once in a while,
when the tilt is right,

you get a few thousand years
of time to have a go at it,

and then you go back
to deep-freeze sleep.

That all sounds fine in theory,

but could any living thing possibly
hibernate for up to 100,000 years?

The answer lies in the salt.

The salt crystals
form in cubes and,

as they form,

you'll have pockets of liquid

that become entrapped

as the solid salt is forming,

and the micro-organisms
that are present become trapped

in those fluid inclusions,

those little pockets of fluid.

How long, then, could a
single bacteria survive

trapped in a salt crystal?

Melanie took a crystal

dated at 97,000 years old

and drilled into its core.

She extracted the fluid,

placed it in a nutrient-rich dish

and walked away.

When she came back a week later,

something astonishing had happened.

97,000-year-old bacteria

were flourishing in the dish.

It was pretty amazing, you know,

to be able to have

such strong evidence.

I mean, taking that
fluid inclusion up

and using it to inoculate
media, you know,

and then having something to grow -

that's pretty...

Pretty powerful stuff.

But how could something survive

for nearly 100,000 years

trapped in a salt crystal?

Only the basic metabolisms

would be still functional,

so these organisms are probably

just expending enough energy

to keep maybe their DNA repaired,

and that's probably about it.

So, right here on earth,

these bacteria have developed
a hibernation strategy

extreme enough to cope with the
length of the Martian ice age

but, even at its warmest,

Mars is much, much colder

than the Bonneville Salt Flats.

Extreme endurance alone
wouldn't be enough.

So, is there any life form capable
of hibernating through extreme cold?

This doesn't look a very likely
place to answer that question,

but biologists Carl Johansson
and Byron Adams

aren't here to drink
in the obvious beauty

of the Bridal Veil Falls in Utah.

What we want to try and
target is that base there,

where the upper falls
are kind of falling down.

Just right below the
main part of the fall,

you can see all the moss
beds that are in there.

That's all pretty good stuff.
You get in there.

That's nice and slick.

THEY LAUGH

All right, let's go. All right, man.

They're looking for a creature
with an unusual ability -

one that might prove crucial

in the search for alien life.

Unsurprisingly, it loves water,

and there's plenty of that here.

Now, this looks good.

Here's a good way around
this way, I think.

It's a good spot.

Watch your step, man.
It's slippery, bro.

Yeah, this looks
really good here, man.

Yo, Carl!

Bag me, bro.

This creature is so small that
it's almost impossible to see

with the naked eye.

Being small doesn't
mean it's insignificant,

it just means they have to
collect lots of very damp moss

to make sure they wrangle one.

Bag 'em and tag 'em.

It's got her.

Dude, I'm taking it right here, bro.

It's, like, raining on me.

I know it.
That's why I wasn't there.

It's only when they
get back to their lab,

at Brigham Young University,

that they can see what they've got.

So, you remember the samples that we
just collected up at the waterfall?

We brought them back
to the lab here

and we put them in some dishes,

and I'm picking the
animals out of those dishes

and putting them onto a slide,

and then I'm going to
hand this slide to Carl

so that he can put it
under the microscope,

and then we'll be able to
get a better look at them.

So, when we look at the
slide that Byron brought us

and we start looking through,

we can see some movement,
right here, of an animal.

This is the tardigrade.

Tardigrade means this

Latin name slow-stepper.

"Tardi" means slow,

and "grade" refers to foot.

You can start to see,

he's got long thin filaments

coming off his body

and some actual...

What almost look like horns

coming off his head
that he uses in feeding.

Tardigrades are aquatic,

so you'd expect them to die

if they weren't in water,

but they have a
very special ability.

As that sample jar
starts to dry out,

as that specimen starts to dry out,

what's cool about these guys is

they can survive that
extreme desiccation,

drying down to like a
crispy little booger.

It's called a tun.

They roll up into a special...

A tight ball, essentially -

they're like a
roly-poly bug almost -

and then go through a series
of radical chemical changes

in the cells in their bodies

to deal with this loss of water.

It looks like it's dead,

but, when they add water,

it springs back to life.

