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Planet Hunters
BBC2 9:30pm Thursday 16th March 2000

Our Solar System NARRATOR (JACK FORTUNE): The only life we know of exists on one planet: ours. Down the ages people have wondered if we were alone in the universe or whether somewhere far beyond our own Solar System there might be a civilisation like ours. If other life existed it would probably be on another, far away planet, something like Earth, but for centuries nobody knew whether these alien worlds actually existed and then, just a few months ago, for the first time ever, scientists in Scotland saw a new planet. It was 51 light years away.

DR ANDREW COLLIER CAMERON (University of St Andrews): At that moment we knew that we'd seen something that nobody else had ever seen before, so after 3 years of working at this we finally had it, the thing that we'd been looking for, and here it is, the first view of a planet orbiting another star.

NARRATOR: What could an alien planet possibly be like? It's a question that has intrigued generations of astronomers. We can only imagine how different it would be from our own Earth.

PROF GEOFF MARCY (University of California, Berkeley): Since I've been a little child I thought to myself wouldn't it be wonderful if we could learn whether or not there are other planets out there like our own and I thought if so, all of the science-fiction novels that we all read might, in fact, have some bearing on reality. They may, in fact be, other beings out there who are indeed thinking about us and wondering if we're here.

NARRATOR: The key to finding other far away planets lay in understanding exactly how our own Solar System formed because these were the only planets we knew of, 9 diverse worlds separated by millions of miles of space. These 9 planets could only have come into being because of the star at the centre of the Solar System that we call the Sun.

The theory is it all began nearly 5 billion years ago. A swirling cloud of dust and gas collapsed to form a star, the Sun. Out of the debris circulating this new star the 9 planets were born. If this theory of star formation holds true across the universe it seems the best place to look for other planets is around other stars and with billions of stars there should be billions of planets orbiting. Tracking down these elusive planets outside our own Solar System has become an obsession for a small group of scientists around the world - the planet hunters.

GEOFF MARCY: Yeah I think it's 20-30 arc seconds away, B is. It looks like it's north and west of A.

MAN: Yeah, you're sure it isn't A is more…

NARRATOR: The planet hunters know exactly what they're looking for.

GEOFF MARCY: The real goal here is to find life.

PROF. KEITH HORNE (University of St Andrews): The goal is to find out whether our Solar System is typical or very rare.

DR GEORGE GATEWOOD (University of Pittsburgh): You always feel that just over the next horizon it's going to be there.

KEITH HORNE: And ultimately to find out if there are planets like Earth with life on them.

GEOFF MARCY: We'd like to know if there's other life out there that's anything like we humans.

GEORGE GATEWOOD: And looking for planets, searching the skies to see one other Earth, a small blue ball somewhere, that's what we're about, that's what we want to do.

NARRATOR: But finding the very first planet is first stage in the quest to find life was to prove more difficult than anyone had imagined. Of all the billions of stars in the universe the planet hunters focus on just a few hundred that are similar to our own Sun in age, size and brightness. That gives them the best chance of finding new life-bearing planets like Earth.

Around every one of these stars there might be planets, but there's a problem. Even the largest planet would be much too small to see across billions of miles of space and what makes it even more difficult is that planets don't generate their own light. They only reflect a small amount of light from their parent star. Seeing a planet against the glare of its star is practically impossible.

GEORGE GATEWOOD: A good analogy of the difficulty is to consider the, the problem of trying to spot a firefly sitting on the edge of a huge searchlight. You can see the searchlight. If the searchlight wasn't there you might be able to see the firefly but in the presence of the searchlight the glare just overpowers you, and this is why we can't just simply look directly.

NARRATOR: Instead the planet hunters don't actually look for planets. They look for stars that wobble. Although a planet is tiny compared to its parent star, its mass is great enough to have a small gravitational effect, As the planet orbits the star it will pull the star off its axis. Astronomers observing the star would see it wobble from side to side. The bigger the planet the bigger its mass and the more the star would wobble. The planet hunters all have different methods to try to find this wobble.

GEORGE GATEWOOD: The technique we use here is called astrometry. Basically what we're doing is collecting single frames in a movie. We look at a section of the sky and we, on a particular night, find where each of the stars in that section of the sky are and we measure the relative positions. Then on a later night we do the same thing again. We take another measurement of the relative positions of all the stars in this area of the sky. To search for the planet, we then compare all of these frames as if they were put together in a single movie to see if the star's motion is linear or if it has that very small wobble that we're seeking.

