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In this course we will discuss the formation of stars and planets. We will explain the, sometimes violent, processes that occur during their formation and explain how the combination of theory and observation have led to our modern insights. Data from state-of-the-art telescopes will be presented and their impact on our current understanding will be discussed.
In this course we will discuss the formation of stars and planets. We will explain the, sometimes violent, processes that occur during their formation and explain how the combination of theory and observation have led to our modern insights. Data from state-of-the-art telescopes will be presented and their impact on our current understanding will be discussed.
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ÉducationTranscription
00:00:00OK, hola. Merci bien.
00:00:05Good afternoon, everybody. We managed to get it to work.
00:00:09I missed you two weeks ago already. Wow.
00:00:13And two weeks ago, it was raining and it was pure.
00:00:17Well, welcome to the last lecture.
00:00:21I was supposed to have five, but there's no time.
00:00:23No slots for a pitfall.
00:00:25So I decided to merge the last two lectures.
00:00:31Today, I'd like to finish the course in star and planet formation,
00:00:37a little bit about planets and a little bit about the future and the search for life.
00:00:43OK, you will not be surprised with my next slide if this works and it doesn't.
00:00:49So let me just talk to my computer.
00:00:54And oh, that's good.
00:00:56OK.
00:00:58You've seen this before, but as I told you, repetition is very important.
00:01:03How do stars form?
00:01:05And it starts off with these huge molecular clouds that contain gas and dust.
00:01:12And dust, it's almost like cigarette smoke.
00:01:15Very fine sound effects.
00:01:17And gravity on one hand wants to make it smaller, but the thermal pressure,
00:01:22the molecules, they want to move out.
00:01:24And there's this balance between the two.
00:01:27And perhaps you remember from two weeks ago, if the balance is basically destroyed by perhaps
00:01:33even a shockwave from a supernova, then the clouds can collapse.
00:01:37And that happens very quickly indeed.
00:01:40And here we start off, for example, with a cloud.
00:01:44That's one bar sec, three light years.
00:01:48And it really can compress very quickly to become a very dense core.
00:01:53It gets denser and it gets hotter.
00:01:56And as it gets smaller, you may remember that even if it started rotating very slowly, when
00:02:04it gets smaller, the rotation speeds up.
00:02:06And that rotation, because it speeds up, gives us that this, simply because of the centrifugal
00:02:13force, is the strongest when the rotation is the previous.
00:02:19And so we end up with a star in the middle, where the densities and the temperatures are
00:02:25so high that we actually have a fusion of hydrogen to heating.
00:02:28A star is born, energy is generated.
00:02:32And now we've got these jets that are shooting out.
00:02:34You may remember how I lost my wedding ring because of these magnetic fields that were rotating.
00:02:43And at some point, we don't have any material left to fall onto the star, because it's all
00:02:47blown away or has fallen onto the star, and we end up with a pizza.
00:02:52And in this pizza, we can form planets.
00:02:55Planets are being formed.
00:02:57And give it a little bit more time, and we end up with a star as the planets surround.
00:03:04And again, this is really quick.
00:03:08I mean, the formation of this particular star in this cartoon, it happens in a million years.
00:03:16And that's nothing compared to the life of our own star, the Sun, which can live for about 10 billion years.
00:03:24So once it started with the birth part of a star, it's a big one.
00:03:32Now, you may also remember that we actually have two different theories for the formation of those planets.
00:03:42And the first one, the first theory that I mentioned was the one that worked perfectly fine for our solar system.
00:03:50Just perhaps you remember, we started off with a disk that is containing all these dusty particles and gas.
00:03:57And these dusty particles, if they meet each other, if they collide, they can stick, right?
00:04:05If you go to the beach and you have very dry sand, it just doesn't stick.
00:04:09If it's wet, oh yes, it sticks.
00:04:12You get some mud, right?
00:04:13And because of that sticking together, the particles become bigger and bigger until we have rocks that are a meter, 10 meters, 100 meters.
00:04:25Then we start talking about planetesimals, small planets.
00:04:29And before you know it, this can happen very quickly.
00:04:33And we now observe it has to happen very quickly as well.
00:04:36You end up with a system where you've got rocky planets close to the star, like Earth, like Mercury, like Venus, and very big, gaseous planets outside.
00:04:48And you may remember outside, at some point, there's ice coatings on the dust grate, so it's actually more material available to stick together.
00:04:59And at some point you get such a massive planet that it even can attract the gas molecules, the gas that is about.
00:05:08So we've got rocky planets close to the star and big gas giants further away.
00:05:14And the method worked perfect for the one solar system that we knew about until 1995.
00:05:22But in 1995, we started detecting many more exo planets, planets outside our own solar system.
00:05:32But we found that some of them had very big planets, very close to the star, which is not what you would expect from what that just lost you.
00:05:41Other ones, that's very big planets, very far away from the star, is also big.
00:05:47So people have been thinking about how can we amend a theory like this.
00:05:53And people did it, they said, well, perhaps if I've got a planet that's really big, perhaps it needs some time,
00:05:59and then it can move towards the star, so it gets close.
00:06:03But then people started thinking, well, hang on, if I've got this pizza, then it's got some cloves in there,
00:06:09at least when I make pizza though, never stood.
00:06:11And perhaps these cloves can collapse gravitationally, just like the big cloud from the beginning as well.
00:06:19So perhaps if I have a disk, perhaps I can form planets into gravity, completely different systems.
00:06:29Now, we don't know yet, it's 2025, which one is correct, but I'm pretty sure that it's a combination.
00:06:39And that's essentially where we are with the planet formation theory.
00:06:46It's a little bit more kind of later than that, but I think the big picture hasn't changed in the last 10, 15 years.
00:06:54That's it. So, what we'd like to do then is, we want to observe, we want to look at the sky and see
00:07:12whether we can find the young stars with disks and see whether they are capable, perhaps, of formed planets.
00:07:19OK? And I think this is perhaps a nice moment to say a little bit about the observing techniques that we have,
00:07:29and especially the electromagnetic radiation that we use.
