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00:00We're discovering the cosmos is full of alien planets.
00:05It's so exciting. In my lifetime, we didn't even know if exoplanets existed.
00:11And now, they're everywhere. It's incredible.
00:14Exoplanets. Strange worlds outside our solar system.
00:19Hellishly hot worlds, violently colliding worlds, worlds getting eaten by their stars.
00:25There's much, much more out there than we had ever imagined.
00:30Exoplanets are rewriting what makes a planet a planet.
00:34It's a bit of a mystery how these planets can even exist.
00:38It seems to defy the laws of physics.
00:41Alien worlds that challenge our understanding of planetary systems.
00:46It's actually been a bit of a wake-up call.
00:49We keep thinking we understand what's happening, and then the universe surprises us with something completely different.
00:54Exoplanets are shaking up our understanding of the universe.
01:00The cosmos is a chaotic array of the odd, the weird, and the wonderful.
01:06The more we find, the less we know.
01:21We've now found over 4,000 exoplanets.
01:26It's a rapidly increasing array of strange alien worlds.
01:30And the more we uncover, the weirder they get.
01:34They don't act at all like what we're seeing in our solar system.
01:38There are planets out there interacting. There are planets dive-bombing their sun.
01:41Gigantic planets orbiting really close in.
01:44Everything, in every kind of combination you can possibly imagine.
01:48One alien world truly stands out.
01:53This is the planet from hell.
01:57When we examine the atmosphere of this planet, what we find is liquid iron.
02:01The iron is heated up so much it's been vaporized.
02:04And it's falling out of the sky like rain.
02:08But why is this planet so much more extreme than the ones in our solar system?
02:13What this is telling us is that the universe is really good at making lots of planets
02:18that are wildly different than the one we live on.
02:23Outside of our apparently stable and calm solar system,
02:27it is the wild, wild west out in the cosmos,
02:31where crazy stuff is happening completely unchecked.
02:35WASP-76b is 640 light-years away in the Pisces constellation.
02:43At first, this planet looks like nothing out of the ordinary.
02:47WASP-76b orbits a star just like our sun,
02:50which is really reassuring in a universe which is full of the unfamiliar.
02:54WASP-76b is a gas giant, a bit like Jupiter in our solar system.
03:01But its location makes a big difference.
03:05You take a star similar to ours, you take a planet similar to Jupiter,
03:10and instead of parking it in the outer solar system, you put it really, really, really close to the star.
03:17Jupiter is almost 500 million miles away from the sun.
03:22WASP-76b is just 3 million miles from its star.
03:27And that's what makes this planet a hot Jupiter.
03:34Temperatures on WASP-76b exceed 4,000 degrees Fahrenheit,
03:39creating one of the most extreme environments in the universe.
03:44If I were fortunate enough to be able to go and visit this world,
03:48I would have to take a lot of precautions, because it is essentially a hellscape on that planet.
03:55The heat is absolutely insane. There is nothing like it in our solar system.
04:01The fact that it's so close to its star has another consequence.
04:05WASP-76b's spin is locked to its star.
04:11The gravity from the star will grip onto the planet, slow its rotation over time, if it had any to start with,
04:17and lock it so that one face always faces toward the star.
04:21This gravitational grip is called tidal locking.
04:26We're used to the idea of tidally locking with our own moon.
04:29We only ever see one side of the moon. The far side of the moon continues to face space.
04:33There are consequences for being a tidally locked planet, and not all of them are good.
04:37That can set up some pretty extreme weather conditions.
04:40Very hot on the daytime side, and extremely cold on the nighttime side.
04:47In 2020, we took a closer look at the atmosphere between the day and night side of the planet.
04:56This twilight zone has plenty of rain, but here it rains molten iron.
05:04I mean, this thing has iron rain.
05:08How lazy is that if you were writing a sci-fi novel? Oh, let's make some iron rain.
05:12But this is reality. It is hot enough to vaporize iron and make it rain.
