All language subtitles for How.the.Universe.Works.S11E02.A.Robots.Guide.to.Mars.1080p.AMZN.WEB-DL.DD+2.0.H.264-playWEB_track3_[eng]

ROWE: Our neighbor, Mars,
fascinates us.

It's a planet
that is similar to Earth,

but with some big differences.

Mars is rusty, dusty,
frigid, and frozen.

It ain't the kind of place
you want to raise your kids.

ROWE: Past missions
suggest that Mars

was once a very
different world.

The Mars we see today has
completely changed

from the Mars of
a few billion years ago.

RADEBAUGH: If I had
a time machine to visit Mars

in the past,
I would go in an instant.

ROWE: Without a time machine
to explore

ancient Mars,
we employ a team of high-tech

robot investigators.

We've got an entire fleet

of robotic spacecraft
exploring the planet.

ROWE: Working together, they dig
into Mars's past to answer

the ultimate question--

did Mars once have life?

February 2021.

The newest robot investigator
speeds towards Mars,

the most advanced rover
NASA has ever sent to

another world.

This is Perseverance.

The goal of
the Perseverance mission is

to look for signs of
past life on Mars.

ROWE: First, it must
navigate safely

to the surface of the planet.

LANZA: Every landing
has its own dangers.

Because the rover must
be autonomous,

it has to do everything
without our help.

ROWE: Perseverance enters
Mars's thin atmosphere at

close to 12,500
miles an hour...

and deploys a parachute.

ROWE: The parachute
slows Perseverance

to 200 miles per hour.

ROWE: Still too fast
to land safely.

To prevent a violent impact,

the rover must activate
the sky crane.

When I first saw
the sky crane concept,

I thought, hm, the engineers
are kind of losing it.

It seemed to me like
a really crazy idea.

ROWE: Perseverance
activates its jetpack.

Retro rockets slow
the lander's descent to a crawl.

Then, 66 feet
above the surface,

the sky crane
uses cables to

gently lower the rover
to the ground.

ROWE: Step one in
the search for Martian life,

find evidence of liquid water.

A good place to start is
the 28-mile-wide

Jezero Crater.

Perseverance has landed in
a crater called Jezero, and this

looks like a place where there
was liquid water in its past.

And the reason we think this
is because

there's this beautiful delta
deposit right in the middle.

ROWE: Perseverance turns
its high-resolution cameras

onto a cliff side
in the crater

and discovers giant five-foot
boulders near the top.

A clue to how they got
there may

come from the first probes
to visit Mars.

One of the very first things
we noticed about Mars

when we first sent probes there

with Mariner and Viking was
that there were these huge

channels on the surface
of Mars.

Looking at
these enormous landforms,

we realized that,
in some places on Mars,

there may have been
enormous floods,

bigger than almost anything
we'd ever seen on Earth.

ROWE: Flash floods on Earth
cause similar rock formations to

those found in Jezero Crater,
suggesting that powerful,

fast-moving torrents carried
the giant rocks found by

Perseverance and dumped them
at the top of the cliff.

Perseverance is just one
member of an elite team

of robots patrolling
the ground

and spying from the air.

The Mars Atmospheric
and Volatile Evolution

Orbiter, or MAVEN,
investigates Mars's atmosphere.

MAVEN smells really good.

It smells
the Martian atmosphere.

It tells us what
the Martian atmosphere

is made of all across
the planet.

ROWE: Then there's the MARS
Reconnaissance Orbiter.

As its name suggests,
an orbiting spacecraft

that images surface
of MARS.

ROWE: The M.R.O.'s
high-resolution cameras

can identify surface features as
small as a kitchen table.

And joining
the orbital crew,

The European Space Agency's
MARS Express.

With its
ground-penetrating radar,

it searches for evidence of
subsurface water.

And, on the Martian surface,
a group of high-tech landers

take a closer look,

including the team's quake
specialist, Insight.

This lander probes
deep beneath the surface

to discover how Mars's interior
shapes the planet over time.

The Insight lander on MARS has
a really simple concept.

You land a spacecraft
on the surface anywhere

on Mars and then just listen
for Mars quakes.

ROWE: And 300 miles south of
Insight, veteran rover,

Curiosity is exploring
the Gale Crater.

