All language subtitles for How the Universe Works s09e11 Mystery of Alien Worlds.eng

We're discovering the
cosmos is full of alien planets.

It's so exciting --
In my lifetime,

we didn't even know
if exoplanets existed,

and now, they're everywhere.

- It's incredible.
- Exoplanets,

Strange worlds outside
our solar system.

Hellishly hot worlds,
violently colliding worlds,

worlds getting eaten by
their stars.

There's much, much more out
there than we had ever imagined.

Exoplanets are rewriting
what makes a planet a planet.

It's a bit of a mystery how
these planets can even exist.

It seems to defy
the laws of physics.

Alien worlds
that challenge our understanding

of planetary systems.

It's actually been
a bit of a wake-up call.

We keep thinking we understand
what's happening,

and then the universe
surprises us with something

completely different.

Exoplanets are shaking up

our understanding
of the universe.

The cosmos is a chaotic array
of the odd,

the weird, and the wonderful.

The more we find,
the less we know.

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We've now found
over 4,000 exoplanets,

a rapidly increasing array
of strange alien worlds,

and the more we uncover,
the weirder they get.

They don't act at all like

what we're seeing
in our solar system.

There are planets out there
interacting, there are planets

dive-bombing their sun,
gigantic planets

orbiting really close in --
Everything, in every kind of

combination you can
possibly imagine.

One alien world truly
stands out.

This is the planet from hell.

When we examine the atmosphere
of this planet,

what we find is liquid iron.

The iron is heated up so much,

it's been vaporized,
and it's falling out of

the sky like rain.

But why is this planet
so much more

extreme than the ones
in our solar system?

What this is telling us is
that the universe is really

good at making lots of planets

that are wildly different
than the one we live on.

Outside of our apparently

stable and calm solar system,
it is the wild,

wild West out in the cosmos,
where crazy stuff is happening,

completely unchecked.

WASP-76b
is 640 light-years away,

in the Pisces constellation.

At first, this planet looks
like nothing out of

the ordinary.

WASP-76b orbits its star,
just like our sun,

which is really reassuring in
a universe which is full of

the unfamiliar.

WASP-76b is a gas giant,

a bit like Jupiter
in our solar system,

but its location makes
a big difference.

You take a star similar to ours,

you take a planet
similar to Jupiter,

but instead of parking it in
the outer solar system,

you put it really, really,
really close to the star.

Jupiter is almost 500
million miles away from the sun.

WASP-76b is just three
million miles from its star,

and that's what makes
this planet a hot Jupiter.

Temperatures on WASP-76b
exceed 4,000 degrees Fahrenheit,

creating one of the most
extreme environments

in the universe.

If I were fortunate enough
to be able to go and visit

this world, I would have

to take a lot of precautions,
because it is

essentially a hellscape
on that planet.

The heat
is absolutely insane.

There is nothing like it
in our solar system.

The fact that it's so close

to its star has
another consequence.

WASP-76b's spin is locked
to its star.

The gravity from the star
will grip onto the planet,

slow its rotation over time, if
it had any to start with, and

lock it so that one face always
faces toward the star.

This gravitational grip
is called tidal locking.

We're used to the idea of
tidally locking

with our own moon -- we only
ever see one side of the moon.

The far side of the moon
continues to face space.

There are consequences for
being a tidally locked planet,

and not all of them are good.

That can set up some pretty
extreme weather conditions,

very hot on the daytime side

and extremely cold on
the nighttime side.

In 2020,
we took a closer look at

the atmosphere between the day
and night side of the planet.

This twilight zone
has plenty of rain,

but here, it rains molten iron.

I mean,
this thing has iron rain.

How lazy is that

if you were writing
a sci-fi novel?

Let's make some iron rain,
but this is reality.

It is hot enough to vaporize
iron and make it rain.

When I grew up watching sci-fi
on TV and reading novels,

there would always be some
planet where there was some

strange condition.

Iron rains out of the sky,
and I'd be like,

that's ridiculous.

And now what I found out
is that nature

is way nuttier than anything
we could have thought of.

How do you get vaporized iron?

Well, most materials can
exist in different states,

so think about water, right?