05:19When I grew up watching sci-fi on TV and reading novels,
05:22there'd always be some planet where there was some strange condition.
05:25Oh, iron rains out of the sky! And I'd be like, that's ridiculous.
05:29And now what I've found out is that nature is way nuttier than anything we could have thought of.
05:36How do you get vaporized iron?
05:38Well, most materials can exist in different states, so think about water, right?
05:43Water can be a solid when it's ice, and then when you heat it up, it becomes water, the liquid part of water.
05:49And then if you heat it up more, it becomes steam, like out of a kettle.
05:52And this is true of every chemical element.
05:55So for iron, if you heat it even more up, it becomes a gas.
05:58So you really can have clouds of iron vapor condensing and raining liquid iron.
06:05These nightmare weather conditions are a direct result of WASP-76b's proximity to its star.
06:14WASP-76b is so close to its star that its star is superheating its atmosphere.
06:18So the upper atmosphere is heated and rises.
06:22The atmosphere on the day side reaches over 4,000 degrees Fahrenheit.
06:27The planet's night side is cooler, at 2,730 degrees Fahrenheit.
06:34This difference in temperature sets up spectacular wind streams.
06:40One of the really cool things about this brand new class of planets we found is discovering weather we've never seen before.
06:46These hot Jupiters have these equatorial jets of wind that are supersonic, traveling at thousands of miles per hour.
06:52And that wind is pulling the rain around to the night side.
06:56The air on the hot side expands because it's being heated and will flow over to the other side.
07:01So you get these torrential winds blowing that hot air to the cooler side.
07:05If there is vaporized iron, gaseous iron, in the atmosphere on the hot side, it will blow over to the cooler side.
07:14On Earth, the fastest recorded winds have reached speeds in excess of 250 miles an hour.
07:21On WASP-76b, winds hit speeds in excess of 11,000 miles an hour.
07:28Strong enough to move millions of tons of iron vapor to the planet's night side, where it undergoes a dramatic change.
07:38It's cooler there, can't be maintained as a gas, so it condenses and becomes a liquid and then rains out.
07:45There are clouds coming up and forming and then rain is falling.
07:48But it's iron, it's iron vapor, it's iron rain.
07:51It would be spectacular to see in that brief moment you have before you vaporize too.
07:59You might think that having clouds of iron rain is WASP-76b's strangest feature.
08:07But astronomers are even more puzzled by the location of this gas giant.
08:14When you look at the planets in our solar system, you can divide them into gas giants like Jupiter and rocky planets like the Earth.
08:21In our solar system, rocky planets are close to the sun and gas giants are farther away.
08:29But in exosystems, the positions of different kinds of planets are all messed up.
08:35We're finding Jupiter-sized planets super close to their stars instead of in the outer parts of the solar system.
08:41And we're finding rocky planets really close to stars and packed in really tight and weird configurations.
08:48These planets orbiting close to their stars survive being blasted with intense radiation.
08:54They're taking part in the ultimate endurance challenge.
08:58But not all worlds are so tough.
09:00Some are so light and delicate, they're barely there at all.
09:05Are these weird puffballs even planets?
09:12The more exoplanets we find, the more we realize how weird these new worlds really are.
09:20Some planets are so unlikely, so odd and so bizarre, scientists wonder, how can they even exist?
09:29Before we discovered exoplanets, we thought that our solar system would be representative, that other solar systems would look like ours.
09:35Rocky planets, gas giants, ice giants.
09:38But when we went out there and found them, they don't look anything like our solar system.
09:44In 2012, we discovered three gas giants orbiting the sun-like star Kepler-51, located 2,615 light years away in the constellation of Cygnus.
10:00At first, there seemed to be little to distinguish these planets from Jupiter.
10:04Then, in 2019, we took a closer look.
10:08You 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.
10:18And then you find something like this, and you're kind of like, you know, what the heck is that?
10:22We've been hunting for exoplanets, and we've gotten used to some weird things, but this is truly out there.
10:29This is a truly alien scenario.