The mission goal for Curiosity
is to look for habitability,

and so that's environments

in which life as we currently
understand it could exist.

ROWE: Curiosity searches
for evidence of calmer,

more permanent water in
Mars's past.

Investigating layers of rock
at the base of Mount Sharp,

a three-mile-high mountain in
the middle of the crater.

RADEBAUGH: The rock layers
start way up at the top of

Mount Sharp, and they move
progressively downward,

and basically, we're going
backwards in time until we get

to the very bottom, and the very
bottom is actually really old.

ROWE: Mount Sharp was built
over millions of years,

layer by layer.

The rocks at the base of

the mountain date to
3.5 billion years ago.

These rocks are made up
of very fine layers

and could only have been
formed in calm water.

These sedimentary layers were
formed when Gale Crater was

a lake, and sediment settles
out, and you get these

beautiful layers.

ROWE: Curiosity explores
more of Gale Crater

and discovers rounded pebbles,
like those we find on Earth.

When you see a rounded
pebble on Earth,

you know that that got rounded
in a river channel.

Some of them used to
be angular,

but their angles all got
knocked off by being rolled

and rounded and moved
by water.

So we're very excited when
we see rounded pebbles on Mars.

ROWE: The rock layers
and rounded pebbles

tell us that over
three billion years ago,

Gale Crater
was a lake fed by rivers.

LANZA: It was so exciting
to understand liquid

water in the context of
Gale Crater,

where Curiosity is, and that's
just because what we see there

is this long-lasting,

freshwater lake, and that's
not like anything else

we've seen on Mars before.

RADEBAUGH: Imagine
standing on the edge

and looking out
at this big, beautiful

blue lake
shining in the distance.

What if there were just
a whole array

of craters filled with water
off in the distance?

It would be so beautiful.

ROWE: And a good place
for life to evolve.

PLAIT:
Mars was a nice place.

It was probably more like
Earth is now.

So it wouldn't surprise me
if it's supported life.

We're talking microbial life.

We're not talking, you know,
Marvin the Martian or anything

like that,
but life still is life.

ROWE:
Any water Mars once had

is now long gone.

To stay liquid,
water needs warmth

and atmospheric pressure.

So, hundreds of miles
above the planet,

orbiting members of the team
investigate the mystery of

Mars's missing atmosphere.

ROWE:
While robot team members,

Curiosity and Perseverance,
work the Martian surface,

eight probes orbit
the planet,

searching for clues about
Mars's ancient wet history.

Leading the pack is MAVEN.

Its mission--

to solve the mystery of
Mars's lost atmosphere.

Today, the atmosphere of Mars
is incredibly thin.

It's only about 1 percent
the atmospheric pressure

here on Earth.

ROWE:
The weight of gas in

an atmosphere pressing down
creates pressure,

and that pressure dictates at
what temperature liquids boil.

Here on Earth
at sea level,

the boiling point of water
is about 212 degrees Fahrenheit,

but up here in the mountains
near Denver,

we're at a higher altitude.

We've got a lot less
atmosphere pressing down on us,

and so it boils
at a lower temperature.

Let's put
a thermometer in here.

There's 200 even right there.

That's a lot cooler boiling
temperature than at sea level.

Now, if you go to even higher
altitudes at 100,000 feet

here on the Earth,
the air pressure is about

what it is
on the surface of Mars.

On the surface of Mars,

water will boil effectively
at ambient temperature.

We wouldn't have
to heat it at all.

You just put a glass of
water on

the surface of Mars, and it'll
boil and disappear away.

ROWE: But the planet's surface
tells us that dry Mars

was very different in the past.

THALLER: When you see things
like river channels

that probably took millions
of years to carve,

that gives you an idea that
the atmosphere was once very,

very different.

It had to be thick to allow

liquid water to exist on
the surface.

ROWE: To investigate
what happened to that thick

Martian atmosphere,

MAVEN swings into action.

THALLER:
One of the main objectives of

the MAVEN mission was to
measure argon on Mars.

There are slightly different
kinds of argon.

We call these isotopes,

and basically,
it means that there's just

an extra neutron in the nucleus.

So there's one type of argon
that's just a little bit

heavier than the other type
just by one neutron,

not by much.

