MIKE ROWE: 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. - ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
[electricity buzzing]
[explosion blasts]
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.
ROWE: 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.
ROWE: 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.
SHIELDS: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
RADEBAUGH: The heat is absolutely insane.
There is nothing like it in our solar system.
ROWE: 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.
ROWE: 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.
ROWE: 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.
RADEBAUGH: I mean, this thing has iron rain.
How lazy is that
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 would always be some planet where there was some
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?
THALLER: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
RADEBAUGH: 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.
ROWE: 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. - ROWE: 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.
WALSH: 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.
ROWE: 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?
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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?
ROWE: 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.
ROWE: Scientists have a theory about how
the super-puff planets formed.
DURDA: 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.
ROWE: 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.
ROWE: 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.
ROWE: These planets have been growing in size for around
500 million years,
and as they've been growing, they've also been moving.
SUTTER: 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.
ROWE: 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.
ROWE: 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?
ROWE: 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.
ROWE: 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 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.
ROWE: When it comes to finding life,
there is one basic element that everyone agrees
is necessary.
SHIELDS: There is a phrase that we use whenever
we talk about the search for life elsewhere --
Follow the water.
ROWE: 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,
ROWE: 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.
ROWE: 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.
ROWE: Unlike Earth, GJ 1214 b most likely has no complex
arrangement of water and land masses.
WALSH: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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?
ROWE: 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.
ROWE: 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.
ROWE: We expect to see exomoons around exoplanets,
because our own solar system is full of moons.
CHRISTIANSEN: 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.
LANZA: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: But there may be another way
the moon orbiting Kepler-1625b could have formed.
RADEBAUGH: 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.
ROWE: 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.
RADEBAUGH: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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?
OLUSEYI: 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.
ROWE: 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.
ROWE: Early in its existence, our solar system was
a demolition derby,
with many, many collisions.
It's how rocky planets like ours formed.
DURDA: 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.
ROWE: 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.
ROWE: 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.
DURDA: It's actually been a bit of a wake-up call.
It's a transformation in our understanding
of how our solar system works.
ROWE: 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.
SHIELDS:: But could this all explain
the case of the Fomalhaut b system?
Could it have collided with another planet,
wiping it out completely?
ROWE: 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.
CHRISTIANSEN: Instead of a planet that we thought
we captured inside the ring,
it was actually a collision between two
smaller objects called planetesimals.
ROWE: Planetesimals are infant planets,
bodies that measure from a few miles to hundreds of
miles across.
CHRISTIANSEN: 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.
ROWE: They didn't spot a planet,
but they did learn a very important lesson.
DURDA: 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.
ROWE: 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?
ROWE: In 4.5 billion years, our sun
will expand to become a red giant.
RADEBAUGH: 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.
ROWE: 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.
ROWE: A stage that's terminal for a planet orbiting this star.
LANZA: 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.
CHRISTIANSEN: 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.
ROWE: 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.
RADEBAUGH: 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.
ROWE: 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.
ROWE: 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.
[dinging sound]
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.
ROWE: The vibrations from the red giant star
reveal something highly surprising.
CHRISTIANSEN: 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.
ROWE: 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.
ROWE: 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.
ROWE: So how can we explain this escape act?
Could it be of this planet changed its orbital position
to allow it to cheat death?
ROWE: 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.
ROWE: 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.
ROWE: This exoplanet may have escaped oblivion,
but its future doesn't look bright.
Its star will shrink down to a cool, dim white dwarf.
LANZA: 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.
ROWE: 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.
ROWE: 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.
PLAIT: 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.
BULLOCK: 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.
CHRISTIANSEN: 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.