All language subtitles for How the Universe Works s07e09 Finding the New Earth.eng

Earth.

The cradle of humanity
throughout our existence.

But it won't be forever.

All it would take would be
one giant meteorite

to wipe us off
the face of the Earth.

It's not just meteors.

Our planet will change.

Our planet could freeze over
or it could heat up.

And our sun will eventually die.

We are actually near the end
of habitability of Earth.

To survive in this universe,
we need an insurance policy...

to colonize other worlds.

Having multiple planets
which are colonized

is really in our interest
for our own survival.

So can we find
a new home in the galaxy?

Can we find Earth 2.0?

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discovery communications

For centuries, we only knew
of the handful of planets

in our own solar system.

Now astronomers are finding
thousands of new worlds

around alien stars...
Exoplanets.

We are discovering exoplanets
by the bucketful.

There are as many planets
out there as there are stars,

and there are hundreds of
billions of stars in the galaxy.

But out of billions
of exoplanets,

are there any that could offer
new opportunities

for humanity to thrive

and provide sanctuary
in a dangerous universe?

Is there an Earth 2.0?

Is Earth 2.0 out there?

That would be truly amazing.

August 2016.

Astronomers announce
that Earth 2.0

could be closer
than anyone ever expected...

a planet orbiting the sun's
nearest stellar neighbor,

the red dwarf Proxima Centauri.

So it turns out that our nearest
star neighbor has an exoplanet.

It's only about
4 light-years away,

so that means that it's actually
potentially possible for us

to get there and to explore it.

Scientists named
the planet after the star,

Proxima Centauri B,
or Proxima B for short...

a world that appears to be
a lot like Earth.

From the way it's tugging
on the star, Proxima Centauri,

we know that it has
1.3 times the Earth's mass.

It's roughly the same size
as the Earth.

Of the exoplanets we know about,

most are uninhabitable
gas giants, like Jupiter.

Proxima B is a rare find,
an Earth-sized planet,

but an Earth-sized planet
might not be Earthlike.

A true second Earth must also be
the right distance

from its star.

The habitable zone,
or some people call it

the Goldilocks region,
is a distance away from the star

where you're not so close
where you're going to burn up

and evaporate
all of your liquids,

and you're not so far away
where you're frigid and cold.

So it's that special region
where it's just, just right.

Does Proxima B
lie in this region?

Could it have liquid water?

Proxima Centauri B orbits
its star once every 11.2 days,

so compare that to the Earth,
which goes around the sun

once every 365 days.

That's because the planet
is much, much closer to the star

than the Earth is to the sun.

Earth orbits
93 million miles from the sun.

Proxima B orbits
20 times closer,

under 5 million miles
from its star.

You might think
that Proxima B should be,

you know, really a fried world,
a burnt-out husk, if you will.

But Proxima B�s sun is
very different than ours.

At just over 5,000 degrees
Fahrenheit,

it's half as hot
and roughly 8 times smaller,

an m-class red dwarf star.

An m-dwarf that Proxima B
is around is much less bright,

much less hot,

so you can orbit
much closer to that star

and be at the same temperature
that we are here on Earth.

Proxima B�s
tight orbit around the red dwarf

could make the planet habitable,

but it would be
very different from Earth.

The star dominates the sky,

lighting any oceans
and mountains

with an alien red glow.

So Proxima B may be
the Earth 2.0

that we've been looking for.

But in 2017,

the dim red dwarf star
erupts in a way

that's unlike anything
we've seen before...

blasting the planet
with radiation...

A megaflare.

They're like solar flares,

but they can be
much more powerful.

In fact, they can outshine
the star itself.

Our sun releases
powerful solar flares

when its magnetic field
becomes tangled.

But the megaflare is
10 times stronger

than our sun's strongest flares.

On an M dwarf star,
that magnetic field

can get a lot more tangled
than on our own sun.

That means that when a flare
happens,

it can release
a lot more energy.

Scientists believe
that megaflares like this

are planet killers.