NARRATOR: The principle is simple but the technique is painstaking. The wobbles these planet hunters are trying to detect are minute. Even a giant planet like Jupiter, some 300 times the mass of Earth, would barely have enough gravitational pull to make a star wobble at all. It's like trying to see a man waving on the Moon and it's made even harder to see by the swirling atmosphere of the Earth. It causes starlight to twinkle and these tiny variations are enough to obscure the wobbles caused by orbiting planets.

This makes the scientists' task almost impossible. One team of planet hunters found a way to get above the chaos. They were looking for wobbles using the Hubble Space Telescope.

DR FRITZ BENEDICT (University of Texas): If you get up above the Earth's atmosphere the hope is that the signal that the Earth's atmosphere impresses on any astronomical research that's done from the ground won't be there and so we'll, we'll get perhaps slightly better results. Yeah, we've got a third of a Jupiter for a 600 day period...

NARRATOR: Whenever he gets the chance Fritz Benedict uses the Hubble to seek out wobbling stars, but the Space Telescope is much in demand and planet hunting is not its main priority.

FRITZ BENEDICT: The problem is you don't get a lot of time with the Hubble Space Telescope, so we certainly can't do as many objects. We say that going above the Earth's atmosphere is the best thing in the world, but perhaps the best thing in the world is to be smart enough to figure out how to make these observations from the surface of this planet because it's the cheapest way to do it.

NARRATOR: Astronomers had to find a reliable way of detecting wobbling stars from the ground. By the late 1980s one planet hunter reckoned he'd finally cracked the problem with an ingenious technique.

GEOFF MARCY: When you look up at the stars at night those white dots actually contain an enormous amount of information, each one of them. The white light can be spread into all of its composite colours - blue through red - much like the Sun's light is spread into all of its colours in a rainbow.

NARRATOR: First the light from stars has to be broken down into its individual colours. Each colour making up the light has a different wavelength. This is the raw material that Geoff Marcy feeds into his computers for analysis.

GEOFF MARCY: In the star's light we have additional information due to the fact that the star's light must pass through the star's atmosphere on its journey towards us at the Earth and the atoms and molecules in the atmosphere of a star absorb the light at very specific wavelengths which represent a sort of fingerprint of the existence of each type of atom and molecule that's in that star's atmosphere.

NARRATOR: Because each star's atmosphere absorbs certain wavelengths of light tiny bands of colour are missing from the spectrum of each star. These dark bands are called absorption lines and their pattern is unique to each star.

GEOFF MARCY: We're getting 20 cavs a second, that's excellent. Here we go, starting. That was…

NARRATOR: Each time Geoff Marcy observes a star his computers analyse its light spectrum and measure the precise position of the dark absorption lines. Over time any tiny shift in these lines could mean that the star is wobbling.

MAN: …I think it's going to be about 150:1.

GEOFF MARCY: There's a glorious effect in physics called the Doppler effect. When the star's coming at you the spectral lines, these absorption features due to atoms and molecules shift one direction and when the star's moving away from you, the spectral lines shift in the other direction. We actually measure the radial velocity of the star, the speed with which it's coming at you and away from you, and we measure this radial velocity by watching the amount of Doppler shift.

Now the interesting thing is is that the larger the Doppler shift back and forth the more massive the planet. A low mass planet can hardly shove the star around at all and so we hardly see any Doppler shift at all. On the other hand, if the mass of the planet is large, we see a great, large, easily detectable Doppler shift.

NARRATOR: Looking for wobbling stars forces all the planet hunters to search for planets much bigger than Earth, giant planets the size of Jupiter or larger, whose gravitational pull is huge enough to push and pull a star around. Geoff Marcy knew exactly how a wobbling star would look on a graph.

GEOFF MARCY: Looking at this graph you can see that the star wobbles upwards and wobbles downwards and then wobbles back upwards again and this is the movement of the star due to the planet pulling gravitationally on the star, so if you see a graph like this you can immediately infer the presence of a planet.

NARRATOR: Using all these different techniques the hunt for alien planets went on for years and after all these years of searching, how many planets had they found?

FRITZ BENEDICT: I haven't found any planets yet.

GEORGE GATEWOOD: We've not found any.

GEOFF MARCY: We were shocked at this.

GEORGE GATEWOOD: This is really quite surprising to us because when we began we assumed that every star, every single star, probably had a planetary system and they must all have Jupiters. Indeed Jupiter was probably just an average run-of-the-mill size large planet.

