Nova (1974–…): Season 45, Episode 103 - NOVA Wonders: Are We Alone? - full transcript

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What do you wonder about?

The unknown.

What our place
in the universe is.

Artificial intelligence.

Hello.

Look at this, what's this?

Animals.

An egg.

Your brain.

Life on a faraway planet.

"NOVA Wonders"... investigating
the biggest mysteries.



We have no idea
what's going on there.

These planets in the middle

we think are
in the habitable zone.

And making incredible
discoveries.

Trying to understand

their behavior, their life,
everything that goes on here.

Building an artificial
intelligence

is going to be the crowning
achievement of humanity.

We're three scientists

exploring the frontiers
of human knowledge.

I'm a neuroscientist

and I study
the biology of memory.

I'm a computer scientist

and I build technology



that can read human emotions.

And I'm a mathematician,

using big data to understand
our modern world.

And we're tackling
the biggest questions...

- Dark energy?
- Dark energy?

Of life...

There's all of these microbes,

and we just don't know
what they are.

And the cosmos.

♪♪

On this episode,

the hunt for alien life is on,
turning up mysterious clues.

The star loves attention.

And it makes everybody crazy.

That's not a planet.

So what is it?

What are the odds?

The ingredients for life
are everywhere.

The universe has
hundreds of billions of planets.

But does anything live there?

The chances of us finding life

is very high.

"NOVA Wonders"... "Are We Alone?"

Right now.

The planet Earth...

A ball of rock
about 8,000 miles in diameter.

We know there's a lot
going on here.

Almost eight billion people
call it home,

along with billions
of other species.

But is this the only place
where the action is?

Our sun is just one of
an estimated 300 billion stars

in the Milky Way.

And we think there are at least
100 billion other galaxies.

So what are the chances that
all the fun is only happening

right here in our tiny corner
of the universe?

♪♪

Today, astronomers and engineers

are building new tools
to probe our solar system

and our galaxy,

hunting for clues
of life beyond Earth.

What are they discovering?

I'm Rana el Kaliouby.

I'm André Fenton.

I'm Talithia Williams.

And in this episode,
"NOVA Wonders"...

"Are We Alone?"

And what will it take
to find out?

♪♪

A few years ago,
a group of amateur astronomers

discovered a mysterious star.

Located about
1,500 light years from Earth,

the star flickers erratically,
and no one knows why.

If a star dims
at regular intervals,

chances are it's caused
by an orbiting planet.

And typically it's only
by a fraction of one percent.

But the light from this star
is dimming by more, much more.

The thing about this star is the
light dims every now and again.

But it's being dimmed by 22%.

So that's not a planet...
That's much too much.

Even for a Jupiter-sized planet,
you don't get anywhere near

that kind of dimming,
so what is it?

Unlocking the star's secrets
becomes the quest

of Tabetha Boyajian,

a stellar astrophysicist.

Soon people are calling it
"Tabby's Star."

I worked with dozens
of other astronomers

for several years
trying to figure out

what could be causing

these strange fluctuations
in its light.

Is it caused by
an asteroid belt?

Or colliding planets?

So we had this
whole long list of ideas.

None of them worked.

Then, one of Tabby's colleagues

offers a possible idea,

a bit outside
the standard astronomy box.

When I showed him this star,

he said, "Wow, this is
really weird,

and we don't
have an explanation for it."

He said, "These things
all look like they could be

caused by some
artificial alien megastructure."

♪♪

An artificial
alien megastructure...

A giant structure built by a
hypothetical alien civilization

to harness the energy
from its own sun.

When the word gets out...

talk about the prospect
of an alien megastructure.

Evidence of alien life.

The strange light pattern makes
it seem more like a death star

planet rather than a star.

The star loves attention,
and it makes everybody crazy.

It is far-fetched.

To dim a star by so much,
an alien megastructure

would have to be at least
half as big as the star itself.

But when the theory
is first proposed,

astronomers can't rule it out.

The behavior of Tabby's Star
is quite weird.

Given that we have no idea
what's going on there,

I'm not too quick
to throw out theories.

Could this be
some alien megastructure?

We don't know.

Tabby and her team
will continue to study the star,

hoping to find more evidence.

For some people,
the idea that there's

a civilization out there
capable of building

a giant structure around its sun
would be a dream come true.

It's the same dream that fuels
our obsession with aliens,

whether they charm us...

I am Groot.

Frighten us...

seduce us...
Oh, no.

Or try to kill Tom Cruise.

Oh, man!

My God...

And it's not just the movies.

Even the Pentagon
recently admitted

that it secretly investigated
UFO sightings for years.