Radiation tears
the atmosphere from the planet,

and these megaflares hit Proxima
B roughly once every year.

Red dwarf stars
are incredibly temperamental.

They are not good parents
to their planets,

so if Proxima B did have
an atmosphere at one point,

it would've been stripped away

by one of these
violent outbursts.

Leaving Proxima B
dangerously exposed to space.

An atmosphere dampens
the temperature gradients

between light and shadow,

so in sunlight,
it is just burning hot,

but right next door in a shadow,
it is freezing cold.

Without an atmosphere,

Proxima B would
be a barren wasteland,

blasted by intense radiation
from its star...

Completely uninhabitable.

Proxima B, our perhaps best shot
at finding Earth 2.0 so far,

is actually
a dried out husk of a world

that has lost its atmosphere,

maybe lost any water
that it also harbored,

simply by being that close
to its parent star.

Proxima B may be
the nearest exoplanet,

but it's not the only option.

The future of humanity may lie
in an incredible star system

just 40 light-years away.

We've just found
a really exciting system

where there's not just one
chance to have a new Earth,

but seven.

In an unforgiving galaxy,

finding Earth 2.0 could be
the difference

between extinction and survival.

It's a pretty wild place
out there.

Our planet is not going
to be here forever,

and it would be wonderful
if we could find a place like it

so that we could live.

The future of humanity
lies on an alien exoplanet.

The question is, where?

2016.

Astronomers scan the skies
with the new

transiting planets and
planetesimals small telescope,

or Trappist.

They look for the flickering
of a star

caused by the silhouette
of a planet.

The planet can pass in front
of the disk of its star

once per orbit,
causing a little mini eclipse,

a little dimming temporarily
in the light of the star.

Scientists spot the dimming

of a nearby red dwarf star

just 40 light-years from Earth,

the first alien system
detected by the telescope,

the incredible
Trappist-1 system.

The Trappist-1 discovery

was a really great
bang for our buck in a sense...

Because we found
seven exoplanets all at once.

But are
any of these seven planets

actually habitable?

With the worlds
of the Trappist system,

there's probably
a range of climates.

The innermost ones
are probably very hot.

You might even be looking
at lava worlds.

Farther away,
they're probably worlds of ice.

But the middle
planets... D, E, and F...

Are all prime candidates.

It's exciting to think that
three of the planets

orbiting Trappist-1
are in the "habitable zone,"

are at the right distance
from that star

to have liquid water
on their surface.

And one planet stands out
as a new Earth,

orbiting just 2.7 million miles
from the star...

Trappist-1E.

The composition of Trappist-1E
suggests that it could have

a pretty significant iron core,
kind of like the Earth does.

There's a potential there for
a very powerful magnetic field.

Like Earth, Trappist-1E

could host
a protective magnetic field,

deflecting the harsh solar winds

and powerful outbursts
that strip away atmospheres.

So magnetic field
is a good thing.

It's a kind of a protection
from the evil forces of the star

that you're orbiting around.

And unlike Proxima Centauri,

the Trappist-1 star
appears unusually quiet.

Trappist-1 is actually
a very old, much calmer star

and doesn't undergo a lot
of these huge flares

like Proxima Centauri does.

And so it's a somewhat perhaps
better system to look

for an Earthlike planet,
an Earth 2.0.

The data suggests
that Trappist-1E

could have vast oceans,

a protective atmosphere,
and habitable temperatures.

But living here would be nothing
like living on Earth.

The thing to keep in
mind about the Trappist system

is that it's very unlike
our own.

The planets are much closer in,
so because they're closer in,

their orbits
are faster and smaller.

On Trappist-1E, an entire year

takes just 6 Earth days.

Can you imagine you're just
basically tearing

your calendar days off day after
day after day really quickly?

Your birthday would be today
and then tomorrow.

Happy birthday, again!

Wedding anniversaries,
you're constantly forgetting

your wedding anniversary,
and it would be hard.

And on this strange and alien
world,

explorers would witness sights
unlike anything seen before.