Water can be
a solid when it's ice,

and then when you heat it up,
it becomes water,

the liquid part of water,
and then if you heat it up more,

it becomes steam,
like out of a kettle.

And this is true of every
chemical element.

So for iron, if you heat it
even more up, it becomes a gas,

so you really can have clouds
of iron vapor condensing

and raining liquid iron.

These nightmare weather
conditions are

a direct result of WASP-76b's

proximity to its star.

WASP-76b is so close
to its star that its star

is super heating its atmosphere.

So the upper atmosphere is
heated and rises.

The atmosphere
on the day side

reaches over 4,000
degrees Fahrenheit.

The planet's night side is
cooler at 2,730

degrees Fahrenheit.

This difference in temperature

sets up spectacular
wind streams.

One of the really cool things
about this brand-new class

of planets we found is
discovering weather

we've never seen before.

These hot Jupiters have these
equatorial jets of wind that

are supersonic, traveling at
thousands of miles per hour,

and that wind is pulling
the rain around

to the night side.

The air on the hot side
expands, because it's

being heated and will flow
over to the other side.

So you get these torrential
winds blowing

that hot air to the cooler side.

If there is vaporized iron,
gaseous iron, in the atmosphere

on the hot side,

it will blow over
to the cooler side.

On Earth, the fastest
recorded winds have reached

speeds in excess
of 250 miles an hour.

On WASP-76b, winds hit speeds

in excess of
11,000 miles an hour,

strong enough to move millions
of tons of iron vapor to

the planet's night side,

where it undergoes
a dramatic change.

It's cooler there,
can't be maintained as a gas,

so it condenses and becomes
a liquid and then rains out.

There are clouds
coming up and forming,

and then rain is falling,

but it's iron, it's iron vapor.

It's iron rain.

It would be spectacular
to see in that

brief moment you have before
you vaporized, too.

You might think that
having clouds of iron

rain is WASP-76b's
strangest feature.

But astronomers are even
more puzzled

by the location
of this gas giant.

When you look at the planets
in our solar system, you can

divide them into gas giants
like Jupiter and rocky planets

- like the Earth.
- In our solar system,

rocky planets are close to
the sun, and gas giants are

farther away.

But in exosystems,
the positions of

different kinds of planets
are all messed up.

We're finding
Jupiter-sized planets

super close to
their stars instead of

in the outer parts of
the solar system.

And we're finding rocky
planets really close to

stars and packed in really
tight and weird configurations.

These planets orbiting
close to their stars

survive being blasted with
intense radiation.

They're taking part in
the ultimate

endurance challenge.

But not all worlds are so tough.

Some are so light and delicate,

they're barely there at all.

Are these weird puffballs
even planets?

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The more exoplanets we find,

the more we realize how weird
these new worlds really are.

Some planets are so unlikely,
so odd, and so bizarre,

scientists wonder,
how can they even exist?

Before we discovered
exoplanets, we thought that our

solar system would
be representative,

that other solar systems
would look like ours.

Rocky planets, gas giants,
ice giants.

But when we went out there
and found them,

they don't look anything like
our solar system.

In 2012,
we discovered three gas giants

orbiting the sun-like star,

Kepler-51, located
2,615 light-years away

in the constellation of Cygnus.

At first, there seemed to be

little to distinguish
these planets from Jupiter.

Then, in 2019,
we took a closer look.

You go into a system like
Kepler-51, a sun-like star,

and you kind of go in expecting
or hoping to find,

you know, Earth-like planets,
planets familiar from our own

solar system.

And then you find something
like this,

and you're kind of like, you
know, what the heck is that?

We've been hunting for
exoplanets, and we've gotten

used to some weird things,

but this is truly out there.

This is a truly alien scenario.

According to how we think
planets are formed,

the worlds orbiting Kepler-51
shouldn't exist.

These three objects
orbiting Kepler-51

are kind of like cosmic conmen,
because they appear to be

like Jupiter, but in fact,

their masses are
just a few times that of Earth.

These are planets that have
like 1/10 of the density

of water.

If you could throw these
things into a giant ocean,

they would float.

The super-puff
planets form from

helium and hydrogen,
just like Jupiter.

But unlike Jupiter, gas on

the super-puffs is not densely
packed together.

It's loose, creating big,
fluffy balls.