But what's the reality?

♪♪

Right now, as far as
technologically advanced life

goes, we have a sample size
of one...

Us.

In fact, when it comes
to any form of life,

whether it looks like this...

or this...

or this, the only examples
we know of are right here

on Earth.

And the truth is, if we found
even one other example

of this kind of life,

it would be
the biggest scientific discovery

in our lifetimes.

So where do we start to look?

♪♪

In 2009, NASA took a major step
in the hunt for life

beyond earth, launching
the Kepler space telescope

to track down signs
of earthlike planets

beyond our solar system.

♪♪

Up until then, astronomers
had found about 300 exoplanets.

But few were
anything like Earth.

Small, rocky planets like ours
are not easy to spot.

Planets are literally lost in
the glare of their parent stars.

The brightness difference,
the contrast between

a star like our sun and the
Earth that's right next to it

is ten billion to one.

So instead of hunting for light

reflecting off
a planet's surface,

the telescope focuses
on starlight.

What Kepler did was look in
a part of the Milky Way galaxy

where we had lots of stars
in a small field,

and it just took pictures
over and over again.

And, occasionally,
if those stars have planets,

then sometimes those planets
would come in front of the star.

As the planet comes around,

it's going to block
part of the star,

and that light won't get to you.

And so that constant level
that you see from the star

suddenly goes down just a bit.

So these momentary
dimmings of light

that repeat once every orbit
are indicative

of a planet orbiting a star.

Astrophysicists like
John Asher Johnson

and his team at Harvard
use Kepler data

to estimate
an orbiting planet's size

and distance from its star.

The dips are pretty deep, so it
must be a fairly large planet.

Deep dips in the star's light

mean the planet is really big,

or the star is really small.

The spacing between those,

what is it, like, a day or two?

And frequent dimming

means gravity has drawn it
close to the star,

making the planet really hot.

Feels pretty much like
a classic hot Jupiter.

A giant broiling
ball of gas like this

would not be a great spot
for life.

So the team looks for signals
that are more subtle.

Looking at this,
it doesn't look like much.

But it looks like there is some
kind of periodic signal there.

So what do we know?
We know the thing is small?

It's blocking out
less than a percent of the light

that we're receiving.

Something is causing the star
to dim ever so slightly,

and at longer intervals.

Could this be a small planet
closer to Earth's size?

And the distance from its sun
suggests temperatures

potentially
comfortable for life.

This is really interesting.

I mean, this exactly
the kind of thing

that we're looking for.

This could be a rocky planet

somewhere near
the habitable zone.

Yeah, this is really exciting.

Yeah.

The discoveries coming from
Kepler have been astounding...

Nearly 3,000 confirmed planets
so far.

The Kepler Space Telescope
blew open our understanding

of planets.

We have found lava worlds.

We've got planets
that are orbiting not one

but two stars.

We have found planets

that may be covered
entirely in liquid water.

And some of these planets
are Earth-sized,

with temperatures
potentially ripe for life.

Kepler allowed us
to see the sheer numbers

and the absolute commonness
of Earth-sized planets

throughout the galaxy.

And so the chances of us finding
life elsewhere, in my view,

is very high.

In fact, using the small sample
of sky observed by Kepler,

astronomers now estimate that
there are tens of billions

of planets in our galaxy
the same size and temperature

as Earth.

These planets could have liquid
water on their surfaces.

Their rocky cores could hold
the building blocks of life.

And their stars should provide
plenty of energy.

But does that mean that life
would thrive there?

Turns out that could depend
a lot on the star itself.

Planets are really at the mercy
of what happens to the stars

that they're orbiting around.

Dad, can you walk slower, maybe?

Jason Kalirai is
a stellar astrophysicist.

What are you guys excited
about seeing today?

I'm excited about seeing Saturn.

Saturn should look amazing...

An expert in
the behavior of stars,

he knows the profound influence
they can have

on orbiting planets.

So by studying those stars,
we can figure out

what kind of planets might be
most suitable for finding life.

All right, so here's
our main mirror.

Do you guys remember
what this is called?

The first mirror?

Primary mirror.
Oh, primary.

Jason's curiosity

about the cosmos started early.

As a young kid,
one of the things

that I found most exciting
was trying to figure out

how the universe works.

Countless times, I would be
in our backyard looking up

at the night sky, wondering what
part of the universe I'm seeing.

Jason had clear views of the sky
in British Columbia,

where he grew up.

His parents moved there from
Punjab, India, in the 1970s.

If they had stayed in India,
I would not be an astronomer.

That's just the way
the system is.