It's not really dead, because

when we add more water to them -

when environmental
conditions are good again -

they can come right back alive.

It's very energetically
costly for them.

They can't go back and
forth and back and forth,

but they can survive some
really extreme conditions

and what happens is,

as their environment
starts to dry out,

in order to survive that,

they actively pump all
the water out of their bodies

and out of the cells.

And so the genes
that are being expressed

for normal cellular
processes shut down

and they completely change the way

they express their DNA.

They've got one operating system,

their genes that operate to put them
into and maintain them in a tun,

and then they switch operating
systems when they're, you know,

carrying out life's activities -

when they're eating and
moving around, and mating,

and all those kinds of things.

It's almost like two complete
life operating systems.

But drying out and thriving
in a temperate lab

is completely different
from surviving

on the chilly surface of Mars.

The coldest place on Earth

that's in any way
comparable to the red planet

is the Antarctic.

Tardigrades have been found here,

but can they be reanimated?

I've got some animals
that have been frozen here

since the last field
season in Antarctica,

so we extracted them
from soils in Antarctica,

shipped them back here frozen solid

and they've been
frozen solid here at

at least minus 60 since 2012.

So, this is the sample that
we pulled out of that freezer

and it's thawed out now.

What I'm going to do now is
I'm going to have a look at it.

So...

Holy moley!

It's mind-blowing, dude.

It's basically the same
community that I saw

when I collected them in Antarctica.

We put them in a tube,

froze them,

shipped them.

Four or five years later,
we want to study them, right?

Pull them out, we thawed them out

and now what I'm seeing now

looks almost exactly like

what I saw when I was looking
at them, like, fresh in Antarctica.

You know, there's a few of them
that didn't survive the trip, right?

But, for the most part,

if you were to show me this, like,

double blind, fresh,

I would struggle to
tell the difference

between the sample that
I got live down there

versus one that's
been in the freezer

for like four, five...

Who knows how long, how many years.

As well as surviving extreme cold,

tardigrades have another
trick up their sleeve.

In 2007, the European Space Agency

sent a sample of tardigrades up
to the International Space Station

for an astonishing experiment.

They took them into space

put them on a satellite,

opened up the door,
sent them outside,

exposed them to
extreme temperatures -

vacuum, hot, cold...

Huge radiation. And then, when
they brought them back to Earth,

they did what you're seeing here.

They dumped some water on them
to see if they actually reanimated.

INTERVIEWER: What happened? Voila!

They take the water up, man,

and they start... Right?

They swap out the molecules
and... Like a machine, man.

You add the water to it,
they take them up,

the cells start to do their thing
again and they come back alive.

It always blows my...

Look, I'm an old, fat dude and
I've looked at these 100 times,

thousands of times,
millions maybe...

You're not that old. Well...

..and when I actually look
at them under the microscope,

every single time, I'm like,
"Dang, that's cool, man."

So, the remarkable tardigrade
can survive the extremes of space

AND the killing cold of Antarctica -

conditions similar
to modern-day Mars.

And, of course,
life can also survive

for tens of thousands of years

locked away in a salt crystal.

So, there could
possibly be life on Mars.

It used to have an ocean

and there might still be traces

of that ocean left today.

But what about the rest
of our solar system?

From the early 1960s,

scientists have
been sending probes out

into the furthest reaches
of our solar system -

looking, in part,
for liquid water...

..but everything appeared largely
frozen, dry and lifeless.

Most of our solar system was
colder than anywhere on Earth -

even the icy wastes of
the high Atacama Desert.

But, in these remote mountains,

scientists have
uncovered tantalising clues

that could help answer the question,

"Are Earth's rich and flourishing
oceans unique or ubiquitous?"

And the Voyager probe launched
by Nasa in 1977 pointed the way.

In 1980, it photographed
a small moon of Saturn

called Enceladus.

It's tiny, about the
same size as the UK -

and, at first, it
looked insignificant.

Enceladus is this
bizarre little moon

that the Voyager spacecraft

took a few snapshots of.

