Finding Life Beyond Earth Page #4

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to fly in from the furthest

edges of the solar system,

slam into Earth and deliver

these organic compounds?

The clues to one

possible process

lie back out in the Kuiper Belt,

the disk of icy objects

that orbits the sun at the edge

of our solar system.

HAL LEVISON:

We expected when we found

the Kuiper Belt

that we would just see objects

in nice circular orbits

about the sun.

NARRATOR:

But observations reveal

that the Kuiper Belt objects

are not orbiting as predicted.

Out here, it's chaotic.

When we look at the Kuiper Belt,

we see something that looks

like somebody took the solar

system, picked it up

and shook it real hard.

And that's

what started us thinking

that something really strange

has happened there.

NARRATOR:

Levison theorizes that

the reason for this mayhem

likely is connected with

the two largest planets

in the solar system.

Jupiter is so big it could

swallow more than 1 ,300 Earths,

and Saturn,

with its vast rings of ice,

is 95 times Earth's mass.

With their enormous size comes

an enormous gravitational pull.

LEVISON:

Everything that we see

is a result of what Jupiter

and Saturn did.

NARRATOR:

Levison wonders if the chaos

of the Kuiper Belt

could have resulted from

a planet smashing into it.

To find out, he runs a number

of computer simulations.

One model creates the conditions

in the Kuiper Belt

that we see today.

3.9 billion years ago, as

Jupiter circled the sun twice,

Saturn made one complete orbit.

Each time these orbits

coincided,

there was a powerful

gravitational surge.

That pushed Saturn's orbit

further from the sun

and destabilized the orbits

of the two outermost planets,

Uranus and Neptune.

Jupiter and Saturn sort of

tugged each other,

and that drove the orbits

of Uranus and Neptune

absolutely nuts.

NARRATOR:

Uranus and Neptune are sent

careening outwards

towards the Kuiper Belt.

Comets ranging in size

from a mile across

to objects the size of Pluto

are blasted out of their orbits

by the planetary invasion.

The disk went kaplooey.

Think of it as sort of a bowling

ball hitting bowling pins.

These things got scattered

all over the place.

NARRATOR:

The end result is

a hundred-million-year period

when comets, kicked out

into the solar system

by Uranus and Neptune,

smash into anything

in their path.

It's a period scientists call

"the late heavy bombardment."

Earth doesn't escape.

LEVISON:

This was so violent

that probably every square inch

of the surface of the Earth

was hit by a comet

during this time.

NARRATOR:

This is one theory

that might explain

how massive amounts

of organic molecules,

the building blocks of life,

made their way to Earth.

Possible evidence of the late

heavy bombardment can be seen

on the surface of other planets

and moons in the solar system.

Impact craters.

Literally the seeds of life,

the amino acids

would have been delivered

to all the planets

and their moons

in our solar system.

NARRATOR:

So if life's building blocks

were delivered by comets

throughout the solar system,

could life also have sprung up

on worlds other than Earth?

It is unlikely that living

organisms exist today

on Venus or Mercury,

as space probes have found

no evidence on these planets

of the other vital ingredient

life needs:
liquid water.

But what about Mars?

Organic compounds

have yet to be found here,

but scientists are searching

the planet

for the other preconditions

of life.

There have been many missions

to Mars, and nearly all suggest

that water once flowed

on the surface.

These detailed images

from satellites orbiting Mars

reveal vast canyons blasted out

by epic floods

and valleys carved

by raging rivers.

But the evidence indicates

that all this water disappeared

from the surface

billions of years ago

as Mars cooled down

and lost its atmosphere.

But on May 25, 2008,

a spacecraft called Phoenix

touches down

near Mars' north pole.

Digging a few inches down,

it exposes a white material

that vaporizes after a few days.

Soil analysis reveals

it is water ice.

We landed

68 degrees north, poof!

Just a few centimeters below the

ground there was a layer of ice.

NARRATOR:

Satellites analyze radar waves

bouncing back

from both polar caps.

They reveal that beneath a layer

of frozen carbon dioxide

there is a lot of water ice.

If it all melted, it would cover

the whole planet

in an ocean

more than 80 feet deep.

GREEN:

When we look at Mars

and we see the reservoirs

of water there,

it's completely surprised us

in terms of the amount of water

and how much water is actually

trapped underground.

NARRATOR:

The same satellites orbiting

Mars are discovering

that buried ice

is also widespread

beneath the desert floors.

McKAY:

When we look at Mars, we see

what looks like a desert world

with no water, but in fact,

Mars has lots of water--

it's ice.

Mars is an ice cube covered

with a layer of dirt.

NARRATOR:

But this doesn't mean that

finding life here is imminent.

Ice doesn't melt the same way

on Mars as it does on Earth.

The atmospheric pressure here

is 1 50 times lower than ours.

It's impossible for water

to exist as a liquid

at the surface.

McKAY:

Ice on Mars behaves

like dry ice does on Earth.

A piece of dry ice on Earth

goes directly

from the solid ice to vapor.

It doesn't form a liquid.

That's why we call it dry ice.

On Mars the pressure is so low

that water ice

does the same thing.

NARRATOR:

No liquid water on the surface

of Mars today

means that vital chemical

reactions cannot take place.

It seems impossible that life

could exist there.

But could it exist

in the buried ice itself?

An expedition to one

of the coldest places on Earth

is looking to answer

that question.

These are the dry valleys

of the Antarctic,

one of the world's

most extreme deserts.

Here, beneath a layer

of dry dirt,

is buried ice similar to Mars.

If life can exist here,

could it exist on Mars too?

We're doing in the Antarctic

exactly what we want to do

on Mars.

We drill down

into this Mars-like soil,

we collect Mars-like ice,

and we look for what we hope

are Mars-like microorganisms.

NARRATOR:

At the point where the dirt

meets the ice,

the team discovers a thin film

of liquid water.

And when they look at the

samples under a microscope,

to their surprise,

there is something moving.

We're finding at the ice

there is life,

which is quite remarkable.

NARRATOR:

Microorganisms thrive

in this thin film of water,

but only for a short time.

McKAY:

They spend most of the year

frozen and dormant,

and they're only active

for a few weeks each summer,

when temperatures get warm.

NARRATOR:

On Mars, summer temperatures

at the equator

can reach 70 degrees.

Could the buried ice melt here

and create conditions

similar to those found

in the Antarctic?

McKAY:

We may be able to find

conditions

where the ice is

close enough to the surface,

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