All language subtitles for Solar.System.S01E01.Volcano.Worlds.1080P.WEB-DL.x264-skorpion_track3_[eng]

So far, we've set foot on one world
beyond our own.

We discovered a desolate, barren rock.

An ancient, unchanging, cratered
world.

And the footprints we left there

could last for millions of years.

Our only direct personal experience of
an alien world is of our moon.

Beautiful, but a dead, inactive world,
frozen in time,

whereas our planet is active and
alive.

If you come to the right places on
Earth,

it's literally seething with energy
beneath our feet.

For a long time,

we wondered if all this activity is
unique to our planet.

But now, thanks to a fleet of
spacecraft,

we know our world is not alone.

We currently have over 40 probes
exploring the solar system,

relaying a stream of information to
Earth,

allowing us to see our sister worlds
in unprecedented detail.

They're revealing planets and moons
covered with volcanoes,

dwarfing anything seen on our planet.

Alien landscapes bursting with fire...

..and ice.

Eruptions so violent,

they reach into space.

So, why are some worlds vibrant and
alive,

while others are cold and dead?

Now, that question is deeper than it
first sounds,

because answering it will have
profound implications

for our understanding of our place in
the universe.

See, geological activity,

the flow of energy from the interior
of a world outwards,

is necessary for the origin of life.

And that's why finding and
understanding those worlds

is a necessary first step in the
search for life beyond Earth.

Let's begin a journey to the volcano
worlds,

by leaving Earth...

..heading away from the sun...

..and setting a course to the planet
next door -

the most visited of them all.

For almost two decades,

the Mars Reconnaissance Orbiter has
pointed its cameras

at the Red Planet.

And the images it has sent back

have revealed volcanoes on a
staggering scale.

One so wide...

..it would span the UK.

And one so tall...

..it rises up through Mars's
atmosphere,

almost to the edge of space.

Over time, these mega volcanoes have
flooded

the Martian surface

with a billion billion tonnes of lava.

So much that they've tipped the entire
planet over

by 20 degrees.

So, what drives a planet's volcanism?

Iceland's one of the most volcanically
active

places on Earth.

This is the Icelandic Met Office,

so this is the weather forecasting
site.

But it also gives you a real-time
update

on earthquakes,

and earthquakes are precursors for
volcanic eruptions.

These dots are all earthquakes that
have happened

in the last few hours, actually.

And we, at the moment, are driving
along a road...

LAUGHTER

..in there!

So, there's...

Is that OK, by the way?

- Oh, yeah, that's normal.

- It's normal?
- Yeah.

- Yeah?

- When you have a collection of
earthquakes like this,

a lot in the same place, at the same
time,

it's called the jardfraedingur.

- Jard...
- Fraedingur

..fraedingur?

Yeah, so it's basically stirring the
earth.

- Stirring the earth.
- Yeah, yeah.

- But recently, the land here did more
than stir.

Just last year, over ten million cubic
metres of lava

flowed out down this valley,

creating brand-new land.

This is planet-building in action.

Activity so recent,

you can still see the afterglow.

So, there's the old volcano in the
distance,

which is old and cold,

and then there's all this new land.

And look, it's glowing!

To drive volcanism on this scale

takes an enormous amount of energy.

So, where does it all come from?

Think about what was happening here
about 4.5 billion years ago.

So, this would've been a cloud of gas
and dust and rocks,

and all those rocks falling together
under the influence of gravity -

ultimately to form the primordial
Earth.

During our planet's formation,

that gravitational energy was
transformed into heat,

adding to the heat released by the
decay of radioactive elements.

Heat is a form of energy.

Now, there's a law of physics, a law
of thermodynamics -

it's called the first law of
thermodynamics.

And it says that energy is neither
created nor destroyed.

So, all the energy released when all
those rocks

were smashing together to form the
primordial Earth

is still here.

It's stored - trapped - ever since.

Just below the surface there, down
that crack,

it's just glowing hot!

Mars formed at the same time, and in
the same way -

the planet trapping enough heat to
raise the largest volcanoes

in the solar system.

But unlike the Earth,

these giant volcanoes fell silent
millions of years ago.

Something happened to Mars's inner
heat.

And in the north of the planet...

..Mars Reconnaissance Orbiter

spotted a clue.

An impact crater...

..whose walls appear to be built

from an intricate array of pillars.

So perfect they look almost
engineered.

They aren't, of course, the work of
Martian sculptors.

They're also found here on Earth.

Just look at these beautiful geometric
shapes.