The surface could be seen
to be cratered in the north -

a lot of craters on its icy surface.

Now, to a planetary
scientist and astronomer,

that means old ice.

But in the south and, in particular,

down near the south pole,

what was seen was a fresh
ice surface, very few craters.

If the ice was fresh,

then where had it come from?

Scientists had to wait for
years before they got an answer,

and it was provided
by the Cassini probe

which span past Enceladus in 2005.

And what Cassini saw
shocked scientists.

Plumes of water vapour

pouring out from the surface

of the little moon's south pole.

So, when Cassini returned
these images of the plumes,

the community just went nuts.

This was astounding to
see these jets of water

erupting out of this
bizarre little moon.

Enceladus is just 500
kilometres in diameter -

that's about the width
of the United Kingdom.

And to see these jets
erupting was phenomenal.

As Cassini got closer to Enceladus,

it revealed the plumes were spewing

not just from one crack,

but from four huge
fractures in the ice.

Each of them was about
130 kilometres long,

two kilometres wide

and about 500 metres deep

with water vapour
pouring out of them.

That amount of water
could only mean one thing.

Enceladus had to
have a liquid ocean

beneath its frozen surface...

..but this dark,
subterranean ocean

would be lacking in one thing

that's crucial for life on Earth.

Life, as we know it,

needs not only liquid water,

it also requires the elemental
building blocks for life -

the carbon, the hydrogen,
the oxygen -

a smattering of the elements
across the periodic table.

And life requires
some form of energy.

On Earth, the energy for life
comes primarily from the sun.

It's captured through the remarkable
process of photosynthesis,

thanks to plant life - like this
very primitive aquatic algae.

This stuff doesn't look like much.

People try and avoid it
when they go into the sea,

but it's changed the world.

This is photosynthesis in action.

The cells that made this up

arose around about two billion
years ago or thereabouts

and they cracked the trick

of using the energy of the sun

to split water and release oxygen,

and they're still about the major
supplier of oxygen on the planet.

These things produce more
oxygen than the rainforests.

It's remarkable.

It looks like slime,

but without this,

there wouldn't be any animals,

there wouldn't be any
complex life on this planet.

This makes the world.

In the darkness of
Enceladus' hidden oceans,

there could be no photosynthesis
to capture the sun's energy -

yet the possibility of finding
life there isn't entirely hopeless.

This is El Tatio.

It's a massive geyser field.

It sits 4,300 metres
above sea level,

high in the Atacama Desert,

and it's a riot of
hydrothermal activity.

And there's something
bubbling up here

that makes the prospect of life
on the distant moon of Enceladus

just a little more feasible.

But the clue is what
we find here on Earth.

If we look alongside of this geyser,

we see these geyser pearls.

This is silica,

SiO2,

that has sintered out
of this geyser water.

And the cosmic dust analyser

on the Cassini spacecraft

has captured grains like this -

except much, much smaller.

And the fact that those grains are
found in the plume of Enceladus

leads us back to the
water/rock interaction

where that silica in
the plumes of Enceladus

could only be there

if the ocean of Enceladus

is cycling with an active, rocky,

potentially hot sea floor.

Cassini's measurements
indicated that,

deep in the oceans of Enceladus,

a process very similar to
the geysers of El Tatio

must be underway.

Imagine this at the bottom
of Enceladus' ocean.

We have reasonably good evidence
that the chemistry and,

in fact, some of the
temperature of the water

that's coming out of
these geysers, right now,

is comparable to the
sea floor of Enceladus.

The bottom of Enceladus'
ocean might look like this,

but it's cut off from the
life-giving properties of the sun

by kilometres of ice.

So, does that make
finding life impossible?

In the deepest abyss
of our own oceans,

every bit as dark as
those on Enceladus,

life was thought to be impossible

until a remarkable discovery,

just a few decades ago,

changed all that.

And so, in the late 1970s,

spring of 1977,

explorers went down to hydrothermal
vents along the East Pacific rise.

Originally, they thought that

they might find some hot springs

at the bottom of the ocean.

