Finding Life Beyond Earth Page #3

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how these impacts created

a habitable world.

There's some magic set of

conditions that has to occur

in a solar system to give you

an Earth-like planet.

NARRATOR:

Figuring out what happens

when a massive planet the size

of Mars hits Earth

is no small feat.

It requires smashing

things together

at extremely high velocities.

We want to simulate what happens

when materials strike the Earth

at very high speeds.

What we can do in the lab

is study little pieces

of the process

and, using the information we

gather from many experiments,

we build computer models

that try and recreate

the whole event.

NARRATOR:

This requires a special piece

of hardware,

a 20-foot cannon that uses

an explosive charge

to fire projectiles at up

to 6,000 miles per hour.

At the other end

is a pressure chamber

and the target, representing

a planet like Earth,

wired up with precision sensors.

STEWART:

We have a 40-millimeter gun

that launches 1 00-gram bullets

into rocks or ices,

and we study what happens

as that shock wave travels

through the material.

NARRATOR:

The gun is set to fire.

(gunshot)

Each test measures the

temperatures and shock waves

generated in different materials

when they are slammed

into each other.

The results are fed

into computer models

of the final stages

of a planet's formation.

STEWART:

Over the past few years,

we've realized how important

the last giant impact is

to the final state of a planet.

That last impact could

fundamentally change

major parts of the planet,

and that could lead

to something that's Earth-like

or something that's

more Mercury-like.

NARRATOR:

Sarah's work, though not

yet conclusive, suggests

that giant impacts could play

a role in producing water

on a planet's surface.

Her results indicate

the collisions were so violent,

they could heat rock

to 2,700 degrees,

hot enough to release water

trapped deep beneath

the surfaces as steam.

Sarah believes this may

have happened

during Earth's final

catastrophic collision.

In its aftermath,

as the raging hot planet cools

over millions of years,

this steam condenses

and falls as rain,

covering the surface

with seas and oceans.

If this hypothesis is correct,

then several million years

after forming,

Earth has two of the three

ingredients needed for life:

water, and energy from the sun.

But what about

organic molecules,

the chemical building blocks

of life?

How did they get to Earth?

Some scientists believe

the answer may lie

in the furthest reaches

of the solar system...

beyond Jupiter...

Saturn...

Uranus...

and even Neptune.

Here, three billion miles

from the sun,

is a vast ring of comets

and other debris

called the Kuiper Belt.

Like asteroids,

comets are remnants from

the dawn of the solar system,

but as well as rock, they are

also made of ices

that only freeze

this far from the sun.

Astrobiologist Danny Glavin

and his team think comets

are the key to understanding

how the final ingredients

necessary for life

arrived on Earth.

GLAVIN:

The reason that comets are

so important to study

is that they really are

windows back in time.

These things formed four-

and-a-half billion years ago,

before the Earth even formed,

and so we're looking at the

chemistry in these objects

that was frozen in time.

NARRATOR:

But analyzing actual

comet material

when the closest sample is more

than three billion miles away

is a major challenge.

Fortunately,

icy comets occasionally fly

in closer to Earth.

As they approach the sun,

comets warm up

and the ice starts to vaporize,

spitting out tiny particles

of ice and dust.

GLAVIN:

So when you're looking

at a comet in the sky,

what you're actually seeing is

predominantly the tail.

You don't see that tiny

rocky ice nucleus,

because it's being dominated

by the sublimation of ices

and rocks.

So you see that long tail

and the solar wind,

which is just dragging it

for millions of miles behind.

NASA ANNOUNCER:

Zero and lift-off

of the Stardust spacecraft.

NARRATOR:

A Delta II rocket blasts

into space.

Onboard is the probe Stardust.

ANNOUNCER:

Gone through mach 1 , vehicle

looks very good, burning nicely.

NARRATOR:

The aim:
to meet up with a comet

speeding through space

at nearly 60,000 miles per hour,

then, fly through

the ice and dust

and bring some of it

back to Earth.

240 million miles from Earth,

Stardust approaches

the comet named Wild 2.

It heads to the heart

of the comet

and takes these images

of its solid icy nucleus.

The surface is broken

and jagged,

and shooting out of it are jets

of dust and ice particles.

Astronomer John Spencer

is an expert

on objects

from the outer solar system.

SPENCER:

The cometary surface is

pretty treacherous.

We have crazy spires that may be

several hundred feet high.

We have overhangs,

we have upturned layers where

the surface really seems

to have been torn apart.

This is a very, very bizarre

landscape.

We have a surface

that is mostly black,

but scattered around

within that we have fresh ice.

We see a mostly black sky

because the atmosphere

is almost negligible.

That black sky is punctuated

by these geyserlike jets

of ice particles

that are shooting up

at supersonic velocities.

NARRATOR:

These icy geysers

bombard Stardust.

These particles hit at almost

1 4,000 miles per hour,

six times faster

than a speeding bullet.

NARRATOR:

Stardust survives intact

and on January 1 5, 2006,

the samples return to Earth.

GLAVIN:

The samples fell down

on Utah and boom--

we had the first comet

sample materials

and there were astrobiologists

all over the Earth

that were, you know,

kind of screaming inside,

because we knew this was

our first chance

to actually analyze

comet material.

NARRATOR:

Inside, scientists discover

over 1 ,000 grains of comet dust.

Glavin and his team analyze

this material for three years.

Then, they make

an incredible discovery.

In the dust from the comet

are traces of the organic

molecule glycine,

an integral part

of living things.

Probably frozen into the comet

when it formed,

glycine consists

of simple elements

found in the cloud

of gas and dust

that gave birth

to our solar system.

Now, glycine is an amino acid.

It's one of the building blocks

for life.

GLAVIN:

These make life go.

They make up proteins

and enzymes,

they catalyze all the reactions

in our bodies,

they're fundamental to life.

Without these

we could not exist at all.

NARRATOR:

All life on Earth,

from these bacteria to us,

uses amino acids.

Glycine is special

because it's the most common

of the 20 amino acids needed

to make proteins, part

of the very fabric of life.

The discovery means that comets

could have been one source

of the organic materials

necessary for life on Earth.

We've proved that in fact

comets could have delivered

the raw ingredients of life

to the early Earth.

NARRATOR:

But what could cause comets

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