They look almost carved into the rock.

They are a beautiful example of one of
-

actually perhaps, in some sense, THE -
most fundamental law

of nature in action, the second law of
thermodynamics.

The second law of thermodynamics, put
really simply,

is that if you get a hot thing - high
temperature -

and bring it into contact with a cold
thing -

low temperature -

then it is inevitable that energy will
be transferred

from the hot thing to the cold thing

until they reach the same temperature.

That's absolutely fundamental.

That's what's happened here.

The hot lava has come out from
underneath the ground,

that inner heat,

it's met the cold atmosphere,

and it's cooled down, it's lost
energy.

And what's true here on Earth is also
true on Mars.

On both planets, the pillars started
life as hot molten rock.

As the lava cooled, it contracted,

causing cracks to form on the surface

that then grew downwards...

..creating the symmetrical columns.

They are a direct consequence of the
second law in action,

as the lava released enormous amounts
of heat -

ultimately out into space.

But the pillars on Mars are likely
millions of years older.

The flows that built them died,

just as Mars's volcanoes did.

Mars lost its inner heat far faster
than Earth.

The question is, why?

God, it's...

BRIAN LAUGHS

..the single simplest invention in
human history.

If I'd have been the cavemen,

we wouldn't have even domesticated
animals.

Ah!

Success!

Take one Earth-sized rock,

add a smaller Mars-sized one,

and roast for 30 minutes.

So, these two rocks have been in the
fire,

they've been heating up,

and I've just got them out of the
fire.

At the moment, they're at...

..the same temperature.

You can see there,

they're both about 200 degrees.

But now remove them from the fire.

In accord with the second law of
thermodynamics, well,

they're going to start losing energy.

So, if we wait,

then the rocks will cool down.

Well, now these two rocks have been
out of the fire

for about 20 minutes or so,

and not surprisingly they've cooled
down -

cos they're in contact with a colder
environment.

The big one has cooled down to
about...

..150, 155 degrees or so.

But the little rock has cooled down
way more.

It's now only at a temperature of
about 50 degrees or so.

I can pretty much touch it with my
finger.

And that's because the small one is
small.

To be more specific, these rocks are
losing heat

to the environment through their
surface area -

and the small one has got much more
surface area

in relation to its volume than the
large one.

That means that it loses heat more
quickly, cools down.

And this is exactly what's happened to
Earth and Mars.

Earth is large enough to have held on
to much of its internal heat.

But Mars's radius is about half that
of Earth's.

So, since the glory days,

when its volcanoes were raised on a
scale seen nowhere else...

..Mars's inner heat has escaped,

lost to the cold of space,

bringing the grandest volcanism

the solar system has ever seen...

..to an end.

Size, then, sets a powerful limit on
volcanic activity.

Yet the next volcano world

seems to break this rule.

Out beyond the asteroid belt

lies the first of the gas giants.

Jupiter commands its own system of
moons -

over 90 at the last count.

Including one that is truly unique.

Io.

Nasa's Juno probe has been circling
Jupiter since 2016.

Its orbit taking it ever closer to Io.

Its infrared camera saw a world
consumed by fire,

each bright patch a volcanic eruption.

Right now, rivers of lava are pouring

across its tortured surface.

In places, the volcanic eruptions are
so violent...

..they throw columns of gas and dust
far out into space.

Io is the most volcanically active
world in the solar system...

..yet its radius is just over half
that of Mars.

You remember that scene in Alien,

where John Hurt and all the astronauts

descend into the cave?

And remember what happens to 'em?

This has a bit of that feel.

The scale of volcanism on Io is hard
to comprehend,

to visualise,

until you come to a place like this.

Here's a photograph of the surface of
Io.

Can you see all those colours?

All those beautiful yellows and
oranges?

Now look at the walls of this cave.

Same colours.

And that's because these are the same
chemical elements -

it's elements like sulphur.

Now, in this case, they were deposited
on the walls

of the cave when the magma seeped away

around 5,000 years ago.

But here, on the surface of Io,

they've been constantly replenished.

Just look at the scale of it!

Imagine that, all on a small world, no
bigger than our moon.

Its small size means that Io's heat of
formation has long gone.

Something else is fuelling these
fires.

The giant planet that looms so large
in its skies.

Io orbits around Jupiter -

and Jupiter, being a very massive
planet,

raises tides on Io.

And that's pretty much the same
mechanism

by which the moon raises the tides on
Earth.

But Jupiter is extremely massive,

and so the tides on Io are extremely
violent.

