SPEAKER 1: It is my great pleasure to introduce Didier Queloz, who is right now, a professor at the University of Cambridge in England. And the one thing about introducing Didier is that in exoplanet's community, he is really, really well known, of course, as he will talk to you about. He will show you how he found the first planet around another star. And I think he'll also tell you that it was his PhD project.
And so the problem is my PhD students are coming. And it's like, so, I want to discover the first planet, or the first something. I was like, no, sorry. You know, that's the Swiss astronomer who actually beat you to that.
Among a lot of prizes that I'm not going to name, Didier has a Frontiers of Knowledge Award. And I think you will see in his talk, that that's what he's doing. He's pushing knowledge. He's pushing technology. And he's finding very interesting things out there. Didier.
DIDIER QUELOZ: Thank you, Lisa.
So it's a real honor to be here. And it's a true pleasure to be part of this fantastic, exciting event. When Lisa invited me to come, it took me half a second to decide, I would just manage my schedule to come. Because I think, for me, it was a great opportunity to come for the first time to Cornell. I never had the chance to come here, and I never had the opportunity and the chance to meet Carl. And in a way, I can claim that I am one of the, kind of son of Carl, in kind of science.
Because when I was a young adult, when I was starting my studies in physics, or just before actually, I encountered this famous Cosmos book and the series. And it's still, right now on the top of my list of the most influential book I ever read that brought me to science. So that was an even better reason for me to come here and to be part of the event.
And I also had the chance to know Lisa since a long time, since '98. The first extrasolar planet school-- I mean, in '98 it had became obvious that it was becoming an official kind of science. And that would have deserved a school. And Lisa was there as a student at that time. And another famous female student was also there. It's [INAUDIBLE] also. So this was an interesting time.
So I'm about to tell you, kind of an old story, which is the story of the discovery of the first planet orbiting a star other than the sun. But that there are a couple of things that I think has been said already, which is very profound. You understood that science is a long continuum. I mean, we're connected to the time, really, in science. And I think it was obvious in all the talks you had before. I mean, all this talk before clearly demonstrated that that was not the first time this idea came. And it's a long idea. And a lot of action had been made, progress been made, surprise been made.
So this continuity, I think, is really at the core of the discovery of this other world. And starting from our own solar system, so just to give you a bit the perspective, before we place this discovery, I think is starting by the solar system. So these are what us-- from the beginning of humanity, practically, have been seeing. It's all the planets you can see by the eyes. You don't see this, like that. You just point, moving around. And you know that the origin of the name "planet" comes from the Greek, which means, "moving body in the sky."
So for a long time, this was the only thing that we had. But it's interesting to realize, as a scientist, that with just this on the eyes, we had build a picture about the solar system. We have understood. And the college where I'm from in Cambridge, which is Trinity College-- and we had Newton there. And Newton described a theory to explain the planets, just by looking at the eyes. So I think it's interesting to give this connection. So in a way, when we are going to the other planets on other stars, it's just a continuity that has been started with early day explorations.
So exploration is really the key word here in this game, and discovery as well. The exploration of the solar system has always been related to discoveries. So you know when we started to get the first telescopes and Sir Herschel-- practically in his garden, he built a telescope big enough able to see Uranus here. And that was the first time we expanded, since so long, the size of the solar systems.
Using the Uranus' orbit, looking at the orbit, and using the mathematics developed by Newton and the gravity theory, people were able to predict there will be another planet a bit farther out, which was Neptune.
A very interesting story. At the end, a big race, and Le Verrier got it right. And then we get a bit less than 100 years later. Then you know this forensic search, and after this, for if there is anything else. So you know this fantastic story of which it was seen for a long time as the outskirt boundary of the solar system. But it was mentioned, with the talk of [? Anne ?] this very influential work of Kuiper, in a way to predict that everything would be a bit more complicated than that.
And you all know that in '92 it became obvious that there were really a whole population of objects-- thi9s is an artistic view. I would love to get this picture from a spacecraft. A bit difficult to get.
You get [INAUDIBLE]. And [INAUDIBLE].
So this is the planets. You see Pluto around, and you see all these bodies, which is no part of a very complex structure. It's called the Kuiper Belt, which is very interesting, because it tells you a lot about the history of the solar system.
So you've seen what we have been from, starting from the few planets that you could get by the eyes, until the point now we have a very complex picture of spacecraft going through most of these bodies, and especially going to the outskirts-- I know, the solar system. So again, explorations. It's all about explorations and knowledge that is connected what has been done before.
