All language subtitles for through.the.wormhole.s02e10.dvdrip.xvid-ingot

Freeman: Across the galaxy
lie exotic worlds...

some made entirely of water,

others stewing
with poisonous gas.

What kinds of creatures
thrive in these places?

Would they resemble
beings on Earth...

...or could life take on
new and unexpected forms?

What do aliens look like?

Space, time, life itself.

The secrets of the cosmos
lie Through the Wormhole.

They're out there.

We can see them.

For the first time
in human history,

we know the Universe is
filled with planets

stranger than we could ever
have imagined -

planets that might be home
to extraterrestrial life.

But what will
these creatures look like?

We're all products
of our environment.

If I was born on a planet
with carbon dioxide air

and gravity three times weaker
than the Earth's,

I might look like... this.

On a planet with five times
more gravity than Earth,

and a star that constantly
blasted it with solar storms,

I might look like this.

We can't know
the face of an alien

until we're staring at it.

But like detectives on the hunt
for an unknown suspect,

biologists and
planetary scientists

are beginning to
piece the puzzle together.

Some of the clues are out there,

but a lot of them
are right here.

To get home from
school every day,

I had to cut through the yard
of a scary, old house.

I never saw anyone come in
or out of it,

but someone or
something lived there.

I could only imagine
who or what it might be.

Harvard paleontologist
Andrew Knoll

has spent his life

studying creatures beyond
our wildest imaginations.

Knoll:
One of the things you learn

when you go through
a museum like this is

that not only is
it hard to imagine

what life might be
on another planet,

but it's hard to imagine
some of the life

that has existed on this planet.

Who would guess that there were
things like dinosaurs

in the absence of their bones?

Freeman:
For the past eight years,

Andrew has served
as mission biologist

on NASA's Mars Rovers.

It's a role
he's uniquely suited for

because of his expertise in
the vast array of life on Earth,

and his ability to read
the history of a planet

from its rocks.

Knoll: There's a tendency for us
to think about the Earth

in terms of the things
we see around us today.

But the one thing that
the geologic record tells us

is that there have been
a series of earths,

and that the Earth
that we see around us -

all the plants and the animals

and the composition
of the atmosphere -

are really an end-member,

the end state
of a long series of transitions

that have happened
over 4 billion years.

For example, this rock,

which formed
about 3� billion years ago,

is full of iron minerals,

which means that iron
had to be able to be transported

through seawater,
and it can only do that

in seawater
that contains no oxygen.

Freeman: The discovery of rocks
like this all over Earth

shows that for nearly
the first 4 billion years

of its existence,

our atmosphere
had almost no oxygen.

That Earth would have
been toxic to us.

Now, there are other things
that are sort of unexpected

when we actually look
at deep-earth history.

This rock was actually
deposited by glacial ice

about 635 million years ago.

There are rocks like this

that formed literally all over
the world at this time,

and it shows us
that there was glacial ice

at sea level at the equator.

In fact, much of the Earth -

perhaps most of the Earth -
was covered with ice,

sometimes called
a snowball Earth.

Freeman:
These various earths -

hotter, colder,
with more or less oxygen -

were essentially alien worlds.

So, for Andrew,
the best place to discover

what aliens might look like
is in our own fossil records.

Knoll:
These are trilobites.

Now, when you look at this,

you'll see things
that are familiar.

There is a jointed,
segmented body.

There are jointed,
segmented legs.

And you might say,

"Well, that looks like a shrimp
or an insect," and that's right.

Freeman: Biologists

call these repeated
similarities of life-forms

over Earth's history
"convergence."

One shape that works well

gets repeated
over and over again.

This giant sea creature
looks like a whale,

but it is actually
an extinct lizard.

Knoll: Repeatedly over
the last 250 million years,

vertebrate animals on land
have re-invaded the oceans.

And every time they've done so,

they've given rise
to these giant sea monsters.

Kronosaurus.

70 million years ago,
there were lizards in the sea.

They were equally large.

In our own lifetimes,
there's whales.

Freeman:
If Earth in the past

has been as alien
as planets orbiting other stars,

then aliens you've
seen in movies -

lizards with two eyes, two arms,
and two legs -

might be pretty close
to the mark.

Labarbera: I must admit,

I watch a lot of old monster
movies from the 1950s

specifically looking
at the physics

and saying, "No, no, no.
That's not gonna work,"

or "Ooh, that's really good."