GEOFF MARCY: It sent chills up my spine frankly, and the reason was is that I thought to myself: hey, we haven't found planets of a little more mass than Jupiter. Who's to say that when we begin detecting planets, or have the ability to detect planets slightly less massive than Jupiter, who's to say that suddenly we're going to find them? Perhaps our own Jupiter is itself a rarity, which then may imply that our own solar system has some very rare characteristics which bodes ill for life in other planetary systems.

NARRATOR: But the planet hunters didn't give up. They all believed there had to be planets out there because the theory of how our own Solar System was formed predicts that planets should be found around practically every other star. But while the planet hunters were searching around stars like our own Sun, 3 planets turned up in a totally unexpected place. They were orbiting a pulsar. Pulsars are thought to be dead stars which have exploded in a supernova. All that's left is a tiny spinning body just the size of a city, but tremendously dense releasing pulses of deadly radiation up to 600 times a second. The 3 new planets were orbiting the remnants of one of these strange, tiny, dead stars. This wasn't what the planet hunters had been looking for.

GEOFF MARCY: Pulsar planets really don't move me emotionally. The reason, of course, is that ultimately the big pay-off in this game is to find a harbour for life and we all know that life can't form around those so-called pulsar planets. The environment is far too harsh with X-rays and radiowaves beaming onto the planet, and so for those reasons it's almost certainly the case that such a planet doesn't yield the possibility of the real excitement, namely intelligent life.

NARRATOR: Pulsar planets proved the theory at last. There were planets out there, but this wasn't enough. The Holy Grail was still a planetary system around a star like our Sun. The planet hunters kept up their nightly vigil looking for wobbles in the dark. Years passed. Then in 1995 on the other side of the world another group of scientists struck gold. Over in France, two Swiss scientists were using the same technique as Geoff Marcy, but they had one crucial advantage. While Marcy was spending years collecting data, this team had the black box.

DR DIDIER QUELOZ (Geneva Observatory): We have a black box and with this black box we compute right after the observation the, the speed of a star. Say 10 minutes after, and that's very original compared to, to Geoff Marcy, and that's a key point because you, as you have your results right after the observation you can interact very rapidly with your data.

NARRATOR: Their unique system allowed the Swiss scientists to analyse their data faster than other planet hunters. They would be able to see whether a star was showing a wobble almost immediately and then focus all their efforts on that star. One of the stars they were studying was 51 Peg. At first it was just another star on the list, but a few months into the search the Swiss team noticed that there was something different about it. Each night for weeks they plotted the star's movements on a graph. Over time they began to see a strange pattern emerging.

DIDIER QUELOZ: At the beginning we saw nothing and, and then let's say 3 months or 4 months after the beginning we had a point very unusual compared to the, the other one and then you say OK, I will try to observe this star again the next, next day and you observe it the next day and the point has changed and then you observe it again and again and again and it was changing every times.

NARRATOR: Eventually the pattern became clear. It showed a wobble. It seemed this could be the very first planet found orbiting a star like our Sun. Before they dared tell anyone else, the Swiss team decided to run the whole experiment again. They were right. They decided to break the news in October 1995 at a press conference in Florence.

DIDIER QUELOZ: The first reaction was unenthusiastic because at that time people thought that it was too difficult to find planets and then we bring this news and we say we can find them, and then people say right, that's, that's nice, we can find them. Then we have to try. Yes, it was fantastic.

PROF MICHEL MAYOR (Geneva Observatory): In fact it was completely crazy time with call from papers, from television, from radio, from, from all, all the world and E-mail, 100 E-mail per day or something like this. It was absolutely completely time where we had no possibility to work at all.

NARRATOR: No-one had ever actually seen the planet orbiting 51 Peg. They'd only seen the star wobble, but this went down in history as the first triumph of the planet hunters. Spurred on by this success the search was on for more planets. Other teams went back to reanalyse their old data, or set about observing more stars. It wasn't long before they began to detect signs of planets around other wobbling stars. 51 Peg had started a gold rush. Eventually more than 30 new planets would be found.

GEOFF MARCY: Today I would like to announce here for the first time the definitive discovery of two new planets around two other stars.

NARRATOR: People were speculating that finding a planet with the potential to support life was only a matter of years away. But there was a problem. There was no direct evidence that alien planets existed. They had all been detected indirectly by the supposed effect of a planet's gravitational pull causing its parent star to wobble, but what if the wobble wasn't caused by a planet at all?