In a lot of ways, it really is
sort of a science fiction sky,

the kind of things
that are envisioned in movies.

You could look up and see
the other planets in your sky

much like how we can see
our own moon.

You could physically resolve
features on the surface

such as continents
with your own eyes.

But could this planet
be too good to be true?

So we could have a potentially
habitable planet

that's really close to its star,

but other issues arise
when you have a solar system

that's that compressed,

and one of those is
the potential for tidal locking.

Orbiting just a few
million miles from the star,

Trappist-1E is likely tidally
locked with one side

facing the star forever.

So you could imagine a situation
where, gosh, it's constant day

and it might just
produce something

that's like a scorched Earth,

kind of like what we see
behind me,

but on the other side,
it is constant night,

and so in that case,
it might just be, like,

a frozen wasteland.

And Trappist-1E's problems
get even more extreme.

If you have a permanent day side
and a permanent night side,

the night side of the planet
is going to get so cold

that everything just freezes
out, including the atmosphere.

The gases of Trappist-1E's
atmosphere

could freeze into solid ice

on the frigid night
side of the planet,

and the gases on the day side
burn away.

The atmosphere thins
and eventually disappears,

and Trappist-1E ends up
completely inhospitable.

So even though we found maybe
a perfect planet around a star,

the type of star
and where it's orbiting

could have
a really important effect

as to whether or not
that planet might be habitable.

Despite its apparent potential,

our future is not
in the Trappist-1 system.

The search for truly
Earthlike planets continues.

In the Trappist-1 system,
we find a very Earthlike world,

but the star its orbiting
is not very sunlike.

So what we should
be looking for, perhaps,

is a Earthlike planet
around a sunlike star.

To find Earth 2.0,
we need a sun 2.0.

The Milky Way...

Home to hundreds of billions
of stars...

ranging from dim,
explosive red dwarves...

to short-lived blazing giants.

But in the middle are stars
like our sun.

Strictly speaking,
if we really want Earth 2.0,

we need to look for planets
around stars like our sun.

Stars like our sun

are calm and stable with
long lives...

and the habitable zone
lies far enough away

that planets avoid
tidal locking.

We stand a much better chance
of colonizing a planet

around a sunlike star.

We're hunting for planets
in the habitable zone of stars

like our own sun,
and we have found worlds there.

Worlds like Kepler-452B,

an exoplanet
1,800 light-years away,

orbiting the same type of star
as our sun.

You really couldn't ask
for a more Earthlike orbit

around this star.

The year is about 385 days.
We're 365 days.

This really is very much
like the Earth.

The planet orbits its star
at roughly the same distance

as the Earth orbits the sun,

and could be
very much like home.

Kepler-452B is in
the habitable zone of its star,

so if there is
liquid water there,

there could be oceans and lakes
and rivers and streams

and blue skies and cloudy days.

Sounds nice, but Kepler-452B

is a lot larger than Earth.

Kepler-452B is
a great Earth 2.0 candidate,

but it's sort of like
Earth on steroids.

This world is about 5 times
more massive than our own planet

and about 60% wider.

Scientists call
large worlds like Kepler-452B

super-Earths.

These worlds are maybe

1.5 or 2 times
the size of the Earth,

with maybe as much
as 10 times the mass.

Could this
super-sized Earthlike planet

be our second home?

A planet like this seems to meet

a lot of our standards
for an Earth 2.0.

It's around a star like our sun.

It's smack-dab in the middle
of the habitable zone.

The problem is there
are other factors at play.

One of those is simply
the mass of the planet.

Kepler-452B's size

has an extreme effect
on its gravity.

Because of its incredible mass,
the gravity on the surface

is about twice
what we feel here on the Earth.

That extra gravity

would make colonizing the planet
difficult.

Just about any chore
you could imagine

doing that you don't
like doing on the Earth,

you're going to like it
even less on a planet like that.

When the garbage can weighs
twice as much as it does here

on the Earth, that's not going
to be very much fun.