But in Canada, I could take
a liking to whatever I liked,

and as a very young kid,
I liked astronomy.

And when I wanted
to become an astronomer

and see that through,
there was nothing stopping me.

Today, he shares
his love of astronomy

with his twin daughters

Suriya and Mira.

Are there any people
on different planets?

So there's lots of stars
in the universe.

And so all of those stars
have planets around them.

So on one of those planets
right now there might be a dad

with his two daughters on a farm
looking up at the night sky,

asking the same question.

OMG!

I love showing my daughters

the night sky
through a telescope.

Is that Saturn?

Because you see

so much more out there that's
otherwise invisible to us.

Is that cool?

Yeah.

That instills that curiosity

to want to go
and find out those answers.

And with astronomy,
they'll never be satisfied,

because it'll always just
throw more questions at you.

♪♪

Jason pursues his questions
about the cosmos

at the Space Telescope Science
Institute in Maryland.

And when it comes to
the search for alien worlds,

he focuses on the kinds of stars
that might be friendliest

for life.

Because not all stars
are created equal.

When we look up
at the night sky,

we're seeing just
the brightest beacons of light.

It's not representative of
the true distribution of stars,

which contains many more
lower-mass stars...

Stars much smaller than the sun.

These low-mass stars,
sometimes called red dwarfs,

are smaller and cooler
than our sun.

And while our own sun will burn
out in about five billion years,

red dwarves could burn
for trillions of years.

Across the Milky Way galaxy,
red dwarves probably host

billions of planets,
many of them small and rocky,

like Earth.

So how likely is it these
planets host life?

One group of planets
just 40 light years away

has enticed scientists like
Jason... the TRAPPIST-1 System.

One of the biggest discoveries
in the last few years

was the discovery
of the TRAPPIST-1 System.

This is an incredible star.

TRAPPIST-1's seven planets
are all close to Earth-size,

and circle it in tight orbits,
like a condensed version

of our own solar system.

These planets

take a few days
to go around their star,

and they're only located
a couple million miles

from their star.

TRAPPIST-1's innermost planet

orbits its host star
every one and a half days.

It's 90 times closer
to the TRAPPIST-1 star

than our Earth is to the sun.

And so it's going to be
very hot on that planet.

Though not a lava world,
it's too hot for liquid water,

or for life as we know it.

The other end of the extreme,

We've got Planet H, which is
going to take about 20 days

going around
the TRAPPIST-1 System,

which is a huge amount of time,
given how faint

the TRAPPIST-1 star is.

And so it's going to be
very cold.

Any water here
is likely frozen solid.

But a few TRAPPIST-1 planets
seem to orbit

in the Goldilocks zone...
Just right, with temperatures

that could be similar
to those on Earth.

We think these
planets in the middle

are in the habitable zone.

Conditions are going to be
just right

where liquid water could exist.

When the discovery
was first announced,

hopes were high that some of
these planets might harbor life.

But Jason is more skeptical...
Not because of the planets,

but because of the star.

♪♪

Red dwarfs may be small and
cool, but they are also

more violent and volatile
than our sun.

These are generally

pretty active stars.

These exhibit a number
of solar flares

where there's material
that can impact a planet.

This material carries
enormous amounts of radiation,

many billions of
hydrogen bombs' worth...

Enough to destroy
the cells of any living thing

on a nearby planet.

Jason fears these
radioactive solar flares

could wipe out any life
that might arise

in the TRAPPIST-1 system.

It's actually unclear
whether or not

the conditions necessary
to sustain life

and the time that life needs

to develop are going to be

stable on these planets.

Jason isn't giving up on planets
that orbit red dwarfs,

but he does worry
that life there may be

so different from our own,
we might never recognize it.

I have no doubt

that planets that are
very different from Earth

and stars that are
very different from the sun

will still lead
to different types of life.

But we don't know
what we're looking for.

So the simplest experiment
is to try and find life

that resembles the life that
we understand well on Earth.

So can we find a twin...

An earth-like planet

orbiting a sun-like star?

Kepler tracked down a few,
but they're more than

a thousand light years away.

How can we find more,
and closer?

Luckily, a new detective
is joining the hunt...

NASA's transiting exoplanet
survey satellite, called TESS.

TESS will now do
a survey of all the nearby stars

so that we can find the very
closest planetary systems to us.

The telescope's four cameras

will observe some 200,000 stars,
many big and bright

like our sun.

TESS will take a snapshot,

and will image all the stars
along the strip of the sky,

and then it'll move on and do
the next set of stars,

and the next set of stars.

