All language subtitles for The.Universe.S09E04.Alien.Worlds.WEBRip.x264-ION10

(male narrator)
Unbelievable new worlds,

planets made of diamond,

planets of raining glass,

worlds in collision...

some plunging into stars...

and others
that just might harbor life.

But had ancient astronomers

as far back as the days
of Greece and Rome

already guessed
what modern science

is about to learn?

We are the generation
of human beings

that are going to know
whether or not we're alone

in the universe.

(narrator)
Ancient mysteries

shrouded
in the shadows of time.

Now can they
finally be solved

by looking
to the heavens?

The truth is up there,

hidden among the stars...

in a place we call...

Ancient Greece...

The greatest minds
look up in wonder

at the strangest objects
in the night sky--

five brilliant points of light
that look like stars

but move
in mysterious ways.

They noticed
that some objects

didn't behave
like the stars

and that they called them
"the wanderers,"

and they mapped them out
in incredible detail.

(narrator)
The ancient Greek word
for "wanderers"

is "planets."

2,000 years later,

the invention
of the telescope

added three more planets,

bringing the accepted total
to eight,

but if anyone thought

that these were the only planets
in the universe,

they were dead wrong.

The problem was,
for years,

there was simply no way
to find any additional planets

that theoretically might exist
around alien stars.

They didn't know
how to find them

because looking at them
with a telescope--

they're just
invisible to us.

They're too small.

(narrator)
Scientists compared
the challenge

of finding such planets

to placing a firefly
next to a Hollywood spotlight.

(Knutson)
Now, imagine flying
to New York City

and taking
your best camera,

attaching it
to your best telescope,

and trying
to take an image

of that spotlight
and that firefly

all the way out here
in Los Angeles,

where you can see
the firefly

separate
from the spotlight,

and that's about the scale
of how difficult it is

to actually take a picture
where you can see the planet

next to the star.

(narrator)
Yet, in just the past few years,

we've discovered hundreds
of new planets

whirling around alien suns.

It's a collection of worlds
that range from the bizarre

to the eerily familiar--

a planet about to be swallowed
by a dying star...

Giant water worlds
awash in global oceans...

A planet in a death plunge
into its star...

Two planets
in the fiery aftermath

of a gigantic collision...

And the holy grail--
Earthlike planets

that just might harbor life.

Could this be one
of the first places

in the universe
we find alien life--

a newly discovered planet

called Gliese 667Cc?

It orbits what's known
as an M dwarf--

a star that's 1/3 less massive
than our Sun

and gives off
a tiny fraction

of the visible light,

but for astronomers seeking
both new worlds

and life
in the universe,

it looms large,

because planet Gliese 667Cc

might actually be inhabited,

even though
it's eight times closer

to its dim star
than Earth is to the Sun.

(Filippenko)
If we on Earth
were orbiting the Sun

at that distance,
we would get fried,

but because Gliese 667
is a low-luminosity M dwarf,

a dim star,
the planet, 667Cc,

that orbits it actually gets
an amount of starlight

that should make
its temperatures

somewhat comparable
to those that we have on Earth.

So what would it be like
to stand on the surface

of this world
and look up into the sky?

Here we are on Earth.

That's our Sun up there.

It's so small,
I can take my little finger

and block it out,
but on Gliese 667C,

come on, the Sun
is ten times larger.

(narrator)
The energy pouring
onto the planet

is not visible light
like on Earth

but infrared light,

otherwise known as heat.

Because the planet
orbits so closely,

it's locked in the tidal grasp
of its star.

(Filippenko)
It's the same side always
that faces the star.

It's like the Moon--
the same side of the Moon

continually faces
the Earth.

Well, so, too,
the same side of this planet

continually faces
Gliese 667C.

(narrator)
Scientists once thought
that such planets

would be too hot for life
on one side

and too cold
on the other,

but simulations now suggest
that heat from the hot side

would flow to the dark side
and vice versa,

evening out
the temperature.