So even though they're
the same size as Jupiter,

their mass is just one percent.

That's like a heavyweight
fighter with

the mass of a prairie dog.

The super-puff planets,
which is the greatest name ever

for a planet, is really
a very low density planet.

Really, what it means is that
it's very, very fluffy

and light -- it's almost like
it has a light,

snow-like consistency.

The extremely
low mass of these planets

presents a problem for
planetary scientists.

This is an incredibly
unlikely situation.

How can these super-puff
worlds even exist?

Gas giants like Jupiter
start with an ice and rock core.

This core grows until
it generates

enough gravity to pull in gas,

building an atmosphere almost
2,000 miles deep.

Do the super-puff planets
form the same way?

It's a bit of a mystery
how these planets can

even exist just based on what
we know about planet formation.

It's really an unusual thing to
have something that is so

light, because that's not how
planets that we recognize

typically form.

Scientists have
a theory about how

the super-puff planets formed.

We see these
three planets relatively close

to their parent star today,

but very likely, given their
composition, they probably

formed a lot farther away,

beyond the snow line,
as we call it.

Star systems split
into two regions,

a warm inner region close to
the star, and a colder

outer region farther away.

The snow line
separates the two zones.

Gas planets only form
outside the snow line,

far from the star, where gas
can clump together.

You're actually able
to grab onto a lot

of hydrogen and helium
and build up an atmosphere.

Beyond the snow line,

water condenses to a solid form.

This process greatly boosts
the formation of

minute planets.

These icy planetesimals
jumpstart the rapid

growth of what will become
gas giants.

The super-puffs formed even
further out than Jupiter, in

a far colder area --
Compared to Jupiter,

the super-puffs had
a relatively small core,

but because they developed in
this colder region, they still

pulled in a huge quantity of
hydrogen and helium.

You end up with something that
is kind of large in size

but still really low density,

low in mass.

These planets have been
growing in size for around

500 million years,

and as they've been growing,
they've also been moving.

The gravity of
their parent star can pull

these planets closer,
so we can see chains of

super-puff planets like --
Like cars on a train,

all marching inwards
towards the star.

The closer
they get to the star,

the more stellar winds batter
the super-puffs.

The winds blast off the loose,

puffy atmosphere in a process
called photoevaporation.

This process of photoevaporation
results in these planets

losing their atmospheres,

literally losing billions of
tons of atmosphere

every second.

These super-puffs are
like orbiting dandelions

that are getting
blown away in the wind.

Scientists predict that
over the next 4.5 billion years,

the super-puff planet closest to

its star will lose
all its atmosphere,

leaving a planet with a radius
smaller than Neptune.

The other two super-puff

planets will escape
largely unscathed.

We are rapidly discovering

a wide range of weird,
oddball worlds.

Planet hunters are also
searching for something

more familiar,

something critical
for life as we know it.

We now think there
could be planets dominated

by water.

But are these water worlds
the oasis

we've been searching for?

On the search for alien
worlds, we've uncovered plenty

of the strange, the scary,

and the incredible,
but we still haven't detected

anything remotely like
our planet.

For all these treasures
that we've been digging up,

we haven't found
the crown jewels --

A planet similar to Earth.

Finding an exoplanet
with conditions suitable

for life takes a lot of luck.

Sifting through these
exoplanets, looking for

something that's habitable

for life, is like
an interstellar dating app.

If we have molten iron rain,
that's definitely out.

You see toxic atmosphere,
and you swipe, and you see

red giant, and you swipe.

So it's like too hot,
too cold,

too small, too thick
in atmosphere.

No UV rays. No, no, no.

Doesn't even have a star.

Ba-da-da,
like it's just not working

again and again and again.

When it comes to finding life,

there is one basic element
that everyone agrees

is necessary.

There is a phrase
that we use whenever

we talk about the search
for life elsewhere --

Follow the water.

And now we think
there could be lots

of worlds out there that do
contain water.

But is there a catch?

Could they hold too much water?

A 2019 study suggests
the Milky Way might contain

many worlds,

with thousands of times more
water than Earth.

Many of these planets are
a bit smaller than Neptune.

We call them sub-Neptunes.