It actually raises the tides in the
rock

of something like 100 metres.

It's not in water, it's in rock!

And it's about the height of this
cavern!

But Io's orbit is not circular.

It's elliptical,

so that means that the moon comes
close to Jupiter,

and far away.

Close, and far away.

Once every 42 hours.

So, that hundred-metre rock tide is
going up and down

and up and down every 42 hours,

as Io goes around Jupiter.

So, imagine the friction as that rock
tide rises and falls,

and rises and falls.

That introduces immense amounts of
heat into the moon.

It's actually about half the energy

that we know is needed to power the
volcanoes.

But it's only about half.

So, where does the other half come
from?

Well, that's where it gets really
cool.

So, let's say Jupiter...

..is there,

and let's say that Io...

..is orbiting around Jupiter...

I'm going to exaggerate it a lot.

..orbiting around Jupiter in an
elliptical orbit.

So Io is moving around like this.

In an elliptical orbit,

there are two foci.

The cross, out here in empty space,
which we call the empty focus,

and the other centred on the planet.

And it turns out that Io...

"It can be shown that..." That's what
you say.

I'm not going to show it, cos it's a
load of mathematics.

But it can be shown that Io is locked
to the empty

focus of the ellipse -

the other focus, not the planet.

But the tide is raised by Jupiter's
gravity.

So, that big, sort of huge, towering
tide

in the rock always points towards the
planet.

As Io goes around,

that tide is dragged backwards and
forwards

across the face of the moon.

So not only have you got this big
hundred-metre tide in the rock

going up and down as it goes around,

it's going side to side,

being dragged backwards and forwards
across the face of the moon.

That also injects a tremendous amount
of energy

into the moon,

and that's the other half of the
energy

that's required to power Io's
volcanoes.

These colossal tides are what enabled
Io, despite its size,

to become so violently volcanic.

The friction may even have melted so
much of the moon

that there's a global ocean of magma

just below the surface.

But there's another twist to Io's
tale.

This is a series of photographs of Io
taken -

it's only a few months ago now -

over a period of several weeks.

And you see the volcanoes, you see all
that activity,

the hot spots switching on and
switching off.

This is an infrared photograph.

So what you're seeing here is heat,

which is useless energy being radiated
off into space.

Energy is being removed from Io's
orbit.

Now, if you remove energy from an
elliptical orbit,

it gets more and more circular.

And if the orbit was circular,

then the tidal heating would die away

and the volcanoes would fall silent.

So, if all there was

was Jupiter and Io,

then Io would not look like that.

Io's extreme activity should've killed
off the tides

that create its internal heat.

So there must be something else

beyond the squeezing of the moon

keeping its fires alive.

Io is not alone in orbit around
Jupiter.

It's one of the four big moons known
as the Galilean satellites.

And Io orbits in what's called an
orbital resonance

with two of them - Europa and
Ganymede.

So here's Jupiter,

and for every four orbits of Io,

Europa goes around twice

and Ganymede goes around exactly once.

That means, on every fourth orbit, the
moons line-up,

and they give a gravitational kick to
Io.

They put energy into the orbit,

which keeps the orbit elliptical.

And so, whereas here on Earth the
volcanoes are driven

by the primordial heat down at the
Earth's core,

Io's volcanoes, ultimately, are driven
by gravity.

This bizarre volcanic moon...

..locked in a seemingly endless cycle

of eruptions by its sister moons...

..is the furthest world from the sun

where we've seen molten rock erupting
onto the surface.

But, beyond Jupiter,

another mission has encountered an
entirely different

type of volcano.

Crossing the great gulf of space,

we encounter the next planet.

Saturn's rings loop for hundreds of
thousands of kilometres

through space.

And just beyond them lies a glittering
gem.

A frozen moon -

perhaps the last place you'd expect to
find a volcano.

Enceladus's surface is a hard mantle
of frozen water

that's a deathly
-200 degrees Celsius.

On such a cold world,

everything should be frigid,
unchanging.

Yet, in 2005,

the Cassini probe witnessed an
extraordinary sight.

Explosive jets roar from the
surface...

..reaching hundreds of kilometres into
space.

The largest volcanic plumes in the
solar system.

How are such epic eruptions possible

on a tiny frozen moon?

Even on Earth, eruptions don't have to
be molten rock.

The geothermal activity so close to
the surface here in Iceland

is kind of a double-edged sword.

I mean, on the one hand it can be
dangerous.

But here, that geothermal activity is
also used

for the benefit of the population of
Iceland.