That's when there's going to be
this firehose

that's going to turn on.

All of a sudden,
we're going to get data

from all the closest stars.

Data that could translate into
thousands of nearby planets...

Including a lot like our own.

We could soon find ourselves
surrounded

by potentially habitable
neighbors.

But then what?

If we find a nearby twin,
could we ever know

if life exists there?

The very closest
potentially habitable planets

are a few light years away.

That's about 25 trillion miles!

Even if we built a spacecraft
that could travel

a million miles an hour,

it would take about
3,000 years to get there.

But even if we can't go there,
it might be possible

to find evidence of life
on a faraway planet

in effect by sniffing
its atmosphere.

♪♪

I mean, we'd all love
to find an alien.

We'll just be lucky
to find anything at all.

So at this point,
it doesn't matter what it is.

We just want to find
some sign of life.

MIT astronomer

Sara Seager thinks that sign

will come in the form of gases
in a planet's atmosphere

called biosignatures.

We call a gas a biosignature gas

if it's a gas
that's produced by life

that accumulates
in the planet atmosphere.

About two-and-a-half
billion years ago,

life on earth began pumping out
a powerful biosignature.

Colonies of bacteria
like these stromatolites

started producing oxygen,
like plants do today.

Now, our atmosphere
is roughly 20% oxygen...

A telltale sign of life.

But how could we ever study
a distant planet's atmosphere,

and detect what gases it holds?

If the planet and star
are fortuitously aligned,

that starlight can shine
through the planet atmosphere.

Different gases will absorb
starlight in different ways.

It turns out that each gas

has its own specific way
of interacting with light.

♪♪

We're all familiar
with glowing colored gases...

They're what light up

the neon signs of cities.

In this tube, for example,

there's mercury showing up
as a blue.

I can change that out
for another gas.

This one is helium.

It looks orange.

When Sara splits the light,

she can see even more detail.

Each gas has a unique
light signature.

These signatures could tell Sara
about the gases

in a planet's atmosphere... gases
that could be signs of life.

But to see them, she'll need
a very powerful telescope.

In 2020,

NASA plans to launch
the James Webb Space Telescope...

The most powerful
spaceborne telescope to date.

The James Webb Space Telescope

has a 21-foot gold mirror
so it can make exquisitely

sensitive measurements

of the atmospheric composition
of other planets.

It makes those measurements
with the help of a device

called a spectrometer,
which, like a prism,

divides light
into constituent colors.

This helps scientists like Sara
identify gases

surrounding a planet.

♪♪

We hope to see gases
like water vapor

on a small rocky planet,
which would indicate

liquid water oceans.

We'd like to see

methane and other gases.

And some of these
on their own or together

would help make the case
for life on another planet.

But even with those gases,
the case might be missing

a crucial piece of evidence.

Those are pieces of the puzzle,

but that puzzle will be
incomplete

until we detect oxygen.

Astrophysicist
Mercedes Lopez-Morales

wants to find oxygen
in another planet's atmosphere.

Remember, Earth got
most of its atmospheric oxygen

only after living creatures
started pumping it out.

But oxygen has a faint signal,

and might be difficult for
the James Webb Space Telescope

to spot on distant planets.

So Mercedes is pinning her hopes
for finding oxygen

on a new telescope being
constructed in a unlikely place.

Underneath the football stadium
at the University of Arizona,

scientists are turning
seven massive slabs of glass

into gigantic mirrors.

This is an 8.4 meter in diameter
mirror that is today

the largest one-piece mirror
that humans can build.

When completed, the mirrors,

each weighing 20 tons,

will travel to a mountain
in Chile, where they will be

assembled into
the giant Magellan telescope...

A mega-telescope expected to be
ten times stronger

than the Hubble Space Telescope.

That power will come from
the near-perfect shaping

and polishing

of seven mirrors
joined into one.

We need to polish this mirror
very, very finely.

Each mirror takes more than
three years to polish

to within 20 nanometers.

That's at least
1,000 times smaller

than the width of a human hair.

Every time I see
one of these mirrors

I see this big bucket
that is collecting light for me.

And the bigger the bucket,
the more light I can collect,

and the easier it will be
to detect oxygen

in an earth-like planet.

The giant Magellan telescope

is going to be
a game changer for us.

The GMT is scheduled
to start hunting for oxygen

on other planets
within the decade.

Technology moves very quickly.

I think we will find life
on another world.

We will find a signature
that's a smoking gun

for life on a nearby planet.

But could we find
more than a smoking gun?

While some alien hunters
set their hopes

on the next generation
of telescopes

to spot life from afar,

some explorers
are searching for E.T.

much closer to home.

