All language subtitles for The.Planets.UK.2019.S01E02-en

COMMS: liftoff of Messenger on NASA ’5
mission to Mercury.

BRIAN COX: Our planetary neighbour, Mars,
is a cold, barren rock.

Its rusted surface
covered in parched sand.

But beneath the dust,

the planet bares the scars
of a former life.

Billions of years ago,
Mars wasjust like Earth.

A world with a thick atmosphere that
supported oceans of water.

But today, that world is gone.

Mars lies dead...

...while the Earth thrives.

Why the two planets
had such different fates

is a mystery that we‘ve onlyjust
begun to answer.

You see that pale red point of light
in the sky?

Just there?

That's Mars.

Through a small telescope,
it appears almost Earth-like.

Our sister world - polar ice caps
and dark surface markings

that 19th-century astronomers
thought were vegetation,

even canals bringing meltwater down from
the poles to arid equatorial cities.

“Across the depths of space,

“the inhabitants watched us
with envious eyes,“

wrote HG Wells.

We now know that there are no eyes
looking back at us.

Mars is a frozen, arid desert world.

But a fleet of spacecraft have revealed
that it hasn't always been that way.

NEWS REPORT: Mariner 4 successfully
launched on time

for its historic 228-day journey to Mars.

Picture information started to come in
onjuly 15th 7965.

A revelation, comparable to Galileo’s

first View of the Moon
through a telescope.

BRIAN COX: During its brief flyby,

Mariner 4 gave us
ourfirst close-up glimpses of Mars.

NEWS REPORT: When Mariner 9 was placed
into an orbit around Mars,

it saw a planet blanketed
by a gigantic dust storm.

In nearly a year of operation,

they transmit more than 7, 000 photographs.

BRIAN COX: From orbit, Mariner9
photographed 80% of the Martian surface.

First of all, there are two eyes,
not only in colour but also in stereo

It has a sense of touch,
it has a sense of hearing,

but by far the most important feature
of the lander is its brain.

BRIAN COX: The Viking programme took us
down to the ground for the first time...

COMMS: Touchdown, we have touchdown.

- BRIAN COX: ...and revealed Mars...
- Perfect set-down.

BRIAN COX: ...like never before.

And there‘s the first piece
of information coming in. Oh! Oh!

BRIAN COX: The data gathered
over the last 50 years

has allowed us to create detailed maps
of the Martian surface...

...and begin to piece together its past.

Maps of Mars are like storybooks -

you can read the history of the planet
written across its surface,

and the reason for that
is that there's virtually no erosion.

There hasn't been for billions of years.

So the scars of events
that happened even 4 billion years ago

can still be seen.

This is a type of map called
an elevation map.

The colours correspond to difference
in heights on the surface.

So blue means low,
and red and white are high.

Now, this region here,

which is much higher, on average,
than the rest of Mars,

is called Tharsis,

and it's covered in volcanoes,

including the largest volcano
in the solar system, Olympus Mons.

At the other side of Tharsis
is the great Valles Marineris,

the Mariner Valley, and it is a canyon
that dwarfs anything we see on Earth.

On the opposite side of the planet
is an impact basin called Hellas.

The height difference
from the crater rim to the crater floor

is nine kilometres.

That means you could fit Everest
in the middle of there

and look down on its summit.

And the region surrounding the basin
reveals Mars's former life.

The Hellas Basin is punched
into the oldest suwiving terrain on Mars.

It's called Noachis Terra,

orthe Land of Noah.
And that's a wonderfully evocative name,

because its surface is sculpted
by flowing water.

All across the earliest Martian surface,

we've glimpsed traces of what appear to
have been lakes and rivers.

And so a new generation of spacecraft
has been sent to Mars

to investigate the existence of water...

...and what happened to the planet
for it all to disappear...

...lead by the most audacious Mars mission
ever attempted...

COMMS 1:
Vehicle reports entry interface.

COMMS 2: We have two-way Doppler
and orbit around the planet Mars.