If life exists in this bath
of infrared light,

it must have evolved
far differently

from life on Earth,

with eyes adapted
to the infrared spectrum.

If you imagine taking
night vision goggles

or something which lets you see
infrared light,

you would see that, in fact,
everything around you is glowing

and that the amount
which it glowed

varied depending
on the temperature.

Things which are hot
will be brighter.

Things which are cold
will be fainter.

(narrator)
Plants, too, would have evolved

in ways hard to imagine.

(Aguilar)
On Earth, everything is green

because that's
the wavelength of light

plants don't like.

They take in the red,

they take in the blue
for energy,

and they
reject the green,

so we live
in a green world.

But on one
of these worlds,

as the infrared wavelengths
are brought into the plants,

everything to us
would look black.

Could you imagine
rolling fields of black grass,

black trees?

(narrator)
But there's a problem
for any potential life.

M dwarf stars
like Gliese 667C

shoot out violent
solar flares

that can double the brightness
of the star in minutes.

Flares like this create
gigantic bursts of radiation,

the kind that can poison life
and cause deadly mutations.

So the question is,

could life survive
on such a planet?

In fact, some suspect

that life might benefit
in a surprising way.

(Filippenko)
Most mutations
are actually harmful to life,

but some lead
to advantages.

Whether this would speed up
evolution of life

on that exoplanet

or tend to kill off
the life completely,

I think we're not
yet sure of.

(narrator)
If life can survive
the turbulence

of an M dwarf star
like Gliese 667C,

that would have
profound implications

for one of humanity's
greatest questions--

How common is life
in the universe?

The reason for that
is that M dwarfs

are the most common
kinds of star.

It might surprise you
to learn that when you look up

at the night sky, even if
you're in a very dark place

and you can see
lots of stars,

you can't see any
of the stars

that are the most common kinds
of stars in the entire universe.

70% of the stars
in our galaxy

are what
we call M dwarfs,

very cool,
small red stars

that are half
the size of the Sun

or even smaller
than that.

(narrator)
Yet these dim suns,
invisible to the naked eye,

may be humming
with life.

We've learned that these
are the most likely stars

to host planets that
are roughly the size of Earth.

At roughly the right distance
away from their star,

they receive similar
amounts of light

from their star
that we receive here on Earth.

(narrator)
One thing seems sure--

if life exists
on Gliese 667Cc,

it would have
far more time to evolve

than life does on Earth.

Our Sun will only last
a few billion more years

before swelling
into a red giant

and sterilizing
the planet.

But M dwarfs
are practically immortal.

We think that there are
some of these stars

which live basically
the age of the universe,

so that's an advantage,
because we know that our Sun

isn't going
to live forever.

(narrator)
Gliese 667Cc is just one

of dozens
of Earthlike planets

that researchers
have recently discovered...

planets that finally confirm
the beliefs

of ancient philosophers

who taught that there were
countless alien worlds.

But as we look
at these new alien planets,

an even bigger question
emerges--

Is anyone
looking back at us?

We finally have the technology
to find out.

(narrator)
As we search deep space
for alien worlds,

the ancient understanding
of what it takes

for a planet
to support life

is encoded
much closer to home.

When the Apollo mission

landed on the Moon's
Sea of Tranquility in 1969...

many people wondered
about the name.

(Neil Armstrong)
Tranquility Base here.

The Eagle has landed.

(narrator)
Why Sea of Tranquility?

The answer goes back
to an ancient belief

about life on other worlds.

In the first century AD,

the Greek philosopher Plutarch
wrote that the Moon

was a planet like Earth

and that it might
even be inhabited.

If so, he argued it would need
oceans of water.

Even back to the days
of Plutarch,

we realized that water
was necessary for life.

Some people think wine
is the elixir of life,

but in the scientific world,
we realize it's water.

(narrator)
Ancients like Plutarch
looked for lunar oceans

and thought they saw them
in the dark splotches

scattered
across the Moon,

so they named them "mares,"

the Latin word for "seas."