Astrobiologist Kevin Hand
is hunting for life

in our own solar system.

But the aliens he dreams of
are very different

from the ones in the movies.

He's looking for a kind of life
that could thrive

in some of the harshest
places on earth.

♪♪

So here we are sitting on

a red-hot blister
on planet Earth, a volcano.

At Lassen Volcanic
National Park in California,

temperatures in these springs
rise to nearly

200 degrees Fahrenheit...

Deadly to most forms of life.

This particular
bubbling hot spring, of course,

does not look like
a good place for life.

It's not a good place

for me, this tree,
or any large creature.

And yet, if you look closely,

the pools are literally
teeming with life.

It's just very tiny...

Microbes.

What's amazing about microbes

is that they can survive
in a variety of different

harsh and extreme conditions.

For example, all of the green
that you see here,

these are microbes
that are doing photosynthesis,

thriving off of
energy from the sun.

♪♪

But not all microbes
need sunlight.

In this stream that's coming
from one of the hot springs,

we've got microbes
that are surviving

on all the compounds
dissolved in the water.

These microbes
don't need sunlight.

♪♪

Kevin thinks he might

find creatures like these

lurking not too far from Earth.

These are the kinds
of life forms

that we think could
potentially inhabit

the deep, dark oceans
of other worlds.

But what oceans?

None of the other planets
in our solar system

have liquid water oceans
on their surfaces.

So, astrobiologists like Kevin
are laying their bets

on two balls of ice that aren't
planets at all, but moons:

Enceladus, a moon of Saturn,

and Europa, a moon of Jupiter.

At first glance,
both appear to be barren.

But cracks on the surface
reveal activity below.

Extreme gravitational forces

created by their
massive parent planets

could be be causing the moons'
rocky cores to heat up.

And when you put together
heat and ice...

Because of frictional heating

of the ice against
the solid core,

you get the formation
of subsurface oceans.

Scientists now believe

that the ice on both moons
covers hidden oceans below,

with Europa holding more water

than all of Earth's oceans
combined.

And here, deep in the oceans
of these tiny moons,

could lie all the fundamental
ingredients of life.

If you have ocean water

coming into contact with rock
at elevated temperatures,

you'll get energy for life
that's not coming from the sun,

but from chemical reactions.

Worlds like Europa
and Enceladus,

where we've got good evidence

for vast, global,
liquid-water oceans

could be where a second
origin of life occurred.

Kevin thinks
there's a strong chance

that life could exist on Europa,
the larger of the two moons.

But how could you ever find it?

You wouldn't want
to go to Europa.

It'd be a beautiful view
of Jupiter,

but as soon as you stepped out
of your spacecraft, you'd die.

It's -280 degrees Fahrenheit,
there's no atmosphere,

and then the radiation
that would rain down onto you

would kill you within a matter
of tens of minutes.

Astronauts won't be attempting

to skate across Europa's
icy surface anytime soon.

So, NASA is studying ways
to send a robotic probe

nearly 400 million miles
to the bright moon

to hunt for traces of life...

But not before we know
what to look for.

If Europan sea creatures,
even microbes, existed,

and made their way
to the surface of the ice,

their cells...

And anything resembling DNA...

Would be heavily altered
by radiation.

But Kevin thinks we can hunt
for remnants of life

in the form of amino acids,
the building blocks of proteins.

So, if we found
amino acids in ice,

that could be
a pretty strong sign of life

within that ocean.

But how likely is it

that traces,
in the form of amino acids,

could survive on the surface

and be detected
by our spacecraft?

To figure that out,
Kevin and his team

are replicating some
of the conditions

on the icy moon right here

at NASA's Jet Propulsion
Laboratory in Pasadena.

In this latest test,

Kevin's molecular guinea pig
is glycine,

the simplest amino acid,

found in every
living thing on Earth.

We're mixing glycine
in with water

to kind of replicate what
could be in Europa's ocean,

were it to have life.

The mixture goes
into a stockpot,

a witch's brew
of water and salts.

Over three weeks,
Kevin pummels the glycine

with the sub-zero temperatures
and dangerously low pressure

you'd experience
on Europa's surface.

Finally, it's time to find out

if any glycine
survived the ordeal.

Okay, well, we've definitely

cooked up something
interesting in here.

If the amino acid
is completely destroyed,

the odds of finding
some sign of life

on Europa's surface
are slim to none.

It doesn't look like ice.

It looks like a very solid
but soft surface.

This is almost like

a creme brulee, I think.

Going in...

Ooh! Interesting.

Do you feel like there
was a... a tough crust?