BRIAN COX: ...to land a one-tonne rover
on the Martian surface.

Its final decent has become known
as the seven minutes of terror.

Curiosity touched down in Gale Crater -

a 150-kilometre-wide impact basin

thought to have been home
to an ancient lake.

The rover is
a $2.5 billion mobile chemistry lab...

...designed to take samples
of the Martian surface

and analyse its composition.

As it explored the crater,
Curiosity saw pebbles,

polished and rounded by running water

in what had once been rivers and streams.

Then, 61 days after landing,

Curiosity identified the perfect spot
to begin its primary mission.

In a sandy area of the crater
called the Rocknest,

the rover took its first scoops
of Martian soil.

Chemical analysis of the fine, dusty sand

revealed something quite unexpected.

Even though the surface of Mars
appears completely dry,

2% of the soil is still made up of water.

Curiosity had found evidence of just
how wet a planet ancient Mars had been.

For hundreds of millions of years...

...Mars was a water world.

Rains fell.

Rivers ran.

And in the northern hemisphere,
water collected in a vast sea

that covered a fifth
of the Martian surface.

The Red Planet was once blue.

All the evidence suggests

that there were large bodies
of standing water on Mars

around 4 billion years ago,

and the atmospheric pressure
was at least that of Earth today,

perhaps even higher.

Temperatures were around 25 degrees.

So I could have sat on Mars
all those years ago,

admittedly with a mask to breathe,
cos there was very little oxygen,

but I could have sat there
and looked out over a view like that.

So you don't have to imagine
what Mars was like in the past -

you can experience it.

It was pretty much like this.

But within a billion years,

all Mars's lakes and seas
had disappeared.

In our solar system,
only one blue planet sun/ives.

Mars's sister - Earth.

70% of our planet's surface
is covered by ocean.

Under the waves,
a million species thrive...

...while, on land, the rains support
Earth's delicate ecosystems...

...providing a home
for an abundance of life.

But it hasn't always been this way.

The early Earth was unrecognisable
from the planet we know today.

Its atmosphere
thick with carbon dioxide.

And its oceans acidic.

4 billion years ago,
Earth was a troubled, toxic world...

...while Mars was flourishing.

But both planets were about to be engulfed
by a cataclysm from space.

To understand what happened,
we have to look beyond our own world.

You can't read the deep history
of the Earth by looking at its surface,

because our planet
is a geologically active world.

The surface is constantly being re-shaped
by volcanic activity

and weathering
and the actions of the oceans.

But we have a companion,

the Moon, which has been inactive
for many billions of years,

and so the history of events that happened
in this region of the solar system

is written all over its surface.

The most distinctive feature
of the Moon's surface are its craters.

It is literally covered
in a record of impacts from space.

And that allows us to estimate

the relative ages of different parts
of the Moon.

And quite simply,
if there are more craters,

then that piece of the Moon
must be older -

there's been more time
forthe impacts to build up.

But we can do better
than just measure the relative ages

because we have rocks -

the Moon rocks brought back
by the Apollo astronauts.

Now, we can estimate the ages of rocks
very precisely

by looking at the rates of decay
of radioactive elements inside them.

They are like little stopwatches

that start ticking
the moment the rocks are formed,

in this case, by the impacts from space.

So the Moon rocks allow us
to tie the number of craters

in a particular region of the Moon
to an absolute age measured by the rocks.

And this doesn'tjust allow us
to date impacts on the lunarsurface.

It means that craters can be used

to read the histories of worlds
across the solar system.

Including Mars.

When we gathered all the data,
we discovered something surprising.

There was a peak
in the crater formation rate

about 3.8 to 3.9 billion years ago

which signified a period
of intense violence in the solar system,

and that is called
the Late Heavy Bombardment.

Countless asteroids fragmented
in Mars's atmosphere,

raining havoc across the planet.

It‘s estimated that 53 tonnes of rock

fell on every square metre of Mars.

Over a third of the planet's surface
was obliterated...

...and Mars was pushed to the
brink of death.