GEOFF MARCY: The biggest concern that I had caused me to lose a lot of sleep actually was a claim by a Canadian astronomer who said that the planets didn't exist at all, that instead the stars were pulsating, breathing in and out in a way that would give us Doppler shift variations, but in fact not due to planets at all, just the star changing its size.

NARRATOR: Our own Sun, like all stars, is an immense nuclear furnace, a ferocious, turbulent place, constantly pulsing with sunspots and flares. Perhaps it was activity like this on other stars that the astronomers had mistaken for wobbles. The planet hunters had to find new evidence that the planets were really there and there was one ingenious way they could try. It was all down to geometry.

They knew that any one of their planets might cross the face of its star as we see it from Earth is the path of its orbit was right. Just like a mini eclipse, the planet would briefly block a tiny proportion of the star's light causing its brightness to dip minutely. This rare event is known as a transit. So the planet hunters now devised a method to detect distant transits across wobbling stars and so prove that the wobbles really were caused by planets.

GEOFF MARCY: Well this transit method is very simple. The star is sitting there all by itself shining with a constant amount of light, but if a planet crosses in front the planet blocks a certain fraction of the light that would have left the star. It's just like when you have a lightbulb and a finger crosses in front of the lightbulb, the light from the bulb would dim due to the blocking of light by the finger.

NARRATOR: Just last year a transit was observed and filmed in our own Solar System when Mercury passed between Earth and the Sun. If a transit like this occurred at another star the planet hunters hoped they could measure the minute dip in light coming from the star.

GEOFF MARCY: If we make a graph something like this, the intensity of light from the star versus time and we make a graph showing constant brightness for the star and then when the planet crosses in front the star dims out, just like that. It's the clear signature of a transiting planet thereby telling you that the planet really exists.

NARRATOR: But detecting a transit across a wobbling star would be extremely difficult. Geoff Marcy needed access to extraordinary telescopes capable of seeing the tiniest dip in the brightness of light from a star. Halfway across the USA in Nashville, Tennessee, was the one person Geoff Marcy knew he could turn to.

DR GREG HENRY (Tennessee State University): What I'm ultimately interested in is long-term brightness variations in stars that are similar to the Sun, similar to the Sun in mass and age and composition.

NARRATOR: Greg Henry uses unique, remote control telescopes that look at just one particular aspect of stars.

GREG HENRY: These particular automatic telescopes that I'm using do not take images, they do not take spectra, but they use what, a device called a photoelectric photometer that measures the total brightness of the star.

NARRATOR: Using these telescopes Greg Henry could try to capture the dip in brightness at the rare moments when a planet might briefly pass in front of a wobbling star. It was a long shot, but he was hopeful.

GREG HENRY: Because these telescopes are set up to precisely measure the brightness of Sun-like stars from day to day, from hour to hour, makes them ideally suited for searching for a planetary transit in the event that a planet moves in front of the disc of a star that will cause the star's apparent brightness to decrease slightly and we can detect that in our observations.

NARRATOR: The plan was simple. Every time Geoff Marcy found a star with a wobble he sent the details over to Greg Henry. Greg Henry's job was to measure the intensity of the light from the wobbling star throughout a night. His computers would then display any change in brightness. If there really was a planet the light intensity would dip minutely. But it didn't happen. In 4 years of study star after star showed no transit at all.

GREG HENRY: Here are several cases of failed transits. The solid line in the graph shows the predicted brightness change that we would expect if the orbit is tilted in such a way to give us a transit. The observations clearly show that at that predicted time there is no decrease in the brightness of the star. Transits do not occur on any of these 9 systems. There's no transit there.

GEOFF MARCY: We were becoming a little nervous, however. The reason we were nervous is that we knew that sooner or later some of these planets should cross in front of the star, but none of them had and I remember several people asking me whether this was causing a little crack in my confidence about the existence of these planets and I told them frankly that yes, we were becoming a little worried.

NARRATOR: And then in November last year Geoff Marcy found a new wobbling star, the imaginatively named HD209458. It wobbled so fast that it looked as though there must be a planet in a close orbit of just 3½ days. The frequency of its orbit gave them a better chance of seeing a transit.

GREG HENRY: When Geoff notified me of the new planet he had discovered around HD209458 that would become the 10th star that I had searched for transits and with negative results on the first 9 I, I certainly was not particularly excited or particularly expecting a, a transit here. I'd been through too many failures before to get too excited about this particular one.