10:32According to how we think planets are formed, the worlds orbiting Kepler-51 shouldn't exist.
10:39These 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.
10:50These are planets that have like a tenth of the density of water.
10:53If you could throw these things into a giant ocean, they would float.
10:58The superpuff planets form from helium and hydrogen, just like Jupiter.
11:04But, unlike Jupiter, gas on the superpuffs is not densely packed together.
11:10It's loose, creating big, fluffy balls.
11:14So, even though they're the same size as Jupiter, their masses are much smaller.
11:19So, even though they're the same size as Jupiter, their mass is just one percent.
11:25That's like a heavyweight fighter with the mass of a prairie dog.
11:29The superpuff planets, which is the greatest name ever for a planet, is really a very low-density planet.
11:36Really what it means is that it's very, very fluffy and light.
11:39It's almost like it has a light snow-like consistency.
11:43The extremely low mass of these planets presents a problem for planetary scientists.
11:50This is an incredibly unlikely situation.
11:54How can these superpuff worlds even exist?
11:59Gas giants like Jupiter start with an ice and rock core.
12:04This core grows until it generates enough gravity to pull in gas,
12:08building an atmosphere almost 2,000 miles deep.
12:14Do the superpuff planets form the same way?
12:18It's a bit of a mystery how these planets can even exist, just based on what we know about planet formation.
12:25It's really an unusual thing to have something that is so light,
12:30because that's not how planets that we recognize typically form.
12:33Scientists have a theory about how the superpuff planets formed.
12:37We see these three planets relatively close to their parent star today,
12:42but very likely, given their composition, they probably formed a lot farther away, beyond the snow line, as we call it.
12:48Star systems split into two regions.
12:52A warm inner region, close to the star, and a colder outer region, farther away.
12:58The snow line separates the two zones.
13:00Gas planets only form outside the snow line, far from the star, where gas can clump together.
13:08You're actually able to grab onto a lot of hydrogen and helium and build up an atmosphere.
13:14Beyond the snow line, water condenses to a solid form.
13:19This process greatly boosts the formation of minute planets.
13:24These icy planets are called superpuffs.
13:28These icy planetesimals jumpstart the rapid growth of what will become gas giants.
13:37The superpuffs formed even further out than Jupiter, in a far colder area.
13:43Compared to Jupiter, the superpuffs had a relatively small core,
13:48but because they developed in this colder region, they still pulled in a huge quantity of hydrogen and helium.
13:54You end up with something that is kind of large in size, but still really low density, low in mass.
14:02These planets have been growing in size for around 500 million years.
14:07And as they've been growing, they've also been moving.
14:11The gravity of their parent star can pull these planets closer,
14:16so we can see chains of superpuff planets, like cars on a train, all marching inwards towards the star.
14:24The closer they get to the star, the more stellar winds batter the superpuffs.
14:30The winds blast off the loose, puffy atmosphere in a process called photoevaporation.
14:37This process of photoevaporation results in these planets losing their atmospheres,
14:44literally losing billions of tons of atmosphere every second.
14:49These superpuffs are like orbiting dandelions that are getting blown away in the wind.
14:57Scientists predict that over the next four and a half billion years,
15:01the superpuff planet closest to its star will lose all its atmosphere,
15:06leaving a planet with a radius smaller than Neptune.
15:10The other two superpuff planets will escape, largely unscathed.
15:15We are rapidly discovering a wide range of weird, oddball worlds.
15:21Planet hunters are also searching for something more familiar.
15:25For all these treasures that we've been digging up, we haven't found the crown jewels, a planet similar to Earth.
15:35But just what are our chances of finding an Earth-like planet?
15:39Finding a world that replicates the Earth is really the holy grail of searching for exoplanets.
15:45And I think it's out there, we just need to keep looking and keep developing new technology and ways of exploring.
15:54The big question, are we going to find another Earth?
15:58The answer is, yes, we will.
