Original subtitles

In July 1976, NASA's Viking I spacecraft

attempted a monumental task.

For hundreds of years, people had been asking

the question, when planets were first discovered,

"Is there life on Mars?"

It's been one of those prevalent questions

throughout history.

This was the first time that we would look

at the possibility of life, any life,

other than life here on the earth.

Can you imagine what it was like at that moment,

when the team, myself, held together,

knew that the signal was coming back,

that the test had started,

and we were soon gonna get some kind of an answer.

There is one thing that sets this planet

apart from the rest.

The Earth is alive.

Is this the only place life exists,

in an otherwise barren universe?

It is, perhaps, the greatest question of our age.

The fundamental question is, are we alone?

Is life on Earth the only type of life there is?

When I look out into the night sky

and see all the planets and stars

that there must be out there,

we can't help but wonder, is there life there?

All we have is the example here on Earth.

And even if we found just the simplest little bug

on another world, and if that bug was different

from all the bugs we have here,

that would tell us that at least in two places,

there was life.

And from two, I think it's clear

that the whole universe must be full of life.

If there is life in the universe,

there is still no sign of it.

For decades, radio dishes have scanned the skies,

listening patiently for a message

beaming its way across the galaxy.

So far, they have heard nothing.

Status check, missile power.

Go.

RF systems. Go.

Propulsion. Go.

AMR telemetry. Go.

Spacecraft. Go.

With he coming of the Space Age,

we could at last go out and search for alien life.

In 1962, America sent Mariner II to Venus.

Was it possible this planet could have life?

Its surface was hidden by a thick layer of cloud.

Exactly what lay below was a mystery.

Some imagined there would be a steaming swamp,

a misty haven teeming with life.

Others thought its clouds were caused

by planet-wide dust storms across a parched desert world.

Mariner II was going to find out.

It took with it the hopes

of the world's first space biologist, Dr. Carl Sagan.

Many theories of the Venus environment

have been suggested.

However, new information eliminates at least

some of these theories.

Measurements with radio telescopes show

that there is a region on Venus

where temperatures are greater than 600 degrees Fahrenheit.

It is just possible that the hot region exists

at a high altitude, in the ionosphere of Venus.

The surface temperature could then be almost Earth-like,

and life as we know it could exist there.

But the Mariner II found

the surface of Venus was a searing 450 degrees.

Life was inconceivable here.

Where else was there to look?

Mercury is just a naked ball of rock, baked by the sun.

Jupiter seemed a better prospect.

Some biologists imagined life forms

floating in its clouds like hot air balloons.

But when the first probe got there,

it found the conditions were atrocious.

The swirling clouds were made of superheated ammonia.

They could never support life.

Spacecraft sent to the planets

were sending back depressing news.

Space was a desolate place.

But there was one world that still held hope.

Humans had been dreaming of going to Mars

for over a century.

Boris Chertok was first drawn to the red planet

in 1924, when he saw the film Aelita,

the story of a beautiful Martian princess.

As a boy, Chertok dreamt of finding life on Mars.

He was inspired by the work of one visionary astronomer.

In 1894, a wealthy Bostonian journeyed out

to Flagstaff, Arizona, and set up an observatory.

Percival Lowell had heard rumors

from European astronomers that Mars was criss-crossed

with a series of straight lines.

He'd heard them called canals.

He was so taken with the idea

of a canal-building civilization on Mars

that he began a systematic study of the planet,

charting the features of these supposed waterways.

The maps he made remained the best records

for nearly a century.

When the first space mission to Mars was ready, it was 1961.

Boris Chertok was now second-in-command

of the Soviet space program.

When it flew by Mars,

the spacecraft was supposed to look for life on the surface,

so before launch, Chertok decided to double-check

that the life-detecting device was working properly.

The truth about life on Mars

remained hidden for another 15 years.

And then came Viking.

It was the most ambitious robotic space mission

NASA had ever undertaken.

It was the summer of 1976.

America was on a bicentennial high,

and a spacecraft was on its way to look

for life on Mars.

We had waited, many of us, our whole career

for this magic moment of when we were actually gonna

do the test for life on Mars.

I mean, can you imagine what it's like to be

the first experimenter, the scientist who's gonna

be able to even ask the question,

even if you don't get the answer.

Once Viking was on the ground,

you can just imagine the excitement.

Everybody with their fingers crossed,

and hoping against hope that maybe we'd get

some kind of result outta this.

For seven days, Viking treated the world

to picture after stunning picture of the red planet.

They showed a Mars that was a frigid desert,

where the temperature hovered

around -100 degrees centigrade.