Maybe LeBron James and I
will be okay,

but normal humans,
I'm not so sure.

And we could be stuck
on the planet's surface.

If you landed on the surface
of one of these super-Earths,

it'd be pretty easy
to get down onto the surface,

but it would be very difficult
to get back up.

It's already
incredibly difficult

for us to leave the Earth.

Think of our giant engines
and rockets,

these incredible miracles
of engineering

that we need to blast off.

You need twice that
to get off of Kepler-452B.

And to make matters worse,
Kepler-452B's atmosphere

is thought to be radically
different from Earth's.

In some sense,
how big the planet is,

how massive it is will determine
what its atmosphere is like.

If you have a lot of mass
and a lot of gravity,

you can hold onto a lot of air.

You can have
a much larger atmosphere,

much thicker, much denser, and
higher pressure at the surface.

The thick atmosphere
could trap heat from the star.

Surface temperatures become
ferociously hot,

and crushing pressures

make the surface
completely uninhabitable.

So it's possible this planet has
a very thick atmosphere

that's become more of
a runaway greenhouse effect.

The planet has gotten hotter
and hotter over time.

Maybe instead of finding
an Earth 2.0,

what we've found is a Venus 2.0.

Super-Earths may have
an appealing name,

but their intense gravity would
make them difficult to live on,

and we could not survive
in their thick atmospheres.

So far, all the worlds
we've found have turned out

to be uninhabitable,

but what if our new home
is not a planet?

Earth 2.0 may not be
an exoplanet at all.

It might be an exomoon.

We live in
a cosmic shooting range

where planets die every day,

but backup planets like our own
seem almost impossible to find.

Have we been looking for
the wrong thing?

I think there's
a pretty good chance

that Earth 2.0 might not be
a planet per Se,

but actually a moon
of a giant planet.

The exciting thing
about an exomoon

is that they could
potentially be habitable.

So is it possible

that as we look
at different solar systems,

the real analog for Earth 2.0
will turn out to be an exomoon?

2017.

The Kepler telescope
scanned a sunlike star

8,000 light-years away,

and professor David kipping
and his team

watched the transiting
exoplanet Kepler-1625B.

Kepler-1625 was one of
the many thousands of planets

discovered by Kepler,

but what made it different
from our perspective

as a moon hunter
was that this is a planet

which was Jupiter-sized,
far away from its star,

and apparently
on a near-circular orbit,

so everything that we want
for finding exomoons.

The exoplanet Kepler-1625B

is an uninhabitable gas giant,
like Jupiter.

But it is in the habitable zone,

and that means its moons
would be, too.

Unfortunately, these exomoons
are incredibly hard to see.

The way that Kepler
finds exoplanets out there

really does relate
to the size of the planet,

and for moons, it's much,
much more difficult

because it's smaller
so it's harder to detect.

The largest moon
in the solar system

is Ganymede around Jupiter.

It's about 40%
the size of the Earth,

and we really very rarely
detect planets that small.

So, of course,
looking for exomoons

is going to be very,
very challenging.

In 2018, the team recruited

the powerful
Hubble space telescope

and used the data to hunt
for the tiny silhouette

of any moons.

If you have an exomoon
orbiting a planet,

sometimes it's going to
lead the planet

when it transits the star,

and sometimes it's going
to trail behind

as it transits the star,

and you see a little bump
in the transit dip itself

at different places.

And the team detected
the signal...

Not one, but two objects
orbiting together,

confirmation of the first
exomoon ever discovered.

It was an amazing discovery.

I've been looking for exomoons
my entire career.

For 10 years, we have been
in this quest to try

and find these things.

This discovery,

this announcement
was absolutely remarkable.

Not only does it mean
that we might find

Earth twins everywhere
in the Milky Way,

but it gives us
something to strive for,

for human exploration.

On this alien exomoon,

the skies would be nothing
like Earth's.

Visually, I think it would be

an absolutely stunning place
to be.

You look up in the sky,
and you see this ringed planet

looming huge in the sky.