ROWE:
High up in the atmosphere,

MAVEN tag teams with Curiosity
down on the surface.

They measure the amount of
light and heavy argon.

THALLER: Now, what's special
about argon?

Well, argon
is not very reactive,

doesn't really get involved in
a lot of chemistry.

It's not really absorbed by
rocks, doesn't change much.

Once it's emitted,
it kind of hangs around.

And that makes it very
valuable, because it means it

stays in pretty much
its pristine, pure form

through the history
of the planet.

ROWE: When the researchers
back on Earth

compare the readings from
the two Martian robots,

something doesn't add up.

SUTTER: With Curiosity

on the surface, we see
a certain ratio of heavy

to light argon.

And we expect that same ratio to
exist up in the atmosphere,

but with MAVEN,
we see a different ratio.

We see far less
of the light argon

than we do down
on the surface.

So something is
messing with that ratio.

The only thing we can think of
that can mess with

the ratio of argon is
the solar wind from the sun.

ROWE:
The sun spits out a constant

stream of particles
called the solar wind.

The wind is over a million
degrees Fahrenheit

and travels at up to
500 miles a second.

When it reaches Mars,
it strips away

gases high up in
the atmosphere.

The lighter the argon is,

the higher it gets up into
the atmosphere.

That means that
that gets blown

away preferentially
by the solar wind.

The heavier argon stays
a little bit

lower down and a little bit
more protected.

So when you look at the ratio
in the atmosphere of the light

argon to the heavy argon,

it gives you an idea of how
much has been lost over time.

ROWE: MAVEN's data
reveals that Mars

has lost 65 percent
of the argon

from its atmosphere,
and the solar wind continues to

bombard the planet.

The atmosphere of Mars is
being stripped away by

solar radiation by a quarter
of a pound every second.

ROWE: This rate of atmospheric
loss leads to one conclusion.

The solar wind
robbed Mars of its once

thick atmosphere, and with it,
the planet's water.

But a question remains.

RADEBAUGH: We know that Mars's
atmosphere was much thicker

in the past,
really similar to Earth's.

So why is it
that Earth's atmosphere

is still mostly there,

whereas Mars's has been
stripped away?

ROWE:
Earth has a protector,

a magnetic field
that shields our atmosphere

from the ravages
of the solar wind.

RADEBAUGH: The Earth's
magnetic field is generated

deep in the core.

There are actually two cores.

There's a solid inner core
and a liquid outer core,

and that solid inner core
is delivering

heat to the outer core,
and as it does this,

it causes convection currents.

The convection currents
pull electric charges around

and cause magnetic fields
to fold in on themselves.

We call this a dynamo,
and this is what's capable

of generating powerful
magnetic fields.

ROWE: The magnetic field forms
a protective bubble around Earth

that deflects the solar wind
away from our planet.

Did Mars once have
its own force field?

To find out,

MAVEN hones in on some
ancient volcanic rocks

on the Martian surface.

It detects faint
magnetic traces.

RADEBAUGH: Martian rocks,
typically in the form of lava,

become magnetic
when the iron particles

in the rocks become aligned
with the magnetic field

that's active at the time,
and then as the rock cools,

those things
get frozen in place.

That sort of freezes
a magnetic field into place.

What that tells us,
that these volcanic materials

were erupted at a time

where there was a magnetic
field present on Mars.

ROWE: Dating the magnetized
rocks reveals that Mars had

an active magnetic field for
almost a billion years.

SUTTER: This means
that the atmosphere of

Mars was protected
for those billion years,

and if the atmosphere
was protected,

the liquid water
was protected.

And if that liquid water was
a home for life,

then that life was protected.

ROWE: But something happened to
bring Mars's force field down.

To discover what, our quake
specialist, Insight, is ready to

burst open the mystery of
the planet's lost

protective shield.

ROWE: Robots are rewriting
the history of Mars.

They found
that Mars once had

a magnetic field that
protected its atmosphere.

Now, another team member, Insight,

probes the planet's interior.

Its mission--
to discover if the secret of

the planet's lost magnetic
field lies

beneath the Martian surface.

Insight was developed with
the world's best seismometer.

This is a really precise,
really delicate,

really sensitive instrument,
and it just was placed on

the surface
and started listening.