They did not necessarily
expect to find

a tremendous amount of biology -

but, lo and behold,

the hydrothermal vents,

despite being at incredible depths,

incredible pressures

and cut off from the energy
of our parent star,

lo and behold, life was thriving.

And so, it may be that
those kinds of eco-systems,

the kind of geology and chemistry

that underlies those eco-systems,

could also power life

within these ocean moons.

This huge abundance of life

was surviving and thriving

despite being totally cut off
from life-giving sunlight.

Instead of photosynthesis,

it was powered by an
entirely separate chemistry.

Here, we're bringing
together the keystones

for life as we know it, the
keystones for habitability.

We've got the water,

we've got the elements

and we've got a lot of energy.

Within that winning combination,

water plays a crucial -
if very simple - role.

If you simply remove the
water and have dry surfaces,

everything would remain stuck
in its place on the surface

and there would be no movement
to bring things together to react,

so I suppose water is the universal
lubricant that makes things happen.

And the evidence for that
can be found throughout

this seemingly
inhospitable environment.

At the most basic level,

biology is a layer on geology.

Biology is harnessing some
of the stored chemical energy

that exists in chemically-rich
waters interacting with rocks.

And, right here,
we've got a beautiful example

of exactly that kind of biology
being a layer on geology.

Everything that you see here,

the red that you see,

those are microbes

utilising the rich
chemistry of the geyser water.

The presence of
these extreme life forms

thriving in almost alien chemistries

raises real hope for scientists -

not just in the search for life,

but in answering one of biology's
most fundamental questions.

Is there a second independent
origin of life elsewhere

within our own solar system?

And if there is,

then that tells us
that life arises

wherever the conditions are right,

and we live in a
biological universe.

If we don't find life
within these worlds,

then that may be an indication

that the origin of life is hard

and that life is quite rare

within our solar system and beyond.

Both outcomes are equally profound.

Our solar system may be
largely cold and inhospitable,

but, against all expectations,

we're now discovering it's also wet.

But just how soggy is it?

Is the ocean on Enceladus
a freakish one-off?

Would it be the only
moon with an ocean?

Or could there be
other bodies out there

with as much water as the earth?

High on the list of possibilities

would have to be Ganymede,

orbiting around Jupiter.

This icy moon is the biggest
in our whole solar system...

..but, initially, it
didn't look that promising.

Back in the 1970s,

when we only had, like, grainy,

pixely images from the moon,

we knew it was icy,

the surface was icy,

but we had no idea what's inside.

What is going on?
Does it have a magnetic field?

Does it have other things
like we have on Earth?

So, it was just a ball of ice.

Nasa sent the Galileo probe

to take a closer look -

and, in 1996,

it found something
completely unprecedented -

a magnetic field.

And this would ultimately lead
to yet another watery discovery.

The Galileo mission was definitely
a breakthrough in a way,

because it discovered
Ganymede's magnetic fields,

and Ganymede was suddenly
not only the largest moon,

but also the first moon we know
of that has its own magnetic field,

interior magnetic field.

Intrigued, Nasa focused the huge
power of the Hubble Telescope

on the surface of Ganymede.

In orbit around Earth,

this telescope has sent back
amazing pictures of the universe

as well as our solar system.

And when it was pointed at Ganymede,

it revealed yet another first -

the moon had auroras encircling
its north and south poles.

Because Ganymede has
a magnetic field,

it can direct the charged particles

from Jupiter's magnetosphere

and they get directed
towards the poles of Ganymede -

and so what that produces is aurora.

So, just like we have the Northern
Lights and Southern Lights of Earth,

in Ganymede's case,
the energetic particles

are hitting the really tenuous
atmosphere which Ganymede has,

and that actually
causes aurora on Ganymede.

But the auroras on Ganymede

held another surprise.

Astronomers had correctly predicted

they would rock like a seesaw

as the moon orbited Jupiter,

tugged by the magnetic
pull of that giant planet.

They'd calculated the rocking

to reach a full six degrees,

but the reality was very different.