A world that could
be like Earth,

only orbiting another planet.

But don't pack your space suit
just yet.

Even though the planet
and the moon

are potentially
the right distance

away from the star
that we might imagine

there being liquid water
on the surface,

both the moon and the planet
are likely gaseous objects

with no solid surface
to speak of.

Although the moon
probably isn't habitable,

it is an important step
for finding worlds

like our own in the galaxy.

If we find exomoons
around exoplanets,

that potentially
hugely increases

the number of habitable worlds
that are out there.

We just need more accurate
measurements,

and then all of a sudden,

the universe is going to be
full of exomoons.

But these worlds need to be more

than just Earth look-alikes.

Everyone gets very excited

when we find Earthlike planets
around other stars,

but "Earthlike" kind of
just means how big it is

and whether it can support
liquid water

where it is in relation
to its star.

All of that is great,
but it's just not enough.

A planet's composition
could be make-or-break

for our new home...

the difference between
the perfect world

and a ticking time bomb.

The hunt for Earth 2.0
is still on.

We've examined intense,
red dwarf systems...

massive super-Earths,
and alien exomoons

but so far,
there's no place like home.

There are all these criteria
we have to tick off...

A sunlike star,

an orbit that puts it at
about the right temperature,

a solid surface, something
that could retain an atmosphere.

But a planet that
appears Earthlike on the outside

may not be Earthlike
on the inside.

One of the things that makes
our world so unique

is its plate tectonics,

and that actually regulates
our climate.

The Earth's climate
depends on cycles of materials,

like carbon dioxide and water.

Molecules move between
the Earth's molten interior

and the surface through
active plate tectonics

and volcanic eruptions.

These cycles help to regulate
the temperature

and composition
of the Earth's atmosphere.

If we were to find another
Earthlike planet out there,

and it had geologic activity,
that means that at least

it has the means to sustain
the carbon cycle

and all of these
natural phenomenon

that makes this planet
habitable and sustainable.

How can we know what's
happening inside a planet?

A clue can be found in
vast ranges across our world...

Mountains.

These topographical
features are an indicator

that the planet is alive
and there is still processes

happening underneath
its surface.

Mountain ranges are created

when a planet's
tectonic plates collide,

and even though exoplanets
are light-years away,

astronomers could work out
whether their surfaces

are smooth or covered in peaks.

Those mountain ranges
are poking out,

and depending on which rotation
the planet is in,

the planet will appear
very slightly bigger

or very slightly smaller
depending on the silhouette

which is being cast.

These tiny changes
in light could be the sign

that an exoplanet
is healthy and active.

But we can only use this method

when a planet
is in front of its star.

What if astronomers
could use starlight itself

to determine
the geology of a planet?

We think that planets form
at roughly the same sort of time

that stars form,

and they all form from this same
giant cloud of material.

And so if you measure
the composition of a star,

then it seems reasonable
to take those values and assume

they're somewhat similar
for the planets as well.

Astronomers can
work out what chemical elements

are present in the star,
by splitting its light

into different wavelengths,
and any planets around that star

will have a similar
chemical composition.

Composition is actually
a really important part

of whether or not it's actually
going to be habitable.

The composition
really is its geology.

Rocky exoplanets are all made

from the same
basic ingredients...

Chemical elements like oxygen,
silicon, and aluminum.

Change the balance of
ingredients,

and you get
very different planets.

If we have some idea

of the composition of
a rocky planet,

we can actually use
that to give us clues

as to whether a world has
or doesn't have plate tectonics.

New research indicates

that exoplanets with too much
silicon and sodium

form different types of rock
than those on Earth,

creating rigid planets
where plate tectonics stall

and carbon dioxide builds up
with devastating consequences.

Without active geology,
we end up with

maybe a venetian atmosphere.

That means there
a runaway greenhouse effect.

It's gotten hotter and hotter.

Gases are baked
out of the rocks.

There's no way to actually
rein them back out,

not a good place for life
at all.

At worse, the planet
becomes a pressure cooker,

waiting to explode.