16:02And the reason I say that is because there are a lot of planets in our galaxy
16:07and just looking at really rough numbers, there are probably billions of planets similar to Earth.
16:14And mixing and matching all of those conditions, it seems to me that the way to bet is that some other planet,
16:21at least one, if not a lot, are going to look a lot like our own.
16:28The numbers are so big out there in the universe.
16:31There's got to be something like Earth.
16:33There's got to be a few things like Earth.
16:34There probably is an exact replica of Earth somewhere.
16:37Will we find it in our galaxy?
16:40Probably not.
16:42We're going to have to accept something that's a little bit different from what we picture as perfect.
16:46I look at that variety thinking, how much more is possible?
16:51And how many more worlds are there out there with life not as we know it?
16:56So for me, I think it's glorious.
16:58I think there's so much more possibility for life than we previously imagined.
17:05Finding an exoplanet with conditions suitable for life takes a lot of luck.
17:12Sifting through these exoplanets, looking for something that's habitable for life,
17:18is like in an interstellar dating app.
17:22If we have molten iron rain, that's definitely out.
17:26You see toxic atmosphere and you swipe and you see red giant and you swipe.
17:30You see toxic atmosphere and you swipe and you see red giant and you swipe.
17:34It's like, oh, too hot, too cold, too small, too thick an atmosphere.
17:38UV rays, no, no, no, doesn't even have a star.
17:41It's just not working again and again and again.
17:45When it comes to finding life, there is one basic element that everyone agrees is necessary.
17:51There is a phrase that we use whenever we talk about the search for life elsewhere.
17:56Follow the water.
17:59And now we think there could be lots of worlds out there that do contain water.
18:05But is there a catch? Could they hold too much water?
18:10A 2019 study suggests the Milky Way might contain many worlds with thousands of times more water than Earth.
18:19Many of these planets are a bit smaller than Neptune.
18:22We call them sub-Neptunes.
18:25What they found were these sub-Neptunes.
18:29Planets smaller than Neptune but bigger than Earth, unlike any planets we'd seen before.
18:34We think we found such a planet, just 40 light years from Earth, in the constellation Baphiacus.
18:42Scientists have nicknamed the planet the water world.
18:47GJ 1214 b could be one of these sub-Neptunes with more water than we would know what to do with.
18:53So far, we're not too sure what GJ 1214 b looks like.
18:59Though Earth is called the blue planet, it's only 0.05% water by mass.
19:06As much as 70% of GJ 1214 b's mass could be water.
19:13The planet is thought to have a rocky core, strange oceans and a hot steamy atmosphere of water vapor.
19:21We spent a lot of time looking for very small amounts of water to establish whether or not a planet could even be habitable.
19:29And so it's kind of amazing that we just found this planet that was essentially nothing but water.
19:35Unlike Earth, GJ 1214 b most likely has no complex arrangement of water and land masses.
19:43The lack of interaction between stable land masses and a healthy long-term stable ocean might really be a killer.
19:52And you might need that land interacting with that water to have a good location for life.
19:58We think life began in the oceans, but it needed chemicals from rocks to start.
20:04Without the interaction between land and oceans, life might not have evolved.
20:12Not only is there no land-sea relationship on GJ 1214 b, evolution here may be limited in another way.
20:21Earth's oceans are replenished with chemicals from hydrothermal vents thousands of feet down on the seabed.
20:29GJ 1214 b's ocean floors are thousands of miles deep.
20:35Right at the bottom of these incredibly deep oceans, you've got very high pressures.
20:40You've got so much water above you, and you've got very cold temperatures.
20:44You're really being shielded from any incoming solar radiation or sunlight, so water itself could turn to ice.
20:51Most ice on Earth is called Ice 1.
20:55When ice is subject to increasing pressure, its categorization number goes up.
20:59We think the ice on GJ 1214 b is Ice 7, the type of ice we believe to be on moons like Enceladus and Europa.
21:10On GJ 1214 b, we believe Ice 7 seals off the seabed, preventing potential nutrients from the rocky core from passing into the ocean.