This was not the sort of place where life ought to flourish.

But Viking was build to detect microscopic life,

lurking in Martian soil.

On the eighth day, a scoop reached out

to grab a sample of red earth, and the tests got underway.

The light went on and told us

that we're incubating, it's working now,

any moment now you're gonna start getting the data.

Inside Viking, nutrients were added

to the soil, and to everyone's amazement,

there was an instant response.

Gas came pouring off.

This was just like the gas bacteria on Earth produce.

Every single point was an emotional moment.

"Look, look, it's going," you know.

"It's going up a little bit!

"It's going up a little bit more,

"it's going up a little bit more!"

Then, when it stops, couldn't believe it.

"Hey, the curve has stopped moving."

As the team poured over the results,

they could hardly believe their eyes.

The sample had done just what it would do

if there were organisms in it.

Viking seemed to be saying there was life on Mars.

We never slept, we didn't think about anything.

Our lives stopped, our children stopped,

our everything stopped.

Bank bills were left unpaid, while we focused on

the events that were going on.

Before they announced their discovery,

mission scientists wanted to make sure

the reaction from the soil was really caused by microbes,

so Viking performed another test,

one that scanned the soil for organic chemicals,

the raw materials from which all life is made.

All of us were so certain it was going to be

organic material on Mars.

And when it came back saying there isn't any,

we said, "Well, we'll look in another place.

"Somehow we picked up a sterile sample or something wrong."

And we picked up, we moved over rocks, we dug down,

we did everything we could.

We did these tests again and again and again,

but it all came out negative.

With that one result,

hopes of life on Mars were dashed.

There were no microbes.

The initial test result was probably due

to a corrosive chemical in the soil,

created by intense ultraviolet radiation from the sun.

Nothing could live in Martian soil.

Viking's mission was over,

and it had taken all our dreams of life on Mars with it.

Of course, Viking had been sent to Mars

with a particular hypothesis to test.

That is, that there was some kind of microbes

living in the soil,

and turns out that there weren't.

And so, I think the sense was that Mars

had come up barren, and no one was thinking

about other environments on other sorts of planets.

But life on Earth had its own surprise.

In 1978, a submarine dived to the bottom

of the Pacific Ocean,

and found something completely unexpected.

People took vehicles like the Alvin deep submersible

to hypothermal vents on the East Pacific rise,

and they found these fantastic environments

with tube worms and clams and crabs

and all these things that were surviving

off the Earth's own geothermal heat,

and it took a while for the significance of this

to sink in, but what it means is that there are

other ways of supporting life,

besides sunlight at the surface of the planet.

And that, all of a sudden, opens up a whole new range

of habitability that just wasn't there before.

Since then, the limits of life on Earth

have been pushed back further than anyone

ever imagined possible.

NASA scientist Chris McKay has chosen to study life

in one of the world's harshest environments,

California's Death Valley.

Here in the salt flats of Death Valley,

so not one of the places you expect to find life,

but since Viking, we've found life in a lot of places

where we wouldn't have expected it.

Underneath the salt crust here, in fact,

just a millimeter or so under the surface,

a layer of blue-green algae.

These organisms are deep enough into the salt

that they can access the moisture.

But they're close enough to the surface

that they're getting sunlight to photosynthesize.

What we found, looking at life on Earth

in very harsh environments, dry, cold, hot environments,

is that wherever there's water,

wherever there's some mechanism trapping water,

life can flourish.

And that's the key.

If some alien civilization called us up and said,

"What kind of life do you have on your planet?"

My answer would be, "It's water-based life.

"What kind of life do you have?"

If water was the key to life,

the search for life in the solar system

suddenly became the search for water.

In 1979, a spacecraft called Voyager

ventured out to Jupiter.

It was going to study this giant world,

and its clutch of planet-sized moons,

Ganymede, Callisto, Europa, and lo.

What we knew about the satellites of Jupiter

before we got there with Voyager was very little.

These things went from four points of light

that were understood only marginally better

than Galileo had understood them

back in the 1600s when he discovered them,

to entire worlds that you can map and study in detail

in the space of like 48 hours.

It was an amazing experience.

Among the moons of Jupiter,

they found one that looked very promising.

Europa was smooth, covered in a layer of ice,

and all over it was an intricate web of cracks.

What could they be?

You can make a lot of mistakes in this business

by saying, "I think I know what's going on here,

"because it looks like something else

"that looks familiar to me."

That's a way to go wrong many times.

But it did not escape our attention

that those fractures looked an awful lot like sea ice.

Could there be an ocean

hiding below Europa's icy skin?

