All language subtitles for Nova S46E13 The Planets Mars.DVDRip.en.PBS

Two rocky worlds formed
at the same time...

now close neighbors.

One blue with oceans
and full of life.

Earth has got
this rampant biosphere.

The other a barren desert.

If you look at Mars,

it's a red, dusty planet,
it's super dry.

♪♪

But it hasn't always been
that way.

There's a lot of evidence

for ancient flowing water
on Mars.

♪♪

It was a bizarre discovery,
it was startling.

Stunning findings reveal
a deep mystery...

Why is Mars so different
from Earth?

Daring us to explore...

♪♪

We knew it landed safely

when we realized that the wheels
sensed the ground.

We had successfully landed
on Mars.

♪♪

And discover.

What we found in those rocks

is a turning point for us.

Finding the organic matter
is the clue

to searching for life.

♪♪

And if life did evolve
in its ancient oceans,

what happened to it?

How far along did it get

and did it go long enough

that life could have taken hold
there?

♪♪

It opens up the possibility

that the universe is full
of life.

♪♪

"The Planets: Mars"

right now, on "NOVA."

♪♪

Doppler and orbit around
the planet Mars.

♪ They'll say
no one can see us ♪

♪ That we're estranged
and all alone ♪

♪ They believe
nothing can reach us ♪

♪ And pull us out
of the boundless gloom ♪

♪ They're wrong ♪

♪ They're wrong ♪

♪♪

Mars.

Our planetary neighbor is
a barren desert world,

its surface red with rusted rock
and parched sand.

But beneath the dust
Mars bears the scars

of a former life.

Four billion years ago,

Mars was
a very different world...

♪♪

Its atmosphere dense enough
to support seas...

and rivers of running water,

what we believe are
the conditions

for life to emerge.

♪♪

But today
that vibrant world is gone.

Its rivers run dry.

♪♪

Oceans evaporated.

♪♪

While clearly visible
from the red planet's surface,

is its neighbor, Earth...

blue with oceans
and teeming with life.

♪♪

On Earth we have this
amazing biosphere

that is super-vigorous.

There's an ocean,

all sorts of things are
happening.

If you look at Mars,

it's a red, dusty planet,
it's super dry.

One of the questions is,
"Why are they different?"

Earth has a thick atmosphere,

Mars has a very thin atmosphere.

Earth is warm almost everywhere,

Mars is freezing cold
almost everywhere.

So these are very different
planets.

But if you go back
into the past,

around four billion years ago,

the two planets were probably
very similar.

♪♪

4.6 billion years ago

an innocuous cloud of dust
and gas

is collapsing,
forming the embryonic sun.

Swirling around it,

the remnants of the dust cloud

are slowly drawn together
by gravity...

forming eight new worlds.

Amongst them:
our smaller neighbor, Mars...

and our home planet Earth
are both rich

with elements like carbon,
metals like iron,

and, crucially, water.

But despite many similarities
at birth,

their differences in size
and distance from the sun

set them
on very different paths.

These two planets started off
very similarly.

It's what I like to call
comparative planetary evolution.

The same things could have been
happening

in the very beginning
of their existence.

And then as the clock ticks
forward geologically,

they actually become
very different from each other.

And that's the fascinating part.

What's happened since?

If they looked and acted similar
in the very beginning,

and life formed on one planet,
possibly on the other,

then what happened?

Five, four...

To find out has taken decades
of pioneering exploration.

Mariner 4 was successfully
launched on time

for its historic 228-day journey
to Mars.

♪♪

Picture information started
to come in

on July 15, 1965.

♪♪

During its brief flyby,

Mariner 4 gives
the first close-up glimpses

of Mars.

A revelation,

comparable to Galileo's
first view of the moon

through a telescope.

♪♪

Beautiful picture.

♪♪

First of all,
there are two eyes.

Not only in color
but also in stereo

and in the infrared part
of the spectrum.

Viking is the first
to successfully land on Mars.

Touchdown, we have touchdown.

Perfect set down.

♪♪

And there's the first piece
of information coming in.