21:21We've been following the water. That's been the key to trying to understand astrobiology.
21:26And then we find these worlds where it's too much of a good thing. There's too much water, perhaps, for life to exist.
21:32So it's certainly one of those things that a little you need, but maybe too much is bad too.
21:39We need to find worlds with just the right amount of water and land for life to evolve.
21:45GJ 1214 b looks like a dead end, but the hunt goes on.
21:52Space is big, and I like the idea that it's not just for us, so I'm hopeful. Whether it will be in my lifetime or my daughter's, I don't know, but I'm hopeful.
22:02As we continue to probe the cosmos, we've discovered one hopeful distant object, a moon.
22:10But this exomoon is a monster. It's four times larger than Earth.
22:16So how did it get so big?
22:21Each time we find new stars and their weird worlds, we have to rethink the rules of our own planetary system.
22:32We keep thinking we understand what's happening, and then the universe surprises us with something completely different.
22:39Our 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.
22:51It'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.
23:01We expect to see exomoons around exoplanets because our own solar system is full of moons.
23:09Almost 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.
23:18So the question is, are moons unusual in general for planets, or are we just not seeing the moons that are out there?
23:29Astronomers find exoplanets when they pass in front of a star.
23:35It's called a transit and creates a dip or a wobble in the light from the star. But moons pose a problem.
23:44They're incredibly small, so to find even one, we'd have to be very lucky.
23:49In October 2017, astronomers took a closer look at a star 8,000 light years away.
23:57The 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.
24:08There 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.
24:19The planet, Kepler-1625b, appeared to have a companion orbiting around it.
24:26By looking at the light that was coming from the system and how it was changing, they thought they discovered the first exomoon.
24:34And that was really exciting.
24:37Known as Kepler-1625bi, this exomoon candidate caused a significant dip in the light. And that could only mean one thing.
24:48When we analyzed the signal caused by this potential moon, it must have been caused by something four times the width of Earth.
24:55So something like the size of Neptune. And we have no moons in our solar system that are Neptune-sized.
25:00In our solar system, objects the size of Neptune are planets, not moons. Neptune, and planets of a similar mass, are ice and gas giants.
25:11Moons in our solar system don't have this composition. They're all solid.
25:18Just when we thought we understood moons and how they worked, now here comes an exoplanet to tell us, not so fast.
25:25One problem with this system is we don't have many good ideas for how it formed.
25:30Everything we know about moon formation comes from solid moons.
25:35There are two main ways that we think moons can form. The first is you have a rocky world, something comes in and smacks it.
25:45And 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.
25:53Another 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.
26:04But there may be another way the moon orbiting Kepler-1625b could have formed.
26:10An exomoon doesn't have to form around the planet itself, like we see around Jupiter or Saturn.
26:15But instead, let's imagine there's some kind of rogue planet wandering by, a larger planet, and it gets captured and becomes a moon.
26:24Perhaps billions of years ago, the planetary core of Kepler-1625b grows in a disk of gas and dust.
26:35It's not alone.
26:37Nearby, another protoplanet forms.
26:41It's a little bit like twins.
26:43Each twin is going to try to argue for their own amount of resources in the womb, and that's sort of the same thing happening here.
26:48It's a battle for resources.
26:51Kepler-1625b grabs more gas and dust than its twin, growing larger and larger.
26:59The now huge exoplanet slowly drags its smaller sibling closer, eventually pulling it into orbit.
27:09The smaller protoplanet becomes Kepler-1625b's moon.
27:15The one thing that exoplanets have taught us is that we have no idea how systems in our universe have to evolve.
27:22And so it's completely feasible that there is a really large Neptune-sized moon around our host planet,
27:28when we just need more evidence in order to make sure that that's true.
27:32Scientists are confident that such evidence will be found when new technology comes online.
27:40But sometimes, astronomers spot things that make them doubt their own instruments.
27:45Events like a planet disappearing.
27:50We've discovered some extraordinary exoplanets.