So speaking then about going to the other stars-- well, the problem you have when you want to find a planet on the other stars is you really dealing with a tremendous difficulty, which is a planet is almost nothing compared to the star. The mass of the planets is 1,000 times smallest than the stars. It produces almost no light, compared to the stars. So you really have to use tricks to have a hint that there is something orbiting that star.
So it was mentioned by Dave that form the early days and the understanding of the Doppler shift-- it's the relation, when you move something, if you have a wave, whatever wave it is, it can be sound, it can be light, you have a shift in the color and the wavelengths of that wave. It's called the Doppler effect, a French physicist from the mid '90s.
And looking at the stars, when you have the orbiting planets around it, you have the motions of the light of that star. Practically what we do, we have more than just the light. We have what's called spectral lines. It's a bit like an imprint of the star, related to the structure of the element that is in the atmosphere of that star. You have iron, for example, that produces a lot of lines and structure that you can use-- it's a bit like a barcode-- that you can use to trace exactly what is the speed.
So this technique was known since a long time, from the first time we got spectra from the star, which was almost 100 years. And the idea that you maybe using the observation of the speed of the stars to detect something that you would not see orbiting that stars is long. But the difficulty you have, when you want to look with something very small, is the amplitude of this motion you have to deal with.
So I don't want to enter into too many details, but I just want to give you a little bit of the 101 flavor, what it means, detecting the speed of the planet, if you build what's called a spectrograph. So a spectrograph is a machine which produces what's called a rainbow. It splits the light, spread the light different wavelengths. And then you can compare with whatever, your cell phone picture and the pixels-- you see when you have a lot of pixels, depending on the size or how new is your phone to take picture.
And in terms of how you measure the speed, we have a similar kind of resolution equivalent, which called the spectrum resolutions. And the best we can do, for plenty of good optical reasons I won't to explain, is having a resolution which is called the 100,000 time. So you resolve the light by 100,000 times. Practically it means that a pixel of your cell phones, seen from a spectrograph, would give you about the speed of 3,000 meters per second, three kilometers per second. Three kilometers.
So it is the sign of the best picture you can do with a spectrograph. So if you have a change of that speed, practically, you will see the change on the pixel scale. So in theory, when you use a spectrograph to measure the speed of a star, you cannot do better than that. If you want to do better than that, you have to use tricks. And that was, what has been described by [? Dave ?] [INAUDIBLE] before, a couple of tricks that can be used to try to detect something below that limit.
So you can imagine how challenging it may be, when you have a machine which is always blind, and you want to see something which is much smaller than that. Because when you want to detect a planet like Jupiter, this is 13 meters you need to get. So you're completely blind. And you really want to see through the blindness, something very small. And to give you a little bit the challenge of detecting the Earth, what it could be. It's again, another order of magnitude here.
So it's something that was in the air since a long time. And there is a couple of key papers in the '60s and the '80s that describe approach and ways to do it. But the practicality to implement that took a long time. And that's the reason why the idea is old, but the outcome of the detection is pretty new. Because we needed to be able to achieve this.
So to understand a bit of the context where we were evolving in the '90s-- and here was the big picture before. Seen from the astronomy perspective, you can simplify your problem as much as you can, where practically you say, OK, this is the solar system. We use it as a template, because that's all that we have. I know. And we just try to-- we don't deal with the structure of the planet. Just look at where they are, and what are the mass.
So this is the mass of the planet, you see in this, against the distance. So 1 AU, it's the distance to the Earth. 1 is the mass of the Jupiter. So you need to do to have 300 times the mass of the Earth to make a Jupiter. So this the solar system seen from a very simple way, from the astronomy point of view.
And there's a lot things that is interesting in this picture. Well, the first thing you get is, the small mass planets are much closer than the big mass planets. The got value here-- and you can challenge it, but it's still a fact. I mean, practically, if you would use the solar system as a template, well, you expect the big planet, which is the more massive, and, practically, the easier is to find, have to be a bit away from the stars. [INAUDIBLE] reason for that is related to the formation mechanism of the planet. The theory, which by the way, is working pretty well for the solar system. It's pretty good as a predictive theory, to explain what's going on in the solar system. So [INAUDIBLE] too long to use it as well on the other stars.
So in the mind of most of the people, when you were looking for a planet, the best expectation you could have is trying to find something like Jupiter, somewhere away from the stars. Maybe it doesn't need to be to be 5 AUs. It could 1 AU. But still, clearly something a bit of the outskirts of the stars.