I mean, here you see thermodynamics in
action.

This is a power station.

These two power stations in this
region

provide over 400 megawatts of power.

It's enough to power Reykjavik, and
also half its hot water.

And so, you can feel the energy,

that primordial energy of the Earth,
rising to the surface,

heading off into the cold of the
atmosphere.

This is precisely what's happening out
there on Enceladus.

It's just...

BRIAN LAUGHS

You get... You do get a sense of the
raw power

just sitting just a few...

Not far, in this case,

below our feet, actually.

But this is nothing compared to
Enceladus...

..where over 300kg of water vapour and
ice

erupts every second

from giant cryovolcanoes.

It was Cassini that first spotted
something odd

about the motion of Enceladus.

As it orbits Saturn, it wobbles on its
axis...

..by a very small but, it turns out,
very significant 0.12 degrees.

Consider an egg.

EGG CRACKS CREW LAUGH

Now, when you spin an object,

so when an object spins on its axis,

it rotates around what's called its
centre of mass.

And for a solid object -

like this hardboiled egg -

if I spin it, it spins nice and
evenly.

Uniformly.

But now...

..look what happens if I take an egg
that hasn't been hardboiled -

so it's filled with fluid.

If I spin this...

..it wobbles all over the place

because the fluid inside is sloshing
around.

Because this egg is raw,

the shell and liquid inside move
independently

of each other when spun, making the
egg wobble.

So the reason that Enceladus wobbles

is because it's not completely solid.

And we now think,

by high-precision measurements and
simulations

of exactly how Enceladus wobbles,

that there is a global liquid ocean

beneath the frozen, icy surface of
Enceladus.

We can infer that

because the laws of physics

that apply to eggs here on Earth

also apply to moons.

I mean, Enceladus isn't going to do
that.

So Enceladus has an outer shell of ice

sitting on top a global ocean of
water.

But how is that water managing to
force its way

through 5km of solid ice?

To find out, Cassini took a much
closer look

at the moon's south pole.

Oh, wow. That's changed, hasn't it?

It's changed - I don't know whether
it's changed for good or bad.

Crikey!

HE CHUCKLES

We've found a really nice,

relaxing place to explain some
complicated physics!

Now, here, about 2km down below my
feet,

there's a hot reservoir of water
that's under pressure.

Now, under normal circumstances, that
couldn't escape, but we've

drilled a borehole and, the moment
that that borehole is present,

then those pressure and temperature
differences will equalise.

And, in this case,

the water comes out of the borehole as
superheated steam.

Now, here is a photograph of
Enceladus's south pole

from Cassini, and you can immediately
see there's

something interesting here -
interesting geology.

Cracks in the thin ice of the south
pole -

these things became known as the tiger
stripes.

They are revealed most clearly by
Cassini's infrared instruments.

The red shows freshly deposited ice
crystals...

..hints of activity along the entire
length of the cracks.

But the real insight comes when you
measure their temperature.

Because those tiger stripes are hot,
really hot, compared to the surface.

The surface of Enceladus is -200,

maybe -220 degrees Celsius.

These tiger stripes are at -80 degrees
Celsius.

You might say, "Well, it's still
cold."

It is cold, but it's a lot hotter than
the surface surrounding

those structures.

And so, what you can see here is
high-temperature,

high-pressure ocean beneath the
surface,

and there's a cold, low-pressure
environment of space above,

and there's a weakness here in the
surface.

That allows that gradient to equalise.

It's exactly what you see there,

other than there, someone has drilled
a hole down into the deep,

underneath the Earth, whereas, here,
the ice happened to be thinner.

We're not really sure why, actually.

Could've been that there was some kind
of impact here.

But the upshot is the same.

You get plumes of water,

ice in this case,

erupting out into space.

The tiger stripes also create a window
into Enceladus's interior.

As Cassini flew through the plumes, it
detected

traces of molecular hydrogen and
silicon dioxide, chemistry that

most likely comes from ocean water
interacting with hot volcanic rock.

This suggests that the ocean beneath
Enceladus's icy shell

has something that on Earth we call
hydrothermal vents.

The discovery of active geology on
Enceladus took

everybody by surprise.

Nobody expected to see it on such a
small world.

But there might be more to Enceladus
than just geology.

See, hydrothermal vents of the kind we
think might be

present on Enceladus are one of the
prime

candidates for the cradle of life on
Earth.

The reason is that, if you think about
what the origin of life

has to be, it has to be, in a sense, a
transition from geochemistry

to biochemistry, from active geology
to active biology.