Whilst the evidence
from the surface of the Moon

tells us that the Late Heavy Bombardment
happened, it doesn't tell us why.

For that, we have to resort
to computer models

of the evolution of the solar system,

and when we do that,
they point the finger at Neptune.

It's thought that Neptune migrated
outwards into the Kuiper Belt...

...a region of icy, rocky objects orbiting
at the edge of the solar system.

The resulting gravitational interactions
disrupted those orbits

and sent many of the objects inwards
to the inner solar system,

and that may have been the cause of the
Late Heavy Bombardment.

Earth also suffered the onslaught.

And for tens of millions of years,

the fortunes of the two sister worlds

hung in the balance.

Butjust when conditions appeared
at their least promising...

...Earth's most precious characteristic
emerged.

Life.

There is good evidence
that life was present on Earth

around 3.8 billion years ago,

and discounting the, Ithink,
remote possibility

that life began elsewhere
in the solar system

and was transported to the Earth
on meteorites or comets,

that means that life must have begun here.

So, somewhere on this planet,
there was a transition from geochemistry,

the chemistw of Earth,

to biochemistry, the chemistry of life.

And whilst the precise details of how that
transition occurred remain a mystery...

...it‘s thought that in warm volcanic
pools or deep-sea hydrothermal vents,

conditions were right

for the chemical building blocks of life
to form spontaneously.

if similar conditions were to be found
elsewhere in the solar system,

it might be possible
that life began there, too.

COMMS: Ignition. And liftoff of the
Atlas Vroc/ret with MRO...

...surveying for the deepest insights into
the mysterious evolution of Mars.

BRIAN COX: So, in 2005,
NASA embarked on a mission

to look for those
same environments on Mars.

For more than a decade,

the Mars Reconnaissance Orbiter
has been our eyes on the Red Planet...

...sending back more data
than all the other Mars missions combined.

MRO has made more than 60,000 orbits,

mapping over 99% of the planet's surface.

Its high-resolution cameras
have revealed Mars as never before...

...discovering polar avalanches...

...shifting sand dunes...

...and what could be seasonal
flows of sand

or even liquid meltwater.

Then, in 2017,

MRO turned its gaze to one
of the Red Planet's oldest features,

the Eridania Basin.

3.8 billion years ago,

the basin was a vast sea...

...holding ten times more water than
the Great Lakes of North America.

And it was here that MRO found
the evidence it was looking for.

ADO-metre thick deposits of minerals
that, on Earth,

form in deep-sea hydrothermal vents.

In the Eridania Basin,

MRO revealed that conditions on Mars

had once been ripe
for the emergence of life.

We won't know for sure
whether life began -

or even perhaps still exists - on Mars

until we go there
and find physical evidence.

So microbes buried deep below the soil
in oases of liquid water,

or maybe microfossils.

But what we do know is that when
life began here on Earth

3.8 billion years ago,
the conditions on Mars were very similar.

There were seas,
there was volcanic activity,

there were even hydrothermal vent systems
on the floors of its oceans.

So it is at least possible

that Earth is not the only world
in the solar system where life began.

The habitable conditions
during what's known as Mars's Noachian Era

persisted for
hundreds of millions of years.

But then prospects for life
on the Red Planet changed dramatically.

Around 3.5 billion years ago,

the Noachian Era drew to a close,

and Mars entered a more frozen,
arid phase known as the Hesperian.

The water that flowed freely
over the surface during the age of Noah

became locked away
in giant resenroirs of ice.

But around the same time,
Mars became more volcanically active,

and the volcanic eruptions
and sub-surface lava flows

occasionally melted the ice,

leading to catastrophic flooding.

They must have been
some of the most spectacular sights

in the history of the solar system.

As molten rock pushed upwards
through the crust,

meltwater poured out onto the surface.

It raged down
from the Southern Highlands...

...until, in a place known
as Echus Chasma,

it plunged over cliffs
four kilometres high...

...creating the largest waterfall the
solar system has ever seen.

Echus Chasma would have been like
no waterfall ever seen on Earth.