If we change the composition
of a planet,

it affects its tectonic system.

That entirely changes
how a planet loses heat,

and the heat builds up
and builds up and builds up,

and then maybe there's
a catastrophic overturn

of the crust.

The solid crust of
the planet collapses.

Oceans of lava bubble up,

and a greenhouse atmosphere
boils the surface...

A violent end
to a potential new home.

Clearly, you need to know

about the composition
of those planets

before you can start
making statements

about how habitable
those worlds truly are.

But there's something
else that a planet needs

to be Earthlike,
an invisible shield

that protects it
from the dangers of space,

providing warmth
and life-giving water...

An atmosphere.

The hunt for Earth 2.0
has turned up plenty of planets,

but for a planet to be
like Earth,

it has to check a lot of boxes.

If you're really looking
for Earth 2.0,

then you're gonna
have to find a planet

that's the same mass
and size as Earth,

orbiting a sunlike star

at about the same distance
with a similar atmosphere

and a lot of surface water
that's in liquid form.

Good luck.

And on the list of requirements,

an exoplanet's atmosphere
is critical.

It protects the planet
from huge temperature swings.

It protects the planet
from small asteroid impacts.

It protects the planet
from dangerous radiation

from space and from the star.

It is almost literally a shield
around the planet,

protecting us from outer space.

But to also has to be
the right kind of atmosphere.

Get it wrong, and the planet
can have crushing,

boiling conditions
on the surface.

Look at our own solar system.

The sun's habitable zone
includes

three different planets,
Venus, Earth and Mars,

but Mars has a thin atmosphere
and is too cold.

Venus has too thick
of an atmosphere and is too hot.

We're the only planet
that happens to be just right.

So far, astronomers
have mostly had to guess

if these exoplanets
have atmospheres,

but now we're looking
for them directly,

searching for
Earthlike atmospheres

around Earthlike planets.

This is incredibly hard to do,

so in order to look at
the details of these atmospheres

in the glare of the star

requires
incredibly precise technology

and precise measurements.

Astronomers detect
atmospheres by watching

a planet pass in front
of the star.

A small fraction of light shines
around the edge of the planet

and through the atmosphere

where molecules like water,
hydrogen, and carbon dioxide

absorb particular wavelengths
of light from the star.

If we can see the light
of the star

shining through
around the planet,

we can maybe deduce
some information about

does it have an atmosphere?

What are the properties
of that atmosphere?

How hot is it?
What's it made out of?

That's how we'll be able
to determine

if things in the atmosphere
might indicate

that the surface
is hospitable to life.

So far, we haven't
seen any exoplanets

with atmospheres
that we could live in,

but that's about to change.

Scientists around the world

are working on the next
generation of telescopes

to revolutionize
exoplanet astronomy.

We've got some ideas,
and some telescopes

that are gonna be built probably
in the next couple of decades

will be big enough,
will be sophisticated enough

to be able to see
this sort of thing.

Missions like the James Webb
space telescope...

Seven times more powerful
than Hubble,

it should allow us to see
the atmospheres of planets

across the galaxy

and be a tool that
finally finds a second Earth.

The key things we'd be looking
for in these atmospheres

are in the infrared part
of the electromagnetic spectrum,

which is where Webb
is designed to work.

The James Webb
space telescope is,

I believe, going to be the next
really critical mission

to help us in our search for
potentially Earthlike planets.

We're still searching
for that perfect Earth twin,

and every day,
we get closed to finding it.

30 years ago,
we had zero exoplanets.

Today, we know of thousands.

With the next generation
of instruments,

we're going to uncover
tens of thousands,

hundreds of thousands,
even millions of exoplanets.

All with the ultimate
aim of leaving Earth,

a civilization
spread across the stars.

One of the things
I love about being a human

is the fact that I'm born
with this curiosity.

This curiosity drives us
to explore, explore Earth,

explore our solar system
and beyond into the galaxy.

We'll be learning about
these planets for a long time.

We have just started
this journey.

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