No, no, it's very powdery.
Oh, look at that.
Hmm.

Kevin was expecting
a hard, icy shell,

but he's surprised to see
that the ingredients

have frozen into a thick powder.

You can see it's almost like

a layered, feathered material.

Now for the real test...

Kevin probes the ice with
a spectrometer,

using light
to seek out and measure

glycine's unique signature.

Can a simple amino acid...

A single building block
of life...

Withstand the harsh environment

of Europa's surface
and be detectable?

Get in nice and close

and we'll get
the maximum signal.

And like a beacon, it appears...

A small but clear
signal of glycine.

It means that if there is
microbial life

in the oceans of Europa,

we might be able to find

some of its building blocks
on the moon's icy surface.

Is this what the signal of life

on a distant world
might look like?

We just don't know.

The next thing to do
is launch a spacecraft

and go look for it

out there in the solar system.

Finding amino acids
on Europa's surface

would be encouraging,

but what we really
want to know is

what might be swimming
around in Europa's vast oceans?

Could there be microbes?

Like the ones that
dominated Earth's own oceans

for billions of years?

Or something more complex?

If we want to find out,

Then we need to send
a mission much deeper,

down through the ice and into

the pitch black oceans below.

But how do you prepare
for such an ambitious trip,

to a place unlike
anywhere on Earth?

♪♪

Engineer Bill Stone believes
he has the answer.

If you ask me
what is exploration,

it is the process
of putting your boot

in a place where no one
has ever been before.

Bill's "boot"

is an underwater vehicle
named Sunfish,

his prototype for
an ocean-exploring robot.

It might not look like much,

but if there's something
swimming around on Europa,

a miniature version
of this robot

could be the first to spot it.

It will be one of
the greatest intellectual feats

of humankind
if we pull this off.

NASA is studying

how to get to Europa's surface
in about 15 years.

Bill is planning for
a much more ambitious journey...

Fly a robotic lander

400 million miles to Europa
and land on the surface.

Bore through an ice cap
some ten to 15 miles thick,

then release an autonomous
underwater vehicle to explore

the mysterious ocean below.

Once you get through the ice,

Sunfish will go out
and map, explore,

and look for life.

This wouldn't be

the first robotic mission
in our solar system.

♪♪

Mars rovers have explored
the red planet

by following commands
that come from Earth,

34 million miles away.

That's not possible on Europa,

which is roughly three times
as distant as Mars.

The problem is there's
a two-hour delay

light travel time
between Europa and Earth,

so we can't sit there
and joystick something.

This robot must be able to think
and explore all on its own...

Or else it won't be able to see
much of the Europan ocean,

and the mission
to Jupiter's moon

could be a wasted opportunity.

Where would you like us

to position the robot?

To do that, it needs practice.

Here we go, heading east...

We're at Peacock Springs State
Park in northern Florida,

because there is
an underwater labyrinth, a maze.

The ground in
this part of Florida

is riddled with winding,
water-filled caves.

Can Bill's robot negotiate

this confusing environment
on his own?

A team of experienced
cave divers

tags along in case
the robot breaks down.

Other than that,
the robot is virtually alone,

using sonar to explore and map

its surroundings, inch by inch.

The robot doesn't know
anything about this cave,

and so it is learning
to explore as it goes.

So we're at 21, 33...

So, 240 points us
down the tunnel.

Things seem to be going well,

until, in one narrow cave,
Sunfish stops.

It suddenly seems confused.

It's drifting a lot.

It is.

What do you do
if something goes wrong?

What's your procedure?

All that has to
go into the code.

Zero, zero, 240-D...

A few lines of code
outline a new strategy:

back up and remap
from a different angle.

♪♪

This time, the robot succeeds.

♪♪

It's achieved the goal

and turning back.

This is a small step
that could one day

lead to giant leap in the search

for life beyond Earth.

If there's going
to be life on Europa,

there is no reason why we can't

have life somewhere else
in the universe.

Be the first validation
that we aren't the only ones.

So, from that standpoint,

it's going to shake
a lot of ground.

If we found evidence of life
on Europa,

even if it were just
a teeny, tiny microbe,

that would be huge!

All it needs is for one microbe,

that is life,
but not as we know it

to make the point

that it can't be that hard
to get going.

Just one microbe.

The importance of that
is to say, "Guess what?

"Biology's not very hard.

"It's an infection
in the universe, right?

It's all over the place."

If a galaxy oozing
with pond scum

doesn't seem too exciting,
then remember...

Over a few billions years,

these tiny creatures evolved
into all the plants and animals

that swim, crawl,
and fly around our planet,

including us.