Oh, oh.

♪♪

But the most surprising
revelations

come from the rovers...
Spirit and Opportunity.

♪♪

Over 50 years
of Mars exploration

has revealed intriguing clues

suggesting Mars has
a surprisingly watery past.

♪♪

There's a lot of evidence

for ancient flowing water
on Mars.

For one thing,
there's a lot of rivers

that once coursed
across the surface

that are now dry today.

There's also evidence for floods

that catastrophically scoured
the surface.

It's undeniable

that the early history of Mars
was much wetter

than it is today.

The surface of Mars is littered

with an uncountable number
of little round things.

These blueberries,

as we nicknamed them,

are what geologists called
concretions.

Concretions form typically
in sedimentary rocks

that are soaked
with liquid water.

And so what those blueberries
told us

was that this was a place where
the ground was once soaked.

♪♪

It might not have been as wet
as the earth.

But it was probably wet enough
for life to evolve.

What everybody wants to know

is whether or not
Mars once had life.

♪♪

Were conditions on Mars
once suitable for life?

To find out,
a new generation of spacecraft

is investigating...

led by the most complex mission

to the red planet
ever attempted.

♪♪

Vehicle reports entry interface.

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

♪♪

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 burn you up
as you're trying to land.

♪♪

To get Curiosity safely
to the surface of Mars,

we basically had to pull out
every trick in the book.

♪♪

At 2,000 pounds,

Curiosity is one of the largest
and heaviest probes

anyone has ever attempted
to land

in the thin Martian atmosphere.

We fired rockets,

and a jet pack flew the rover
down to the surface.

♪♪

♪♪

We knew it landed safely

when we realized that
the wheels sensed the ground.

♪♪

At that point
a signal was received,

and all of us sort of melted
in our seats,

knowing that we had successfully
landed on Mars.

Safe on Mars.

♪♪

Just a few minutes
after landing,

we had the first images
come back.

It's a thrill to see images
of a new world,

you know, from eye level

for the first time.

Curiosity touches down
in Gale Crater,

the remains of
an asteroid impact

about a hundred miles wide

thought to have been home
to ancient lakes and rivers.

As we drove out
of our landing site,

we came across what looked like
an upturned sidewalk

with like
concrete kind of breaking apart

and pebbles falling out of it.

This was a rock that had been
cemented together,

and when the geologists studied
those rounded pebbles,

they realized this rock probably
was once the bed of a river

flowing on Mars, with water
maybe, like, knee-deep.

♪♪

To find out if these ancient
waters had the basic ingredients

for life, or endured long enough
to support it,

requires careful analysis.

Curiosity is
a roving laboratory.

We collect samples,

by scooping it or by drilling,

that allow us to pick apart
the story

that those things hold.

♪♪

61 days after landing,

Curiosity takes the first
of many scoops of soil.

♪♪

Analyzing the sand and stone
across the crater

reveals something surprising.

Not only is the Martian soil
bound with water molecules,

but also a small amount
of carbon-rich organic material.

Organic matter is
actually composed of carbon.

It's carbon molecules put
together.

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.

And, crucially,
these ingredients are present

for millions of years.

Really, the central discovery
of the mission so far

is that there were lakes
that survived

for maybe tens of millions
of years.

And within those lakes,
there was fresh water,

there were the raw materials
that life requires.

♪♪

Just beneath the surface,

amongst ephemeral droplets
of concentrated brine,

lie the raw chemical ingredients
for life...

The final tears
of a long-lost world.

♪♪

For hundreds of millions
of years,

Mars is a water world,

rich with the building blocks
for life.

Rains fall, rivers run,

and in the northern hemisphere

evidence suggests water collects
in a vast sea

bigger than the Arctic Ocean

that covers a fifth
of the Martian surface.

♪♪

The red planet was once blue.

♪♪

But it didn't last.

The fascination to me

about the early warm, wet Mars
is not what happened,

although
that's an interesting question,

why did it dry up?

The billion-dollar question is
whether or not

Mars actually originated life

before all the water was lost.

How far along did it get?