350 cubic kilometres of water
flowed over it.

That‘s like a cube - 70 kilometres
by 70 kilometres by 70 kilometres.

It all emptied into a canyon

10 kilometres wide
and 100 kilometres long,

and that happened in a few weeks.

Once the flood subsided,
the water disappeared...

...leaving the evidence of the falls
etched into the face of the planet.

We don't know precisely why
the climate of Mars

changed from warm and wet
to cold and arid.

We're talking about events
that happened 3.5 billion years ago

on a planet hundreds of millions
of kilometres away.

So it is a hard problem.

But we do strongly suspect

that changes happening
on the planet's surface were driven,

at least in part,

by changes in the planet's interior.

Deep within Mars's core,

something was causing the planet to die,

and the evidence can be found
in Mars's atmosphere.

COMMS: Tminus ten, nine,

eight, seven, six, five, four,

three, two, one...

Main engines start.

Ignition.
And liftoff of the Atlas V with MA VE/V,

loo/ring for clues about the evolution
of Mars through its atmosphere.

BRIAN COX: In September 2014,

NASA's MAVEN probe
made its final approach to the Red Planet.

Its mission -

to understand what drove
the planet's dramatic climate change.

MAVEN is equipped
with an array of instruments

designed to measure the behaviour
of the atoms and molecules

in Mars's atmosphere.

The spacecraft circles Mars
in an elliptical orbit...

...allowing it to measure the full profile

of the planet's upper atmosphere.

At its lowest point, it's just
150 kilometres above the surface.

At its highest,
a little over 6,000 kilometres.

And it was at the very top
of Mars's atmosphere

that MAVEN found the key to the mystery
of what happened to Mars.

(STATICKY CLICKING)

Detailed measurements revealed

escaping to space

at a rate of about two kilograms
every second.

Over time, it‘s thought this gradual
stripping away of Mars's atmosphere

has slowly thinned the insulating layer
surrounding the planet...

...causing surface temperatures
to plummet.

But what was it that caused Mars
to lose its atmosphere

while Earth clung onto hers?

150 million kilometres away
in that direction is the setting Sun -

a giant nuclear fusion reactor.

You could fit a million Earths inside it.

Now, the surface temperature
is only around 6,000 degrees Celsius,

but the Sun's atmosphere,
known as its corona,

is at a million degrees.

And that means it‘s in the form of
what's known as a plasma -

a soup of electrically charged particles.

Now, some of those particles
are moving around so fast

that they can escape,

and they stream away
in what‘s known as the solar wind.

They reach the Earth travelling
at a few hundred kilometres per second,

and if we weren't protected,
they would strip away our atmosphere.

And when the Sun dips below the horizon...

...there are times when that protective
force field is revealed.

just look at that!

I mean, there is the aurora.

It‘s the laws of nature,
all of them, written across the sky.

Electrically charged particles
are being driven away from the Sun,

ultimately from nuclear fusion reactions
in the core of a star.

They‘re crossing the solar system,
hitting the Earths magnetic field,

stretching it out
on the dark side of the planet.

The field then snaps back
like an elastic band,

accelerating all those charged particles
up and down the field lines

to the poles, which is here,
in the skies over Iceland,

and they hit nitrogen and oxygen molecules
in the atmosphere...

And you‘re seeing quantum mechanics.

They're exciting the molecules

so that they emit light
in characteristic colours.

And if you think about it,
this is the only time that we really see

the Earth's magnetic field.

It‘s one of the reasons why life on Earth

has been able to persist
for 4 billion years.

So, in a sense,
that's the reason that you exist.

It's Earth's magnetic field
that protects our atmosphere

from the ravages of the solar wind,

and that protective shield has its origins
deep in the planet‘s interior.

Thousands of kilometres down,
below my feet -

actually below your feet now -

is the Earth‘s outer core,

which is a seething mass of molten iron.

Now, convection currents
cause the molten iron to rise,

then the Earth's rotation causes it
to spiral around.