What they found were these
sub-Neptunes,

planets smaller than Neptune
but bigger than Earth,

Unlike any planets
we'd seen before.

We think we found such
a planet just 40 light-years

from Earth in the constellation
Ophiuchus.

Scientists have nicknamed
the planet the Waterworld.

GJ 1214 b could be one of
these sub-Neptunes,

with more water than
we would know what to do with.

So far, we're not
too sure what GJ 1214 b

looks like -- though Earth is
called the Blue Planet,

It's only .05 percent
water by mass.

As much as 70 percent
of GJ 1214 b's mass

could be water.

The planet is thought to have
a rocky core,

strange oceans, and a hot,
steamy atmosphere of

water vapor.

We spent a lot of time looking
for very small amounts of

water to establish whether
or not a planet could even

be habitable,

and so it's kind of amazing
that we just

found this planet that was
essentially nothing but water.

Unlike Earth, GJ 1214 b
most likely has no complex

arrangement of water
and land masses.

The lack of interaction

between stable land masses
and a healthy,

long-term stable ocean might
really be a killer,

and you might need that land

interacting with that water to
have a good location for life.

We think life began in
the oceans,

but it needed chemicals from
rocks to start.

Without the interaction
between land and oceans,

life might not have evolved.

Not only is there no land-sea
relationship on GJ 1214 b,

evolution here may
be limited in another way.

Earth's oceans are
replenished with chemicals

from hydrothermal vents

thousands of feet down
on the seabed.

GJ 1214 b's ocean floors are
thousands of miles deep,

Right at the bottom of
these incredibly deep oceans,

you've got very high pressures.

You've got so much
water above you,

and you got very
cold temperatures.

You're really being shielded
from any incoming

solar radiation or sunlight,

so the water itself
could turn to ice.

Most ice on Earth
is called Ice I.

When ice is subject to
increasing pressure,

its categorization number
goes up.

We think the ice on GJ 1214 b

is Ice VII, the type of ice

we believe to be on moons
like Enceladus and Europa.

On GJ 1214 b,

we believe Ice VII
seals off the seabed,

preventing potential nutrients
from the rocky core from

passing into the ocean.

We've been following the water,
that's been the key to trying

to understand astrobiology,

and then we find these worlds
where it's too much

of a good thing,
there's too much

water for --
Perhaps for life to exist,

so it's certainly one of those
things that a little you need,

but maybe too much is bad, too.

We need to find worlds
with just the right

amount of water and land for
life to evolve.

GJ 1214 b looks like a dead
end, but the hunt goes on.

Space is big, and I like
the idea that it's not just

for us, so I'm hopeful,

whether it'll be in my lifetime
or my daughter's,

I don't know, but I'm hopeful.

As we continue
to probe the cosmos,

we've discovered one hopeful,
distant object, a moon.

But this exomoon is a monster.

It's four times larger
than Earth.

So how did it get so big?

Each time we find new
stars and their weird worlds,

we have to rethink the rules
of our own planetary system.

We keep thinking
we understand what's happening,

and then the universe
surprises us with something

completely different.

Our search for exoplanets
has been remarkably successful,

but we've yet to spot those
highly familiar objects that

orbit many planets
in the solar system.

It's been an incredibly
exciting time finding over

4,000 exoplanets,

but there's still something we
haven't found that we're really

excited by -- exomoons.

We expect to see
exomoons around exoplanets,

because our own solar system
is full of moons.

Almost all
the planets in our solar system

have moons around them.

In fact, Earth is the only
planet that only has one moon.

Most have more.

So the question is,

you know, are moons
unusual in general for planets?

Or are we just not seeing
the moons that are out there?

Astronomers find exoplanets
when they pass in front of

a star.

It's called a transit
and creates a dip

or a wobble in the light
from the star.

But moons pose a problem.

They're incredibly small,
so to find even one,

we'd have to be very lucky.

In October 2017,
astronomers took a closer

look at a star 8,000
light-years away.

The light dipped
as a Jupiter-sized

exoplanet passed
in front of the star.

Then, 3.5 hours later,
they saw the light dip again.

There was actually evidence as
this planet transited

and went across the star,

blocking out a little bit of
light of the star, that there

was another large object
rotating around the planet.

The planet, Kepler-1625b,
appeared to have a companion

orbiting around it.