So, all the conditions seem to be
present on Enceladus

for the origin of life, and we don't
even need to land or find

some way of getting into that ocean to
test that hypothesis because

Enceladus is throwing the evidence,
potentially, out into space.

All we need to do is fly a spacecraft
through those plumes.

So Enceladus has to be one of the
prime candidates for exploration

in the solar system to search for the
origin of life beyond Earth.

Enceladus is not the only world with
cryovolcanoes.

Even at the furthest planet from the
sun...

..we've found evidence of them.

Only one ship has ever made the
journey.

It was on one of Neptune's frozen
moons that Voyager 2 caught

a glimpse of recent activity.

Its camera sent back images of dark
smudges on Triton's face.

Trails left by plumes erupting from
its surface.

Making Triton the most distant of the
active volcanic worlds

that we've witnessed.

It seemed that the inventory of the
solar system's

active volcano worlds was complete.

But, recently, we found something we'd
missed far closer to home.

Venus is shrouded in thick clouds of
sulphur dioxide...

..making it very difficult to see the
surface.

So the spacecraft deployed here use
radar to peer through

the dense atmosphere.

Magellan's radar imagery revealed
Venus to be a hellish world...

..its landscapes dominated by
volcanoes...

..over 85,000 at the last count.

Including truly bizarre examples, with
deeply rutted sides...

..and lines of flattened volcanic
domes like chains of pancakes.

But with only snapshots from orbit to
go on, no-one knew

if any of these volcanoes were
active...

..until, in 2023, a new analysis

of the Magellan data revealed,

on a volcano the size of Mount
Everest,

an eruption along its northern flank.

Proof after all that there's activity
on the most

volcano-ridden planet in the solar
system.

So why does Venus have such strange

and diverse volcanoes littered across
its surface?

A clue can be found in Iceland's
remote volcanic interior.

In 1783, for a period of eight months,
one of the most

catastrophic volcanic eruptions in
human history happened here.

15 cubic kilometres of lava emerged
from these eruptions.

You see this, it's a remarkable
landscape, a line of volcanoes.

And they're really classic volcanoes,

like a child has drawn a volcano.

And then, everywhere else that you
look across this valley,

it's just lava.

The fact that such a violent eruption
happened here

is not down to chance.

If I take a map of the Earth and draw
all the volcanoes,

then they form a very distinct
pattern.

So, there's a line all the way down
North and South America,

on the Pacific Coast, and then, the
other side of the Pacific,

there's another line of volcanoes
through places like Indonesia.

Down here in the Rift Valley, Tanzania
and Ethiopia.

And then there's a line of volcanoes
through Iceland and, actually,

under the ocean, down the middle of
the North and South Atlantic.

So there's a very distinct pattern
here.

And that's because the surface of the
Earth is not just one big

slab - it's carved up into plates.

The Earth has what's known as plate
tectonics.

So, here, for example, down the
Pacific Coast of North

and South America, the Pacific Ocean
crust, the floor of the Pacific,

is moving down, this way,

underneath the continent.

And you get eruptions, you get
volcanoes.

In the Atlantic, here, through

Iceland, the opposite is happening.

The Earth's crust is spreading.

You can see it, actually. I'm sat on
it.

So, over there, in the west, is North
America, the North

American Plate, and, over there, in
the east, is the Eurasian Plate.

They're spreading apart here,
literally here,

and that's why there's a line of
volcanoes moving down through

here and straight onwards down into
the South Atlantic.

So, Earth's pattern of volcanoes is
telling us

that there's what's called plate
tectonics on the Earth.

Now look at a map of the volcanoes on
Venus.

Look at that.

It's absolutely covered, completely
randomly,

in pretty much every kind of volcano
you can imagine,

scattered across the entire face of
the planet.

And the reason for that is that there
are no

plate tectonics on Venus.

We don't fully understand why Venus
and Earth are so different.

Why Earth developed plate tectonics
and Venus didn't.

But we do know that Venus's outer
crust is much thinner.

The planets Venus and Earth are
roughly the same size,

they probably started life with about
the same amount of internal

heat, but it's how the heat escapes
that makes all the difference.

So, here on Earth,

it escapes mainly at those boundaries
between the plates.

But Venus has a much softer and
thinner crust, a lithosphere,

than Earth, and so the heat can escape
anywhere.

And that's why you see this surface
covered in a plethora of volcanoes.

With less of a barrier, Venus's inner
heat has built

vast lava flows that run for thousands
of kilometres.