Now, a spiralling, circling flow of an
electrically conducting liquid

is a dynamo.

A dynamo generates a magnetic field,

and the Earth's field rises up
not just to the surface here

but out into space,
forming our protective shield.

And that...what you see there.

And just like Earth,

ancient Mars was also shielded
from the Sun.

Aurora once danced above its poles...

...keeping guard over the
Martian atmosphere and seas below.

But between 3.5 and 4 billion years ago,
Mars's dynamo switched off.

The aurora surrounding the poles
slowly faded away,

as the magnetic field diminished...

...allowing the atmosphere
to be stripped away by the solar wind.

Without protection,
seas evaporated,

the surface froze,

and Mars was transformed.

At the same time,
the fortunes of Mars's sister world

were about to take a very different turn.

For the next billion years or so,

Earth was indistinguishable
from the landscapes of early Mars -

barren continents surrounded by ocean.

But in Earth's oceans,

life was beginning to transform
the planet.

Primitive algae started to neutralise
the ocean‘s acidity

and replace the dense red fog of Earth's
methane-rich atmosphere with oxygen.

Around 600 million years ago,

that oxygen-rich atmosphere

allowed complex life
to evolve in the oceans,

colonise the land,

and ultimately produce this almost
infinitely rich living world today

of which we are a part.

While Mars died, Earth flourished.

To understand why the two sisters
had such different destinies,

you have to go right back
to the time the planets were forming.

When Mars and Earth were born,

the solar system was a chaotic vortex
of gas and rock.

Material clumped together and grew...

...only to be smashed apart.

Overtime, some of the objects became
large enough to survive

at least the smaller impacts
and continue to grow,

including the embryonic planets
Earth and Mars.

But there was one crucial difference
between the young planets.

Mars formed
in a region of the solar system

with considerably less rocky material...

...and that had a profound impact
on the planet's growth.

Mars is a significantly smallerworld -

it‘s about half
the diameter of the Earth -

and that makes all the difference.

Although the details
are not yet fully understood,

it seems clear that Mars's smaller size

meant that its dynamo switched off
many billions of years ago.

Being smaller meant Mars‘s core cooled
more quickly than Earth's.

And this is certainly part of the reason
why Mars lost its magnetic field.

Even though the planet is further away
from the Sun than we are,

that meant that the solar wind stripped
away its atmosphere, and Mars died.

So even though Earth and Mars
are so similar in so many ways,

the difference in position and size
in the solar system

lead to very different fates.

Long ago, two sister worlds were born.

In childhood, Mars was warm and wet...

...whilst the Earth
was inhospitable and toxic.

Both young planets survived the violence
of the Late Heavy Bombardment...

...emerging as mature worlds...

...primed with all
the ingredients for life.

But deep inside,
the smaller of the two was dying.

Mars's seas dried up.

And as the planet's interior cooled,

one by one, her fires went out.

Olympus Mons, the largest volcano
in the solar system,

last erupted around 25 million years ago.

As the lava turned to stone,

Mars was frozen in time.

And so, today, her surface lies rusted
and gathering dust.

But that might not be
the end of Mars's stow.

Because the next generation of spacecraft
are already on their way.

NASA Orion -

currently in advanced testing.

ESA Exomars -

a fleet of spacecraft
designed to search for signs of life.

And the most ambitious
private space mission ever conceived.

A launch vehicle developed to take humans
to the surface of Mars.

Mars is, in a sense, a failed world,

a faded ember etched with the memories
of a more enticing past,

but there have been - and may still be -
life on Mars,

and the discovery of a second genesis
in our solar system

would have profound philosophical,
scientific and cultural consequences,

because it would mean there is a sense
of inevitability about the origin of life.

And that would mean that the universe
is most likely teeming with life,

that we are not alone.

But equally importantly, I think,

is the role that a planet with a history
like Mars could play in ourfuture.

Mars is rich in resources.

It has vast reservoirs of frozen water
below the surface

and minerals - iron, nitrogen,
carbon, oxygen -

all the things you need
to support a civilisation.