So practically what happened-- I mean, you know that the object that was found was a real shock. And I will come back on some detail of detections. Because on that diagram, the planet orbiting the star, 51 Peg, is here. It's log scale. So there a lot, a lot of distance between this Jupiter and that Jupiter. So it's about the mass of Jupiter, but it's farther, farther off what you would expect, in terms of distance.
And if you want to compare with this planet, it's even closer to the star, and it's not the right mass at all. So practically, that planet should not exist at all, according to what we know from the solar systems. So we know that there is ways to understand this. But at the time it was a real shock to get this.
And I can say that very few people believed that it was a planet for a long time, until another team found what's called the transit. And there will be a talk after that on a planet similar to that. So this planet is very close to the star. It is so close that the planet is extremely hot. That's the reason why they bear the name of hot Jupiter, because they have the mass of Jupiter, but they're far, far closer to the star-- 20 times closer than the Earth orbit, and ending up to be very hot, because just too much energy beaming from the star to the planet.
So practically this is how it looks like in this system. And in terms of discovery, the picture of the planet we have is this. So this is the evidence, the fact that we have found a planet. Practically what we have here is the amplitude of the motion that we detected. This is meters per second. So it's about 67 meter amplitude here. And that's the time. And we phase it because at the time of the orbit. so you can just [? wrap ?] the time of the orbit.
So this is a change of discovery. And you can appreciate, I mean, how precise is the measurements. And that's practically the key of the discovery. Practically, to detect this, what happened in real time is one day you measure one point here. Another day you measure another one here. The day after you measure one here. The day after you measure-- then you really see that something is moving into the star in real time, practically. And you don't need a clever algorithm to find it out. It's obvious. Because your machine you build is so accurate that it gives you right away the evidence there is something.
Well, practically, in the real life, it didn't happen exactly like that. This is a theory of the way it goes. Because when we started the program in '94, we had a couple of-- well, we had a couple of issues. First of all, it was the first brand new machine that we had. So it means that we have no experience of that kind of new machinery.
And the other one-- we were expecting a planet much farther out than this one, not a short-period planet. So after so much time designing and building the instrument, my PhD advisor decided it was good time for him to take up a sabbatical in Hawaii. Good choice. So off he went in April '94. And left me the key of the machinery. And he said, OK, just have fun, and just start the program. And he told me on purpose, you know, Didier, don't expect to find any planet. It's going to take time. You cannot do that in your PhD. And I actually don't care. I think it's so much fun to go and watch [INAUDIBLE] Observatoire de Haute-Provence, to go there, to observe. Off I go.
So you cannot imagine my surprise when out of the few stars I decided to pick as the standout stars, exactly like you, Dave, about 15 stars we picked to be the one that we measure every time, I found this. After two or three measurements, it was somewhere in the summer that they didn't match. It was a real panic, because I realized that after four years of PhD, I had built a machine that didn't work.
What else to hope? Nobody could imagine that such a star, such a planet would exist. So I am really in a frenzied panic in a way I had really to find out what's wrong. So I had been working for a couple of months until the end of the year, trying to re-observe the star without telling anyone, not even Michel. I was so scared.
So I was continuing measuring, comparing, until the point at which I said, well, this is real. There is something real. And that day I remember very well because I was completely ill-prepared for that. And I decided maybe it would be good time to make an orbit. Well, I had no software to do an orbit, because we were not ready. Because nothing was supposed to happen that fast.
So in a way, luckily, I had bad weather-- a couple of days of bad weather. So I went to the library of the Observatoire de Haute-Provence. Read a book, and programmed the software to solve the orbit of that [INAUDIBLE], and find a period that was not the right one at the beginning, and came back in January out to the point-- then I'm talking '95 right now, where it was obvious that they were a real object. They were the real orbit with a real period.
And at that time I was convinced there was something here. And I was brave enough to send a famous fax to Michel Mayor, saying, look, Michel, I think I've found a planet. I was a bit scared of the answer. And Michel had this wonderful answer. Oh, yes, it's interesting. Maybe.
This is great. I mean, I hope all the PhD advisors will be the same. And then he came back and we had to work quite hard to convince either the referees or the people. And then you know the story. That becomes public there.