27:53Super-hot worlds with molten iron rain.
27:56Super-puff planets, so fragile they might blow away.
28:01Exoplanets that defy physics.
28:04But stranger still is the case of the disappearing planet.
28:08Over a decade ago, the Hubble Telescope spotted a planet orbiting Fomalhaut,
28:14one of the brightest stars in the night sky.
28:19Fomalhaut is a very nearby, very young star.
28:22And the images of this system are incredible, because what you see is a very, very young star.
28:28It's a very, very young star.
28:31Fomalhaut is a very nearby, very young star.
28:35And the images of this system are incredible, because what you see is the central star surrounded by a bright ring.
28:41It looks just like the RF Sauron.
28:45We observed the new planet, called Fomalhaut b, for six years.
28:50Then, something surprising happened.
28:55All of a sudden, it just wasn't there anymore.
28:57Where did this planet go?
28:59For it to suddenly be gone, it was amazing.
29:02It was astounding.
29:03It was terrifying.
29:07If Fomalhaut b can suddenly vanish, what could that mean for other planets, and us?
29:14We live on a planet, so we have a vested interest in understanding how planets could disappear,
29:19if that's a phenomenon that exists.
29:23October 2019.
29:26Astronomers investigate the idea of a vanishing planet by looking at BD plus 20 307,
29:33a star system straight out of the movies.
29:36Just like that iconic image from Star Wars, from Tatooine, where you look up and there's two stars in the sky.
29:42It's actually not that crazy.
29:45Out there in the wild, wild west of the universe, you have lots of different kinds of star systems.
29:49In fact, it's more common to have pairs of stars orbiting each other than have stars by themselves.
29:55If two star systems are the norm, what makes BD plus 20 307 different?
30:03The two stars lie within a bright disk of gas and dust, like Fomalhaut.
30:08But Fomalhaut is a young system, less than 500 million years old.
30:14BD plus 20 307 is a billion years old.
30:18And that's weird, because the material in the disk is so old, it should have formed new planets long ago.
30:26So what's going on?
30:29Rings of dust are a characteristic of young planetary systems.
30:33What does it mean when we see a disk of material surrounding an older star, a star over a billion years old?
30:40Well, one thing could be the collisions of planets.
30:45We think that in this system, planets collided, and that formed the disk that we see.
30:53When planets collide, they don't just spew out masses of material.
30:57The violence of the event shakes up the whole planetary neighborhood.
31:02Planetary objects come in with such energy and such speed that essentially they are vaporizing each other.
31:09Observing a planet essentially being destroyed tells us something about what might happen in our own solar system.
31:18Our 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.
31:30Early in its existence, our solar system was a demolition derby, with many, many collisions.
31:39It's how rocky planets like ours formed.
31:43Back then, there were more than eight or nine planets in our solar system.
31:46There were hundreds, and planets were running into each other and interacting with each other all the time.
31:52Eventually, the planets we see today formed, and our solar system settled into a nice, regular arrangement.
32:01Finding strange systems, like BD plus 20 307, makes us question that narrative.
32:09One of the really valuable lessons that astronomers have learned from studying planets around other stars is that
32:14it appears very clear now that planets don't necessarily stay where they are in a solar system.
32:20Over time, the orbits of planets in our solar system slowly shift.
32:26The repercussions of these orbital fluctuations could shatter our cosmic neighborhood.
32:32The odds are slim, but billions of years from now, Mercury could be pulled out of its orbit by gravitational interactions with Jupiter.
32:41This action would set Mercury on a fateful course.
32:46One 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.
32:59So what we see in BD plus 20 307 is theoretically possible in our own solar system.
33:08It's actually been a bit of a wake-up call.
33:11It's a transformation in our understanding of how our solar system works.
33:16Studying other systems shows us just how vulnerable planets can be.
33:21Things can change at any time in a planetary system.
33:24That we could be watching a planet on its orbit one day, and poof, it could suffer that really big collision the next.
