Finding Life Beyond Earth Page #6

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would have been delivered to all

the planets and their moons

in our solar system.

NARRATOR:

But what about the colder,

outer reaches

of our solar system and beyond?

Could life exist out here, too?

New missions are revealing

strange worlds,

moons that could have

vast oceans concealed

beneath miles of ice...

Landscapes littered with

hundreds of active volcanoes.

ASHLEY DAVIES:

So now the zone where life

could possibly exist

has expanded out from Earth

to the outer reaches

of the solar system.

NARRATOR:

And places where jets erupt

hundreds of miles into space.

CAROLYN PORCO:

We could hold in our hands

evidence for extra-terrestrial

life.

NARRATOR:

And the same epic forces that

gave birth to our solar system

are at work throughout

the universe.

Tens of billions of planets

are estimated to be orbiting

other stars

in our own galaxy alone.

Could there be an Earth-like

planet among them?

GEOFF MARCY:

We will find

habitable worlds for sure,

if not this week

or next month or next year,

sooner or later.

NARRATOR:

Finding "Life Beyond Earth,"

up now on NOVA.

NARRATOR:

The possibility of life beyond

Earth is a tantalizing idea,

long prompting our species

to wonder

if there are other worlds

where life exists.

Now, as space technology

advances,

the chances of finding it

are greater than ever.

GREEN:

I would love to find

life beyond Earth.

I'd like to think

that we could do that,

and I'd like to think

that we could do that

in the next several years.

NARRATOR:

The search focuses

on three key ingredients.

The first one is life's basic

chemical building blocks

made from simple elements found

in the cloud of gas and dust

that gave birth to all

the planets and moons.

These chemicals were

possibly delivered

throughout the solar system

billions of years ago...

by comets and asteroids.

They are compounds called

organics,

containing carbon, oxygen,

hydrogen and nitrogen.

Next, life needs a liquid

like water

that allows these compounds

to mix and interact.

And finally, an energy source

like the sun

to power the chemical reactions

that make life possible.

Scientists were once convinced

that all three ingredients

could only be found, if at all,

on planets that are at just the

right distance from the sun.

Too close and it's too hot.

Any further away than Mars

and it's too cold.

But now, missions

to the outer solar system

are calling this assumption

into question.

This is Jupiter as seen by

the space probe Voyager 1,

launched decades ago to explore

the outer solar system.

Half a billion miles

from the sun,

it seems unlikely

that life could exist out here

in such extreme cold.

Voyager approaches Io, one of

Jupiter's more than 60 moons,

orbiting in the shadow

of the gas giant.

Io should be a frozen,

icy, barren world.

But Voyager spots something

completely unexpected.

These actual images of Io's

surface

reveal hundreds of giant,

active volcanoes.

Later probes expose vast lakes

of molten lava.

On Earth, volcanic activity is

driven by heat in the interior,

but Io is so small

that it should have cooled down

billions of years ago.

There must be another source

of energy inside the moon.

The discovery of active

volcanism on Io

was one of the greatest

discoveries

of planetary science.

NARRATOR:

By observing Earth's volcanoes

and studying the huge amount

of data gathered from Io,

Ashley Davies pictures

what walking on Io's surface

would be like.

DAVIES:

Walking across the surface

of Io,

it's a very, very hostile

environment.

It's either very, very cold

or it's very, very hot

where there's volcanic activity

taking place.

Of course, there's

no atmosphere.

There'd be a bounce in your step

because the gravity of Io

is about the same on the moon:

one sixth of the Earth.

You could feel the crunch

underfoot

as you head from one volcano

to another

across these vast plains.

Well, here we are in the middle

of a vast lava flow field.

It's dark, it's quite hot.

This is comprised of lava flows

that have erupted from one

of Io's many volcanoes

like that one over there.

NARRATOR:

The probe New Horizons

flies past Io.

It takes this photograph

of an enormous eruption from

a volcano called Tvashtar.

A vast plume of sulfur shoots

200 miles into space.

These actual images reveal

the plume as it spreads out

and rains back to the surface.

DAVIES:

On Io, we see these large

volcanic eruptions.

The gases that are coming

out of the lava

blast this material high into

space, into the vacuum of space.

It's very, very spectacular.

NARRATOR:

What could be generating

so much energy

in a moon that should be

frozen solid?

And where is the power

coming from?

The key to understanding

Io's volcanic activity

is its parent planet, Jupiter.

Io orbits Jupiter in a slight

ellipse rather than a circle.

With every orbit, Io experiences

gravitational pushes and pulls

from Jupiter and other moons.

When Io is closest

to the giant planet,

it is stretched

by more than 330 feet.

Over billions of years,

this has created

an immense amount of friction

deep inside the moon.

DAVIES:

This continual flexing

of the satellite

is like bending a piece

of metal-- it heats up.

And this is the ultimate source

of Io's volcanic energy

and its volcanic heart.

NARRATOR:

The powerful tidal force,

generated by the massive

gravitational pull of Jupiter,

creates an alternate source

of energy

far from the warmth of the sun,

a source of energy that could,

in principle, support life.

DAVIES:

What's so important about Io is

that it moves our perceptions

away from a habitable zone

around the sun

where energy is just derived

completely from the sun.

So now the zone

where life could possibly exist

has expanded out from Earth

to the outer reaches

of the solar system.

NARRATOR:

But the chances of life existing

on Io itself are slim.

Even though

it has an energy source

and could have the right

chemical building blocks,

possibly delivered by comets and

asteroids billions of years ago,

scientists have not yet detected

the third key ingredient:

a liquid like water.

But Io is not the only moon

circling Jupiter.

NASA's unmanned space probe

Galileo

flies by the next moon out,

Europa.

GREEN:

It passed by Europa

1 2 times and only 1 2 times.

Virtually everything we know

about Europa

is from those 1 2 passes.

And each and every one of them

has excited us beyond belief.

NARRATOR:

Slightly smaller

than our own moon,

Europa is covered with ice.

Data collected by Galileo shows

that the surface is minus-260

degrees Fahrenheit,

surely hostile to life.

But as the probe gets closer,

it takes these images.

A mysterious network

of dark cracks

is etched into Europa's

icy surface.

JOHN SPENCER:

We see places where very clearly

the ice has cracked and two

sides have spread apart.

Material has come up and frozen

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