Freeman: University of Chicago
Professor Michael Labarbera

is an expert in biomechanics.

He's trying to predict

how aliens will walk,
fly, and swim

by searching for the basic rule
of how animals move.

You could call it

the lowest common
denominator of locomotion.

Labarbera:
Things like horseshoe crabs

were crawling out on the beach
and laying their eggs

when pterodactyls
were flying in the sky.

One of the features that
we share with these animals

is a lever-type skeleton.

I have levers in my hands.

That's what allows me
to do that.

I have levers in my elbows,
in my shoulders.

The basic idea is

to use a lever that has
a high mechanical advantage,

that delivers a lot
of the muscle force

to the output side of the lever.

Freeman:
Successful designs

like jointed limbs
and hard skeletons

show up again and again
in the fossil record.

We see them all around us today,

and Michael expects to see them
on other worlds, too.

And it doesn't matter
whether the skeleton

is made out of hydroxyapatite
like our bones,

made out of chitin
like this animal,

or carbon nanotubes.

When a principle
is easy enough

for natural selection
to stumble across,

then it will evolve
over and over again.

On this planet,
it has evolved independently

at least half a dozen
different times.

And there's every
reason to believe

they will be just as common

in any other ecosystem
on any other planet.

Freeman: A torso with jointed
limbs acting as levers.

It's a good basic
anatomy of an alien,

but can we get closer
to imagining their true form?

In the 19th century,

Charles Darwin
kept a series of notebooks

chronicling how the shapes
of animals had evolved

to adapt to the
environments they lived in.

What would a book of life
on other planets look like?

What mind-bending,
anatomical adaptations

might develop
in alien surroundings?

The environment shapes creatures
depending on their ecology.

Density of the atmosphere,

whether or not you have
a world-covering ocean,

is gonna make a big
difference in the history

and, thus, in the shape
of the organisms.

Freeman: Which is why

to know what aliens look like,

we must learn more about
the planets they live on.

Until very recently,

we had no proof
other planets existed,

let alone any idea what
their landscapes or atmospheres

might be like.

But now, for the first time
in human history,

we can see worlds
far outside our solar system.

And now that we know
where E.T.s could live,

we're getting closer to
revealing their hidden faces.

If we want to know
what aliens look like,

we first have to know something
about the places they live.

Until recently,
this was impossible.

Our telescopes
could only see stars,

not the planets that orbit them.

Today, alien hunters have
a dedicated research ship

floating 20 million miles
from Earth,

and it's discovering new worlds
by the thousand.

Man: 3... 2...

Man # 2: Engines start.

Man: Zero.

And liftoff of the Delta II
rocket with Kepler.

Freeman: In 2009,

NASA launched its latest
space telescope -

Kepler.

It's designed
not to take pictures,

but to detect
the tiniest changes

in the brightness
of distant stars.

Its target area is a patch
of our arm of the Milky Way

stretching out 3,000
light-years away from us.

Harvard professor
Dimitar Sasselov

is one of Kepler's
lead scientists.

The beauty of how
the Kepler telescope

discovers planets
as small as the earth

is the method,

which we call
the transit method.

It's very easy to understand.

So, the planet
is passing on its orbit

in front of the star.

Its shadow causes that light
to dip just a little bit,

and that's how we know
there is a planet there.

Freeman: By the time Kepler
is done with its mission,

Dimitar expects
it will have found

around 100 planets
the size of Earth.

But the vast majority
of the planets it is finding

have almost nothing in common
with our world.

Sasselov: Kepler already has
a treasure chest

of weird planets,
if you will -

very interesting,
diverse planets.

So, we have Kepler-10,
which is as hard as iron.

Then we have
two or three planets

in the Kepler-11 system of six.

One or two of them
are water planets -

endless ocean.

Then we have planets

almost the density
of a beach ball or styrofoam.

Freeman: Perhaps the most
intriguing of Kepler's discoveries

are around 300 super-sized
versions of Earth -

planets made of rock,
but up to five times as heavy.

If anyone can imagine
the landscapes

where aliens might
jog, swim, or glide,

it's Diana Valencia.

Part-time triathlete,

she's one of the
first geologists

to break ground
on these super earths.

Valencia:
I do not have a hammer.

I do not break up rocks.

What I do is I do
numerical models

to understand
how the Earth works

and use that to understand

how bigger earths and
similar planets work, as well.