How far along did the process go

and did it go long enough

that life could have taken hold
there?

♪♪

Today only one blue planet
survives.

♪♪

70% of Earth's surface
is covered by oceans.

♪♪

Under the waves,

up to a million species
thrive...

♪♪

While on land

the rains support
Earth's delicate ecosystems...

♪♪

Providing a home
for complex life to evolve.

♪♪

But our planet hasn't always
been so hospitable.

♪♪

The early Earth
is unrecognizable

compared to the planet
we know today.

When Earth first formed,
it was this molten body

and it probably had a crust that
was forming around the outside,

and it was moving around a lot;

it was turning
into something rocky.

And then at the same time
that the rocks are forming,

we've also got gases
in the atmosphere,

liquid water to form oceans.

Chemical analyses
of our planet's oldest rocks

reveal its atmosphere
was choked with carbon dioxide

spewing from myriad
active volcanoes...

♪♪

Making its newly formed
oceans acidic.

Early Earth was
a very different place

from today's Earth.

So if one looked at Earth

from another solar system

and asked, "Is Earth alive?"

it would have been hard to tell
four billion years ago.

♪♪

And then everything changed,

and chaos ensued.

♪♪

Clues as to what happened next

can be seen when the moon rises
in the night sky above us.

♪♪

Etched into the moon's surface

are vast areas of impact craters
and lava fields...

traces of a violent past
revealed by the lunar landings.

Two, one, zero...

♪♪

♪♪

♪♪

Over three years,

Apollo astronauts take samples
from across the moon's surface.

The age of the rocks
they collect

suggests the majority
of the craters form

in a narrow window of time

peaking 3.9 billion years ago.

♪♪

And traveling
to the far side of the moon...

a side we never see from Earth,

reveal even more.

Countless craters,

a permanent record
of a ferocious bombardment

unleashed throughout
the inner solar system

thought to date
from the most violent period

since the planets themselves
formed,

known as the
Late Heavy Bombardment.

This Late Heavy Bombardment

turns out to be a critical event
in the history

especially
of the terrestrial planets.

All of the rocky planets were
being hit by other rocks

from other places
in the solar system.

♪♪

Around four billion years ago,

while the outer planets are
settling into their orbits,

it's thought they disrupt
a cloud of icy objects

circling the edges of the
developing solar system...

sending many hurtling inwards
toward the sun.

And so these fragments
and pieces of rock

all arrive
at about the same time

in the inner part
of the solar system

to hit the planets like
Mercury, Venus, Mars,

Earth, and the moon.

Imagine meteorites hitting
on a regular basis.

It caused turmoil on the surface
of all those planets.

They basically hit
with such energy

that they resurface the planets.

♪♪

As rocky asteroids fragment
in Mars's atmosphere,

havoc rains on every corner
of the planet.

♪♪

♪♪

Based on the rates of crater
formation on the moon,

it's thought at least 50 tons
of rock fall

for every square meter
of Mars's surface

in a hard rain that lasts
tens of millions of years.

♪♪

Over a third of the
planet's crust is resurfaced...

as Mars descends into chaos.

♪♪

Earth suffers the onslaught
just as Mars does...

relentlessly smashed
by falling rock.

Both young planets endure
a catastrophic pounding.

But just when conditions appear

at their least promising
on Earth,

the raw organic molecules on
its surface come together...

♪♪

To produce its most
precious creation...

♪♪

Life.

The kind of environment
that's needed for life to start,

we need to be converting

the first organic molecules
to whole cells.

And those kind of conditions

require a dynamic geological
environment,

and that kind of environment
would have been everywhere

on the early Earth.

♪♪

The volatile conditions on Earth
may be responsible

for turning the simple organic
molecules already present

into complex organic material
capable of replicating itself...

DNA.

♪♪

We don't know precisely
where life started.

It could have been an
environment like this,

a terrestrial geothermal system.

♪♪

It could have been even
delivered from space,

perhaps organic molecules
delivered

into exactly
this kind of setting.

To me it seems more likely that
it started under the oceans

in deep-sea hydrothermal vents.