00:07:34OK? Here I've got a spectrum, and this bit is what we call the visible.
00:07:40This is what we can see with our own eyes, OK? And the wavelengths, this is red, it's longer wavelengths than blue,
00:07:48but I think blue light is about 0.4 micrometer, and this red light is about 0.8 micrometer.
00:08:02OK? So, it's a very small range, because if I go to shorter wavelengths, nanometers perhaps, or even shorter,
00:08:10I'm going to the ultraviolet, which we can't see, I'm going to the x-rays, and I'm going to gamma rays.
00:08:17To observe those, I actually have to go outside the atmosphere. Fortunately, out in the atmosphere,
00:08:25walking most of the x-rays and gamma rays, I can also go to longer wavelengths. So, I can go from the
00:08:33optical to the infrared. And with night goggles, computer games, for example, you know that you can
00:08:41detect humans very well. We are about 37 degrees centigrade. And at infrared wavelengths, that's where
00:08:48we shine, actually, we get off light. So, that's the infrared. I can even go with longer wavelengths to
00:08:56microwaves. The wavelength is millimeter. It turns out that molecules really like to absorb millimeter
00:09:08wavelength radiation. That's why a microwave, micro-ohm, works. The water is being heated up by millimeter
00:09:16radiation, right? And then I can go to even longer wavelengths to radio wavelengths. And another thing
00:09:24that you might find interesting in this graph is that if I'm here in the optical, I can see all the
00:09:31optical light that's coming from space. The sky is transparent. We knew that because we can see the
00:09:39most, right? But if I'm going to the shorter wavelengths, the atmosphere is opaque. That's what I actually
00:09:47mentioned already. We have to go outside. And for ultraviolet, etc., really, we start our heads. In
00:09:54infrared, some parts we can see through, and other parts we can't. So, we actually have windows that we can
00:10:03basically look at particular wavelengths. And otherwise, we need to go outside. And this range is basically
00:10:11where the James Webb telescope is operating, and we can look at wavelengths that we cannot observe in the graph.
00:10:18Then there's a whole range we can't see anything. The microwaves, if you go higher in the atmosphere,
00:10:25then we stand a chance. And the telescope I'm showing on the next graph, which I have mentioned before,
00:10:31is at one of the highest sites in the world. It's at five kilometers. And at five kilometers height,
00:10:37you can imagine I've got much less atmosphere between the telescope and the stars than if you're
00:10:44radio. You can see everything. And if you go to very, very long wavelengths, it doesn't work either.
00:10:52Ah, it works. So, I thought I'd better remind you of the Atacama Large Millimeter Array,
00:11:00which is an array of telescopes that's operating at large millimeters.
00:11:07And it's in the Atacama Desert, okay, which is in Chile. It's actually not operating at large
00:11:14millimeters, right? It's a large array, because one millimeter in Chile is as big as a millimeter
00:11:21here in Brussels. Astronomers, if they go there, they actually need breathing equipment,
00:11:27because there's not enough oxygen. The next one, I think, is just a very pretty picture,
00:11:33with the Milky Way. But this telescope has been operational for about 10 to 15 years,
00:11:40and really opened up our insights and many things in the sky, including especially about the formation
00:11:49of stars and planets, and these pizzas, these proto-planetary disks around the stars.
00:11:55And here was one of the first images that were taken back then of the Young Object
00:12:02in the constellation of Taurus, and it's called H-Alt. And you can see it looks remarkably like
00:12:13this cartoon, even the colors are the same.
00:12:15And you see these curves here. And what we think currently, but there are some dissenting forces,
00:12:26which is fair enough, is that probably a planet was formed, and it's basically just like a snowplow,
00:12:32emptying the space in this ring, taking the cob. And yeah, just to give you an idea about how big
00:12:40this is compared to our own solar system, at least the planets. You may remember that the solar system
00:12:46is a little bit bigger than just the inner planets, right? Okay. And this was really a revolution,
00:12:55because when I started working on the topic, we didn't even know there were disks around these objects.
00:13:03because actually one of my jobs was to find disks around them. Okay. And now we see them everywhere,
00:13:11and that's essentially because of the progress in technology. And here's, I think I've shown this one
00:13:19before, it's just a set of these disks that have been observed. And you can see that many of them,
00:13:28and this brings, right? So it's probably the scientists of planets. But recently, actually,
00:13:38oh yeah, sorry. And recently, we've not only been able to make these nice images of, in this case,
00:13:45the dust around these walls. But because ALMA is operating with millimeter wavelengths, it can actually
00:13:53fine-tune and say, I'm interested in water. And then we look at the wavelength that water would like
00:14:00to be made. Or it can say, let's look at something else. And we can now make maps of particular molecules.
00:14:09And here I've got one, two, three, four, five objects. For astronomers, they're very famous objects.
00:14:15There's telephone number. I can actually, if I wake up, I can tell you that one. Not the phone number of my wife,
00:14:20but I can tell you the name of this type. And here I've got some complex molecules. This is HC3N.
00:14:28I could not know, honestly, what the name is of this molecule. But as you can see, these are quite
00:14:34complicated molecules. And you can also see that there are different places in the disks. But the bottom line,
00:14:41what is really important to break through as well, is that we not only find these disks, in which planets
00:14:49may form, but there are already molecules that are very complex. And because they've got carbon
00:14:57inside them, we call them organic molecules. But in a way, they're prebiotic. They're not like the DNA
00:15:06that we're made of, but they are the start of getting to even more complex molecules. So that's, in a way,
00:15:14reassuring. I don't know whether that's the right word. But if we're looking for the cradles of life,
00:15:22well, we start already with some very complicated molecules. And if the conditions are right,
00:15:29they might meet each other, create more complicated molecules, etc. But this is, I think,
00:15:35apart from the fact that we find these fantastically nice disks to look at, that we already find,
00:15:41I can't read this out, H2, NCO, and H2. Sounds quite complex. And this is the typical spectrum
00:15:50where you see such a line, okay? I just want to point out that when we take telescopes to the limit,
00:15:59the data is always a little bit noisy, right? But there's a lot of checks that you can do,
00:16:04and definitely we have a detection here. Okay. So that's what we find in these disks.