Freeman: To understand

whether the super earths
could harbor life,

Diana is zeroing in
on the basic geological engine

that powers rocky planets -

plate tectonics.

The movement of a
planet's hard outer crust

is driven by a hot
and viscous layer

of semi-molten rock below it

moving much like a jar
of bubbling honey.

This experiment here shows us
in broad lines what happens.

The mantle is
a very viscous fluid,

and both fluids are
very sensitive to temperature.

So, as we turn this heat up
to simulate Earth's engine,

you will start seeing motion
underneath the surface.

Now you see the overturn.

Now you start seeing things

that are moving
all sorts of directions.

It's not just moving up.

Freeman: As heat rises,

it forms convective cells
in the mantle,

which cause the plates
on the surface to shift.

These shifts trigger volcanic
eruptions and earthquakes -

events we associate
more with death than life.

But that's just
the short-term view.

From Diana's
geological perspective,

this cycling of material
from the inside of our planet

to the atmosphere has been vital
to the evolution of life.

Valencia:
Thanks to this process,

the surface temperature
of the Earth

has not swung very much,

and it has been around
that of liquid water

for over billions of years.

Freeman:
Super earths are bigger

and therefore hotter
on the inside.

And when you turn up the heat,

plate tectonics
kicks into a higher gear.

That may mean more volcanoes
and more earthquakes.

But also, a planet with
a much more stable temperature.

Valencia:
On super earths,

because convection
would be much faster,

this cycle could respond
much quicker -

perhaps an order
of magnitude quicker.

And then we can speculate

that that has enabled
the evolution of complex life.

Freeman:
Think about how a super earth

would have dealt with the impact

of the meteorite that
wiped out the dinosaurs.

On Earth, this event triggered
an extended global winter

that spelled the demise
of those cold-blooded giants.

But on a bigger planet,

better able to control
its temperature,

dinosaurs might survive

and have the chance
to evolve bigger brains.

However, there is
one major downside

to living on a giant version
of Earth.

The core of our world is
a spinning ball of liquid metal

generating a powerful
magnetic field.

That field deflects a torrent of
dangerous radiation from the Sun

and forms a protective cocoon
for all life here.

Diana's models predict

that super earths
may not have these force fields.

Valencia:
It's very possible

that these planets
do not have a molten core,

because their interiors
are under so much pressure.

So, if you are a
creature in a planet

that doesn't have
a geomagnetic field,

you are being bombarded
by high-energy particles,

and those are interacting
with your cells,

causing mutations, probably.

So, you have to be clever,
as an organism,

to adapt to those conditions.

Freeman:
What kind of alien could survive

on a radiation-soaked
super earth?

It would need
a protective shell,

perhaps laced
with heavy metals like lead.

It would have powerful limbs
and sharp claws

to let it burrow
under the ground

during heavy radiation bursts.

Most important, it would need

effective genetic
repair mechanisms

to fix the inevitable radiation
damage to its cells.

Pure fantasy?
Maybe not.

Similar life-forms,

albeit much smaller,
called water bears,

survive in boiling-hot,

radiation-blasted regions
on Earth.

Inhabitants
of rocky super earths

might look
surprisingly familiar.

But imagine a world
where there is no rock,

and where creatures
living in the ocean

also fly through the sky.

On Earth,

evolution has produced
countless variations on life -

animals that glide
through the water

and soar through the sky.

Beings that slither,
crawl, walk, and run.

If life on other worlds

follows the evolutionary
pattern of life here,

what other mind-bending
features might arise?

Okay. So, you got the planet,
you've got the atmosphere.

Exaggerated.

Yeah.

At MIT in Cambridge,

astrophysicist Sara Seager
and biochemist William Bains

are beginning to imagine

what these distant
worlds will be like.

The atmosphere's
gonna come from somewhere,

so you're gonna have volcanoes
producing atmosphere.

They're trying to predict how
a planet's size and composition

will shape its biosphere.

Before the discovery
of exoplanets,

people thought
that all planetary systems

would be like our solar system.

And since that time,

discoveries of exoplanets
and exoplanetary systems

have surprised us over
and over and over again.

So, what has changed?
Everything has changed.

Most science fiction assumes

that aliens are gonna
be walking around,

they're gonna be
breathing air.

You know,
they landed a starship,

and they shared dinner
with the captain.

You look at some
of the planetary environments

out there,

and that is not gonna happen.

It's gonna be
very different.