ROWE: 2021.

Insight listens for seismic
vibrations, called Mars quakes,

as they travel through
the planet's interior.

PLAIT: It's detected
quite a few Mars quakes,

but these were very small,

but then it detected
two much larger ones.

And these were interesting.

Not only were they more
powerful, but they were coming

from the direction of
Cerberus Fossae,

which is a very interesting
region on Mars.

ROWE: The magnitude 3.1
and 3.3 quakes

came from Cerberus Fossae,

a series of trenches that
stretched for 750 miles across

the Martian surface.

Some fissures cut through
impact craters that

are only a few million
years old.

This means Cerberus Fossae

must be younger.

Insight teams up with
the Mars Reconnaissance Orbiter,

flying hundreds of miles above.

This eye in the sky

spots an ancient lava flow,

spreading out
over a three mile area.

Dating of the flow
reveals that it's recent.

The Mars Reconnaissance Orbiter spotted,

in the Cerberus Fossae region,

some lavas that appear to be
about 50,000 years old.

This is crazy young for Mars.

Mars has been around
for billions of years.

50,000 years is nothing.

Humans were around on Earth
that long ago.

So this is really recent.

RADEBAUGH: Based on
the fact that we had

these two Mars quakes recently,
plus the evidence of

the volcanic eruption
just 50,000 years ago,

I mean, now we cannot
say that Mars is dead.

We have to say
Mars is active.

ROWE:
A volcanically active Mars

suggests its interior may
still be warm-- if it is,

why did the planet's
magnetic field die?

Insight probes
deep into the interior of

the Red Planet using vibrations
from small Mars quakes.

Insight uses these to kind of
construct what the interior of

Mars was like,

because these waves
bounce off different layers

inside the interior of Mars
in different ways.

ROWE: Insight's seismometer
builds a picture of Mars

by completely redrawing the map
of the interior of the planet.

RADEBAUGH: It turns out
the crust is thinner

than we thought--
it's only 12 to 23 miles thick.

So there's this whole picture
of Mars that is unfolding in

front of us that is
vastly different

than we ever predicted.

ROWE: Insight's new and improved
layout of Mars reveals

a 969-mile-deep mantle
surrounding a metal-rich core.

New analysis of data from
Insight reveals the size of

the core of Mars,
and we haven't had this before.

It's so exciting.

It's about 1,100 miles
in radius.

This is a little more than
half the radius of the body,

which is pretty big, and is
much bigger than we expected

for the size
of the core of Mars.

ROWE:
Mars's larger core

makes up about a quarter
of the planet's mass.

And Insight's journey to

the center of Mars
reveals another surprise.

LANZA: We have always thought
that the core of Mars

was long since solidified
and wasn't warm at all.

And Insight is now showing us
that actually,

part of the core is probably
still molten,

which is shocking.

There's a liquid core at Mars.
I mean, this is crazy.

ROWE: Data from past missions
may help

explain why Mars's core
is still liquid.

Scientists discovered high
levels of sulfur in the crust.

Mars seems to have
a bit more sulfur,

at least in the surface,
than Earth does.

If we extend that composition
to the core

and add more sulfur to
the iron-nickel core,

that would actually reduce
its melting temperature,

making it possible for this
core to be molten today.

ROWE: We thought that Mars
lost its magnetic field

when the core
cooled and solidified.

A molten core
changes everything.

Well, how can we explain
this lack of a magnetic field

at Mars even though
there's a liquid core?

Well, in order to have
a magnetic field,

you need the fluid to be moving
and rotating and convecting.

ROWE: Over time, as Mars
lost heat and cooled down

its core stayed molten
thanks to the sulfur.

But, with less heat,
there was not enough

energy to power the churning
convection of liquid metal

that creates
an electric current.

The convection in that core
would have slowed down

to the point where no magnetic
field would be generated.

ROWE: 3.7 billion years ago,
Mars's magnetic shield dies.

The solar wind's
relentless attack

strips the planet of
its atmosphere.

As the atmosphere disappears,

water on the surface
gradually boils away.

But did all of the planet's
water dissipate?

To find out,
our robots once again team up.

ROWE: Since the first probe
visited Mars in 1971,

16 missions have investigated
the Red Planet from orbit,

while 10 landers
have explored the surface.