00:16:12And since recently, we actually found, well, we, when I say we, I mean us, scientists, mankind,
00:16:21find young stars with planets inside them, okay? And we can even see them move as a function of time.
00:16:29So we now are at the position, and this is very difficult to get, but we now find not only young stars
00:16:40with disks, but we also find young stars with disks, and the planets are around them already, okay?
00:16:50So the mere fact that we see planets already in these young stars, and remember that I said that the
00:16:56formation of the stars is very quick, that means that the planets must perform very quickly indeed as well,
00:17:03right? Which is not inconsistent with the models. When people were making these models 30 years ago,
00:17:11before we knew any of our exoplanets, it turned out that the sticking around of all these dust grades,
00:17:18the typical planetesimals and the planets, was very quick. So I think this is the major progress that we have made, really,
00:17:29in the last 30 years. We find these disks, we find evidence of planets, and we find a lot of information
00:17:36about the chemistry that's occurring there. And I don't think I exaggerate that after astronomy,
00:17:45which is hard to be looking at the stars, that astrophysics, which is really trying to work out,
00:17:52using physics, how they work. The astrophysics is a blooming discipline as well, right?
00:18:01So I went from the formation of the disks to the formation of the planets, I mentioned prebiotic molecules,
00:18:08so I thought why don't I give you an update about what we know about planets at this moment in time.
00:18:16And here I've got a little movie, where I've got the period, which basically, if you look at Earth,
00:18:25it orbits around the Sun in one year. I look at Mercury, it's a little bit quicker. And here I've got
00:18:33the Mars for the planet. So I've got the solar system planets here, and as a function of time,
00:18:42I will run this movie again. I show you all the planets that have been discovered so far.
00:18:49Okay? And I think this one stops in 2020. It starts at 1700. I mean, you have six planets,
00:18:58right? All the way to Saturn. Then suddenly we discovered Uranus and Neptune. And in the meantime,
00:19:06there was also a planet, a mini planet called Ceres that for 30 years was called the planet, and it was
00:19:12demoted. Then we discovered Pluto was a planet, was demoted. And from 1995, you can see that for hundreds
00:19:21of years, we had six, eight or nine planets. And at the moment, that's the next movie, we've got about
00:19:29six thousandths of them. Okay? So the next movie is more or less the same. But there's a reason why
00:19:37I show it because it shows our solar system planets a little bit better. And it's also a bit reasonable.
00:19:43So it's the same graph. I've got the period here now in days instead of years. And here I've got a
00:19:50feeling for the mass of the planet as well. And here we've got Venus and the Earth. They're about the same
00:19:57mass, almost as far away from the Sun. Here we've got Jupiter, which is of course much bigger. And
00:20:02Uranus and Neptune and Saturn. And the very first planets that were discovered were the so-called hot
00:20:11Jupiters. They were very hot because they were very close to the stars. So the orbital periods were very
00:20:17small and it was quite massive. That's why we called them Jupiters. Okay? And it turns out that the first
00:20:24planets that we discovered were of course the easiest ones to discover. And if you don't have
00:20:3110 years observing time, but only two weeks, then you can imagine that it's easier to find a shorter
00:20:37period of planets. And we detect these planets due to the effect that they have on the star. And it's
00:20:45a kind of a gravitational pull. And Jupiter, being much more massive than Earth, is a bigger pull on the
00:20:52Solomon of the Earth. So we start off by detecting, discovering the babies that are very massive. Then
00:20:59we have some very different techniques, which I will not go into in this course. And this graph has
00:21:05filled in. But what I really would like you to appreciate is that we really haven't found that many
00:21:13planets like our own. And this is not because they don't exist, but that's because this part of the
00:21:21graph is just more difficult to discover. Right? So close to me, easier because of the short
00:21:29time skills. And further out, the bigger the planet, the easier it is. I think it's that basic.
00:21:36And that's why I showed this graph, so that you can see that there's a whole big space, parameter space,
00:21:45that we need to probe. And that's why I would like to look a little bit at the fusion later on.
00:21:53Also note that this is a bit empty, which basically is not really what I can explain to you with these
00:22:00so-called selection effects. Because if I can detect planets here, and I can detect planets here,
00:22:07then surely I should be able to find out. Right? And so we actually know for a fact that there's just
00:22:17fewer planets in these masses than these masses from these masses. Which must tell us something about
00:22:26the planet formation mechanism. And that's all I can tell you about it. I think I'll show this on the next
00:22:31graph. Yeah, not much yet. So we can say something already, but there's a lot of planets that we are missing.
00:22:44Now, yeah, I should not have done this, but you can see that still a lot of planets have the same
00:22:51mass and the same distance to stars. And then you might think, oh, they're the same, I can treat them the same.
00:22:58But if I look at our own solar system, I see, I notice that even if planets really,
00:23:07to all intents and purposes, are the same, especially the Earth and Venus, they are basically the same size.
00:23:15They've got the same mass. And Venus is only 30% closer to the Sun than the Earth.
00:23:24But there's a big difference. You may know that. I mean, Venus is incredibly 400 degrees centigrade.
00:23:33Mostly due, not because it's closer to the Sun, but because it's got a very thick atmosphere.
00:23:39It's got a very, very strong greenhouse effect. Something has happened on the planet to make
00:23:46it's so different from the Earth. And for example, so we've got, if we're looking at the atmosphere,
00:23:55probably now, because it's 80% nitrogen molecules, 20% oxygen, and 0.03% CO2 for carbon dioxide,
00:24:06and Venus, 96% of carbon dioxide. So what I really want to say is,
00:24:12we might think from the little we know of exoplanets, like a mass or a radius, that they're the same,
00:24:19but they are not. There's a whole diversity. I really like the next one, because here I'm looking at
00:24:26moons in our own solar system. So here we've got the moon, and then we've got some of the moons of Jupiter,
00:24:34and we've got the moon around seven, and I think this is around Uranus, but I'm actually not sure.