What we saw is that it was always
rocked by only two degrees -

so not six -

but it seems like
a small difference,

but it is significant

so we see it's only
rocking by two degrees,

and so there must be an effect

that suppresses this rocking.

This apparently trivial detail

led scientists to a
thrilling conclusion.

The only possible explanation

for this suppressed
rocking of the aurora

is basically magnetic
induction in a liquid...

In a salty, liquid global
ocean inside Ganymede.

They'd discovered
an immense ocean

calculated to be
100 kilometres deep -

ten times deeper than
any ocean on Earth -

and it encircles the whole moon.

In Ganymede's ocean,

there's more water than
the whole of the Earth,

but it lies under
150 kilometres of ice.

It's still, even for me, really
hard to imagine these worlds.

I mean, I see images of Ganymede

and four of the moons every day,

and I have a really good
idea of what they look like,

but it's still most exciting

when you look through
a, like, small telescope

and see, like, a bright
dot next to Jupiter

and then you know that
the moon really exists.

And knowing now that this bright
dot I see in the telescope,

next to Jupiter, does have
an ocean is really exciting.

Each new ocean discovered
gives a boost to the chances

of finding life in the solar system.

In 2022,

the European Space Agency
will send a probe

to peer beneath the
icy surface of Ganymede

in the hope of revealing
some of the secrets

hidden in the icy depths
of that huge ocean.

But is there only one
way to cook up life?

Could you make it from a
different set of ingredients?

Science fiction writers
have speculated wildly

about alternative life forms -

but, in the cold,
hard world of science,

we only have proof
of life as we know it.

But if an ocean really is critical,

does it have to be
an ocean of water?

That's a question that
drives Nasa's Chris McKay.

What I'm really
interested in finding is

what I call a
second genesis of life.

Organisms that are clearly not
related to any life on Earth.

All life on Earth is related
to itself, forms a single tree.

You can call that Life One.

What I'm looking for is Life Two -

something that's not related.

It doesn't have to be
profoundly different,

but it has to be different enough

that we can say with
very high confidence

that they are not related to us.

We do not have a common ancestor.

Where such a life form
could feasibly emerge

was anyone's guess -

until, in 2005, the world's
attention turned to Titan,

the biggest of the moons
which orbit around Saturn.

At that time, all we knew of it

was that it looked gassy,
orange and lifeless.

We knew that Titan was a
fuzz ball from telescopes.

Before a spacecraft
ever went to Titan,

just looking at Titan
with a telescope,

we could tell that it
had a thick atmosphere.

We didn't know the composition
of the atmosphere

or the temperature of it, but we
knew it had a thick atmosphere.

But then, in 2005,

the Cassini-Huygens probe span by,

revealing a surface that
was unexpectedly Earth-like.

It was dotted with huge lakes

bearing an uncanny
geographical similarity

to the Great Lakes of North America.

From a physical point of view,

the presence of liquid

creates all these
other similarities,

and so we realised that liquid
on Earth, liquid on Titan -

we're going to expect a lot
of commonality, and we see it.

So, visually, when we look
at these images of the lakes,

we see reflections of
what we see in aeroplanes

when we look down as we
fly over the Great Lakes.

There was one crucial
difference, though.

These weren't lakes of water,

they were lakes of methane -

and, at minus 180 degrees Celsius,

they're too cold for any life form

with an Earth-like chemistry.

I would contend that
we don't understand

the role of temperature
directly in life.

Now, on Earth, of course,

we're used to living
in a high-temperature liquid

at high temperature.
We're in the fast lane.

We metabolise very rapidly

because we're living
at high temperature.

While on Titan,

the liquid there is cold,

the temperatures are cold.

If there's life there, it's
obviously in the slow lane.

It's metabolising very slowly

but, so what? What's the rush?

There's not an absolute tempo

that life must keep to.

But is that possible?

Can you have life using
methane rather than water?

With this in mind, scientists at
the picturesque and very watery

Cornell University, in New York,

are trying to establish
whether methane-based life

is even theoretically possible.

They took the chemical
ingredients that exist on Titan

and mixed them up.

Not in a test tube,

but inside a computer.