So we have the Sea of Storms,
the Sea of Tranquility,

all these different seas.

The idea that water
was very critical to life

goes way back
in our historical records.

(narrator)
Today we know
that the Moon's seas

are simply large basins
of dark volcanic rock,

but Plutarch's
original idea--

that to find life
on other planets,

look for liquid water--

has survived
the test of time.

All known life on Earth
appears to require

the presence
of liquid water.

Molecules can get bigger
and can form complex structures.

If life elsewhere
is like life on Earth,

then the mantra should be
"follow the water."

(narrator)
Water is common
in the universe,

but liquid water is rare.

On the surface
of planets,

it only exists
in the so-called Goldilocks,

or habitable zone
near a star,

where things are not too hot
and not too cold.

The size
of this habitable zone

depends on the size
and temperature of the star

that the planets
are circling.

Our Sun is a fairly
ordinary mid-size star,

so our habitable zone,
where Earth resides,

is one astronomical unit away,
way out here--

millions of miles.

Now, in the case
of low-mass stars,

they're much smaller,

and they have
much less luminosity,

or light output.

So that means that
the habitable zone goes

from being way out here
to being much closer in

to the central star.

(narrator)
So life could exist on planets

much closer to dim stars,

and as we've seen,
the universe is teeming

with planets like that.

Another key thing
that affects the possibility

of liquid water and life
is the planet's size.

(Seager)
If a planet is too small,

we think it will lose
its atmosphere

because it does not have
enough gravity to hold on

to its atmosphere.

That's what
happened to Mercury

and to some extent Mars.

If the planet's too big,
it becomes a gas giant,

which, actually,
are very hot planets

as one would travel down
into the atmosphere.

So the planet has to be
just the right size.

So the habitable zone is
actually the sum of two parts.

One is being the right distance
from the star,

and the other is having
the right kind of planet.

(narrator)
These, then, are
the two requirements for life,

but how often do they exist?

It turns out
they're everywhere,

including here

on this incredible,
newly discovered planet

called Kepler-22b.

Kepler-22b is what
we call a Super Earth.

These are planets
that are larger than Earth,

but smaller than
the planet Neptune.

We don't have anything like
that in our own solar system,

yet these planets
appear everywhere

when we look
at other stars.

(narrator)
As the list of planets

that fit these
precise requirements grows,

the surprises keep coming.

Consider an alien star

only slightly smaller
than our Sun

that has not one
but two planets

that might be in the right spot
and be the right size

to harbor life.

Kepler-62e and "f"
are both Super Earths.

They've got about 1 1/2 times
the diameter of the Earth,

and both of them are in,
broadly speaking,

the habitable zone.

(narrator)
They're so close to each other

that if technological beings
evolved on one,

they could
easily visit the other.

If you could travel
on a rocket ship,

it would take about 12 days
to go between these two worlds.

(narrator)
That could only happen
if these planets

have dry continents,

but some suspect
that they're water worlds

covered
in a deep global ocean.

These would be planets
with a small, rocky core

and then a very massive
water envelope surrounding that,

so that would certainly
be an example

of a kind of planet
which is fundamentally different

than anything we see
in our own solar system.

(narrator)
A water world
might be great for life,

even intelligent life,

but technological civilization
is probably impossible

for a simple reason.

(Aguilar)
You can't light
a match under water.

You can't have electricity.

Probably intelligent life
that is capable

of making
and building things

wouldn't exist there
because they can't use fire.

(narrator)
Still, this does not rule out
life in the atmosphere.

After all, some fish on Earth
have evolved flight

to escape predators,

so scientists speculate
that the skies of Kepler-62e

could swarm
with alien birds.

Planets like Kepler-22b

and surprising twins
like Kepler-62e and "f"

are revolutionizing
our understanding

of what kinds of worlds
might harbor life,

but how does this strange class
of planet

make our solar system look
like the freak of the universe?

