How the Universe Works - S09E11 - Mystery of Alien Worlds
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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,
39:00you're going to get cooked.
39:02Exoplanet HD-2039-49B orbits within this zone.
39:10So is this planet toast?
39:16September 2019
39:19We take a closer look at the red giant threatening the planet
39:23using a technique called astroseismology.
39:26Astro-seismology measures the vibrations of stars.
39:31Astro-seismology 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.
39:40Vibrations go back and forth within the stars and we can see those by monitoring the surface.
39:45One of the things that happens when these stars get to their red giant phase is they start ringing like a bell.
39:50When we hear these stars ringing, it actually gives us the most precise information we have about any stars.
39:57We can measure their mass, their radius, their density much more exquisitely than any other star.
40:03The vibrations from the red giant star reveal something highly surprising.
40:08When we analysed the way this star was ringing, we realised it was actually less massive than we'd determined from other methods.
40:14It told us that star probably has already gone through its red giant phase.
40:19The star we see today is a little smaller than it should have been quite a while back.
40:24This star has lost some of its outer layers and has started to shrink.
40:30If 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.
40:37If the planet was within the red giant zone, it should have been destroyed, but somehow it remained intact.
40:44By all accounts, this planet shouldn't exist, but somehow we see it there today, cheating death. What a survivor.
40:50So how can we explain this escape act?
40:54Could it be that this planet changed its orbital position to allow it to cheat death?
41:00Or maybe, H2O has changed its orbital position.
41:03To allow it to cheat death?
41:06Or maybe, HD203949b was never even in the kill zone.
41:12Perhaps this planet originally formed further out and migrated in after the red giant phase was completed.
41:20Maybe some of the clouds of gas shed from the star reached the planet.
41:26This gas dragged on the planet, slowing its orbit down.
41:29Gradually, the planet migrated inwards after the star reached its maximum size.
41:36And we then evolved down to the system that we see today, a post-red giant star with a planet that shouldn't be there, so to speak.
41:45This exoplanet may have escaped oblivion, but 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 that I would live afterward.
42:01Just because it would be so different. It would be cold and dark.
42:04And I would still be bound with a star that is no longer there, in the same way that it was.
42:11This is our future.
42:14But it won't happen for another five billion years.
42:18In the meantime, we can be thankful we live on Earth, rather than one of the weird worlds of the past.
42:24Rather than one of the weird worlds we've discovered in our galaxy.
42:30The more and more exoplanets we find, the more we realize how lucky we really are.
42:37We 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.
42:47Everything on Earth is just right.
42:49Compared to our home world, exoplanets push and twist and stretch the boundaries of planetary science.
42:57But every new world we discover expands our knowledge and 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, and how they evolve,
43:13then we can know our past, present, and future even better.
43:20I 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.
43:29A lot of times we think about other planets and 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 than we had ever imagined.
43:42We'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 everywhere else.