The computer built a
three-dimensional membrane -

the outside wall of a cell.

Except this alien membrane
functions in methane, not water.

It's not life yet,
it's just a house.

But the very first thing
that you have to do is

you have to have
somewhere to shelter,

and a membrane is a way of
keeping the outside to the outside.

A small step,

but this was
ground-breaking science.

For the first time, it
opened up the possibility

that there could be
a second tree of life.

We tend to think that
life would look like us.

You just have to look at
the Star Trek movies.

All the aliens kind
of look like insects

and things that we already know,

but why not be something
completely different?

Something that we can't imagine,

but something perfectly suited to
the conditions that are on Titan?

But if this extraordinary computer
model's right, how would we know?

At the moment, we can't physically
search for life on Titan,

but that doesn't mean there
wouldn't be other telltale signs

that we can detect.

If we look at carbon dioxide,

just out in the field,
down the road -

during winter, it rises

and during summer, it drops.

And that's because plants
take it up to make leaves.

They pull in the carbon
dioxide, it drops,

they make leaves.

In the fall, those
leaves fall, decompose,

the carbon dioxide comes back up.

So, there's a seasonal
phase in carbon dioxide

that's directly due to biological
activity at the surface

consuming, and then releasing,
that carbon dioxide.

We're pretty sure there's
no vegetation on Titan,

but what could be the equivalent

of the fluctuations
of carbon dioxide

that would indicate that something

was alive on the distant moon?

And the answer, we think,
is hydrogen.

Organisms on Titan would
derive their energy

by reacting hydrogen with
various other organic compounds

and so, if there was life on Titan,

that life should
represent a strong sink -

a strong loss -

of hydrogen at the surface.

And that loss of
hydrogen at the surface

would have an effect on
the hydrogen distribution.

So, we've said that the way
to detect life on Titan

is to look at the
distribution of hydrogen.

If there's no life,

the distribution will just
be flat, uninteresting,

but if there is life, and
the life is growing vigorously,

it will eat out the lower part
of that hydrogen concentration.

There will be a depletion
in hydrogen near the surface.

In 2005,

astronomers finally had an
opportunity to test this hypothesis

when the Cassini spacecraft sent
down a probe called Huygens

to land on Titan.

The pictures the probe
sent back were stunning.

Unfortunately, there were
no obvious signs of life...

..but Huygens was doing more
than taking images of Titan -

it was making detailed measurements
of the mysterious atmosphere.

As it turned out, the most important
were the readings it took

of hydrogen levels as it floated
down from space to the surface.

As the probe landed, scientists
noticed something remarkable -

the hydrogen levels
dropped abruptly.

When I heard about this result,

for a couple of minutes,
I was ecstatic, thinking,

"Oh, my God, this is
just textbook science -

"prediction, confirmation and a
Nobel Prize comes next," right?

But reality set in soon after

as I looked at the paper in detail

and considered how easy it is

to jump to the answer you want.

It's really a question
of excluding other possibilities.

On its own, Huygens' sensational
measurement was inconclusive.

What they needed was verification.

So, Nasa put together
a team of their best

and brightest engineers

to design a spacecraft
capable of exploring

the unique and technically
challenging oceans

of this liquid world.

And, after a number of
false starts and dead ends,

they came up with this -

a submarine.

I was reading 20,000
Leagues Under The Sea

and thought, you know,

"Titan has this wonderful group
of seas. What's underneath there?"

If we don't look there,

we really haven't seen
what's going on in Titan.

So, we came up with a
fairly long submarine.

As you see from
terrestrial submarines,

they're usually about
10:1 on dimensions,

length to the diameter,

and the reason for this is,
it really reduces your drag.

We are obviously a
little power-limited.

We have a lot of
communications to do.

We have four thrusters
in the back, here,

which use electrical energy - so we
went with a very long submarine.

If you can get below
the surface of the sea

and get all the way down to
the bottom in certain areas,

and actually touch the silt
that's on the bottom and sample it,

and learn what that's made of,

it'll tell you so much about
the environment that you're in.