By looking
at the light that was coming

from the system
and how it was changing,

they thought they discovered
the first exomoon,

and that was really exciting.

Known as Kepler-1625b I,

this exomoon candidate

caused a significant dip in
the light.

And that can only mean
one thing.

When we analyze the signal
caused by this potential moon,

it must have been caused by
something four times the width

of Earth, so something like
the size of Neptune,

and we have no moons
in our solar system

that are Neptune-sized.

In our solar system,

objects the size of Neptune

are planets, not moons.

Neptune and planets of
a similar mass are ice

and gas giants.

Moons in our solar system
don't have this composition.

They're all solid.

Just when we thought
we understood moons

and how they worked,

now here comes an exoplanet
to tell us not so fast.

One problem with this system
is we don't

have many good ideas
for how it formed.

Everything we know about
moon formation comes from

solid moons.

There are two main ways that
we think moons can form.

The first is you have
a rocky world,

something comes in
and smacks it,

and the thing that smacks it,
plus the debris that's ejected

from that world,
then go on to form

a new moon,
which is how we think

the Earth's moon formed.

Another way,

potentially, is that when that
planet was forming and there

was a big cloud of dust
and it was swirling

around that the moons
formed out of that

dust at the same time
of the planet.

But there may be another way

the moon orbiting Kepler-1625b
could have formed.

An exomoon

doesn't have to form around
the planet itself like we see

around Jupiter or Saturn.

But instead, let's imagine
there's some kind of rogue

planet wandering by
a larger planet,

and it gets captured
and becomes a moon.

Perhaps billions of years ago,

the planetary core
of Kepler-1625b

grows in a disk of gas and dust.

It's not alone.

Nearby,
another protoplanet forms.

It's a little bit like twins.

Each twin is gonna try to
argue for their own amount of

resources in the womb,

and that's sort of the same
thing happening here.

It's a battle for resources.

Kepler-1625b grabs
more gas and dust

than its twin,
growing larger and larger.

The now huge exoplanet slowly

drags its smaller
sibling closer,

eventually pulling it
into orbit.

The smaller, protoplanet
becomes Kepler-1625b's moon.

The one thing that exoplanets
have taught us is that we

have no idea how systems in
our universe have to evolve.

And so it's completely
feasible that this -- there is

a really large Neptune-sized
moon around

a host planet, and we just
need more evidence in order to

make sure that that's true.

Scientists are confident
that such evidence will

be found when new technology
comes online.

But sometimes astronomers spot
things that

make them doubt
their own instruments,

events like
a planet disappearing.

We've discovered some
extraordinary exoplanets,

super-hot worlds
with molten iron rain,

super-puff planets so fragile
they might blow away,

exoplanets that defy physics.

But stranger still is the case
of the disappearing planet.

Over a decade ago, the Hubble
telescope spotted a planet

orbiting Fomalhaut,

one of the brightest stars in
the night sky.

Fomalhaut is a very nearby,
very young star.

And the images of this system
are incredible, because what

you see is the central star
surrounded by a bright ring.

It looks just like
the Eye of Sauron.

We observed the new
planet, called Fomalhaut b,

for six years.

Then something
surprising happened.

All of a sudden,
it just wasn't there anymore.

Where did this planet go?
- For it to suddenly be gone,

it was amazing.
It was astounding.

It was terrifying.

If Fomalhaut b can
suddenly vanish,

what could that mean for other
planets and us?

We live on a planet,
so we have a vested interest

in understanding how planets
could disappear, if that's

a phenomenon that exists.

October 2019.

Astronomers investigate
the idea of a vanishing planet

by looking at BD+20307,

a star system
straight out of the movies.

Just like that iconic image
from Star Wars from Tatooine,

where you look up,

and there's two stars
in the sky.

That's actually not that crazy.

Out there in the wild,
wild West of the universe,

you have lots of different
kinds of star systems.

In fact, it's more common to
have pairs of

stars orbiting each other than
have stars by themselves.

If two star systems
are the norm,

what makes BD+20307 different?

The two stars lie
within a bright

disk of gas and dust
like Fomalhaut.

But Fomalhaut is a young

system less than
500 million years old.