00:24:43Anyway, so, and you can see even from the colors, they are different. They are basically the same size,
00:24:50but they are completely different. And it's fascinating to read up about why the various moons are
00:24:57different and have a different composition. And I really would like to highlight the moon and Titan,
00:25:05because they are really comparable. They've got the same mass.
00:25:14Here I've got Titan, it's around Saturn, and it's got a very dense atmosphere with nitrogen.
00:25:21And here I've got the moon, same mass, and it does not have an atmosphere.
00:25:27And then you wonder, how can that be? Because I teach our students that you have an atmosphere,
00:25:40because the gravity, in our case of the Earth, is strong enough to keep the molecules here.
00:25:48The only reason that we've got the air that we breathe here in this room, well, okay, there's a ceiling,
00:25:53but if we would be outside, then it would be the Earth's gravity, okay? But what we also can do,
00:26:00with very basic physics that probably is taught at high school, is that the hotter it is, the higher
00:26:09the temperature, the faster the molecules move, okay? And we can now work out that the moon does not have
00:26:18an atmosphere because every single molecule has escaped already. And you can actually work that
00:26:27out on the next graph. I'll show this on the next graph. But I'm looking here at the temperature,
00:26:33and I'm looking at the speed of the various molecules. Let's first look at Earth, okay? Earth,
00:26:40well, I think it's a little bit... Yeah, it's a temperature in Kelvin there. You may remember that
00:26:47zero degrees centigrade is 273 Kelvin. And we don't have hydrogen in our various atmosphere because
00:26:55they're so light, these molecules, that at this temperature that we are, they move too fast and
00:27:01they escape. And the same with helium. Every day helium is leaking from our atmosphere.
00:27:08But if we're looking at oxygen and nitrogen molecules, they actually don't move that fast
00:27:15and they stick to it, okay? So that's essentially why Earth has a nice atmosphere of molecules with no
00:27:23hydrogen. But you can see that Jupiter, the escape speed from Jupiter is much higher than what hydrogen
00:27:30and the velocity that hydrogen would have, and how the gas giant plants are less enough to keep those molecules.
00:27:37And that's what I really like about Titan. It's got more or less the same escape speed as the Moon,
00:27:44but because it's so far away in the solar system, it's so cold that these nitrogen molecules in this
00:27:52atmosphere and move so slowly that they stay there. But if I remove that nitrogen molecule and bring it
00:27:59to the Moon, it would be so fast it was clear. I think that's quite funny. Yeah, funny in the sense,
00:28:06like interesting, that you've got two heavenly bodies, same mass, etc. They're so different, and one of the
00:28:14reasons is the temperature. The reason that these other moons don't have an atmosphere, but they are
00:28:22cold as well, is because it must have been active and volcanoes will have shot from all the material in this atmosphere.
00:28:30Anyway, so that was my caveat. And so, as I mentioned, the first exoplanets that we found were very hot and
00:28:43very massive. And I think this was the first one. The planet was about half the mass of Jupiter, but it was
00:28:53four times closer than Mercury. So you can well imagine it must have been very hot.
00:29:00But what we now know, they were the first ones that we discovered, but they are very rare indeed.
00:29:06And this is what I basically alluded to already. If I'm looking at the numbers of planets that have
00:29:13been discovered, and this is the number of planets that we can actually get the mass for. And this is the
00:29:20mass of a lot of radius. So this is one Jupiter radius. So if I'm here, then I'm talking about planets that
00:29:28are as big as Jupiter. Okay, this is the size of Neptune. So when I'm looking at planets that are
00:29:39here, they are the size of Neptune. And this is the Earth. And when I'm looking here, I'm looking at
00:29:44planets that are the size of the size of the Earth. You can see that there's a peak between the Earth
00:29:52and Neptune, and then it's going down. A little bit of a bit there, and then it's going down. So although
00:30:00these hot Jupiters were the very first planets that we discovered, they are in a vast minority.
00:30:07Okay. And most planets, and this is something that we start to appreciate now, sub-Neptune or
00:30:15super-Earth. You may have seen terms like that already. So the next challenge in planet formation
00:30:22theories is actually to understand why that would be. Why would actually be that the most frequent
00:30:30planets that we know of are not in our solar system? And it turns out that this looks lower already,
00:30:39but this turns out to be formally real in the sense like now that we've got more and more data,
00:30:47that's actually a little bit here. So we've got real super-Earths and still Neptune. So that's the
00:30:53next challenge. And the next time I give this lecture, I don't know when I will give it, but I will give you an update.
00:30:58So that's a little bit of an adventure in what kind of planets we now know of.
00:31:10I'd like to talk a little bit about life. If life elsewhere in the universe,
00:31:20if it is similar to ours, then when you really would like to have a sleep with water.
00:31:30You can work out temperature of a planet depending on what distance to its star.
00:31:36You can imagine that if you're very close to the zone, it's boiling hot. When you're far away from the zone,
00:31:43it's ice cold. What we then call the habitable zone is the region when water is just about boiling
00:31:53and just about freezing. Venus is the old one because of the greenhouse effect.
00:32:00Because normally I would hope to see liquid water on Venus, but it's so hot because of the greenhouse
00:32:07effects we don't see it. But you can see that Earth is smack in the middle of this habitable zone.
00:32:17Fair enough. We have found similar systems with planets already in the habitable zone.
00:32:28This is the Trappist system. I made a joke about it in the first lecture already. It was actually,
00:32:33it is a Belgian discovery, and every person in the field knows about this system. They all know it.
00:32:42And the successor project of Trappist Spekulose. I don't know what the next one will do, probably.