They've revealed Mars may
still be an active planet,

one that once had the right
conditions for life.

Mars used to be
thought of as this dry,

arid, inhospitable environment.

And thanks to the recent
Mars missions,

we know now that they could
have sustained life.

ROWE: Could there be any
ancient Martian

water left,
hidden inside the planet today?

MAVEN investigates by
analyzing Mars's atmosphere

for one of water's
components-- hydrogen.

The MAVEN mission
is looking at

hydrogen that's currently in
the Mars atmosphere.

This is a really important
thing to study.

ROWE: The gas is produced when
the solar wind slams into Mars's

thin atmosphere
and smashes apart

molecules of water
into hydrogen and oxygen.

Hydrogen molecules
come in two forms--

light, regular hydrogen
and the heavier deuterium.

The ratio of
the different types

tells us about the history of
water on the Red Planet.

It turns out that it's much
easier to lose the lighter

version, because gravity

just you can't hold on to
something that's light as

easily as a heavier thing.

So we expect that,
as time goes on,

we'll have less and less
light hydrogen

and more and more
heavy hydrogen.

DARTNELL: So if we can measure
the outflow of hydrogen from

the Martian atmosphere today,

and specifically, whether
it's light or heavy hydrogen,

we can start to get some kind
of idea about how much water

has been lost from Mars

and therefore how much might
still be there today.

ROWE: 2021--
scientists at Caltech

analyze data from Mars's
rovers and orbiters

to discover the ratio of

deuterium to hydrogen
in the atmosphere.

They find less of the heavy
hydrogen than expected.

If Mars had lost a lot of
its original water

out into outer space,

we'd expect to find lots of
heavy hydrogen

left behind
in the atmosphere.

But, in fact, what we found
was that the ratio

told us that Mars didn't lose
much of its water upwards.

And so maybe
the water went downwards.

ROWE: Where is
Mars's water hiding?

Some scientists
think it could be

stashed away
in the Martian rocks.

When we look at a rock,
we often think this is a really

dry thing,
there's no water in there.

But, in fact,
there's often a lot of water

in rocks, and it's because
it's bound up in minerals.

ROWE: Changes in the crust
can drive

these minerals
to suck up huge

volumes of water,
equivalent to a global layer

over 300 feet deep.

Researchers estimate
that as much as 99 percent of

Mars's water could be locked
away below the surface.

And Mars hides water
in other ways, too.

Enter the European
Space Agency's orbiter,

Mars Express--
probing one mile

beneath the Martian
South Pole,

it finds a secret store
of water.

Really exciting.
We've discovered a system of

lakes beneath the Martian
polar ice caps,

lakes of what appears
to be liquid water.

THALLER: Now, these lakes
are not very deep.

They're probably only
a couple of feet deep,

maybe in some places even
a couple of inches deep,

but they're quite large.

Some of these are
about 20 miles across.

And there's even some
suggestion that these are

connected with channels, kind of
a system of very shallow

great lakes near
the South Pole of Mars.

ROWE: The Martian poles are

the coldest regions
on the planet.

Temperatures can
reach 200 degrees below zero.

So why is it that
underneath this cold ice,

you might even find
liquid water?

Well, remember,
you're actually going down

closer into the interior

of Mars there,
and so that's warm.

It's possible that
the geologic activity inside

Mars is warming the ice
from the underneath.

ROWE: But heat from
the interior of Mars

wouldn't be enough to keep
these lakes liquid.

The secret ingredient
may be salt.

THALLER: If you've ever spread
salt on an icy driveway,

you'll notice that where
the salt hits the driveway,

the ice begins to melt.

Saltwater actually freezes at

a much lower temperature
than water that's fresh.

So if it's salty water,

it could actually stay liquid
at lower temperatures.

ROWE: We still aren't
100 percent sure that the lakes

are completely liquid.

Some scientists think they
could be lakes of frozen clay.

Until we have a rover that can
explore beneath the poles,

we won't know for sure.

The only real way we can tell
for sure is to send

some kind of mission
that drills

right down through
that polar ice and samples

what we find at the bottom.

ROWE: Wherever it may
be hiding,

Mars's water is locked away,

but in its past, the planet had
impressive lakes and rivers.