But if you have a boat that
just drives on the surface,

figuring out how to get a probe
all the way down to the bottom,

get that sample all the way back
up to the surface and sample it,

it really becomes an
intractable problem.

There's so many things
that can go wrong doing that.

And, instead, we said, "If we can
encapsulate everything together

"in a submarine,
then we could go right down

"and do that sampling and come all
the way back up to the surface."

And so the submarine allows us
to explore the atmosphere,

the wind, the waves,

to sound with a sonar to the bottom,

to measure the topography,

to see what the contours
of the bottom look like

and then to go down
and actually touch the silt

that's been settling there for
thousands and thousands of years.

But sailing a large, one-tonne sub

around Titan's super-cold,
methane-rich seas

isn't without its problems.

Fortunately, Nasa
has the technology

to replicate conditions
on the freezing moon,

and this is it.

Inside this huge tank,

scientists can safely
and accurately mix up

the highly volatile
cocktail of chemicals

that make up the atmosphere
of the huge moon.

As we design and build the craft,

we can basically use this facility

to test problems or issues

that come up for the submarine,

so we can use this facility

to basically create
the seas of Titan,

the coldness of Titan,
the pressures of Titan.

They have discovered that
one of the biggest problems

of Titan's methane seas

is that they're rich in nitrogen,

and that could make it very
difficult to sail the sub around.

There could be so much nitrogen
dissolved in the sea that,

when the propellers
turn on our jets,

it might just make a lot of bubbles

and not be able to
push against the liquid.

So we're doing analysis now

and we hope to do some testing
in the near future that shows us

what happens if you spin a
propeller in liquid methane

and liquid ethane with lots
of nitrogen dissolved in it,

and can you get any
thrust out or not?

This is a really important
question to answer.

There's other ways to propel the
submarine if that doesn't work,

but the design that we came up with

helps us get to that simple place,

in terms of space operations.

The sub will be packed full
of scientific instruments

and bristling with cameras,

but there's one thing
the scientists feel

will make the mission
more than anything else.

That first picture, are you kidding?

That first picture from a submarine,

from anybody's submarine,

on the surface of a sea on another
planet in our solar system,

changes the world.

I mean, that's something that none
of us have ever seen before.

That is true discovery.

That is why we do any of this

and that would be awesome.

That first picture alone would
make this entire mission worth it.

No scientist is saying that
the cameras of the Titan sub

will definitely ping back
pictures of living organisms,

but they believe sending
a sub to this strange moon

gives them the best chance of
finding a new form of life.

I grew up when Star Trek

was just coming out,

and it was an inspiration to me,

but the key moment
was when I realised

that the job I wanted
was not Kirk's job,

but Spock's job.

He's the one with the tricorder.

He's the one that's detecting life

and my favourite saying is,

"It's life, Jim, but
not as we know it."

That's what I want
to be able to say.

I want to get data
back from a probe -

Titan, Mars, Enceladus, wherever -

and be able to say, "It's life,
Jim, but not as we know it."

Is it possible that
we could see stuff

that hints really strongly at life?

It's possible. I mean,
we might see things

that look like lichens or algae

growing on the rocks on the shore.

We might see massive
stuff on the surface,

but we have no idea.

We used to think that the
rest of our solar system

was frozen and dead,

but we now know that there
are oceans of water and liquid

in places we never thought possible.

In 2015, the New Horizon
mission to Pluto

ticked off the last
of the great worlds

to be explored in the solar system,

but we're only at
the beginning of the quest

to find the Holy Grail
of space science -

life.

We're through with
the age of discovery.

We've discovered all the planets,
we know what's there.

We've got a rough map of them all

and a rough understanding
of how they work.

The next question -

the question that I think should
motivate and guide planetary science

for the next 20 years - is,

"Is there any life in these
various and diverse oceans?"

Nearly two centuries ago,

Charles Darwin set out
on a voyage of discovery

that changed the world.

Perhaps Nasa's Titan submarine

will be a modern counterpart

to Darwin's ship, the Beagle -

and, in the search for
a new form of life,

will boldly go where
no-one has gone before.