Freeman:
Recently, Sara and William

have been studying GJ 1214B,

a planet about 40
light-years away

that's more than twice
the size of Earth

and shows signs
of having an atmosphere.

Together they are working
to discover

what it might be like

to descend beneath the clouds
of 1214B.

Now, this planet -

we're not totally sure
what it's made of,

but it could be a water planet
with a steam atmosphere.

And depending on the
temperature of the planet,

the clean division
between liquid water

and air with water vapor in it
may not exist.

Freeman: What sort of life
could possibly emerge

on a boiling-hot, steam world?

Bains: So, on Earth,

an environment like this
with boiling water and steam

is inimicable
to nearly all life.

But we're trying to imagine
an alien world

in which this is
the normal environment,

and we can now start
to model a planet

that has a huge ocean
covering it

and nevertheless
is incredibly hot.

That makes us think about,

"Could there be life
in the ocean?

Can the chemistry work?

And if it can,
what would it look like?"

A molecule like DNA wouldn't
survive these conditions,

but William believes

more heat-tolerant
genetic material

would likely evolve.

And he's beginning to imagine

what entries might fill
the pages of a book of life

for GJ 1214B.

The atmosphere of this planet
would be mostly water.

It would be steam.

It would be very dense
and be very hot.

So, as you go down through it,

you'll find drifting plants,
flying plant life,

and a whole range of organisms
that eats that plant life.

Organisms would be
sort of flying fish

or swimming birds,
depending on how you look at it.

So, they'll be able
to actually fly through

or swim through this zone
almost as if it was ocean.

Freeman: Earth's oceans gave
rise to creatures of all sizes,

but the kings of the deep
are the giant filter feeders -

whales.

1214B could have them, too.

So, the organism
we're imagining here

works in a very similar way.

It might have
a very different shape.

But it moves through the ocean

and then can move up
into this interfacial zone.

They can spend much longer
in the interfacial zone

and move much further up into it
than, say, a whale breaching

because the density is greater.

Freeman:
This aquatic world is a vision

of what Earth
might have been like

if it were larger and wetter.

Humans couldn't survive here,
but could life find a way?

We don't know... yet.

There are many
important things in science,

and one of the most important
ones is imagination.

So, what is so fascinating
so far -

in exoplanets,
anything is possible

within the laws of physics
and chemistry,

and anything we imagine
will exist somewhere.

Follow the water.
There, you'll find life.

That's what the astrobiologists
like to say.

But what if there is no water?

What about planets
enveloped in toxic air

where the building blocks
of life

are completely different
from our own?

Could they also be alive?

Life is tenacious.

Everywhere on Earth,

from the coldest depths
of the sea

to the boiling fissures
of volcanoes,

living things find a way
to thrive.

But the conditions
on alien planets

could be even more extreme.

We're discovering
worlds of fire and ice,

worlds of permanent night,

worlds where hurricanes
are constant and global.

What kind of alien could live
in these hellish places?

Gliese 581D floats
20 light-years away from Earth

in the constellation Libra.

It's one of the small group
of planets we have spotted

that might harbor alien life.

Its red star burns

with only half the heat
of our Sun,

but because the planet
spins very slowly,

one side is much hotter
than the other.

And its rocky surface
is blasted by constant wind -

a great place to fly a kite.

Biomechanics expert
Michael Labarbera

believes the thick atmosphere
on Gliese 581D

would shroud the surface
in darkness,

so life would have to climb up
in search of light.

He imagines kite-shaped plants
that rise above the storm clouds

to get their daily dose
of solar energy.

These kite plants
have to be able to get up

into the higher regions
of the atmosphere

in order to get enough light,

and the way they do that is

to utilize the shear
in the atmosphere.

Freeman: Michael's kite
requires two forces

to stay aloft and stable -

wind to lift the kite,

and an anchor to keep it
from blowing ever upward.

The alien kite plant
works much the same way.

So, what we've posited
for this particular plant is

a lifting surface
on one end of the string,

and at the other end
of the string,

something that functions
like a parachute

that produces a drag force.

And because the wind changes
with altitude,

they're moving
at different speeds.

You then get a lift force
that keeps the kite up

and it pulls on the drag chute,

but that keeps the tension
on the string

and the whole system is stable.

Freeman: Sounds unlikely?

Michael doesn't think so.

Years of studying organisms
on Earth has convinced him

that life would evolve
to suit any environment.