(narrator)
As we search the heavens
for new worlds,

we expected
to find solar systems

that look like our own,

but instead, we're discovering
that our solar system

might be
a freak of nature,

challenging a view
of the cosmos

that developed
over thousands of years.

Some astronomers
in the ancient world

correctly guessed
that Earth was a globe

that revolved
around the Sun,

but the most famous
of all ancient philosophers

strongly disagreed.

In the 300s BC,

Aristotle argued
that the Earth

was at the center
of the universe,

and his ideas
were accepted for centuries.

The Catholic Church
adopted this

because it worked so well
in their theology

of how the universe worked.

God had created man.
Man was special.

The Earth was special,
and because of this,

this was what
everybody believed.

(narrator)
It wasn't until the 1600s
that Copernicus

proposed that we inhabit
a solar system

with the Sun
at the center

and all the planets
revolving around it,

including Earth.

By the late 20th century,

scientists believed
that they fully understood

the mechanics
of how solar systems evolve.

For many years, the only example
of a solar system that we had

was our solar system

and the eight planets
that orbit here around our Sun.

(narrator)
We based our entire view
of how solar systems are born

on our own solar system...

but the sudden discovery
of thousands of exoplanets

has shown that apparently
we were wrong.

Now we have a plethora
of different systems,

all of which
are totally different

and some very similar to ours
and then some very alien.

(narrator)
The way our solar system formed

produced essentially
two kinds of planets.

One type is
the rocky planets.

We call them
terrestrial planets.

The other would be
giant planets

like Jupiter and Saturn.

(narrator)
This made sense

because of how we thought
solar systems evolve.

(Walkowicz)
When solar systems form,
they collapse

from a large cloud of gas,

and the central mass of them
becomes the star,

whereas the disk
of material that's left over

around that central star
becomes the planets.

(narrator)
Close to the star's warmth,

the most common elements,
hydrogen and helium,

are heated into gases
and blown away by solar winds.

So, near the star,
the only materials left

for making planets
are heavier, rocky elements.

This is where
its warm enough

that you can really
only condense out

rock and metal to form
these little planets.

However, further out
in the solar system,

beyond what we call
the snow line,

temperatures
are cool enough

where you can condense gases

and form these
very large envelopes

that eventually become planets
like Jupiter and Saturn.

We thought,
"This is the plan

for all solar systems."

Boy, were we wrong.

(narrator)
The tip-off
for how wrong we were

was the discovery
of a class of exoplanets

that theoretically
can't exist,

except they do,

the so-called "hot Jupiters."

A lot of the first
exoplanets found

are what are called
"hot Jupiters"--

big, massive planets
that actually orbit

very close to a star,

having a orbital period
of a day or only a few days

or ten days.

(narrator)
HD 209458b

zips around its Sun-like star
in 3 1/2 days...

While our Sun's
closest planet, Mercury,

takes 88 days.

(Seager)
HD 209458b
is an iconic planet.

We also think that
the atmosphere's being blown off

by interacting with the star
and heating up

and by wind from the star
hitting the planet,

and its atmosphere
will be slowly whittled away.

(narrator)
Losing about 10,000 tons of gas
every second,

this planet is,
in effect, evaporating.

It looks like a comet
with a huge tail

stretched out
behind it.

Eventually that atmosphere's
going to be gone,

and all that's
going to be left

is a little molten core
of what this planet used to be,

orbiting nearby
this bright star.

(narrator)
But these hot Jupiters
are far too close to their stars

to have formed there
originally,

so what happened?

Scientists now believe
these hot Jupiter solar systems

began like ours,

with the gas giants
forming out past the snow line,

but then the gravitational pull
of the disk

or of various planets
or even passing stars

caused the orbits
of the gas giants to go haywire.

They migrated inwards,
spiraling toward their suns,

and that process spelled doom
for the smaller,

Earthlike planets
closer to the star.

Well, you'd have
the star over here.

You'd have
a Jupiter-size planet here,

and as it moved in,
the little, rocky planets

would either be thrown
into the star

or thrown
out of the solar system,

or they could be captured
by that big Jupiter

and orbit around it
like a moon.