00:32:51And this system has a faint red star in the center, known as the one, two, three, four, five, six,
00:33:00seven planets that are rocked. And because it's such a faint star, the habitable zone is a little bit
00:33:10closer to the star because you're not that boiling hole close to a red star than to the sun. But you can
00:33:16see we already have a couple of rocky planets around another star in the habitable zone. If you're looking
00:33:26for life on other planets, and if we need liquid water, then this might be a nice system to look at.
00:33:34And a very recent plot that I found is the following. It shows essentially the same speed result, but a better
00:33:44rundown. So here I've got the star like the sun and the habitable zone is far away from the star,
00:33:52and look at our contributors, right? Then Kepler 452b, don't worry about the names, this guy is circling a
00:34:02star that's almost as bright as the star, and it's also in the habitable zone. If I go to Trappist,
00:34:09then it's a circling faint red star, and there's a couple of them in the habitable zone. But you can
00:34:15see already that we now know of many planets already that are in the Goldilocks zone, the zone which you
00:34:24would expect. In case you think these are images, they're not. This is just someone who made a nice painting.
00:34:32I want to make that clear. It basically just gives you an idea how big they are compared to each other.
00:34:37Okay? So, well, that's a nice step, and I think also that the shocker, or the big insight that we
00:34:45also had from the last step, is that rocky planets in the habitable zone are very common indeed.
00:34:54If I were to give to, if I came to this talk in 1992, I would have said, well, perhaps we are the only
00:35:02solar system in the galaxy. And even if there are other systems, perhaps Earth is special because it's in
00:35:09the habitable zone. But now we find that we're not alone, not special in that sense at all. And I think
00:35:17that's a major piece of progress of information that we got in the last couple of years as well.
00:35:26Now then, going to life. How can we get evidence for life on these other planets?
00:35:37One thing that people are doing, have done, is to search for an actual terrestrial life project,
00:35:46where people have pointed telescopes to stars in the hope that these aliens send messages to us.
00:35:52If the aliens actually would be listening to us, they might not find messages from us, but they might
00:36:01find early 1920s television programs. I try to think what they will think of us one day, see some of the
00:36:09television series. But our television signals are now 95 years away from it. I think the deep radar
00:36:23from the armies, I think these signals are also probably into space. So that's one way of looking
00:36:30for extraterrestrial life. And people have been improving the telescopes many times over the past
00:36:37decades or so. But so far, we haven't found anything yet. What Carl Sagan, a very famous astronomer,
00:36:47did, he actually made a television series called Cosmos. I think it's his book that I'm here now.
00:36:54He's American, and I still remember that when he said billions, he didn't say billions, he said billions.
00:37:00So if you look him up, Carl Sagan, and then he will find he says billions, billions of years.
00:37:05Anyway, he said, if we're looking for life on other planets, why don't we actually first have a look at how
00:37:15we would look like to the aliens? And there was a spacecraft called Galileo that took spectroscopy,
00:37:25which is absorption and emission lines, and they looked back at Earth.
00:37:30And here, this is what we call a spectrum. We unravel the light, functional wavelength.
00:37:38So this is in the red, because if she paid attention, I said that red light was 0.8 micron,
00:37:47and that's here. So this is red light. And if you're looking at the Earth, then there's some
00:37:53absorption light. Just like what I told you about the atmosphere is blocking light, the Earth is blocking light here as well.
00:38:02These ones are due to water, and this is due to oxygen.
00:38:08If I'm looking at Mars or Venus, I don't see any oxygen. And it turns out that oxygen is not in equilibrium on Earth.
00:38:25If we would switch off life on Earth, then we would lose oxygen into chemical reactions very quickly.
00:38:32It's thanks to life, to the trees and everything else, that the oxygen still is present in the atmosphere.
00:38:41And we can see this oxygen, okay? So, yeah, it works. So, Carl Sagan said, this is 1993.
00:38:52Okay, so if we would take a spectrum of a planet and we find oxygen, that might be a diagnostic.
00:39:00Here, we're looking at another part of the spectrum from 2.4 to 3.6 micrometers, which is in infrared.
00:39:09And there's the water again, it's N2O. It turns out that CH4 is also something that is a hallmark of life, okay?
00:39:22Perhaps you've heard about cows and methane, but it's basically produced by bacteria.
00:39:28So, I'm not saying that if I see CH4 and oxygen in another planet, there's life, but it sure helps, okay?
00:39:38So, that's the state. And this was a very nice experiment.
00:39:42And it also tells you like, oh, perhaps the next step in finding to search for life on other planets,
00:39:49perhaps being able to get data to take a spectrum like this would help.
00:39:57Now, 10 years ago, we would be happy already with detecting a planet.
00:40:05Now we're at the stage that we can even take a spectrum of the planet.
00:40:09Also, a big thing that's happened in the last couple of years.
00:40:13And how do you do that? Now, if I have a star, a beautiful star,
00:40:22and if the planet is in front of it, the planet is blocking light from the star, right?
00:40:29But the light from the star can go through the atmosphere of the planet.
00:40:32Remember that I told you that our own atmosphere is blocking light?
00:40:38So, the atmosphere of other planets will block light as well.
00:40:41And the way it's blocking light, we can perhaps, it's quite an evidence, for oxygen.
00:40:48So, that's one. And the other one, that was something I couldn't believe it or people told me.
00:40:53But the planet is really, the only medium you can see the planets are due to reflected light,
00:41:01just like we see the moon.
00:41:03And the difference in brightness between the star and the Earth is a factor of a hundred million.
00:41:13The sun is about a hundred million times brighter than the Earth.
00:41:16That is a challenge. I think I was listening to a podcast the other day,
00:41:23and the astronomers said that it's basically like a firefly next to a lighthouse.
00:41:29Okay? And if the planet is behind the star,
00:41:36that helps. Because in this case, I see the light from the star and the planet,
00:41:41but the planets behind it, I only see the light from the star.
00:41:44So, the difference is the light into the planet. And I can't believe, I can't look at the thing,
00:41:51but we can do it now. And some results are on the following. This is done with hot Jupiters.
00:42:02Why? Because Jupiter itself is less, the Earth is much smaller and fainter than Jupiter.