Labarbera: Evolution goes
through very strange pathways

to get to an endpoint.

This particular one,

we don't have an example
here on Earth,

but on the planet posited here

with low solar input
for the ground level

and a high wind shear,

it's entirely possible
that it could function.

Freeman: Closer to the
surface of Gliese 581D,

the once bright sunlight dims

as this exoplanet enters
a permanent, hazy twilight.

The atmosphere
is thick and murky,

but warm enough to sustain life.

In fact, Michael
Labarbera speculates

that it could host
a thriving ecosystem

of hunters and prey.

What kind of predator
would evolve here?

An aerial hunter -
thin-winged and bat-like,

but able to soar and glide
for days like an albatross.

A... bat-atross?

Labarbera: Now, this animal,

because the atmosphere
is relatively opaque,

has to be able to travel
long distances at minimal cost

in order to find their prey.

It's got long wings.

It's got relatively narrow wings
because they're more efficient.

It has a big wing area
relative to its body.

Freeman: On Earth,

albatrosses use a technique
called dynamic soaring

to travel thousands of miles

while barely flapping
their wings.

Gliding in long loops,

the bat-atross
would also conserve energy

by letting air currents
carry it along.

Labarbera: The animal actually
covers many times the distance

in these loops that
it's covering on the ground,

but it doesn't matter.

It doesn't cost it anything.
It's free.

It's energy that's supplied
by the environment,

not by the organism.

Freeman: But how, in a world
of permanent twilight,

does this hunter find its prey?

In the absence of light,

there's got to be some other way
of locating prey.

One way is just to sit
and listen

and wait for your prey
to make noise.

The other way
is for you to make noise

and listen for echoes -
what we call sonar.

So that you send
a sound beam out

and you wait for a reflection.

I can get a lot of information

from the response of the ball
as it comes back.

So, the delay between when
I throw and when it returns

tells me how far away
the object is.

If it comes back faster
than I threw it out,

then the object
is coming towards me.

If it's going
in the other direction,

it will come back slower.

If you're looking for prey,
this is a wonderful idea,

unless your prey, of course,
can detect the sound.

Freeman: The bat-atross
would be an effective killer,

so its prey would need to
develop effective defenses.

William Bains imagines an animal

similar to the
hard-shelled marine life

that evolved on Earth

hundreds of millions
of years ago.

Bains: The nautilus is
natural prey for the hunters,

and they'll have
three defense mechanisms.

First is, of course,
they have a shell.

The second is if you're being
hunted by sonar,

then you develop very good ears
so you can hear sonar.

When you hear the ping
of a sonar, you run for it.

And it has a jet
propulsion system

that can squirt itself forward
in emergencies.

These guys will be able to

jet themselves
through the atmosphere

in short bursts,
moving very quickly.

So, at the last minute,

they'll jet to one side
and escape being eaten.

Freeman:
But even with these defenses,

the bat-atross would be
a fearsome opponent,

and the nautilus
won't always get away.

Labarbera:
It's life on the edge.

There always is a top predator.

It's the rarest animal,

but it's not the guy you want to
meet in a dark alley.

Freeman: Brutal conditions
breed brutal life-forms.

Here on Earth, over hundreds
of millions of years,

billions of different creatures
competed for survival,

but eventually, a special
mutation enabled one animal

to become the planet's
top predator.

That mutation
was the human brain.

Somewhere out in space,

alien evolution
should have created beings

at least as smart as we are.

What do intelligent
extraterrestrials look like?

This man thinks he knows,

and the answer could be
bad news for life on Earth.

With each new world we discover,

we come one step closer
to finding evidence

of life beyond Earth

and perhaps
to fulfilling our dreams

of communicating
with alien life-forms.

But if that day ever comes,

we'd better brace ourselves
for a shock,

because many scientists think

they may not look like
living beings at all.

For the past 50 years,

the search for extra-terrestrial
intelligence, SETI,

has attempted to capture
any glimmer of communication

from alien worlds.

For Seth Shostack,
SETI's senior astronomer,

it's a search for our
distant cosmic image,

for a species with a brain
at least as smart as ours.

When it comes
to intelligent life,

we haven't found it.

So, there are people
on all sides of the issue.

But the one thing
that can convince you -

I think can convince anybody -
is that even if you think

the processes
that could lead to life,

lead to intelligent life,

are not going to occur
very often,

there's so many chances
for it to happen in the cosmos,

it would be miraculous

if we were the only world
with intelligent beings.

