NOVA

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 to 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."

Major funding for "NOVA" is provided by the following:

Doppler and orbit around the planet Mars.

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.