(narrator)
The planets tossed
out of the solar system

are doomed to wander forever
in deep space.

Some researchers now believe
that the galaxy holds billions

of these dark,
lost worlds.

So it turns out
that our orderly solar system,

with the rocky planets
close to the sun

and the gas giants
further out,

may be a lucky exception.

(Filippenko)
Earth has achieved a stability

that allowed life
to develop and evolve

in a relatively un-hassled way
for billions of years,

and in many other
planetary systems,

that may not be
the case.

(narrator)
But while the discovery
of new planets

has challenged some ideas
of how solar systems evolve,

it's confirming others,

including the catastrophic idea

of colliding worlds

and even how the Earth
will one day die.

(narrator)
Many ancient ideas about planets

seem simplistic...

but around 400 BC,
the Greek philosopher Democritus

proposed ideas that seemed

straight out
of a modern science textbook,

including ideas
about fiery cataclysms

in the Earth's past...

and a terrifying idea

about how the Earth
will one day die.

He was the first
to come up with the idea

that things were made
of smaller things.

He called them atoms,

and they came together
and grew and grew

into stars,
into planets,

into everything
that is around us.

(narrator)
When it comes to planets,

Democritus wrote that

"there are innumerable worlds
of different sizes.

"In some," he wrote,
"there is neither sun nor moon.

"In others,
their sun is larger than ours,

and others have
more than one sun"...

all of which,
amazingly, is true.

The interesting
philosophical question is,

how did he come up
with this idea?

It shows the uniqueness
of the human mind

to be able to project
and ask, "What if?"

And then, using logic,
put together

a philosophy
of how everything works.

(narrator)
Today, as we discover planets
around alien suns,

many of Democritus'
ancient ideas

have been confirmed
by modern science.

For example, he wrote
that some planets

are destroyed by collision...

and now we're actually watching
that happen.

This is the hot Jupiter
called WASP-18b,

a planet caught in the act
of plunging into its star.

It's been orbiting
for possibly 2 billion years,

but within the next
million years,

it's going into its star,

and the whole shape
of this round world

will be stretched
like an egg.

(narrator)
While WASP-18b confirms
Democritus' idea

of how planets can die,

another new discovery
confirms his ancient prediction

that planets
can crash head-on.

The planet HD 172555

is a world in the aftermath
of a collision.

What we think we're seeing
is two large rocky planets

which had just crashed
into each other,

thrown up
a bunch of dust,

melted rock
kind of accreted together.

(narrator)
Scientists have long speculated
that a collision like this

happened
to the early Earth,

tossing up debris
that created our moon.

For decades,
that was just a theory.

Now they can actually
watch it happen.

Gases were given off.
Glass was created.

And now they're fusing
back into this remain

of this world
that will be cooling down,

but right before
our very eyes.

There's a space wreck
right in front of us.

(narrator)
Democritus' ancient theories
about the death of planets

are bolstered
by another major discovery:

a dying planet
called Kepler-91b.

Scientists have long believed
that in the distant future

the Sun will swell up,

engulfing the dying Earth
in an inferno.

And this isn't
just a theory now

because we think
we see this with Kepler-91b.

(narrator)
Kepler-91b's star,
about the same mass as the Sun,

has already swollen
into a red giant.

It's now about six times
our Sun's radius

and growing rapidly.

If there were oceans here...

they're already evaporated.

If there is life,

it's in trouble.

On this world,
if you wanted to see life,

you'd be there at night.

Everything would come out
when it's cooler,

and then in the day,
it would disappear once again,

and the most precious commodity
on this world would be water.

Everybody, everything
would be looking for water,

and yet this is our future.

We're seeing it now.

(narrator)
Like Earth, Kepler-91b

is doomed to be swallowed
by its sun.

Unlike Earth,
its time is almost up,

but could a planet
survive that fate?

Apparently
we found one that did.

V391 Pegasi is an example
of an exoplanet

that has physically survived
the red giant stage

of the star
that it orbits.