So very often after, retrospectively, I'm thinking about why this discovery has been possible. There's a couple of good reasons why. And it was touched upon bye by Dave. I mean, the importance of the technology here. Clearly the optical fiber, the CCD, the new design of the spectrograph, also the global context. And we were aware that [INAUDIBLE] are very rare at that time, from the work of Dave. And all this [INAUDIBLE] backgrounds, all of us knowledge from the past experiments. And also a couple of tricks that we had to be a bit creative to make sure that we would reach this accuracy, which is pictured on the vital data here.
Coming back then to the situation today, I mean, right now we started with this point. And it may look a bit bizarre, but practically that point, which is the tip of the iceberg here. Because the situation today, this is it. This is the planets today, found by the Doppler techniques-- about half of the planets that's been confirmed that way.
So there's a couple of things, which is pretty obvious here. It doesn't require a lot of study to understand that. Well, first of all, it's not very clear, what is the upper mass of a planet. That's why Dave is very eager to wait for the Gaia data, and there you find a planet. Possibly. I think it's a high chance it is a planet, because when you consider all the objects we have here. But at that time it was impossible to imagine they would exist. It was too far fetched, compared to the global consensus. And nobody would have understood this.
The other one is we're finding planets about the mass of the Earth. They're not exactly that here, but we have reached that level. It means that the number I showed you is not exactly the number I showed you, but very close. So tremendous progress has been made in the technology to get you to this point.
But the key point here is, we have really nothing here. Well, I think it's exciting for the PhD students in the room. Because there is a lot of work to be done. There is really a lot of work to be done. I mean, all the planets we have found-- and practically there is one planet out of two or three stars, which is like that, they're all different from the solar systems. We have a series of some small mass planets, a very close orbit. We call that the Super Earth here. But it's not very clear whether we have something equivalent to the solar systems.
And the reason why is because it's tough. Because the more you move here, the smaller the signal becomes. So it's extremely tough to get to detect this object. So the good side of this is the fact that we have this whole population of small-period planets had a tremendous impact. And we'll have this talk after. Because we have tons of transit. If this population did not exist, the number of transiting planets would be extremely, extremely small. But we have a vast majority of planets on a very sharp orbit. And because they have a short orbit, the chance of transit is very high. And having a transit gives you an access to the density of the planet.
So this is all these planet for which we have the mass and the size, pictured in terms of the density here. So if you're not familiar with the density, well, this is the water, this is the iron here. And what you do see on this picture is why we don't have really yet understood what's going on, on the size of the planet that may look like the Earth.
We have a very interesting regime when you move off from Saturn to Jupiter. And this relation may seem to be bizarre. You may be puzzled whether or not [INAUDIBLE] after about this that we have planets like Jupiter that looks like an iron density planet. It's kind of very bizarre. It's the structure of the mantle, but it's different. But it's not iron actually. It's still hydrogen and helium that is the most component here on this planet.
And then we have this kind of [? indeterminate ?] region where nobody understands what's going on. Because this is between the Saturn and the Earth. This is the regime where we don't really know exactly where is the planet. And there is a big debate and a lot of discussion about exactly the nature of this planet. And this is where you're going to have later, very likely the discussions about the outcome of Kepler that play a significant role into this area here.
So you see it's interesting because you start looking at something, and you find something different. But actually it gives you access to something even more interesting, by the way, than the original idea. But we are coming back to the original idea, for sure, eventually.
I cannot do this talk without that picture, I think. And I think, because this picture tells-- there is a lot to be said about this picture. It was said that the picture has been done. And I'm very pleased the picture has been done. I think I'm showing this picture almost every time I do a public talk. Because first of all, it's an inspiration. I mean, the idea that the planet Earth, like we see it, it's just a dot for an astrophysicist, I think is the center of the game here.
Because maybe in 20, 50 years, we will do some similar picture on an other planet, but it still will be a dot, and it will remain a dot for a long, long time, all these other planets. So just to tell you how tremendously difficult.
And the other thing I like very much is the perceptions you can get. So the perception should be an inspiration here to us. And that is nothing best that this famous sentence of Carl Sagan to try to translate this inspirations and this energy and this enthusiasm that us scientists are having, and trying to do our best to share. And Carl was really a master into sharing his excitement. So I'm very pleased that I'm here and I hope you will enjoy this fantastic day Thank you very much.
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Didier Queloz of Cambridge, UK, speaks at the inauguration of the Carl Sagan Institute, May 9, 2015. The inauguration event, "(un)Discovered Worlds," featured a day of public talks given by leading scientists and renowned astronomy pioneers.