Space's Deepest Secrets

In a sky full of stars,

one deeply mysterious light

has set the world of astronomy on fire.

Stars simply do not behave like this.

This strange star is dimming erratically.

It looks like something colossal blocks its light, but what?

It's dimming in a way that seemed absolutely impossible.

What the heck is going on?

Scientists scramble to identify the culprit.

Could it be a vast swarm of comets,

the fallout from a planetary smashup,

or something even stranger?

It's possible that an alien civilization

would look a lot like what we're seeing.

Scientists have long predicted an advanced alien race

might reveal itself by blocking the light from its parent star.

Is what we're seeing an alien megastructure?

You should not throw away ideas because they seem farfetched.

They might be right.

This is the inside story

of one of the greatest puzzles in modern astronomy...

This is why I do what I do. It's a blast.

The race to unlock the secrets

of the alien megastructure.

captions paid for by discovery communications

Astronomers around the world are locked in a race

to solve one of the greatest mysteries of the 21st century.

They have discovered an extremely strange star.

They call it Tabby's star.

Tabby's star appears to have

something enormous in orbit around it.

From time to time, this object passes in front of the star

and causes its light to dip.

You have to understand, we see millions of stars in the sky.

Tabby's star is the only star

out of all of these that we've seen this happen.

All stars vary to some degree,

but no stars vary as sharply or as rapidly

or as irregularly as Tabby's star does.

What could be blocking the light from Tabby's star?

One theory stands out.

Is the star being gradually encased by an alien civilization

with a thirst for large-scale construction?

I cannot overstate what kind of scales would be involved

in creating an object that could encompass a star.

It's just really, really hard to imagine.

So what's got reputable scientists

talking about alien megastructures?

The story begins with a simple,

but baffling, observation made by astronomer Tabby Boyajian.

Tabby is the first scientist

to discover the bizarre behavior of this star.

Previously, it went by the catchy name

of KIC846-2852.

This is an image showing the stars

around KIC846-2852.

And if we zoom in to the center here, this is the star...

The most mysterious star in the galaxy.

Tabby uses NASA's Kepler telescope

to study the star that now bears her name.

This innovative telescope is built to detect

the faint shadow of distant worlds

as they pass in front of their home stars.

The idea behind the Kepler mission is so elegant

because it's so simple.

You take an area of the sky,

and you just stare at it for years.

When you see this small planet going across its star,

the light dims, but in a regular pattern,

again and again and again,

and then you know you've found a planet.

In just nine years,

the Kepler mission discovers over 2,000 new worlds.

Most planets block out less than 1% of their parent star's light.

But when the telescope looks at Tabby's star,

it seems dips in brightness on another scale.

Most of the time, the star is at normal brightness.

But then about two years into the Kepler mission

is the first really big drop we saw, which is like 15%.

A drop in brightness of 15% is enormous.

But two years later,

the team captures something even more astonishing.

Over here on the far right,

you can see we have this huge complex of dips.

The star goes nuts here.

The brightness is fluctuating in manic ways.

The deepest one here goes to over 20%,

and this is huge.

We've never seen anything else like it.

The dips don't last long.

Each event spans just a few days,

but the drops in light are enormous.

What causes this star

to erratically dip by over 20%?

As the sun rises over mt. Wilson observatory,

Tabby can use the solar telescope

to show us why such deep dips

in the star's brightness are so unusual.

Because with this telescope,

she can demonstrate just how big an object would have to be

to create such enormous dips in light.

Roll my sleeves up. We're gonna control the sun.

Here we go.

The telescope above Tabby's head

projects a live image of the sun.

If this projected image were Tabby's star,

what percentage of the star's light

would the planets we're familiar with block out?

So if you had an earth-like planet,

it would look something like this.

This is a ball bearing here, and it is blocking out

a very tiny fraction of the star's light.

The earth may seem big to us,

but compared to a star, it's tiny.

It would block out just 0.01% of Tabby's star's light.

What about the biggest planet in our solar system?

How much starlight would Jupiter block?

In the case of a Jupiter-sized planet,

we would have something the size of this coin

that's passing in front of the star,

blocking out about 0.5% of the star's light itself,

which is still a pretty small fraction

of the overall light output of the star.

Even enormous Jupiter is too small

to account for Tabby's star's drops in brightness.

So how big would an object have to be?

So you would have something along the size of this.

And this is blocking a huge amount of light.

We're talking up to 22%.

If this were a planet, it would be almost 373,000 miles across.

A world almost 100 times bigger than Jupiter.

That would make it the largest planet ever discovered.

But for physicists, that's a problem.

It turns out it's impossible for a planet to grow this big.

The biggest planet you can get is roughly Jupiter-sized.

If you start adding more mass to Jupiter, it won't get bigger.

It'll get denser.

A dip in the star's brightness of 22% is just too big

to be caused by a planet.

Scientists know that something is blocking out

the light from Tabby's star.

If not a planet, what is it?

The race to find answers is on.

With no obvious natural suspect,

some astronomers begin to investigate

unnatural explanations.

The behavior of Tabby's star was so weird,

and we had no idea what was going on

that we were willing to entertain almost anything,

including aliens.

There's a secret in the scientific community.

Even though we can't say out loud that we believe in aliens,

I think we all have a sense that maybe there is life out there.

But why would an alien race want to build a structure

big enough to block out more than 20% of their star's light?

A clue lies in the heart of Nevada.

Spread out over two square miles of desert

stand 10,000 reflective panels.

Each bows to worship the sun.

Steve croft is an alien hunter.

Scientists love a good head scratcher,

and Tabby's star is really one of the biggest mysteries

to come along in astronomy in the last few years.

Steve believes that this solar facility

might be a miniature version of the megastructure

that could be blocking Tabby's star.

Could advanced aliens have built a monstrous solar farm

around the star to harvest energy from it?

Tabby's star, the strangest star in the galaxy,

has astronomers stumped.

Its brightness dips erratically.

Could a colossal alien megastructure

be blocking out the star's light?

At a solar facility in the heart of a Nevada desert,

astronomer Steve croft believes the answer is yes.

Right behind me is a huge nuclear reactor

that's in the center of our solar system

that's been here for billions of years

and will continue to be here for billions of years,

just putting out vast amounts of energy.

And so that energy really is coming for free,

and all we have to do is capture it.

This solar power plant can power 75,000 homes,

but Steve thinks this is small fry

compared to what aliens might build

because their energy needs will far outstrip our own.

I think alien technology may be as far beyond our imagination

as the technology that we have today is beyond the imagination

of people a couple of hundred years ago.

If you're traveling between the stars,

if you're building huge structures in space,

if you're powering some technology

that is beyond our wildest imaginings,

the power requirements for these things may be huge.

And this tremendous thirst for energy

may mean that planet-based power plants just don't cut it.

As energy needs increase,

you could build more and more solar farms like this

until you've covered the whole surface of your planet.

What do you do then?