I had to spend some time Sunday programming the telescope, picking comparison stars and setting up the requested observations to send to the telescope. I spent Sunday afternoon doing that, downloaded it to the telescopes over the Internet and went home to get a good night's sleep. Monday morning when I came back in the resulting data were waiting for me on my computer. I processed the observations as usual. Fortunately it was a, a clear night and a first look at the data indicated that indeed it looked like something had happened.

NARRATOR: Finally, after 9 failures, just last November they saw this.

GREG HENRY: Well the data showed that the star faded by about 1½% which is almost exactly the amount we would expect for a gas giant planet moving in front of its star. In other words, the data looked like we have a planetary transit at exactly the right time.

GEOFF MARCY: Well I'll never forget the morning that I came in to Berkeley here, walked in to my office bright and early in the morning, looked at my e-mail like I always do and I answered a few other e-mails and then among the stack of 15 or so e-mails there was one from Greg Henry. I'm sorry now to this day that I didn't answer it first, but when I popped it open it simply said 'call me immediately' and I was shocked at this. Greg Henry never asks me to telephone him. In fact I don't think I've ever spoken to him on the phone at all and of course I knew right at that instant what it meant.

NARRATOR: Unknown to Geoff Marcy, another team of scientists had already observed a transit on the same star. Together it was all the proof the planet hunters needed. At last there was no doubt that there really were other worlds out there. But nobody had ever actually seen one of these distant planets. Knowing they existed made these alien worlds all the more tantalising.

GEOFF MARCY: We don't know anything about the composition, what the planets are made of and so what we need is some sort of technique in which we can actually analyse the type of chemicals, the molecules that make up the planet and its atmosphere.

NARRATOR: Many believe that actually seeing these planets against the glare of their stars was impossible but the planet hunters didn't give up. A team working in Scotland decided to join the growing number of scientists who were trying to find a way of seeing a planet.

ANDREW COLLIER CAMERON: Being first to find a planet like this is entirely a matter of luck. There are several groups in the world who are all in communication each, with each other and all of us are striving towards the same goal. When, when one of us gets one of the prizes ahead of one of the other we're all equally ecstatic.

NARRATOR: But to reach their goal of seeing a planet they now have to tackle the greatest challenge of all: how to distinguish the one tiny speck of faint light reflecting off the planet from the overwhelming brightness of its parent star?

ANDREW COLLIER CAMERON: Separating the light of the planet from the light of the star is like looking for a needle in a haystack. It's amazingly difficult unless you know where to look for the needle. The real trick is to know exactly what the light of the star looks like so that you can subtract it off and be left just with that little spark, that one part in 20,000 that's coming from the planet.

NARRATOR: To be able to distinguish between them you need to know the one key difference between the light from a star and the light from its orbiting planet and there is one key difference. The light from the star is fairly constant, but the light from the planet continuously changes in brightness and wavelength as it orbits the star.

ANDREW COLLIER CAMERON: OK, well let's suppose that you have here a star represented by my trusty mag light, and here we have a planet, represented by good old St. Andrews golf ball. The planet's light comes from the star, but as it bounces off the planet its properties are changed in a way that we can measure simply by the fact that the planet is moving very fast, at about 150 kilometres per second as it goes round the star in its orbit. That tiny fraction of the light that is coming from the planet and that has been changed by its motion is the part that we're looking for.

NARRATOR: To see this changing speck of light in all the glare of a star means analysing all the light coming from the star in minute detail. But when they began there was no way of doing it.

KEITH HORNE: There weren't any computer programmes around to analyse the data in the way we needed to analyse it so we had to write them ourselves. The purpose of the computer programme is to subtract the light from the star without also subtracted the light from the planet.

NARRATOR: It took them 2 years to write a computer programme capable of separating the constant light of a star from the changing light of a planet, but finally they had it.

ANDREW COLLIER CAMERON: After the computer has finished processing all these mountains of data we need to display them in a way that we can understand and the way we do that is to make a single plot that tells us whether we've separated the light of the planet from the star and if we have then you will see a large peak on this plot and that's the signal that tells us that we've got the planet.

NARRATOR: Once again all their hopes were pinned on a graph. With a method in place all they needed was a likely star.

KEITH HORNE: We chose the star Tau Bootis. At the time there were 4 other stars that were possible and we chose Tau Bootis because we wanted to pick the star with the strongest expected signal so this meant the star, the planet closest to its star with the shortest orbit period and with the largest star wobble and that was Tau Bootis.