Did they ever host life?

To find out, the rovers

take a deep dive into Mars.

Veteran crew member, Curiosity,
explores the Gale Crater.

The rover's mission?
To find evidence

of whether Mars could have
supported life.

Los Alamos National Laboratory.

Principal investigator
of Curiosity's

ChemCam, Nina Lanza,
works closely with the rover

patrolling Mars 34 million
miles away.

In many ways, Curiosity
is like my first child.

We had to take such good care
of her while she was still here

on Earth, but like all children,
she had to forge her own path.

And so we had to send her
on her way

to discover new things
on Mars by herself.

ROWE: ChemCam uses
a precision laser that

analyzes the chemical
composition of Martian rocks.

LANZA: We have a laser that
we focus onto a target

up to 23 feet away, and we
vaporize a little material,

and then we look
at the light

made by this vaporized material
and figure out

what elements are in the rock.

Working with an instrument
like ChemCam is really

a childhood dream come true,
because I was always hoping

to work on a spaceship,
and today, I work on

a spaceship with lasers.

How cool is that?

ROWE: With their
long-distance teamwork, Nina

and Curiosity discover rocks
with a shiny coating,

laced with manganese.

LANZA: One of the most exciting
discoveries from Curiosity in

Gale Crater was the existence
of high concentrations

of an element called manganese,
and that's because manganese on

Earth is very closely tied
to life.

Could the manganese of Mars
be linked to life forms?

To investigate, scientists
look at similar coatings

called varnish on desert rocks
here on Earth.

So I have an example here
of some rock varnish,

and you can see,
it's actually incredibly dark.

It has a lot of iron oxide,

manganese oxide,
and clay minerals in them.

And the rocks
can sometimes have

none of these things
in the rock itself.

So the question is, where does
this coating come from?

RADEBAUGH: Often,
we find microbes associated

with the varnishes
and so possibly,

these microbes
actually helped fix

the manganese
onto the surface.

ROWE: The age of these Earth
varnishes may provide

a clue to Mars's
distant past-- here,

they only appear after
a significant event in

our history--

the creation of
the oxygen we breathe.

A couple of billion years ago

on Earth was the great
oxygenation event.

Basically, the Earth's
atmosphere did not have

a lot of oxygen in it.

It was locked up in
minerals and chemicals.

Well, some bacteria discovered
how to photosynthesize light,

how to convert energy from
light into their metabolism.

And via the chemistry of this,
they wound up emitting oxygen.

ROWE: The oxygen was poison
to many life forms,

so they died out.

But others thrived,
pumping more

and more oxygen
into the atmosphere.

Oxygen reacts with
the manganese,

binding it to the rocks.

We don't really see
these minerals until

after the rise of oxygen
in the atmosphere,

so after photosynthesis.

ROWE: For Mars to have
these same manganese varnishes,

there must have once been
more oxygen

in the planet's atmosphere.

Is it possible
that Mars had a lot

of oxygen in its atmosphere
in the past,

and there were wee little
beasties processing it?

ROWE: And so the search
continues, and Curiosity uses

another piece of equipment

to sniff out
traces of past Martian life.

One of the key instruments
aboard Curiosity is a piece of

lab kit called a gas

chromatography
mass spectrometer,

or GC-MS, and all this really
is, in essence, is, like,

a very sensitive
electronic nose.

Curiosity digs up some
Martian soil

and heats it
in its portable chem lab.

Like a robotic bloodhound,

it sniffs the vaporized dirt
and picks up

the faint smell of
a rare molecular compound.

What Curiosity discovered was
a compound called thiophene.

This is interesting,
because at least on Earth,

thiophene is often found

in fossil material,
in coal,

in oil, as well as
stromatolites or micro fossils

of ancient life
in the fossil record.

So maybe this thiophene
we've now discovered on

Mars is some trace chemical
fossil of ancient Martian life.

Or possibly, it was produced
by non-biological processes.

DURDA: Curiosity is knocking
on the door

of finding the evidence
for life on Mars.

We haven't found life,
but we've found the interesting

bits that are pieces of
the puzzle,

the organic puzzle of life
on Mars.

And so it's getting us to that
ultimate question, is there

or was there ever life
on the planet?