Freeman:
Humans aren't the largest

or the fastest

or the most agile
animals on Earth,

but we are the smartest.

Our brains have put us on top.

There is, however, plenty
of room for improvement.

There's an unavoidable tendency
to think

that we're kind of
the crown of creation.

This is it.

You know, 4 billion years
of evolution

from the beginnings
of life to us.

You know, I think
if you asked the dinosaurs

the same question -

"Do you think you're
the crown of creation?"

I bet they would
have said "Yes,"

if they could have talked.

"This is it.
This is the end of evolution."

Well, they were wrong.

And it would be wrong
for us to think

we're the end of evolution,
too, obviously.

Freeman: So, where will
evolution take us next?

And where is it likely to have
taken alien civilizations?

Seth thinks we need to look
at our computers for the answer.

Since the 1970s,

when floppy disks
were the gold standard,

this speed at which
computers process instructions

has increased
more than 100,000 times.

Today, for $1,000,
you can buy a computer

that has, if you will,
the thinking capability -

or at least the computational
capability of a lizard.

Not so interesting.

But by 2020 or 2025,
$1,000 will buy you a laptop

that has the same computational
power as a human brain.

Freeman:
The IQs of artificial brains

are going from zero to 200

in the historic blink of an eye.

How would a similar
trajectory play out

on a planet that is
a mere 500 years ahead of us?

The interesting thing
about artificial intelligence,

of course,
is its pace of evolution.

I mean, we're stuck
with Darwinian evolution,

but the machines wouldn't be.

What it means is that if you
develop a thinking machine,

it's going to improve itself
very, very quickly.

Freeman: In 1948,
mathematician John Von Neumann

imagined a machine
so intelligent

it could make copies of itself.

Each copy would improve
on the previous model,

much as nature continually
improves on its designs.

But this machine's evolution
would take place much faster

than biological evolution.

Today, Von Neumann machines
exist in crude form.

On a planet more advanced
than our own,

could they be the most
intelligent life-form,

the dominant life-form?

Will our first contact be

with a race
of super-intelligent machines?

You're only gonna
hear from a species

that's at least as
clever as we are.

So, what are the odds that
they're within 50 or 100 years

of our level of development?

Pretty slim.

They're likely to be
thousands, millions,

maybe even more years
ahead of us.

So, if you think about that
for a moment,

you recognize
that if we do find a signal,

the odds are pretty good

that that signal's coming
from artificial intelligence,

not some soft, squishy, little
gray guy with big eyeballs.

Freeman:
On some distant planet,

the book of life may no longer
contain any biological forms.

And if mechanical life
has enough power,

there's no limit to how large
or complex it can become.

Shostack: Or maybe they've
reorganized themselves

so that they can share
the thinking load

amongst many members
of the species,

like distributed processing
with computers.

I mean,
why should the aliens be content

to be stuck
with a kind of intelligence

that can fit inside their heads?

Freeman:
Alien evolution

could produce
a living machine planet

throbbing with
the combined intelligence

of billions of alien minds.

If such advanced life exists,
how would we spot it?

And should we even want to?

Will aliens welcome us
as friends

or view us as threats?

Or perhaps see Earth
as a world to conquer?

We wonder what aliens look like,

but what do we look like
to them?

This woman has put herself
inside their heads,

and she believes
she has the answer.

As long as humans have
looked up at the night sky,

we have wondered whether
something or someone out there

is looking back.

We want to know
what aliens look like.

What do we look like to aliens?

If there is intelligent life
out there,

does the Earth look like a place
worth visiting?

May 29, 2008.

31 million miles out in space,

the eyes of a technologically
advanced race

scan our planet
for the signatures of life.

Not aliens, but this was still
a close encounter

of an extraordinary kind.

It was the NASA
space probe Epoxi.

Sent out to get closeups
of comets,

Epoxi briefly turned its lens
back to its mother planet.

And for the first time,

we saw the Earth
as aliens might see us.

Astrophysicist Sara Seager
was part of the Epoxi team.

Sara normally
studies exoplanets,

looking for clues

about alien atmospheres
and ecosystems.

The Epoxi probe gave her
the chance to find out

what Earth might look like
to an alien astronomer.

If you pretend you know
nothing about Earth,

what could you learn
about Earth?

An alien would be able to pick
out Earth's rotation rate.

