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?