Beneath the cracked surface, could life exist

as it does deep down in the Earth's oceans?

We know that life is resourceful enough

to use a lot of different sorts of energy.

Energy sources are pretty widespread,

when you talk about either sunlight at the surface

of a body or geothermal energy from within.

And that was what we suddenly realized,

hey, maybe we had a potential to have on Europa.

NASA already plans to go back to Europa

to try and find proof of an underground ocean.

Stephen Squyres hopes that one day,

he will design a mission to dive into it.

First thing you would do, yes, you would land,

you would then have to get down through the ice.

So you would have a probe with some kind

of heat source in it,

and it would melt its way down.

So then, once you're in the water,

it's gotta somehow transform what it does

form being a melting probe to a swimming probe,

and then, when you get down to the bottom,

you're gonna want to start lookin', jeez,

for all kinds of stuff.

I would wanna take pictures,

which means you gotta take a light source.

It's gonna be, if we do it, one of the most challenging

planetary missions we've ever done.

Hey, it's going after one of the most important

questions that we've got out there.

Could life have arisen on Europa?

It's difficult to be sure until we know more

about how life began on Earth.

How easily did life emerge?

Was it a miracle never to be repeated?

To answer that, you have to travel back in time

to the beginning of Earth's history.

Life must have arisen after the formation of the planet,

about four and a half billion years ago.

But how soon after, how quickly after?

These are questions that we're trying to answer

from studying the geological record

of the oldest rocks.

Steve Moysis is a geologist turned fossil hunter.

To probe the earliest secrets of the planet,

he traveled to Greenland, where a rare outcrop

of ancient rock survives almost unscathed

from when the Earth was young.

In these rocks, he hoped to find microscopic traces

of the most ancient lifeforms imaginable.

During a field trip in 1995, he gathered a horde

of sedimentary rocks, minerals that had formed

at the bottom of the world's first ocean.

The rocks that are the oldest sediments of all

have been through everything that you can do to a rock

without quite melting it.

They've been thrust up, regurgitated, ground up,

heated, crushed...

When Moysis broke open the rocks,

he found tiny mineral grains inside them.

He suspected they might be the charred remnants

of primitive microbes.

It's a preserved kind of a time capsule,

this little mineral.

Moysis put some grains into a machine

called an ion probe, which deciphers the precise

composition and age of minerals.

If the small lumps were once living things,

they should have a certain type of chemical fingerprint.

We found that it was spot on, a veritable stamp

of life that's unique to it.

But the real surprise was the age.

The ion probe showed that the fossils

were nearly four billion years old.

As far back as we can go, 3.9 billion years ago,

there is evidence of life, that life did exist here,

and it existed soon after the Earth formed.

And that became something of a surprise to us.

It had been thought the Earth

was uninhabitable for nearly a billion years,

but now it seems life started almost as soon

as the Earth itself came to be.

As long as life appeared here so quickly,

then perhaps its a kind of cosmic imperative

that life should appear as a chemical consequence

of the evolution of a planet.

Life took hold here

not in mild temperatures like today,

but when the heat on Earth

would have been almost unbearable.

If life began so easily,

then perhaps the Earth isn't so special after all.

If life started when Earth was a much more hostile place,

what happened billions of years ago on the other planets?

Venus will never tell its secrets.

Its boiling atmosphere has turned any evidence to vapor.

But the barren, cratered surface of Mars

just might provide some clues.

Trying to decipher what happened in Mars' history

became an obsession for some astronomers.

It's interesting, all the personalities

that have actually emerged in the course

of Martian history, or Martian history on Earth.

First of all, Lowell built this extraordinary telescope

and actually dominated the scene of his day

and had this great vision.

We fault him for calling them canals and so forth,

but the fact is he understood the importance of water,

H2O, to living things.

It was an important mark on history.

Lowell saw his canals as traces

of an ancient civilization on a planet starved of water.

In 1976, when the Viking landers were proving

that the surface of Mars was an arid desert,

the orbiters were photographing the planet

from pole to pole in unprecedented detail.

They didn't see canals, but something just as exciting.

Snaking across the southern hemisphere

was a network of eroded channels,

floodplains, and river valleys.

Billions of years ago, this must have been

a world of rivers and oceans.

Mars, too, was a place where life could have begun.

In 1969, Apollo XII made man's second trip to the moon,

and changed all our ideas of life in the solar system.

Roger.

All dressed up and no place to go.

Oh, we're going someplace.

We can see it gettin' bigger and bigger all the time.

Roger, we copy that, Twelve.

The challenge of Apollo XII was pinpoint landing,

and at a crater that contained Surveyor III.