33:33But could this all explain the case of the formal hull B system?
33:37Could it have collided with another planet, wiping it out completely?
33:41Well, maybe.
33:45April 2020.
33:47Astronomers at the University of Arizona come up with a new theory about Fomalhaut.
33:52Every good mystery needs a shocking twist at the end.
33:56And the twist in this tale could be that the planet disappeared before Hubble's eyes.
34:03Because it never was there to begin with.
34:07Instead of a planet that we thought we captured inside the ring, it was actually a collision between two smaller objects called planets.
34:14Planetesimals are infant planets.
34:18Bodies that measure from a few miles to hundreds of miles across.
34:23They smashed together and created a huge dust cloud, which we caught with Hubble.
34:28All we saw was a bright blob of light that looked like a planet.
34:32They didn't spot a planet, but they did learn a very important lesson.
34:37We've actually been able to capture a planet that we've never seen before.
34:41They did learn a very important lesson.
34:44We're actually observing a process, part of the way that solar systems grow and are born.
34:49And in many ways, that's, I think, more important and more useful to us than having spotted yet another planet.
34:56So to observe those characteristics in this system means that we got really lucky to observe it right now.
35:02Because if we came back in hundreds or tens of thousands of years, that dust would have gone away.
35:08It would have eliminated itself, and we wouldn't see it anymore.
35:11We'd be lucky to see it right now when it was still around.
35:14That was still a pretty neat thing to find, the evidence of two small, unseen planets colliding.
35:20And that should remind you that solar systems are not necessarily all that safe.
35:23The same thing could happen here.
35:25For life to exist on another planet, you typically want to look for a nice, calm, safe neighborhood for that life to exist.
35:34And so if we have systems where planets are disappearing without a trace, that's not a great sign.
35:40So when we look at a system that's a billion years old and has apparently had a huge collision between planets,
35:48it's a good time to step back and look at our solar system.
35:51Say, you know, we're four and a half billion years in, and so far, our planets are pretty stable.
35:57Some things have moved around here and there, but we're not seemingly at risk of having two planets collide.
36:03It's a scary lesson to learn, the possibility of ongoing planetary collisions.
36:10Exoplanets are opening our eyes to the way the universe works.
36:15We must question some long-held assumptions.
36:20One standard text predicts the sun will eventually engulf the Earth.
36:26But could there be a way out?
36:28Do some planets cheat death?
36:39In four and a half billion years, our sun will expand to become a red giant.
36:45When our own star turns into a red giant in four and a half billion years from now,
36:50then it will expand, and it will engulf Mercury and Venus and the Earth and the Moon,
36:54and it will cook the surfaces of all of those bodies.
36:58But is there a way of escaping this apocalypse?
37:06When we look beyond our solar system to the Aquarius constellation, we find hope.
37:14Planet HD 203949b is living on borrowed time.
37:20It orbits a red giant.
37:22It orbits a red giant star.
37:25Red giant stars have burned up all the hydrogen in the middle,
37:29and they've moved to the next stage of their development.
37:32A stage that's terminal for a planet orbiting this star.
37:36If you're a planet and you've been orbiting fairly close to your star for billions of years,
37:41you might feel like you've got a good relationship, that it's pretty safe,
37:45but in fact you would be wrong.
37:46In fact, this star that has been taking care of you for billions of years is now going to destroy you.
37:54After billions of years of generating heat and light, a star's hydrogen fuel runs out.
38:01The star's core becomes unstable and contracts.
38:06Gravity just pulls everything to the center,
38:09and then there's a rebound, everything comes back again,
38:11and that creates this big envelope of gas around the star.
38:16The outer layers of gas blow off and expand outwards.
38:21As the gas envelope gets bigger, the surface cools to under 10,000 degrees Fahrenheit.
38:28The coolest stars appear red.
38:31So late in stars' lives, they are big, bloated red giants.
38:36When a star goes red giant, it expands, and it expands outward,
38:40and it's likely that it's going to come and engulf some of the planets that orbit that star.