So, could the same thing
happen somewhere else?

What do we think aliens that
evolved on another planet

would be like?

Flying saucers have
invaded our planet...

In lots of movies,

aliens look remarkably like us,

with two arms and legs...

Only you of Earth,
you and your women,

can give us life.

Get back or I'll fire.

You fool.

And, of course, those eyes.

From the standpoint
of Hollywood,

the aliens tend to be

these little gray guys
with big eyeballs,

and, you know,
no sense of humor,

and no clothes, by the way.

They seem very dispassionate.

They don't seem to get angry,
they don't seem

to have a lot of fun, either.

Come on down,
Mr. Ambassador.

Science fiction aliens usually

have something else in common
with us: intelligence.

But what are
the chances that life...

If it did arise elsewhere...

Would evolve into creatures
with big brains?

After all, aren't we the only
smart ones on this planet?

Come here.

Some biologists would say no...

Good job, buddy!

And they're not just talking

about our closest relatives.

From dolphins,

to birds,

to even the octopus...

A creature more closely related
to snails and clams than to us,

but smart enough to use tools
and open jars...

We're not the only animals

who've evolved
impressive brains.

Of course, none
of these creatures

will build a spaceship
anytime soon.

But for many scientists,
the idea that

we're the only technologically
advanced creatures

in the universe

seems a bit, well, presumptuous.

We used to think the earth

was the center of the universe,
that was wrong.

Then we thought the sun
was the center of the universe,

and that was wrong.

Then we thought our galaxy

was the center of the universe,
and that was wrong.

Every time we've thought we were
really special, we were wrong.

And so, the idea
that we're somehow special

in terms of being alive
or being intelligent,

I mean, that's
probably wrong, too.

I find it extremely hard
to believe that

in the vastness of our universe,

that a rocky planet that harbors
intelligent, sentient life

happened just once.

♪♪

Some scientists have spent
their entire careers

hunting the vast emptiness
of space,

trying to pick up a signal.

I always just took for granted
that there would be

other stars that would be suns
for other creatures,

and that just seemed to me
the natural way of the world.

More than three decades ago,

astronomer Jill Tarter
co-founded the SETI Institute,

dedicated to the search
for extraterrestrial intelligence.

It's been amazing
to be able to spend

a career on a question
that I'm fascinated with

and a question
that everybody else out there

is curious
to know the answer to.

She was the inspiration

for the character
Dr. Ellie Arroway

in Carl Sagan's book "Contact,"

which was adapted
to a feature film in 1997.

Today, SETI conducts searches

with the Allen Telescope Array,

a network of 42 radio telescopes
in Hat Creek, California.

The telescopes comb the skies
for radio waves,

which can carry signals

and information across
the great distances of space.

Radio waves are an excellent way
to communicate

because they cut through
the atmosphere of our earth

and also cut through
the space between the stars.

In fact, we've been sending out

our own radio waves since

the dawn of broadcasting,
about a century ago.

Good morning, honey.

If any aliens are listening,

their ideas about earthlings

could be based on
"The Dick Van Dyke Show."

I said, how's my old lady?

Well, I don't know,

I haven't spoken
to your mother lately,

but I'm fine.

The hope of SETI

is that some aliens
might also be broadcasting.

The idea is that

if life has sprung up
on some other worlds

and it's technological life,

in other words,
they've, you know,

they've learned
a little bit of physics,

they build some equipment,
this, that, and the other,

they could build
radio transmitters

that are sending
signals into space

that we could pick up here.

At Hat Creek, the telescopes

listen in on millions
of radio channels at a time,

looking for unique patterns

that could be
alien transmissions.

When something shows up

that we don't think
is interference,

something that
we've not seen before,

immediately we follow up
on that signal

to try and figure out
what it is,

and whether it's, in fact,
our technology

or potentially someone else's.

But unique signals are rare...

Just one or two a year.

And so far, even
the most promising ones

have turned out
to be human interference.

Still, the event
that SETI is waiting for

could happen any day.

Okay! Point source confirmed.

Whatever it is, it ain't local.

While Hollywood has fantasized
about this moment of discovery,

it's harder than it looks.

The Allen Telescope Array
can only listen

to a few hundred million
out of billions

of possible radio frequencies
at a time.

We haven't yet figured out
how to look at all the sky,

all the time,
at all frequencies,

but that's ultimately
what we want to do.

In fact, we've been listening

for nearly 60 years,
and so far... crickets.

But the fraction of stars
we've searched carefully

and the amount of time
we've been listening

are still both quite small.