00:42:10So, the difference for the Earth and the Sun is a hundred million. For Jupiter and the Sun, it's a million.
00:42:18Easy. Well, that was a joke, of course. But it's easier because they're bigger.
00:42:22And the James Webb telescope has been able to take spectra already. This is from the optimal 0.6 microns to 9 microns.
00:42:32And you have to look at the black dots. And you can see real windows in the spectrum of these planets.
00:42:42Okay? If you've got a very, very bright object, then the black dots are very close to each other.
00:42:49If you've got a very faint object, it's a little bit choicier, right? And what people can do now,
00:42:56is they have a computer model of an atmosphere. They say, well, let's put 10% this and 20% that,
00:43:03and let's see whether we can reproduce the data. That's what they do.
00:43:09So, this is indeed big progress as we made. But the level of detail is, of course, much different
00:43:17than if I would go to Mars. But we're getting there. I think the next one can show some idea
00:43:24that these are the data. And all these different colors are modeled. And if I look at this color,
00:43:34for example, this is CO2. They say, okay, if you put in 80% CO2, what would I get?
00:43:40And you can tweak it a little bit if I would be interested in sodium.
00:43:48Can I reproduce that? And this is how we do that.
00:43:51So, this gives you an idea that if you have the right equipment and the right planet,
00:44:01you might be able to do this for rocky planets as well. But that's, at the moment,
00:44:06a big challenge because they are so small and so afraid. So, the best I could find is a year old.
00:44:14And here we're looking at rocky planets. And you can see that this doesn't look as nice
00:44:21as this, doesn't it. But we are finding them. We are getting data. And it's just a matter of time
00:44:31that we can perhaps get quality data good enough to decide whether or not there is, for example,
00:44:39oxygen in these planets. So, first again, in some cases, we now can say almost for sure that there's no
00:44:50atmosphere at all, just like with the moon. I think it's these flat lines are statistically
00:44:58sometimes really consistent with the idea. But we're getting there. So, this is really very recent.
00:45:06So, 2025.
00:45:08So, now then, I'd like to spend a few minutes on the future.
00:45:13I wanted to spend some time with you doing an equation just to do some mathematics. I will do
00:45:22that quickly because I see that I don't want to go up over time as much as I did the last touch.
00:45:27But the future, at the moment, ESA, the European Space Agency, is due to launch a satellite that's dedicated
00:45:37to discover rocky planets around other objects. So, we have been finding them.
00:45:47But you can well imagine that if we would have more sensitive equipment, we will find more.
00:45:53That's essentially the bottom line. And Plato is really expected to discover so many more rocky
00:46:01planets that we probably have our hands full for quite a while. So, that's one thing and that's quite
00:46:08close to time. Ariel, also an ESA initiative,
00:46:15is basically designed to follow up on the discoveries of Plato to make spectra.
00:46:23So, this is due to launch, at least planned to launch in 2029. So, based on what I just told you,
00:46:31they are taking it to the next level indeed. And when you think about this, 2029 is only four years away.
00:46:39Wow. Something else in 2030 is the ELT, the Extremely Large Telescope.
00:46:49This is a telescope that's being built, I'll show you a picture in a moment, and it will be the biggest
00:46:56optical telescope ever. So, the biggest telescopes we've got now are called Very Large Telescope,
00:47:02a VLT, and about eight meters across. Americans have a 10-meter telescope. The Spanish, I think,
00:47:10have a 10-meter, 30-centimeter telescope because they wanted to have the biggest.
00:47:13That's what we call it. So, here are the VLTs. And yeah, I think this is French, isn't it?
00:47:22It's being built. And this is how it looked like last month, or one and a half months ago. It's with
00:47:27the fish, but the Italian dome is in there already. Half of the mirrors are built already.
00:47:34And just look at the perspective. This is a truck. This is a proper truck. This thing is big.
00:47:42And it's really in the middle of nowhere. And they actually chopped off the top of the mountain to
00:47:49actually have a flat-level platform to build that telescope. Okay? Another thing in the future.
00:47:59It's a nice initiative. Oh, sorry. I forgot. I did have it here. The idea of this 39-meter telescope is
00:48:08that we can actually take an inch of such a blank. And so, if you can see the star, then it's going next to it.
00:48:14And the ELT should be able to pull that off for five nearest systems. A handful. Okay? But even get one. It's already a very big
00:48:29progress. But if you want to take it to the next level again, then we need to go to NASA initiative,
00:48:37and that's planned for the 2040s. A little bit longer. It's called the Habitable Worlds Observatory. You
00:48:44can guess already where they got the name from. It's the Holospace Telescope of steroids. It will do
00:48:52everything. But of course, the Habitable Worlds is probably where the money was coming from. But they
00:48:57are hoping to really get proper images. And here, this is a simulation. If you would have a solar system
00:49:07that's about 30 light years away, they think they will actually go that far 35 than Earth. If I understand
00:49:16the documentation correctly, they aim for off-corder, I think, hundreds of these steps. So, we'll be talking to each other in 2050.
00:49:24I might actually tell you something about that. Okay. I couldn't resist, because I was talking about the
00:49:35search for life. We have made a lot of progress. I think one of the big things for you to take away
00:49:43is that rocky planets in the Habitable Zone are really very common. This is something that we didn't
00:49:51know even 10 years ago, right? And there was a person called Drake. And his question was,
00:49:59are we alone? How many civilizations do we actually have in our own galaxy?
00:50:06Because if you meet me on the street waiting for Zephyrus saying, he asked me,
00:50:12is the life more dependent on the same old universe is maybe big? So why not?
00:50:15So we've got 100 billion stars in the galaxy. We've got billions of galaxies, surely, surely.
00:50:22But he actually decided to make an equation that actually worked it out. And I thought,
00:50:28well, why wouldn't my farewell be an equation? And it's this one. And I'll read it out to you.