38:45The surface is cooled, but temperatures still exceed 8,000 degrees Fahrenheit.
38:51If you're in the red giant expansion zone, you're going to get cooked.
38:57Exoplanet HD-2039,
39:00Exoplanet HD-2039,
39:05exoplanet HD-2039-49B,
39:09exoplanet HD-2039-49B,
39:12orbits within this zone.
39:14So is this planet toast?
39:19September 2019.
39:21We take a closer look at the red giant threatening the planet,
39:25using a technique called astroseismology.
39:28Astro-seismology measures the vibrations of stars.
39:32Astro-seismology applied to these stars is a really useful way to get at more information
39:36than we might normally get by just looking at their brightness or their temperatures.
39:40Vibrations go back and forth within the stars and we can see those by monitoring the surface.
39:44One of the things that happens when these stars get to their red giant phase
39:48is they start ringing like a bell.
39:52When we hear these stars ringing
39:56it actually gives us the most precise information we have about any stars.
40:00We can measure their mass, their radius, their density much more exquisitely than any other star.
40:04The vibrations from the red giant star
40:08reveal something highly surprising.
40:12When we analysed the way this star was ringing, we realised it was actually less massive
40:16than we'd determined from other methods.
40:20It told us that star probably has already gone through its red giant phase.
40:24The red giant today is a little smaller than it should have been quite a while back.
40:28This star has lost some of its outer layers
40:32and has started to shrink.
40:36If this star has already gone through its red giant phase and is shrinking again,
40:40that means at one point it was bigger than the orbit of this planet.
40:44If the planet was within the red giant zone, it should have been destroyed,
40:48but somehow it remained intact.
40:52Somehow we see it there today, cheating death. What a survivor.
40:56So how can we explain this escape act?
41:00Could it be that this planet changed its orbital position to allow it to cheat death?
41:04Or maybe HD 203949b
41:08was never even in the kill zone.
41:12Perhaps this planet originally formed further out and migrated in
41:16after the red giant phase was completed.
41:20Maybe some of the clouds of gas shed from the star
41:24reached the planet. This gas dragged on the planet,
41:28slowing its orbit down.
41:32Gradually, the planet migrated inwards after the star reached its maximum size.
41:36And we then evolved down to the system that we see today,
41:40a post-red giant star with a planet that shouldn't be there, so to speak.
41:44This exoplanet may have escaped oblivion,
41:48but its future doesn't look bright.
41:52Its star will shrink down to a cool, dim white dwarf.
41:56If I were a planet, you know, I would be sad at the existence
42:00that I would live afterward, just because it would be so different.
42:04It would be cold and dark, and I would still be bound with a star
42:08that is no longer there in the same way that it was.
42:12This is our future.
42:16But it won't happen for another 5 billion years.
42:20In the meantime, we can be thankful we live on Earth
42:24rather than one of the weird worlds we've discovered in our galaxy.
42:28The more and more exoplanets
42:32we find, the more we realize how lucky we really are.
42:36We see planets that are too big, too small, too much atmosphere,
42:40too little atmosphere, too close to their star, too far from their star,
42:44too little water, too much water.
42:48Everything on Earth is just right.
42:52Compared to our home world, exoplanets push and twist and stretch
42:56the boundaries of planetary science.
43:00But every new world we discover expands our knowledge
43:04and moves us closer to understanding our place in the universe.
43:08If we can understand how planets form, and why they form the way they do,
43:12and how they evolve, then we can know
43:16our past, present, and future even better.
43:20I think as we find more and more of these planets, we're going to find out
43:24more about our own solar system and our place in this menagerie.
43:28A lot of times we think about other planets
43:32and even life in the universe as resembling very much our own.
43:36But these weird worlds open the possibility that there's much, much more out there
43:40than we had ever imagined.
43:44We've found so many different kinds of crazy worlds and crazy places doing crazy things.
43:48It's so interesting. Imagine how boring it would be if we only found our solar system
43:52everywhere else.