Surveyor III had landed on the moon

in 1967, one of the robotic trailblazers

for the Apollo astronauts.

Now, they were going to pay it a visit.

We didn't expect anything else.

We didn't train for anything else, Pete.

You better believe it.

One of the things they wanted us to do

if we were successful was to bring pieces

of the surveyor back for the engineers to examine

what it meant for this structure to stay

33 months on the moon,

and to have the total radiation from the sun

for half that time, to be in the vacuum of space,

which is almost total,

realize the temperature changes from -250 to +250,

practically a 500 degree almost temperature spread,

and so they wanted to see what the effect was

on those parts.

But first, they had to find that crater.

I got something on the horizon out here,

I got the craters too, but I don't know where I am yet.

We were three days in the warm day

with the sun about 15 or 20 degrees behind our back,

when we came in to land,

and when we had this crater pattern all picked out,

when I pitched over at 7,500 feet above the lunar surface,

where I could see for the first time,

and I thought, "Now, I'll pick out this crater pattern."

It just wasn't near us.

10,000 craters, I went, "Wow, where am I?"

But Al gave me the number to look down,

and I did that and the thing popped out

and we were right on the money,

we were headed right for the crater.

That crater right where it's supposed to be.

You're beautiful, 240.

Hey, you're really movin' around.

Okay, coming down in four, you're lookin' good.

50 feet comin' down, watch for the dust.

40 comin' down, lookin' good.

Hang in there.

Almost there, 24 feet.

Contact.

Roger, copy contact.

Okay, got your...

Command override off.

Once we landed, I mean, I knew I was

at the right crater pattern,

but I hadn't seen the surveyor on the way in.

So, I went down the ladder, and the first thing

I wanted to do was to go around to the back

and look at the crater, and sure enough,

there was the surveyor sitting there,

and that made my whole day.

I knew it was all downhill from there.

We have surveyor, yes sir.

And so, Pete Conrad went for a stroll,

and, with a pair of heavy-duty bolt cutters,

snipped the camera off the defunct robotic ship.

We're ready to start getting the TV camera.

Okay.

Big smile, okay.

And so they got the television camera off the surveyor,

which we brought back.

And when they opened it up in the lunar receiving lab,

apparently, when it was assembles some more now,

over three years before this,

when it was assembled, the worker that assembled it

must have had a cold, and he sneezed into the Styrofoam,

and they found these little spicules,

all dried, of course, in there,

but a good microbiologist took that,

put it in their petri dishes, and put it in the right

whatever you do with that sort of thing,

and lo and behold, this bacteria came back to life.

Just took off like nothing had happened.

Apollo XII proved that bacteria

can survive the harsh vacuum of space.

Life is tougher than anyone imagined.

It is almost indestructible.

Microbes have made a journey from one world to another

and survived.

Could life have taken a trip like this before?

The idea that meteorites could have carried life

from one planet to another had existed for decades.

It was considered crazy.

But there were some unusual meteorites around.

No one had a clue where they were from.

Then, two young scientists proposed what seemed like

another mad idea.

20 years ago, at a bar in Houston,

a colleague and I discussed this problem,

and came to a rather startling conclusion.

That is that these particular samples

were rocks from the planet Mars

that had been knocked off in a large impact

and had arrived on Earth.

We were students at the time, graduate students at Harvard,

and we didn't realize, I think, the resistance

that this idea would enjoy, and in fact,

the idea was considered impossible

by the scientific community.

But, as we discussed it, the more of these we consumed,

the more plausible the idea seemed.

For several years, the idea floated around.

Then, a NASA scientist took a close look

at one of these mysterious rocks.

So, did you think this idea was crazy

when you first heard it?

I didn't think it was crazy.

Of course, the idea of meteorites from Mars

had been developing for two, three years.

I would say that I was a non-believer,

but willing to be converted

if the right evidence came along.

This is just a small piece of the original meteorite,

but I guess these little black areas

are like what you analyzed?

Yes, one like this black inclusion on top

is very similar, although the one that we measured

was a little larger and more spherical in shape.

The greater surprise was the nature of the evidence.

When Don Beaugard analyzed a grain of glass

inside the rock, he found it contained gas.

To his amazement, it was an exact match with the gas

sampled by the Viking landers.

This rock had to have come from Mars.

I think that probably no one had anticipated

that you would get direct evidence for that process

in such an unlikely way as going into a small piece

of glass in one of these meteorites

and showing that a bit of the Martian atmosphere

was actually trapped inside it.

We now know that pieces of Mars

have been raining down on Earth for billions of years.

Could life have once traveled with them?

