Original subtitles

NARRATOR: 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.

JESSIE: We think 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.

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 examined the atmosphere of this planet, what we find is liquid iron.

The iron is heated up so much, it's been vaporised 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.

AOMAWA: 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 a 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 it's 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 close to the star.

Jupiter is almost 500 million miles away from the Sun.

WASP-76b is just 3,000,000 miles from its star.

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

Temperatures on WASP-76b exceed 4,000 degree F,

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.

JANI: 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 towards the star.

This gravitational grip is called tidal locking.

We're used to the idea of tidal 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.

If you were writing a sci-fi novel,

"Oh, 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'd always be a planet where there was a strange condition,

"Oh, 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 vapour,

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 superheating its atmosphere.

So the upper atmosphere is heated and rises.

The atmosphere on the day side reaches over 4,000 degree F.

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

This difference in temperature sets up spectacular wind streams.

One of the really cool things about this brand new class of planets we've 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 vaporize too. (LAUGHS)

(INTENSE MUSIC PLAYING)

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.

KEVIN: 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 in 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?

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.

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 kinda 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, a tenth 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 planet, 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.

DAN: 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, 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 farther 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 photo evaporation.

This process of photo evaporation

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 four and a half 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.

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

we haven't found the crown jewels,

a planet similar to Earth.

But just what are our chances of finding an Earth-like planet?

Finding a world that replicates the Earth

is really the holy grail of searching for exoplanets,

and I think it's out there,

we just need to keep looking and keep developing new technology and ways of exploring.

PHIL: The big question, are we going to find another Earth?

The answer is, "Yes, we will."

And the reason I say that is because

there are a lot of planets in our galaxy,

and just looking at really rough numbers,

there are probably billions of planets similar to Earth,

and mixing and matching all of those conditions,

it seems to me that the way to bet is that some other planet,

at least one, if not a lot, are gonna look a lot like our own.

The numbers are so big out there in the universe.

There's gotta be something like Earth.

There's gotta be a few things like Earth.

There probably is an exact replica of Earth somewhere.

Will we find it in our galaxy? Probably not.

We're gonna have to accept something that's a bit different from what we picture as perfect.

I look at that variety thinking how much more is possible

and how many more worlds are there out there with life, not as we know it.

So for me I think it's glorious.

There's so much more possibility for life than we previously imagined.

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, "Oh, too hot, too cold, too small, too thick an atmosphere."

No UV rays, no, no, no, doesn't even have a star, but, 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've found such a planet,

just 40 light years from Earth in the constellation Ophiuchus.

Scientists have nicknamed the planet the Water World.

GJ1214b 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 GJ1214b looks like.

Though Earth is called the Blue Planet,

it's only 0.05 percent water by mass.

As much as 70 percent of GJ1214b'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 spend 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, GJ1214b

most likely has no complex arrangement of water and land masses.

The lack of interaction between stable land masses

and a, 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 GJ1214b,

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.

GJ1214b'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've got very cold temperatures.

You're really being sheltered from any incoming solar radiation or sunlight.

So, the water itself could turn to ice.

Most ice on Earth is called ice 1.

When ice is subject to increasing pressure,

its categorization number goes up.

We think the ice on GJ1214b is ice 7,

the type of ice we believe to be on moons like Enceladus and Europa.

On GJ1214b, we believe ice 7 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, the key to trying to understand astrobiology

and then we, 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.

GJ1214b 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 exo-moon 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 think 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, exo-moons.

We expect to see exo-moons 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, 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 three and a half 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'd discovered the first exo-moon.

And that was really exciting.

Known as Kepler-1625b I, this exo-moon candidate

caused a significant dip in the light

and that could only mean one thing.

When we analysed 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 as the planet.

But there may be another way the moon orbiting Kepler-1525b could have formed.

An exo-moon 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 disc of gas and dust.

It's not alone.

Nearby another protoplanet forms.

It's a little bit like twins.

Each twin is going 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,

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+20 307,

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 in the Wild Wild West of the universe,

you have lots of different star systems.

In fact it's more common to have pairs of stars orbiting each other

than to have stars by themselves.

If two star systems are the norm,

what makes BD+20 307 different?

The two stars lie within a bright disc of gas and dust, like Fomalhaut.

But Fomalhaut is a young system,

less than 500 million years old.

BD+20 307 is a billion years old

and that's weird because the material in the disc 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 disc 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 disc 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 neighbourhood.

Planetary objects come in with such energy and such speed

that essentially they are vaporising 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 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+20 307

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 neighbourhood.

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+20 307 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'd 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 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're 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.

So to observe those characteristics in this system

mean that we got really lucky to observe it right now

because if we came back in hundreds or tens of thousands of years,

that dust would have gone away, it would have eliminated itself and we wouldn't see it anymore.

So we got lucky to see it right now when it was still around.

That was still a pretty neat thing to find,

the evidence of two small unseen planets colliding

and that should remind you that solar systems

are not necessarily all that safe, the same thing could happen here.

For life to exist on another planet,

you'd typically wanna look for a nice calm safe neighbourhood for that life to exist.

And so if we have systems where planets are disappearing without a trace,

that's not a great sign.

So when we look at a system that's a billion years old

and has apparently had a huge collision between planets,

it's a good time to step back and look at our solar system

and say, you know, we're four and a half billion years in

and so far our planets are pretty stable.

Some things have moved around here and there

but we're not seemingly at risk of having two planets collide.

It's a scary lesson to learn, the possibility of ongoing planetary collisions.

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 four and a half billion years, our Sun will expand to become a red giant.

When our own star turns into a red giant

in four and a half 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 centre.

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 degree F.

The cooler stars appear red

so later in stars' lives, they're big bloated red giants.

When a star goes red giant, it expands and it expands outwards

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

and engulf some of the planets that orbit that star.

The surface has cooled but temperatures still exceed 8,000 degree F.

If you're in the red giant expansion zone, you're going to 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 asteroseismology.

Asteroseismology measures the vibrations of stars.

Asteroseismology applied to these stars

is a really useful way to get at more information

than we might 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 analysed the way this star was ringing,

we realized it was actually less massive than we'd determined from other methods.

It told us that star probably has already gone through its red giant phase.

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 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,

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 more out there than we had ever imagined.

We've 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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