(Aguilar)
It's sun turned into a red giant
and grew larger

and larger and larger

until it actually consumed
this world.

And then as its sun
has shrunken back down,

the world remains.

(narrator)
Since V391 Pegasi
is still there,

it's the first known planet
to survive a close encounter

with the kind of red giant
that will one day threaten

to destroy Earth...

if you can call that survival.

That world now
is one burnt, rocky planet.

Anything that
was living is gone.

It's disappeared.

(narrator)
Newly discovered planets
like these

give us a glimpse
into Earth's future,

but there are other planets
out there so strange,

they seem ripped
from an alternate universe.

What is mankind's
secret weapon

for unmasking
these mysterious worlds?

(narrator)
Less than 20 years ago,

scientists were still struggling
to discover

a single planet
outside our solar system.

Today we've discovered
thousands.

How did we do all this
and do it so quickly?

The revolution begins
in the 1990s.

Scientists knew that planets
cause their host stars to wobble

and finally developed a way
to detect this.

(Aguilar)
We now have instruments
with microelectronics,

a spectrograph,

that could act like
a policeman's radar gun.

We could take
a look at a star,

and we could see
if it was moving towards us

or away from us.

(narrator)
Using that technique,

scientists discovered something
that had eluded

not only the ancients,
but even modern astronomers--

the very first planets
outside our solar system.

But were there
even better ways to search?

Once we knew there were planets
around other stars,

people suggested
that there might be another way

in which
you could find planets.

(narrator)
That way was to look
for little eclipses

caused when the planets passed
between their host stars

and our vantage point
on Earth.

These tiny eclipses
are called transits...

like the transit of Venus
we saw from Earth

in 2012.

This creates a tiny dip
in the brightness of the star,

which we can measure
as it happens again and again

as the exoplanet
goes around in its orbit.

(narrator)
But from Earth's surface,

the transit technique
had serious limitations.

You really need to monitor
the star all the time

without interruption
in order to have

a good chance
of not missing any transits.

(narrator)
That's where NASA's
Kepler space telescope comes in.

Launched high above
Earth's distorting atmosphere,

it pointed at just one spot
in the sky--

a field of 150,000 stars,

taking continuous pictures
of that region

over and over again
for four years,

with space-age precision.

Would it find a sky
brimming with planets

or a dark and empty void?

Lo and behold, planets started
moving across their stars,

and we started
seeing their orbits.

And we waited and waited--

another year,
another crossing,

another year,
another crossing.

(narrator)
But scientists quickly turned
to a larger question.

Could any of these planets
be similar to Earth?

(Knutson)
The majority of the stars
in the Kepler field

seemed to have planets,

and Kepler was actually
sensitive enough

to detect a planet
the same size

or even smaller
than the size of the Earth,

and it found enough of those
that we now know

that small planets are much
more common than large ones.

(narrator)
That, in fact, was Kepler's
revolutionary purpose...

To find Earthlike planets
that could harbor life.

In this mission,
we found them,

but we found a lot
of other surprises too.

(narrator)
But as scientists
struggled to discover

the total number of planets
that exist in the galaxy,

they ran up against Kepler's
major limitation--

it can only spot planets
that transit their star

as seen from Earth,

and most planets do not.

If we have
a transiting planet system,

then we need
the alignment to be perfect

for that planet
to go around its star

and to block just
a little bit of that light

from getting to us
from our point of view.

However, if we took
this system

and we tilted it up
such that that alignment

no longer happened,

then the planet would
still be going around its star,

but it would never block
any of the star's light

from getting to us,

and we wouldn't
see a transit at all.

(narrator)
Scientists realized
that the chances

that an Earthlike planet
will transit

are 1 in 210.

Using that ratio
gives us a staggering estimate

of how many planets
actually exist.

(Aguilar)
What this tells us
is that in our Milky Way galaxy,

which has between 200 billion
and 400 billion stars,

there may be almost
230 million

other planet Earths
out there.