BD+20307 is a billion years old,

and that's weird, because
the material in the disk is so

old, it should have formed
new planets long ago.

So what's going on?

Rings of dust are
characteristic of

young planetary systems.

What does it mean when we see
a disk of material surrounding

an older star,

a star over a billion years old?

Well, one thing could be
the collisions of planets.

We think that, in this system,

planets collided, and that
formed the disk that we see.

When planets collide,

they don't just spew out
masses of material.

The violence of the event

shakes up the whole
planetary neighborhood.

Planetary objects come
in with such energy

and such speed that essentially
they are vaporizing each other.

Observing a planet essentially
being destroyed

tells us something

about what might happen
in our own solar system.

Our planets feel very stable
in their orbits,

but we don't realize that, in
the future, those orbits might

be very different
than they are today.

Early in its existence,
our solar system was

a demolition derby,

with many, many collisions.

It's how rocky planets
like ours formed.

Back then,
there were more than eight

or nine planets
in our solar system.

There were hundreds,
and planets were running

into each other and interacting
with each other all the time.

Eventually, the planets
we see today formed,

and our solar system

settled into a nice,
regular arrangement.

Finding strange systems
like BD+20307

makes us question
that narrative.

One of the really valuable
lessons that astronomers have

learned from studying planets
around other stars is

that it appears very clear now
that planets don't necessarily

stay where they are
in a solar system.

Over time,
the orbits of planets

in our solar system
slowly shift.

The repercussions
of these orbital

fluctuations could shatter
our cosmic neighborhood.

The odds are slim,
but billions of years from now,

Mercury could be pulled out of
its orbit by gravitational

interactions with Jupiter.

This action would set Mercury
on a fateful course.

One potential future that
our solar system may have is

actually that Mercury could
collide with Earth,

which sounds crazy but would
also be a real bummer.

So what we see in BD+20307

is theoretically possible
in our own solar system.

It's actually been
a bit of a wake-up call.

It's a transformation
in our understanding

of how our solar system works.

Studying other systems
shows us

just how vulnerable planets
can be.

Things can change at any time
in a planetary system, that we

could be watching a planet
on its orbit one day and poof,

it could suffer that really
big collision the next.

But could this all explain

the case of
the Fomalhaut b system?

Could it have collided
with another planet,

wiping it out completely?

Well, maybe.

April 2020.

Astronomers at
the University of Arizona come

up with a new theory
about Fomalhaut.

Every good mystery needs
a shocking twist at the end,

and the twist in this tale
could be that the planet

disappeared
before Hubble's eyes,

because it never was there
to begin with.

Instead of
a planet that we thought

we captured inside the ring,

it was actually a collision
between two

smaller objects called
planetesimals.

Planetesimals
are infant planets,

bodies that measure
from a few miles to hundreds of

miles across.

They smashed together

and created a huge dust cloud,

which we caught up with Hubble.

All we saw was a bright blob

of light that looked
like a planet.

They didn't spot a planet,

but they did learn a very
important lesson.

We were actually
observing a process, part of

the way that solar systems
grow and are born.

And, in many ways,
that's, I think,

more important and more useful
to us than having spotted yet

another planet.

Exoplanets are opening
our eyes to the way

the universe works.

We must question some
long-held assumptions.

One standard text predicts

the sun will eventually
engulf the Earth.

But could there be a way out?

Do some planets cheat death?

In 4.5
billion years, our sun

will expand to become
a red giant.

When our own star turns into

a red giant in 4.5 billion
years from now,

then it will expand, and it
will engulf Mercury and Venus

and the Earth and the moon,

and it will cook the surfaces
of all of those bodies.

But is there a way of
escaping this apocalypse?

When we look beyond
our solar system to

the Aquarius constellation,
we find hope.

Planet HD 203949 b is living
on borrowed time.

It orbits a red giant star.

Red giant stars have burned up
all the hydrogen in

the middle, and they've moved
to the next stage of

their development.

A stage that's terminal
for a planet orbiting this star.

If you're a planet,
and you've been orbiting

fairly close to your star
for billions of years,

you might feel like you've got
a good relationship,

that it's pretty safe.

But in fact, you would be wrong.

In fact, this star that has
been taking care of

you for billions of years
is now going to destroy you.