Volcanic activity erupting deep
in the oceans

would create
a high-energy system.

That pressure makes reactions
happen faster

and more likely to give rise
to life.

♪♪

And the emergence of life

need not be limited
to just one planet.

Life should really start

wherever these geologically
active conditions are met,

where we have a continuous
bubbling of gases

from in the bowels of the planet
or the moon,

to react with gases in
the atmosphere or in the oceans.

These conditions are
very similar

to what we think might have been
present on Mars

four billion years ago.

But how can we be sure

that catalysts for life
like this

existed on Mars that long ago?

♪♪

Ignition and liftoff
of the Atlas V rocket

with MRO.

Surveying
for the deepest insights

into the mysterious evolution
of Mars.

♪♪

Searching for conditions
that could kickstart life

is NASA's
Mars Reconnaissance Orbiter.

♪♪

Sent to map Mars
in intricate detail,

MRO sends back more data

than all other Mars missions
combined.

♪♪

MRO has three cameras onboard.

The first is
the MARCI weather camera.

It sees horizon to horizon
on every orbit,

so it builds up a map of
the entire planet every day.

So you can see a global
weather map ever day on Mars.

♪♪

The second camera is
the context camera.

It provides high resolution,

and it's covered
about 99% of the surface.

♪♪

MRO has made
more than 60,000 orbits...

♪♪

Its high-resolution cameras
revealing Mars

in unprecedented detail...

Discovering polar avalanches,

shifting sand dunes,

and what look like
seasonal flows of sand

or even liquid meltwater.

♪♪

Then, in 2017,
MRO turns its gaze

to some of the red planet's
oldest rocks:

in the Eridania Basin,

thought to have once been home
to an ancient sea.

Eridania Basin is a huge basin

in some of the
most ancient crust on Mars.

It formed
about 3.8 billion years ago,

and it held more water

than ten times that
of the Great Lakes

or three times that
of the Caspian Sea on Earth.

♪♪

And it's on this ancient seabed

that MRO sees something
remarkable...

a potential catalyst for life.

MRO saw a massive,
400-meter-thick deposit

formed from a mineral

that forms in deep-sea
hydrothermal environments,

such as one that might have
undersea vents.

Analysis shows the deposits are
rich with saponite,

a mineral found on Earth
at hydrothermal vents...

suggesting in the past

Mars not only had the same
ingredients for life as Earth

but also an active environment
to spark it into action.

Eridania Basin was
an ancient sea

3.7 to 3.8 billion years ago.

And that's about the same time

when life was first emerging
on Earth.

This might have been a place
where life could have existed,

because those hydrothermal vents
underneath that sea

might have created a very
conducive environment for life.

These initial conditions
in the history of both planets

look so similar that
it seems reasonable to expect

that this could
eventually lead to life.

♪♪

These actively fertile
conditions

are thought to survive in
places like the Eridania Basin

for hundreds of millions
of years,

with Mars, like Earth, rich
with the potential for life.

But then, 3.7 billion years ago,
something happens

that transforms prospects
for life on Mars forever.

Analysis
of the ancient Martian surface

reveals a dramatic change.

Mars underwent through a fairly
substantial transformation

in its climate.

The climate got colder.

What liquid water there was

either soaked into the ground
and froze

or froze at the surface.

A lot of it ultimately would get
transported to the poles,

where it forms these big,
thick icecaps

that we see today.

♪♪

At the same time
as the temperature plummets...

Mars becomes
more volcanically active...

leading to catastrophic flooding

with water raging
for hundreds of miles.

♪♪

Until, in a place known
as Echus Chasma,

it plunges over cliffs
two-and-half miles high...

♪♪

Creating the largest waterfall

the solar system has ever
seen...

♪♪

Cascading
into a spectacular canyon

six miles wide
and 60 miles long.

♪♪

Once the floods subside,
the water disappears,

the only trace it ever existed

etched into
the planet's surface.

So what causes
this dramatic change in climate?

That's being investigated

by NASA's most active
Mars orbiter.