They would be able to notice

that we have surfaces of
very different reflectivity -

that's cloud, land, and ocean.

And they could also see
that we have weather.

They would see variability

that isn't related to
the rotation rate of Earth.

The second thing Epoxi did was
look at a spectrum of Earth -

that is, take the white light

and split it up
into the different colors

and to check and see if any
of those colors were missing.

We call that a spectrum.

Freeman:
The spectrum of Earth's colors

are like a flag

announcing the presence
of life on our planet.

The blue of the oceans,
the white of the clouds,

the green of the land

are all markers
of an active ecosystem.

Seager: If an alien is looking
back at us from far away,

the aliens would see

that we have oxygen
in the atmosphere.

In fact, our atmosphere
has 20% oxygen by volume.

What's so fascinating is that,
without life,

our Earth would have basically
10 billion times less oxygen.

So, oxygen would be essentially
non-existent on Earth.

And oxygen on Earth
is created by life,

so those aliens would know that
oxygen in such large quantities

should not be in our atmosphere

unless it is being continually
produced by something.

And nothing that we know of
in geophysics

can produce so much oxygen.

And that's why
we attribute it to life.

Freeman: Aliens might see
that our planet supports life,

but they might not see

that Earth is
technologically advanced.

They would have to
look carefully

to detect things
like atmospheric pollution

or the heat signatures
of our cities.

Reading the colors of our world

and the millions of others
like it out in the Universe

would be easy for an advanced
alien civilization.

Unfortunately,
it is not yet easy for us.

Spotting exoplanets

pushes the limits
of current technology.

If we want to see colors,
we need a new set of tools.

Astrophysicist Dimitar Sasselov

wants to do
something about that.

Sheila:
These are little round planets.

I'm gonna just drop a few on
to show transiting planets.

I guess there's two transiting.

Dimitar's wife, Sheila,
paints scenes of deep space

inspired by his research on
the Kepler planet-finding probe.

This is the kind of thing
we want to discover with Kepler.

A transiting planet,
and there is a moon around it.

That would be great.

So, there it is.

That's the planet with life
on it - right here.

We have a big problem.

This challenge relates
to our inability to measure

the colors of the star
or the planets separately

to very high precision.

And the challenge is
about the factor of 10 to 100

beyond what
current technology works.

Freeman:
The biggest barrier we have

to seeing the colors
of other planets

is something every
photographer has run into -

camera shake.

If you take a picture
in the dark,

you need as much light
as possible,

which means you
can't move the camera

or you'll get a blurry image.

Earth-like planets
are so small and so far away

that their images only fill
one thousandth of a single pixel

of a digital camera.

If that pixel moves
even slightly,

the camera shake
will ruin the picture.

But how can you possibly keep
one pixel perfectly still

over the days and years it takes

to track an object
in distant space?

Dimitar's solution
is the astro-comb.

It uses lasers to keep
a telescope's camera sensor

precisely calibrated
over a period of decades.

Sasselov:
The astro-comb that you see here

is the technological
breakthrough

which was needed
to bridge that gap.

Freeman: When we see
the true colors of other worlds,

we will know where and
how life is distributed

across the Universe.

And the next phase of our quest
for alien life will begin.

Where will it take us?

What exciting, new worlds
will we see?

What new and unexpected
creatures might live on them?

Biologists think that life
out there might look earth-like,

but it won't look human.

With so many planets out there,
so many chances at life,

we could have human-like
relatives on a far-away earth.

Creatures like us,

perhaps as anxious
as we are to know

if they are alone
in the Universe.

As our tools improve,
so do our odds of finding them.

Sasselov: It is clear
that we're in a new age

of exploration and discovery.

It hasn't been for 500 years

that people have
tried to discover planets

around other stars.

Now we have them.

We have much more to explore,
and the best is yet to come.

1,000 years from now,

when people look back
at our generation and ask,

"What are the biggest
accomplishments?"

I like to think of these people
making interstellar journeys

and looking back and thinking

we were the ones
who started it all.

Freeman:
What do aliens look like?

What are the limits
of our imagination?

The true face of an alien

will probably defy
our scientific speculations.

But our efforts won't be wasted,

even if we do get
all the details wrong.

Our eternal intrigue
about alien life

and our persistent fear of it

both rise from
the same source -

the quest to
understand our place

in the family of life-forms
that populate the cosmos.

Know that,

and we'll know the
destiny of humankind.