00:50:36Basically, it's actually common sense. I'm going to tell you what these factors are,
00:50:43and you will think, yeah, fair enough. So he said, okay, the number of civilizations that we have,
00:50:49well, depends actually on how many stars are being formed. If a million stars are being formed every year,
00:50:57well, the chances that you've got more civilization than if it's only one. So I think that makes sense.
00:51:03Then he said, well, and then it depends on how many of these stars have planets.
00:51:10If you want life, you probably need a planet. If you don't have any planets, that's it.
00:51:15So the fraction of planets is good. But then the question is, well,
00:51:21how many of these planets can sustain life? Have liquid water, for example.
00:51:27And then the number of planets on which you actually get life.
00:51:34And then how many of those will get intelligent life? Right? Because I wanted to talk about
00:51:41civilizations. If you ask me, I think we're still looking for intelligent life on Earth,
00:51:46let alone in the universe. But then the question is, but how many of them
00:51:53are actually trying to get in contact? How many of them would want to communicate?
00:51:59If they all sit there like a bear with, talk to each other, read poetry to each other?
00:52:06Well, no. And then, of course, how long will they be doing that? Right? Because if a civilization is
00:52:13there for one year, then the chance of meeting them is a little bit smaller than if they were around for a billion years.
00:52:19So Drake set out to put numbers there. Now, I've got six slides. I don't think I want
00:52:31to go all of them. So I'm going to skip a couple of slides in the interest of time.
00:52:36Okay. But you may want to know that if you do the numbers, it's about a couple of stars
00:52:46per year being formed in our own galaxy. So that's nice. But you don't want to have too low a mass star,
00:52:55too high a mass star, because you may remember that massive stars, they explode very quickly.
00:53:01Then you don't have time for life to occur. So that's one thing. Then the probability of planets,
00:53:07and this is something that we now know is a big number. I think if you go away today and if you
00:53:17tell your neighbor that basically every star in the galaxy has a planet, that's not an exaggeration.
00:53:23And that's progress. Then the question is, how many of those are in the habitable zone?
00:53:30And that's a number that we now start to realize is pretty high as well. And currently roughly 20% of
00:53:37all the systems that we know of will have a planet in the habitable zone. Oh, that's a nice number.
00:53:43And that's also something that we were guessing 20 years ago. Then the probability of life.
00:53:49Well, I think this is a nice one, that we now have these prebiotic molecules. So we already see
00:53:56building blocks. And this fella is what you call an extremophile. And it's interesting to mention it,
00:54:07because life on Earth is in very uninhabitable places. And this guy, let him go to a volcano,
00:54:16he can live there. Let him go to the Mount Everest where it's very cold, he can live there. Let him go
00:54:20to Antarctica. Let him go into the deep sea. So life can be very resilient. So that could actually
00:54:28imply that life could be easier to stay on than we might say. But we don't know the answer for it. But
00:54:38people are now trying to understand extremophiles more. Not all of them need some life or oxygen.
00:54:47Yeah, the probability of intelligent life. Well, that's probably, well, at the moment,
00:54:52okay, let's assume that we're intelligent. At the moment, it's 100% of all the planets with life have
00:54:57intelligent life. But then the chance that life, that they actually will become a technological
00:55:09civilization. Well, we don't know that either, right? We know that we are. But we don't know the
00:55:18answer. And then the lifetime factor. So we still got 5 billion years. But it's also interesting to know
00:55:25that the US has been around for 4.6 billion years already. And arguably, we've only been doing
00:55:32technology in 100 years. So out of the 4.6 billion years that the US has been around, it's a very tiny
00:55:42fraction of time that we have been technological. So that means that that brings down the normal
00:55:49space drive, of course. So yeah, okay, all interesting, but no, I won't tell you. So if I now look at N,
00:55:59so which was R times P times N times C, so we've got about one star here. We've got about one planet per
00:56:08star. We've got more than 42 habitable planets per planet. We have the chance of getting life, we don't know.
00:56:17The chance of getting intelligent life, we don't know. The chance of getting
00:56:24symbolized technological civilizations, we don't know. And L, based on us, could be 100 years,
00:56:31because we've been going for 100 years. And we might be going for another 5 billion. So it should
00:56:37be a big race. But if you just assume that this is wrong, this is wrong. And this is wrong,
00:56:42at the moment that we could have as we speak in our own galaxy, perhaps 10 civilizations,
00:56:51or perhaps even a billion. Now, 10, that's all nice and good, but it's a big galaxy out there, right?
00:57:00And this site is 100,000 light years away from this site. So if this guy says hello,
00:57:09then it takes 100,000 years for them to receive that. It takes two years to understand what they said.
00:57:17I make this up on the spot. So sometimes they could, and sometimes they reach it there.
00:57:20And then it takes 100,000. So you can imagine there might be 10, but we will never encounter them.
00:57:26But if you take anything away from the course, we are filling in this site already pretty well.
00:57:35People are working in labs to see how easy life can actually start going if you get some soup with all
00:57:43kinds of molecules. And I'm not saying that 10 years from now we will know the answer, but we are making progress.
00:57:52And that's what I wanted to tell you. I don't know what the camera is, but someone changed my life.
00:57:59I said, you should give something at the end. So there you go.
00:58:04I started off by this lecture by saying, we now find forming planets in disks around young stars.
00:58:11Quite new. We find prebiotic molecules in these disks. Quite new.
00:58:17We now find many rocky planets in habitable zones. Quite, quite, quite a big thing.
00:58:23We are looking for signatures of life. Today, I think it's technologically a little bit difficult,
00:58:30but we've got some very new missions and telescopes on the way. We might be making progress,
00:58:36but we still have to wait a while. And finally, I don't know the answer to that. Are we alone?
00:58:43But it's a nice question to finish this lecture course. So thank you very much for your attention.
00:58:49And if you've got some questions, I'm happy to try to answer that.
00:59:01Yeah, I'm happy to answer that. But we also consider like other phrases in this system,
00:59:15what is that? So the music and cylinders, where they have liquid water, even though it's far away.