And that's why I think that,
in my lifetime, there will be Martians.

But the Martians will be us.

We will go to Mars and make it our home,

and that old red world will become
our first step beyond the cradle

and out to the stars.

Mars really captures our imagination,

partly because it‘s so close.

I think people are really interested
in Mars

because it actually is so similar
to Earth.

It's close by, it's easy to travel there
with robots and space missions,

and so we've done a lot of exploration,

and every time you go and look,
you discover something new.

BRIAN COX: NASA Curiosity launched
on 26th November 201 1.

But the biggest obstacle facing
the mission team wasn't leaving the Earth.

Mars has a unique set of challenges

compared to other places
we go with spacecraft.

Mars has an atmosphere, but it's thin,

so it's not enough
to really slow you down,

but it is enough to actually burn you up
as you're twing to land.

BRIAN COX: Curiosity reached
the top of the Martian atmosphere

travelling at 20,000 kilometres per hour.

Curiosity is a big rover - it weighs
a metric tonne - and so landing that

required every trick in the book
of how we've learned to land on Mars

with previous missions.

BRIAN COX: To land safety,
the rover had to be slowed

to less than four kilometres per hour.

ASHWIN VASAVADA: You end up arriving at
Mars going really fast,

so you actually have to slow down,

and we do that using a heat shield,

which burns off a lot of energy
and creates a lot of heat,

so you have to absorb that somehow
and not damage the spacecraft.

Then a parachute comes out.

The biggest parachute
we've ever used in a planetanr mission.

And that even doesn't slow Curiosity
down enough,

because Mars's atmosphere
is quite thin,

so then rockets carry the spacecraft

and guide the spacecraft
to the surface.

There's nothing you can do
at that point to ensure its success

or prevent its crashing.

And yet, you've invested so much
in the outcome.

All I could do
was sort of curl up in a ball

and wait for the green light
that Curiosity was safely on Mars.

(BEEPING)

BRIAN COX: Seven years
and $2.5 billion in the making,

Curiosity finally touched down

at 6:32 UniversalTime
on 6th August 2012.

I was sitting in the control room,

watching the engineers
who were actually monitoring

the signals coming in from Curiosity,

and so they were reading out
the data that they were getting,

and they detected
the wheels touching the soil.

Then a few seconds went by
when cables had to be cut

and the rocket jet pack had to fly away.

And only then they understood
that Curiosity was safe on the ground,

and the whole room
just erupted in celebration.

BRIAN COX: Since it landed,

Curiosity has been exploring
Gale Crater for more than six years.

JENNIFER EIGENBRODE:
Curiosity is a roving laboratory.

We actually collect samples by scooping it
or by drilling

orjust by sucking in
some of the atmospheric gas.

And it's that type of data that allow us

to peck apart the story
that those things hold.

In 2015, we made our first identification
of organic molecules

that we think were coming
from the Martian materials.

And that is a turning point for us.

What we found in those rocks

is what we expected
of natural organic matter.

It‘s what you would expect to find
on Earth.

Finding the organic matter
is the clue to searching for life.

What everybody wants to know
is whether or not Mars once had life,

and the short answer is,
we don't know.

The somewhat longer answer is,

we see all the signs of materials
that could have supported life.

We have evidence
for lots of water early on.

We see the nutrients.

We see carbon. We see oxygen.

We see nitrogen. We see phosphorus.

We see all the stuff that life needs
in orderto reproduce and survive

as simple microorganisms.

ASHWIN VASAVADA: For me, personally,

I find it might actually be
more surprising

if we never found evidence
of life on Mars.

Everything we've found suggests

that Mars was such a friendly, supportive
place for life in its early history,

and there should be a lot of planets
like that around other stars

and lots of life in the universe.

So maybe we're getting to the point
where it'll be more surprising

if we neverfind other life.

BRIAN COX: And so,
thanks to Curiosity‘s discoveries,

the latest wave of spacecraft
might finally answer the question,

has there ever been life on Mars?