So plenty of people
remain hopeful

that technologically advanced
civilizations are out there.

And that's why
the mysterious dimming

of one particular star
was, for some, so tantalizing.

♪♪

In 2015, astronomer
Tabetha Boyajian

and her colleagues
published their findings

about a very weird star.

According to data
from the Kepler Space Telescope,

Tabby's Star was dimming
at strange, irregular intervals,

sparking theories
about an enormous structure

built by a hypothetical
advanced alien civilization.

The buzz spurred more research.

Today, a worldwide network

of powerful
ground-based telescopes stare

at Tabby's Star
around the clock.

We can actually process the data
in near real-time,

and when we see something
start to happen, we can trigger

more intense observations

of what is passing in front of
the star at that time.

For a while,
the star was silent.

Then, suddenly, it started
dimming erratically again.

The ground-based telescopes
provide information

about the star
that Kepler couldn't see.

Not just the dimming
of the star,

but how those dips
in brightness appear

in different colored
wavelengths.

Something is happening
with our star here...

We sent off alerts via Twitter

and data of all sorts
started coming our way.

At this point,

it's like we're swimming
in data.

Tabby and her team
at Louisiana State

are looking for patterns

in the color data

that could tell them
what kind of material

is passing in front of the star.

Blue light and red light
will react differently

to material that's passing

in front of the star,

and you'll have
a different signature

in how far down these dips go.

Whatever is passing
in front of Tabby's Star

appears to be blocking
more blue light

than red and orange light.

But what would block out
more blue light?

Tabby has a theory:
space dust.

Dust scatters blue light

more than it does red light.

And so, that indicates

that there's some sort of dusty,

semi-opaque, you know, material

that's crossing
in front of the star

and blocking out the light.

It's got the signatures

of being dust, rather than...

it can't be some kind of
completely opaque object,

like a planet or
an alien megastructure.

That's right.

The culprit is likely
scattered dust,

and not a solid
alien megastructure.

But the mystery
is hardly solved.

What created
this giant cloud of dust?

Why is it centered
around Tabby's Star?

Astronomers will need more data

if they're ever going
to crack this one.

Nature is a lot more creative
than we are,

and you know,
we're just going to have to,

you know, really buckle down

and try and, and,
and figure this one out.

Tabby's Star is one
in a long line of mysteries

that at first raised hopes
for finding E.T.,

but later were revealed

to have solutions
unrelated to life.

For some, the lack
of firm evidence is troubling.

In 1950, physicist Enrico Fermi

went to lunch
with some colleagues

and asked a simple question:

"Where is everybody?"

If there are billions of
habitable planets out there,

and life is common...

Why haven't a bunch of aliens

already shown up
on our doorstep?

What could explain the silence?

For some, the quietness
of the cosmos

is evidence that
we really could be alone.

But many astronomers disagree.

The idea that there's
intelligent life out there

that has never
interacted with us

or that we've never seen it...

That, to me,
is not confusing at all.

I mean, I think that's
perfectly consistent.

You know, it's no different than

a child looking at an ant farm.

The child is not going to be

compelled to interact
with an individual ant

and more so, the ants
probably don't even know

that the child
is analyzing the ant farm.

And so there's very likely
intelligent civilizations

out there that
may be looking at us.

But what do they have to gain
from interacting with us?

We might be very

basic and insignificant
compared to them.

Or perhaps interstellar travel

is too challenging,
even for super-smart aliens.

Or maybe they did exist,

but ended up
destroying themselves.

♪♪

For many, the universe
is simply too large.

Too many stars,
with too many planets.

Too many potential homes

for creatures
that might start small,

but could, like us,
thrive and grow.

The universe is mind-boggling.

It's bigger than
what we humans can actually

wrap our consciousness around.

The universe has hundreds
of billions of planets

in hundreds of billions
of galaxies.

So it just seems like
when you roll the dice

many, many times, one of them
is going to luck out.

We live in a groundbreaking era.

We might be the first generation

that will be able to say

that there is life elsewhere
in the universe.

Our young people

have a much greater opportunity

to see themselves as earthlings.

But we also could find out that

to the best
of our ability to measure,

we really are alone.

If it turns out
that Earth is rare,

then that's all the more reason
to look after what we've got.

Because if we destroy ourselves,
the flame of mind

and the flame of culture
will be snuffed out for good.

I hope that we aren't
the only things out there.

There's gotta be something else.

You know, there's just
a lot of room up there.

It's hard to believe that

everything interesting
is down here.

It just never struck me

as a very reasonable
point of view.

Are we alone in the universe?

Not a chance.

♪♪