Finding Life Beyond Earth

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NARRATOR:

Is Earth the only planet

of its kind in the universe?

Or is there somewhere else

like this out there?

Is there life beyond Earth?

The search for alien life

is one of humankind's greatest

technological challenges.

And scientists are seeking

new ways to find answers.

We're pushing the boundary

of information

of where life can exist

past the Earth and out

into the solar system.

NARRATOR:

Leading the search are

sophisticated telescopes

that scan the sky

and an armada of robotic probes

exploring the outer reaches

of our solar system...

all revealing the planets,

moons, asteroids and comets

like never before.

WOMAN:

We can go places and see things

that there's no other way

we could have ever seen.

NARRATOR:

The search reveals evidence of

strange and unexpected worlds--

places with lakes,

storms and rain,

violent places driven

by powerful forces

deep underground.

Worlds that may have

hidden oceans

hundreds of millions of miles

from the heat of the sun.

The pace of discovery, just

in the last couple of years,

is just mind-boggling.

NARRATOR:

New missions are helping

to unlock the mysteries

of what makes a planet

habitable,

raising the question of whether

the building blocks of life

are more prevalent

than previously imagined,

not just

in our own solar system,

but possibly

throughout our galaxy.

We now have for the first time

in human history

definite planets out there

among the stars

that remind us of home.

NARRATOR:

"Finding Life Beyond Earth,"

up now on NOVA.

Major funding for NOVA is

provided by the following:

And...

And the Corporation

for Public Broadcasting

and by PBS viewers like you.

Additional funding is provided

by Millicent Bell, through:

NARRATOR:

After a seven-year,

two-billion-mile voyage,

the spacecraft Cassini

enters orbit around Saturn.

Cassini heads towards the

largest of Saturn's 62 moons...

Titan.

Bigger than the planet Mercury,

Titan is hidden

by a thick orange haze.

No one has ever seen

its surface.

But a small probe named Huygens,

released by Cassini,

is about to change everything.

This mission will challenge

long-held notions

of where life could exist

beyond Earth.

These are the actual images

Huygens takes

as it breaks through

the clouds and haze.

Titan is a land of mountains

and valleys,

a place that looks surprisingly

like Earth.

Then, images reveal something

no one expects.

The surface is littered

with smooth rocks,

the type normally found

in river beds on Earth.

CHRIS McKAY:

My response was shock.

We look out on the surface and

we see what looks like a desert

and at the same time,

the data from the probe

told us that the ground

around the site was wet.

NARRATOR:

Hundreds of miles overhead,

Cassini's radar

sweeps the surface.

The images show a landscape

covered with what appear

to be hundreds of lakes.

This one covers an area

of 6,000 square miles,

about the size of Lake Ontario,

one of the Great Lakes.

It's a surprising discovery.

It's the only world

other than the Earth

that has a liquid

on its surface.

NARRATOR:

But what exactly is this liquid?

Titan is minus-290 degrees

Fahrenheit.

If it's water,

it should be frozen solid.

Then, one of Cassini's

instruments analyzes

the infrared light reflected

off the lakes.

The readings are consistent

not with water

but with liquid methane

and ethane,

substances that on Earth

are volatile, flammable gases.

The data from Cassini are so

detailed, scientists can imagine

what it would be like to stand

on this cold, distant world.

McKAY:

Standing on the surface

of Titan,

you see Saturn just sitting

there in the sky,

big, huge, stationary object,

almost like a door

to another dimension.

Here we see lakes,

lakes of liquid methane.

And in the horizon,

we see mountains.

These are mountains made of ice,

made of water ice,

frozen so hard

that it acts like rocks.

And the features

that we see in them

are carved by the liquid methane

that's forming these lakes.

Looking across the horizon

on Titan,

you might see a thunderstorm

or a range of thunderstorms

coming at you.

We see rain coming down.

It's not drops like we're

familiar with on Earth.

This is methane

instead of water.

It falls much more slowly

due to the low gravity

and the drops are bigger.

NARRATOR:

So what are the implications

of finding a liquid flowing

on Titan's surface for a

scientist like Chris McKay?

McKAY:

Liquid seemed to be

the key to life,

so maybe there's life

in that liquid on Titan,

little things

swimming in liquid methane,

being quite happy

at these low, cold temperatures.

NARRATOR:

There is no evidence

that living things like microbes

exist in these lakes.

But if such evidence

were found here,

it would fundamentally

change perceptions

about life beyond Earth.

If life could evolve

on worlds as drastically

different

as the Earth and Titan,

then perhaps life could evolve

in many other ways

on many different worlds.

NASA's director of planetary

science is Jim Green.

GREEN:

One of the questions

that we all want to know,

I think, deep down inside,

is, "Are we alone?"

I mean, that's really

fundamental.

NARRATOR:

Jim is at the forefront of

a global effort to understand

whether the conditions for life

exist beyond our planet.

GREEN:

We're pushing the boundary

of information

of where life can exist

past the Earth and out

into the solar system.

NARRATOR:

So, where in our solar system

could life potentially exist?

Heading out from the sun,

the first planet is Mercury.

It's an extremely hostile

environment.

In March 201 1 ,

NASA's Messenger probe becomes

the first spacecraft to orbit

this small ball

of rock and iron.

These are some of the first

images sent back.

Three times closer to the sun

than Earth is,

Mercury bakes in 800-degree heat

on its side facing the sun,

while on the night side,

temperatures plummet

to minus 290.

Mercury is the ultimate

desert world.

Life of any kind here

seems unlikely.

Mercury's closest neighbor,

Venus, is almost as hostile.

Though nearly twice as far

from the sun,

temperatures here

exceed 880 degrees.

Decades of observations

have revealed

a planet shrouded

in carbon dioxide

and toxic clouds

of sulfuric acid.

These radar images reveal

thousands of ancient volcanoes

on a surface hot enough

to melt lead.

And with an atmospheric pressure

that is 90 times greater

than on Earth,

it is hard to imagine that

anything could live down here.

But based on chemical analysis

of the atmosphere,

scientists believe that water

once flowed on Venus's surface.

If life ever did exist here,

evidence has yet to be found.

So what is it about Earth, the

third planet out from the sun,

that makes life possible?

The answer lies

in three key ingredients.

First, all life is made up

of organic molecules

consisting of carbon in

compounds that include nitrogen,

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