And we now think that at least one of
its volcanoes,

and we suspect many more, remain
active to this day.

But only further missions will reveal
just how alive

volcanoes on our sister planet really
are.

Our exploration of the solar system
has shown us that there's

active geology in the strangest and
most unexpected of places.

The ice fountains of Enceladus, the
Galilean moons of Jupiter,

even the frozen outer moon of the
solar system, Triton.

But amongst all those geologically
active worlds

scattered across the solar system, it
still remains the case

that there's only one place where we
know for certain that the

active geology became biology, and
that's here, on Earth.

And if that really is the case, if
we're alone here on Earth,

then I think that raises a deep and
very profound question.

It's why? What is so special,
possibly, about this place?

Wonderfully, at least part of the
answer appears to be

a consequence of plate tectonics.

Volcanoes, when they erupt,

emit huge amounts of greenhouse gases,
like carbon dioxide.

And as we all know, greenhouse gases
heat a planet up.

Now, Earth has a natural regulatory
system.

When it rains, the carbon dioxide is
dissolved in the water

and falls on the ground and the carbon
dioxide reacts with

the rock of the mountains to form
minerals.

Then, plate tectonics can take those
rocks and send them

back down into the Earth.

So there's a cycle from volcano to
atmosphere to land

and back into the interior of the
planet.

Over geological time, this wonderful
relationship between volcanoes,

plate tectonics and our atmosphere has
kept Earth's climate in check.

And that stability has helped sustain
an unbroken

chain of life that stretches back
almost four billion years.

It's only here on Earth that a range
of geological processes,

from volcanoes, to plate tectonics,
and hydrothermal vents,

have conspired together to produce an
environment that not only

allowed life to begin, but also was
stable enough to allow life to

flourish, from the simplest living
organisms to the endless forms

most beautiful that we see covering
the surface of the Earth today.

The question is, how special is Earth?

Well, I think the answer might be
found in this giant laboratory,

the solar system, in exploring the
eclectic

and diverse collection of worlds that
we find orbiting the sun.

- Current velocity is 145 metres per
second, at an altitude

of about 9.5km above the surface.

- In February 2021,

an astonishing new piece of hardware
arrived on the surface of Mars.

Perseverance is looking for evidence
of ancient life, which may have

started on the planet, thanks in part
to its giant volcanoes.

- Volcanism played such an important
role in the history of our planet,

but also in the origin of life and
evolution of life.

Mars is like Earth's cousin.

Very early in their history, they had
these volcanic activities.

We found evidence that Mars had liquid
water on its surface,

it had a thicker atmosphere.

- So, at that time, when life was
emerging on Earth, Mars also

was creating similar environments.

So it's possible that there was

the potential for life on Mars.

- Mars's volcanism faded away, and so
did the water on its surface

and the chance for life to flourish on
the Red Planet.

But if life did at least get started,
crucial evidence

could be locked in the Martian rocks,
waiting to be discovered.

- Perseverance, or, as team members
called it, Percy, went to Mars,

to a crater known as Jezero, which
used to be an ancient lake.

And so Percy is looking for evidence

about the habitability of this
environment.

- We're looking for signatures that
there was life on the planet,

but it would be absolutely amazing if
we actually found cells,

or something similar, in these rocks

that indicated that there is life on
Mars today.

- As it makes its way across the dry
lakebed, Perseverance

leaves behind a series of small,
carefully sealed rock samples.

The plan is to analyse these in a lab
here on Earth.

But right now, they're stuck on the
surface of Mars.

- Retrieving our samples from Mars is
not going to be an easy task.

First we have to land on the surface,

then we have to pick the samples up,

make sure they're packed into the
spacecraft...

..and make sure that the spacecraft
gets back to Earth.

So there's quite a bit of coordination
that has to be done.

- The schedule is still uncertain.

But Nasa's hope is to return the
cannisters back to Earth...

..in the mid-2030s.

- It's exciting to me, because I study
these rocks,

and so this would be a unique
opportunity to have samples

directly collected from the surface
that I could analyse.

- Being able to have samples from a
planet is

so much better than just having to
look at a planet through

a telescope or through data sent back
by a spacecraft.

So, regardless of all the effort it's
going to take to get

the samples back from Mars, it's
definitely going to be worth it.

At that point in time, we'll have a
piece of Mars in our hands.

- Next time, we venture to the hidden
realms of our solar system.

The dark worlds...

..where mysteries lurk in the
shadows...

..and a distant hinterland sends
unexpected visitors

hurtling towards Earth.