If life was present on Earth at the end

of the formation of the Earth,

at that period, the impacts would have been

much more numerous than they are today.

And so, material would've been constantly

being knocked off the planets, all of the planets,

and exchanging between the planets,

so they could've carried organisms

from one planet to another.

The planets would not have been biologically isolated.

This material going back and forth would have been

sort of like swapping spit between the planets.

In 1996, for a while, some scientists

believed they had found proof that life had traveled

to Earth from the red planet.

One Martian meteorite seemed to have remnants

of microbes in it that were at first thought to be Martian.

But sadly, that turned out not to be the case.

The truth about life on Mars will not be revealed so easily.

If life did once exist on Mars,

it only had a billion years to evolve

before the planet lost its atmosphere,

and became too cold and dry.

On the Earth, there is one place that comes close

to how Mars must have been when any life there

would have died out,

the dry valleys of Antarctica.

This is how Mars must look like.

The Antarctic desert is cold and dry.

Mars is also a cold and dry desert,

only colder and drier than Antarctica.

In the high mountains, it is absolutely dry,

and on the surface is lifeless.

But biologist Imre Friedmann

thought there was one refuge for life here,

the type of life he believed was the most advanced organism

that could've existed on Mars.

We thought that life exists more inside rocks,

where microorganisms can find a protective habitat,

rather than in soil, which is more exposed

to the extremes of the environment.

In 1976, Friedmanm found sandstone rocks

with strangely mottled surfaces.

And when he broke them open,

there were the signs of life he was looking for.

You see, under the surface, it continues green layer

of photosynthetic microorganisms.

So when you look from the outside,

you think that the rock is dead, it is brown.

But in fact, just one millimeter below the surface,

the rock is green, so these rocks are not brown,

these are green!

The microbes cling to life,

because even when it's freezing outside,

water can form in droplets inside the rock.

These microorganisms have a very hard life,

because most of the time, they are hard frozen,

and only very few hours in a year

that they are coming to life,

they have the water, the temperature, and the light

that they can photosynthesize,

and really live actively.

These microbes are just about

the toughest form of life on this planet.

They could have survived on Mars

three or four billion years ago.

These organisms live at the limit of existence,

so to say, at the precipice.

And if conditions deteriorate only a little bit,

they die, and the result is extinction.

Perhaps the last life on Mars

left its traces locked inside rocks

on the planet's surface.

We're on the threshold of a new search for life

on the red planet.

This time, expectations have changed.

Our whole attitude towards life in a planet

is different now than it was back in 1976.

We've gone through a revolution in thinking.

We're looking at what could be a Mars that had life,

but doesn't have life anymore.

Is Mars a world that has fossils?

NASA has committed itself to finding out.

It has embarked on a series of missions

to scour the planet for signs of ancient life.

NASA sent rovers that arrived on Mars in 2004,

equipped with drills and microscopes

to help them search the planet's surface.

Stephen Squyres is the mission designer.

This is totally different from Viking.

The objective in Viking was to test the idea

that there are, today on Mars,

microbes living in the soil.

That's not what this is about.

What we are trying to do is we're trying to study

what the environment was like long ago,

whether or not there was life there back then

that today would be present only in fossil,

you know, some kind of remnant form.

The evidence is in the rocks, and that's why the mission

is very strongly focused on rocks.

There are many places on Mars

where fossils might be found.

Dry lake beds, river valleys, deep canyons.

These are the places where the rover will search.

We see places like this on Mars,

dried lake beds, with deposits on the surface

that could contain organisms that lived

in salt crusts like this here billions of years ago.

Imagine if you lived on Mars billions of years ago

and were preserved, this would be a great place

to be preserved, because in not too many years,

we might be going there and drilling down

and pulling out those remains and seeing what's there.

Suppose we find, on Mars, evidence that life

actually did come into being.

If that's the case, Mars, literally half of the planet,

I think, is covered with roughly

four, four-and-a-half billion-year-old rocks.

In other words, there's a chance that the record

of that process, the process of life coming into being

from non-living material,

that record is still there to be read

in the Martian geologic record.

So it may be that by going to Mars,

we can actually understand better where we came from.

The search for alien life

is really a desire to understand our origins.

Did life begin on Earth?

Did it travel here from Mars,

or even from a more distant world?

The answers may lie somewhere across the solar system.

20, 30 years ago, our view of life

was very much bounded by the Earth.

We conceived of life having originated on Earth,

and having written its full history here on Earth.

But now we realize that Earth is not an island.

It's connected to the other planets.

We realize that Earth is living in a neighborhood,

and that neighborhood influences the life here.