NARRATOR: The team set off for the Canary Islands. Night after night they trained the giant William Herschel telescope on Tau Bootis.

ANDREW COLLIER CAMERON: As each night's data came in we would feed it into the computer and leave it running overnight, rush back in to work in the morning full of anticipation 'cos by that stage the huge amount of data that we'd poured in had been boiled down into a single bump on a graph that would tell us whether we had seen the light from the planet or not.

NARRATOR: The scientists could only wait and hope for the magic sign on their graph that would tell them they'd actually seen a planet and finally, just a few months ago, they saw this.

ANDREW COLLIER CAMERON: That bump showed us that we had a signal. We'd seen the light from the planet.

KEITH HORNE: It felt fantastic. We were elated, but at the same time we were relieved because after such a long effort we had finally reached our goal.

NARRATOR: For the first time ever we could see the light from a planet outside our own Solar System. Now everyone wanted to know what this alien world was actually like.

KEITH HORNE: The next step was to divide the data up into segments of different coloured light to see what colour the planet was and when we did this we found that the, the red light and the purple light were missing. The reflected signal was very weak at those colours, but for blue and green light we had the strongest reflection.

ANDREW COLLIER CAMERON: So what we were left with was a pretty blue/green planet, just like Earth except for the temperature.

NARRATOR: A blue/green world in a distant part of our galaxy. Our own blue/green planet is the only known life support machine in our Solar System. Its colour comes from its essential life-giving elements: water and our planet's atmosphere. Earth is also the perfect distance from the Sun. Nearer to the Sun it would fry, further away it would freeze. Putting together data from all the observations of Tau Bootis, its particular wobble and the light from its planet, the team began to piece together as picture of what this world could be like. Might this new, blue/green planet harbour life?

ANDREW COLLIER CAMERON: The search for life probably doesn't even begin on this brand new planet. Anything that you find there is going to be well toasted.

KEITH HORNE: It's 20 times closer to its star than the Earth is to the Sun and Earth takes a full year to go around the Sun, whereas this planet goes around its star in only 3½ days. it's so close that it's scorched to a temperature of 1700 degrees Centigrade.

NARRATOR: The blue/green colour of the planet at Tau Bootis isn't water and trees. This mysterious world is a gas giant like Jupiter, but it must contain different gases to give it its different colour. This planet must be stranger even than Jupiter. It's orbiting so close to Tau Bootis that the star's gravitational grip almost certainly holds it with the same side facing Tau Bootis all the time. This planet doesn't spin. The difference in temperature between the lit side and the dark could cause enormous hurricanes to sweep across the planet, hurricanes with a terrifying difference.

ANDREW COLLIER CAMERON: On Earth we have clouds that are made of water which is a substance that condenses at the temperatures that we like to live at. At the temperature of this new planet iron and, and substances that we normally think of as rocks are the ones that can condense out of those temperatures to form clouds, so we have this alien environment in which, if there are clouds present, they're probably made of things that we normally think of as being metals and rocks.

NARRATOR: But terrible as this world sounds, there are characteristics that we might recognise.

ANDREW COLLIER CAMERON: It's great fun to speculate about what the weather systems on a planet like that might look like. If it has a magnetic field there may be other things going up around the poles. For instance, particles from the Sun may be impacting on the magnetic poles and lighting up the atmosphere in aurorae just as we get at these latitudes. We suspect that there might be sodium gas in the air and so perhaps the aurorae on this planet might be yellow/red instead of green and red.

NARRATOR: So the search for life does not end here, but science finally has a technique to unveil worlds beyond our Solar System that might harbour intelligent life.

KEITH HORNE: We started about 5 years ago with the discovery of the first wobbling stars which showed that big planets were out there. Now we've seen the light from the first big planets. Our next goal is to find low mass planets like the Earth and then obtain spectra of those planets to see if there's oxygen in their atmosphere and hence biological activity, life in other words, producing that oxygen.

NARRATOR: We are a step closer to finding whether we are unique in the universe. For the planet hunters the search for a planet like Earth goes on.

ANDREW COLLIER CAMERON: Once every few days I get the chance to sit back for 5 minutes and I think how incredibly lucky we are to be living in a time when we've been able to make this first step and when we know that the Holy Grail is perhaps only 10 or 12 years away and it's going to happen in our lifetimes. We're going to be able to detect Earth-like planets within the next 10 or 15 years and we're going to be here and we're going to be part of it. That's pretty exciting. There are, there can't be many more exhilarating things to be doing with your life.

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