(narrator)
Once Kepler detects
a possible planet,

scientists across the globe
race into action.

(Aguilar)
Another group
of astronomers takes over

with telescopes
here on the Earth

with huge spectrographs,

and they take a look
at this world

and look for the star
to wobble.

We need both
these processes now

to determine
what the planet is

and how far away it is
and what it looks like

and even what
it's made out of.

[rumbling]

(narrator)
Kepler roared into space
in March 2009

on a Delta II rocket.

In the first six weeks,

it discovered
five previously unknown worlds.

Today it has discovered
thousands.

It's nearly impossible
to describe how revolutionary

Kepler was for exoplanets.

Kepler made so many discoveries
we never even expected.

(narrator)
So far, some of the newly
discovered planets

have challenged
and others have confirmed

ancient theories
of how worlds

are born and die,

but even the ancients
never dreamed

of the kinds of wondrous worlds
we're discovering today.

How does the universe

make a planet
of solid diamond?

(narrator)
Ancient philosophers
like Democritus

believed in a universe aglow
with amazing planets.

But today's planet hunters
have discovered worlds

far stranger than the ancients
ever suspected.

You are orbiting
55 Cancri e.

It's mostly made
of carbon,

and due to extreme pressure

and a surface temperature
of 4,892 degrees Fahrenheit,

it just might be
a jeweler's dream.

Now, think about this.

What happens if you take
a piece of carbon

and you have
the strength of Superman

and you crush it
like this?

What do you get?

A diamond.

(narrator)
If a diamond planet
isn't strange enough,

let's descend
to another new discovery--

HD 189773b.

Its blue color makes
it look surprisingly like Earth,

but in this case,
looks can be deceiving.

This is a glass planet.

It has mostly silicon,

and the silicon
with the sunlight

passing through it
appears to be blue,

and it's very hot.

In fact, the temperatures
near the surface are such

that the silicate
can condense

into fine little
particles of glass,

so it might actually
rain glass

on this exoplanet.

But that rain would
move largely sideways

because there are huge winds
in the atmosphere,

up to 4,000 miles an hour.

(narrator)
And the ancients
never predicted a planet

covered with
a seeming impossibility--

burning ice--

yet that's what we find
on Gliese 436b.

If you touched it,
you would be burned.

This is a world
made of hot ice--

something we never imagined
on Earth.

(narrator)
Diamond planets,
planets of raining glass,

worlds of burning hot ice--

thanks to projects
like Kepler,

the universe
is proving far stranger

than either the ancients
or modern astronomers

ever imagined,

but more is soon to come.

Scientists are bracing
for the discoveries of TESS,

the Transiting Exoplanet
Survey Satellite,

due to launch in 2017.

Unlike Kepler,
which looks at one patch of sky,

TESS will scan only the stars
that are so close,

we might actually
visit them someday.

(Seager)
We're mapping
the nearby stars for planets

that we hope,
eventually in the future,

our descendents will actually
be able to travel to.

So we have a huge interest
in trying to find planets

orbiting stars
that are very close to Earth.

(narrator)
Other new projects
have actually begun searching

not just for life

but for intelligence
and technology.

One surprising key
is to look for stars

that twinkle and pulse
in bizarre ways

that could only be caused

by advanced
alien civilizations.

I used large databases
of observations of stars

to try and understand
whether any of those stars

could be varying

in a way that was caused
by something artificial.

(narrator)
But can we ever visit
the planets

we are now discovering
in such abundance?

I'm hopeful that at one point,
we'll eventually be able to send

robotic probes to some
of these nearby solar systems.

(Seager)
Not everyone believes
that it'll happen,

but we're born explorers.

We'll want to go.

We have to have hope
that, in the future,

if there's a will,
there's a way.

(narrator)
Whether such a thing will happen
is anyone's guess,

but one thing
is certain...

thanks to today's
planet hunters,

our views of the universe
and of our place in it

are undergoing one
of the greatest revolutions

in scientific history.