ROWE:
To help answer that question,

scientists bring in
pinch hitter, Perseverance.

The newest member of the crew

has the latest tech, tools
designed based on lessons from

previous missions.

Perseverance is so important,
because it leverages all of

the knowledge of the previous
rovers, which set the stage for

taking samples
on the surface of Mars,

searching for life, and setting
up a place for humans to

explore in the future.

ROWE: Perseverance gathers
rock and soil samples,

testing some itself and leaving
others to be collected

and returned to Earth later.

We are just at
the beginning of

the Perseverance mission.

We have so much to learn.

But I think all of us
would be so thrilled

if we could actually find
definitive signs of past

Martian life--
that would be incredible.

I don't know what form
that would take,

but we're going to look for it
in every way that we know how.

ROWE: While Perseverance
hunts for evidence

of ancient life on Mars,

Curiosity detects
hints that life may

exist on the Red Planet now.

ROWE: In Gale Crater,
Curiosity detects

a huge surge of methane gas.

DARTNELL: The methane we've
detected in the atmosphere of

Mars is potentially very,
very exciting.

Most of the methane
in our own air,

in Earth's atmosphere,
is biogenic.

It was released
by living organisms.

Curiosity's result
is exciting, because we know

that this can't be
ancient methane.

Methane is really interesting,
because it has a short

residency time in
an atmosphere,

which means it breaks down
very quickly.

Whatever is making methane
in Gale Crater

is doing it right now.

ROWE: Curiosity has detected
methane many times before.

But this is the largest
amount so far.

The question is,
what created it?

Maybe this Martian methane is

the first trace we found of
Martian life,

micro organisms living
deep underground.

Or maybe that methane is
not biological, but geological.

It's methane that's been given
off by volcanic processes in

the past.

The frustration is,
we can't quite tell

the difference
between the two just yet.

All we can do is continue
to sniff

the air and document
when and where we see it.

ROWE: The picture becomes more
intriguing when Curiosity

detects oxygen in greater
quantities than expected.

There's a lot more oxygen on
Mars than we had suspected,

which is weird
in the first place.

And the amount of oxygen
is changing seasonally.

There's something
in or on Mars

that is adding oxygen
to the Martian atmosphere

during the spring and summer
and then taking it away during

the fall and winter.

There is something that is
actively controlling

the amount of oxygen in
the Martian atmosphere.

What is that?

ROWE: Most of Earth's oxygen
comes from living organisms

photosynthesizing, and it
changes with the seasons.

SUTTER: We have normal,
cyclical, seasonal variations in

the amount of oxygen here
on Earth because of life.

RADEBAUGH:
The most landmass on the Earth

is located in
the Northern Hemisphere.

And so that means that during
northern summer,

most of the oxygen
on Earth is generated.

So there's a peak in oxygen
during the northern summer.

ROWE: So where is the oxygen
on Mars coming from?

Oxygen is a known result of
life of photosynthesis.

It's a biosignature.

It's a sign of life.

Is this a sign
of life on Mars?

ROWE: The atmospheric
changes in oxygen

and methane are
a fascinating puzzle

and a tantalizing hint
of life.

Life on Mars
explaining these changes in

methane and oxygen would be
incredibly interesting.

So it's probably wrong.

The answer is probably more
boring, and not that chemistry

is boring, but it's--

it's a little less
interesting than life.

We Mars scientists, of course,
are always very excited

about seeing signs of maybe
extent life on Mars,

but we're going to require
really big proof before we feel

truly excited that
we've made this discovery.

ROWE: The army of robotic
explorers continues

to rewrite the story of Mars,

discovering a once warm,
wet world

with the potential for life.

Now, a new generation of robots

led by Perseverance will dig

deeper into the Red Planet's
troubled past

and its frozen present

and maybe hit the mother lode,
life itself.

THALLER: With every
new mission to Mars,

I hope that somebody really is
going to find evidence

that life
either existed there

in the past or maybe even
still does now.

And with all of these missions
on many places on this planet,

maybe now is the best time to
actually answer that question.

Whether or not it's likely

that Perseverance finds life
on Mars,

we have set ourselves up
for success, and I am

so hopeful that we get to
finally answer that question,

the big question.

Are we alone?