T-minus ten, nine, eight, seven,

six, five, four,
three, two, one.

Main engines start,

ignition, and lift off

of the Atlas V with MAVEN,

looking for clues
about the evolution of Mars

through its atmosphere.

♪♪

In September 2014,

NASA's MAVEN probe is on
its final approach

to the red planet.

Its mission:

to understand the processes
that transformed Mars.

♪♪

We know that the Mars climate
has changed through time.

The geological evidence tells us

there was lots of water
early on,

and that it's been cold and dry

in the last couple
of billion years.

Maven was sent there

to understand what processes
drove this climate change.

Based on observed
navigation data,

congratulations.

♪♪

♪♪

♪♪

MAVEN flies in an elliptical
orbit around the planet.

At its lowest point,

it's only 150 kilometers
above the surface.

At its highest point,
it's over 6,000 kilometers.

That means that on every orbit,

we're able to measure
the full profile

of the entire upper atmosphere.

♪♪

The previous missions
we've sent had cameras

to look at the geology
of the surface

or the behavior of the clouds
and dust

in the lower atmosphere.

We're making measurements
in the upper atmosphere,

where we're more interested

in the behavior of atoms
and molecules,

so our instruments are focused
on taking measurements of those.

♪♪

MAVEN carries an array
of instruments

designed to measure the behavior
of atoms and molecules

in Mars's atmosphere.

♪♪

From the measurements
that MAVEN has made now

over an entire Martian year,

we've confirmed that gas is
being lost to space today

out of the atmosphere.

And it's being lost at a rate

of about two to three kilograms
every second.

♪♪

By measuring the gas being
stripped from its atmosphere,

MAVEN is witnessing the process
that transformed Mars's climate

over three-and-a-half
billion years ago.

♪♪

We think that this stripping
of the atmosphere over time

has been responsible
for the change in climate

which Mars has suffered.

♪♪

Mars lost much of its water

and the atmosphere
that insulated it

from the cold of space...

leaving it frozen and dry.

So what was it that sent Mars
down such a different path

from Earth?

♪♪

The sun's outer corona burns at
a scorching one million degrees.

It releases a barrage
of charged particles that travel

at hundreds of miles a second...

The solar wind.

♪♪

This onslaught would strip away
our atmosphere,

but for the powerful magnetic
field that protects us

♪♪

The solar wind is
this stream of charged particles

that come streaming out
from the sun.

And at Earth,

which has
a powerful magnetic field,

when those charged particles
begin to get close to Earth,

they get diverted around Earth

by interactions
with that magnetic field.

That protection keeps solar wind

and other ionizing radiation

off of the surface.

So on Earth,

where we have this really great
magnetic field,

we are nice, safe, and sound
inside the shell of that,

protected
from all that radiation.

The magnetic field of Earth

effectively forms
a protective bubble

around the Earth's atmosphere.

And when the sun dips
below the horizon,

there are times when Earth's
protective force field

is visible.

♪♪

The aurora is a stunning display

of Earth's magnetic field
in action.

It's best seen at the poles,

but across Earth
it's protecting our atmosphere

and all life on our planet.

♪♪

This vital protective shield
is generated deep within.

♪♪

The way a magnetic field is
generated inside a planet

is when you have
convective motion

in a fluid that is capable
of conducting electricity.

And in the Earth, that
electrically conducting fluid

is liquid iron.

And the molten portion
of the Earth's core

is a place where these motions
take place,

and it can set up
a magnetic field.

Just like Earth,

Mars once had
a molten metallic core,

generating a magnetic field
around the planet.

♪♪

Auroras danced
above Mars's poles...

protecting its atmosphere
and seas below.

♪♪

But the field didn't last.

In the oldest rocks on Mars,

you see evidence of
a once-powerful magnetic field.

You get to the younger rocks,

the rocks that are
three billion, two billion,

one billion years old,

no evidence of a magnetic field
whatsoever.

And there is no intrinsic
magnetic field on Mars today.

This invisible magnetic field
around the planet,

something we can't see,

it's like this layer of
protection around the planet...

disappeared.