After billions of years of
generating heat

and light, a star's
hydrogen fuel runs out.

The star's core becomes
unstable and contracts.

Gravity just pulls
everything to the center.

And then there's a rebound.

Everything comes back again,
and that creates

this big envelope of gas
around the star.

The outer layers of gas
blow off and expand outwards.

As the gas envelope gets bigger,

the surface cools to
under 10,000 degrees Fahrenheit.

The coolest stars appear red,
so late in stars' lives, they're

big, bloated red giants.

When a star goes
red giant, it expands,

and it expands outward,

and it's likely that it's
going to come and engulf some

of the planets that orbit
that star.

The surface is cooled,

but temperatures still exceed
8,000 degrees Fahrenheit.

If you're in the red giant
expansion zone,

you're gonna get cooked.

Exoplanet HD 203949 B
orbits within this zone.

So is this planet toast?

September 2019.

We take a closer look
at the red giant

threatening the planet
using a technique called

astroseismology.

Astroseismology measures
the vibrations of stars.

Astroseismology applied to
these stars is a really useful

way to get at more information

than we might normally get
by just looking at

their brightness
or their temperatures.

Vibrations go back and forth
within the stars,

and we can see those by
monitoring the surface.

One of the things that happens
when these stars get to

their red giant phase is
they start ringing like a bell.

When we hear these
stars ringing,

it actually gives us the most
precise information we have

about any stars.

We can measure their mass,
their radius,

their density much more
exquisitely than any

other star.

The vibrations from
the red giant star

reveal something
highly surprising.

When we analyzed
the way this star was ringing,

we realized it was actually
less massive than we determined

from other methods.

It told us that star
probably has

already gone through
its red giant phase.

Um, the star we see today is
a little smaller than it should

have been quite a while back.

This star has lost some of

its outer layers and has
started to shrink.

If this star has already gone
through its red giant phase

and is shrinking again,

that means at one point, it was
bigger than the orbit of

this planet.

If the planet was
within the red giant zone,

it should have been destroyed.

But somehow, it remained intact.

By all accounts,
this planet shouldn't exist.

But somehow,
we see it there today,

cheating death --
What a survivor.

So how can we explain
this escape act?

Could it be of this planet
changed its orbital position

to allow it to cheat death?

Or maybe HD 203949 b was
never even in the kill zone.

Perhaps this planet originally
formed further out

and migrated in after the red
giant phase was completed.

Maybe some of
the clouds of gas

shed from the star reached
the planet.

This gas dragged on the planet,

slowing its orbit down.

Gradually, the planet migrated
inwards after

the star reached
its maximum size.

And we then evolve down to
the system that we see today,

a post red giant star with
a planet

that shouldn't be there,
so to speak.

This exoplanet may have
escaped oblivion,

but its future doesn't
look bright.

Its star will shrink down to
a cool, dim white dwarf.

If I were a planet, you know,

I would be sad at
the existence that I would live

afterward, just because it would

be so different, it would
be cold and dark,

and I would still be bound
with a star

that is no longer there in
the same way that it was.

This is our future,

but it won't happen for
another five billion years.

In the meantime, we can be
thankful we live on Earth

rather than one of
the weird worlds

we've discovered in our galaxy.

The more and more
exoplanets we find,

the more we realize how lucky
we really are.

We see planets that are
too big, too small,

too much atmosphere,

too little atmosphere,
too close to their star,

too far from their star.

Too little water,
too much water.

Everything on Earth is
just right.

Compared to our home world,

exoplanets push and twist

and stretch the boundaries
of planetary science.

But every new world
we discover expands our

knowledge and moves us closer
to understanding our place

in the universe.

If we can understand how
planets form and why they form

the way they do
and how they evolve,

then we can know our past,
present, and future even better.

I think as we find more
and more of these planets,

we're going to find out more
about our own solar system

and our place in this menagerie.

A lot of times,
we think about other planets

and even life in the universe
as resembling

very much our own.

But these weird worlds open
the possibility that

there's much, much more out
there than we had ever imagined.

We found so many
different kinds of crazy worlds

in crazy places,
doing crazy things.

It's so interesting.

Imagine how boring
it would be if

we only found our solar system
everywhere else.

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