00:59:23Fantastic question. I've got a repeating question. So I was talking about the Goldilocks
00:59:28stuff. But as the gentleman rightly says with Hengel, we are sending probes to these icy giant
00:59:35planets and icy moons of Jupiter, for example. And why are we doing this? Because these moons are
00:59:43pretty good. But just like we've got the tides on Earth, we've got high tides on Earth, because
00:59:48the moon has a lot of energy. These moons are basically being so affected by Jupiter or Saturn
00:59:55and that they are warmed up by these tidal forces. And some of these, I told you there was a lot of
01:00:03diversity in these moons, but some of them we think, well, we're pretty sure, have liquid water
01:00:08underneath the ice. And life needs energy. And we know from our extreme of ours that we don't
01:00:15necessarily need sunlight. Heat might not. So yes, very good point. Moons, where the conditions are different
01:00:25than the habitable zone, could help us well. So in that case, I should not put a multiplication sign
01:00:34in the equation of a plus. Right? Very nice question. Anybody else?
01:00:43And you know the drill. No one is leaving this room until I've got another two questions.
01:00:48So save them, save me. No, I think it might be a silly question,
01:00:57but I still want to know the answer. The disks that you showed at the very beginning,
01:01:01are the disks. So you have the disks where the darks, where planets are forming, potentially.
01:01:07And then you had these very shiny, bright circles around stars. Was that gases? I'm trying to remember
01:01:17what? Yeah, no, I don't. I think I said it in a side sentence in a mobile. Most, okay,
01:01:25there's two ways. Some of them have been done in gas molecules like monocytes that are so prevalent
01:01:35that you can get really nice pictures. And some of them are due to thermal emission from dust that's
01:01:41warmed up. So it's the two. And I think the first one I showed you was basically the thermal emission,
01:01:50the radiation from the dust rather than... Sorry?
01:01:56It looks very quickly. Yeah, yeah, yeah. Sometimes we have pretty pictures in the stormy.
01:02:01It's a building. The changing of this orbit, fast from the sun, or from the stars, or is it changing closer?
01:02:16Or is it changing closer? Are we going from the stars during this lifetime?
01:02:19Oh, oh. Do planets change position during the lifetime? That's something I have not touched. Well,
01:02:28I have to come back to the Thailand. I have not touched upon that at all. But yes,
01:02:37planets have been bouncing off each other. That's well, sometimes literally, because you think that
01:02:42the Moon might actually be tuned to another planet like the size of Mars, just banging into the Earth,
01:02:48splitting it into two. So that tells you already that the big bodies have been moving around.
01:02:53And we're pretty sure that Jupiter, by itself, has deflected a lot of small bodies. And
01:03:05it has to live a little bit longer. So there's a lot of... So one of the theories was that these
01:03:12gas giants were moving, are vibrating. But apart from that, there's a lot of moving about.
01:03:21stars formed in clusters. I haven't shown in the clusters, but I saw a study last year,
01:03:30and so on, and said that actually, sometimes stars can steal a planet from one another star.
01:03:35So there's a flyby, and then...
01:03:40Or, I don't know, stone kidnets? I don't know. I think that he's doing like kidnapping.
01:03:46So yeah, there's a lot of stuff going on at the time.
01:03:52Just on kind of the same subject, are there any traces of Exo Moons yet?
01:03:58Well, and are there Exo Moons? Now Exo Moons, that's, you can guess already,
01:04:04that's a moon around an Exo planet, right? I am so excited last week, because we had a...
01:04:09the research group, we had a literature lunch, so we talked about the literature,
01:04:15yeah. And there was an Exo Moons detected, and I was really excited.
01:04:18Ah, moon, I've got this lecture, I need to read this. Okay? But this was a star,
01:04:28and it had a very small company called the brown dwarf, which is a field star.
01:04:35They were 20 times bigger than Jupiter. And that brown dwarf had a Jupiter mass companion,
01:04:43so something was circling that brown dwarf. They called it an Exo Moon.
01:04:48Yeah, for some reason I thought if you talk about Exo Moons, you talk about the moons that we know of.
01:04:55So I think at the moment, it's based in our life that we're a little bit liberal and optimistic.
01:05:01it disperse. The only other Exo Moon I can think of is this phenomenon called gravitational lensing.
01:05:11If I'm looking at the star, and by sheer coincidence, if something moves in front of it,
01:05:17then it can act as an Einstein lens. This star becomes a little bit brighter,
01:05:22and people have found that it became brighter because of a star, then another time brighter because
01:05:26of a planet, and then a certain brighter perhaps because of a moon. But as far as I can judge,
01:05:35it's more PR than real moons. Yeah, it should be just because we don't see them.
01:05:41It's not that they're not that they're recovered. Oh yeah, absolutely. But why not?
01:05:46As I said 30 years ago, we've said that it must be all the planets, why not?
01:05:49And the planets around Jupiter, the moons around Jupiter, were formed in a similar way,
01:06:04as I was actually talking about the planets from here. And some moons have been captured.
01:06:10Oh, the back. And what about the Loch Ness of the solar system, the ninth planet?
01:06:23The question is about the ninth planet, but now my problem is that I don't know anymore when we
01:06:27talk about the ninth planet, what to talk about. So are we talking about Pluto was demoted, or are we
01:06:33talking about there might be a ninth planet and we haven't seen it yet?
01:06:36I know as much as you, but I don't think some people have said, well, there could be a planet
01:06:48just behind the sun all the time and we won't see it. That stuff I don't think is really believable.
01:06:55What I do think is, and I mentioned that in the software, planets, objects that are so far from the sun,
01:07:03you can only see them because of reflected light. They are very dim because they're so far from the sun.
01:07:09I would not be surprised if we keep on finding objects like Pluto, dwarf planets, simply because
01:07:17we haven't seen them yet because they're so dim. But I don't think we will find another Earth or
01:07:22another Uranus or something like that. But I have been wrong before.
01:07:26Okay. Well, can I thank you again also for the nice questions and see you sometime next time. Thank you very much.