♪♪

Half a billion years
after it formed,

Mars's magnetic field dies out.

♪♪

The bright auroras above
its poles slowly fade away...

♪♪

As the shield
that protects the planet

shuts down for good.

♪♪

Once it stops,

then what happens is
all the atmospheric components,

things like hydrogen and oxygen
that make up water,

they get stripped away

because you don't have
the shield,

the magnetic shield anymore.

So the high-energy particles

that come in from the sun
and from outer space,

they begin to strip away the
components that make up water.

Without its magnetic field
to protect it,

Mars's atmosphere and then water

slip away into space.

♪♪

So why did Mars lose
its protective shield?

What happened
deep beneath its surface

that stopped Mars from
developing like Earth?

The answer lies at the beginning
of Mars's story...

at its very creation.

♪♪

4.6 billion years ago,
when the planets were forming

from the dust cloud
circling the sun,

early differences
between Mars and Earth

set the young planets
on very different paths.

Crucially, Mars forms farther
from the sun,

where there is simply
less rocky material

to build a planet.

♪♪

Mars is different

because it's not
just further out,

it's actually much smaller.

If a planet gets to be
too small,

it just freezes
all the way through.

Because Mars is so much smaller,

there's less thermal energy

coming from the interior
of the planet.

The planet is fundamentally
different

from the interior out,

and that is what separates Mars
from Earth.

♪♪

It's this critical
size difference

that seals Mars's fate
and shapes its surprising story.

♪♪

Four-and-a-half billion
years ago,

two young planets are born.

Initially inhospitable
and toxic...

both young planet develop
into warm, watery worlds.

They both survive the violence
of the Late Heavy Bombardment...

♪♪

Emerging as mature planets,

primed with all the ingredients
for life to begin.

♪♪

But while Mars appears
to be thriving,

deep in its cooling core,
the planet is dying.

♪♪

Its once-great ocean is lost
to space.

♪♪

One by one,
its volcanoes go out.

♪♪

As the lava turns to stone,

all hope of recovery is
extinguished.

♪♪

Today, Mars traces a lonely path
through the solar system,

rusted and gathering dust.

But this is far from the end
of what we hope to discover.

The next generation
of spacecraft

will soon be on their way...

with missions like
European Space Agency's ExoMars

and Mars 2020 searching
for signs of life...

♪♪

And NASA's Orion,

currently undergoing
advance testing...

♪♪

NASA's first step toward
sending humans to Mars.

♪♪

My hopes for the future

eventually there's boot-prints
on the surface.

You know, humans on the surface
doing what humans do... explore.

Humans are going to go to Mars.

I can't wait to see someone else
not virtually explore Mars

but really explore Mars,
as a human being,

walking on the surface.

♪♪

Future generations will be able
to look closer than ever before

for evidence of life.

So the next step is to search
for life on Mars.

We're probably going
to bring samples home.

We'll study them here, and
we'll learn all sorts of things

about ancient Mars
and even modern Mars.

♪♪

And if we do find life on Mars,

the consequences will be
profound.

♪♪

If you could show that
life independently took hold,

independently,
on two different worlds

just in this one solar system,

then when you consider the
multitude of planetary systems

that we now know are out there,
it takes no great leap

of imagination, faith,
or anything else

to believe that life could be
a universal phenomenon.

It's a situation where two is
a much bigger number than one.

♪♪

I think if one was
to ever discover life

anywhere outside of Earth,

it opens up the possibility that
the universe is full of life.

♪♪

Because if you find just
one example in our solar system,

now you imagine
all the solar systems

that have been discovered
that we call exoplanets,

and then you multiply
these things,

and it must mean
that life is everywhere.

♪♪

I often wonder
how the world would react

if we found life on Mars.

For me personally,

it almost feels like
we're reaching the point

where it would be more
surprising not to find life.

I think it still would shock
all of us,

and we'd be amazed that
such a discovery was made,

but I've personally come to
think that life must be present

all over the universe,

and maybe even on a planet
as close as Mars.

♪♪

♪♪