HOMETV SCHEDULESUPPORTSHOPWATCH ONLINETEACHERSPODCASTSRSS "HUNT FOR ALIEN WORLDS" PBS Airdate: February 18, 1997 Go to the companion Web site : Tonight on NOVA. : Here we go, starting. : Science on the verge of a breakthrough. : We're going to find a universe filled with different kinds of planets than we ever dreamed. : Are we ready for what's out there? : All of the science fiction novels that we all read might, in fact, have some bearing on reality. : New discoveries from the farthest reaches of the universe. Hunt for Alien Worlds. NOVA is funded by Prudential. : Prudential. Insurance, health care, real estate and financial services. For more than a century, bringing strength and stability to America's families. : And by Merck. : Merck. Pharmaceutical research, dedicated to preventing disease and improving health. Merck, committed to bringing out the best in medicine. : The Corporation for Public Broadcasting, and viewers like you. GEOFF MARCY: 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. There may, in fact, be other beings out there who are indeed thinking about us and wondering if we are DANIEL GOLDIN: I just relate my own experiences and experiences of people who I've talked to around the world who look up at the night sky and wonder, "Are we alone?" We may never know the answer to that question, but we're at such an exciting time. We are on the cutting edge of having the technology to begin to understand this. NARRATOR: Throughout the century, astronomers have been searching for evidence of other planets beyond the solar system. Finally, their telescopes have become so powerfulwith the ability to capture images light years away the worlds they have dreamed of finding are now within reach. The only planets that we can directly observe are those within our own solar system. Some can be seen with the naked eye. Those in the farthest reaching orbits took centuries to discover. With the aid of telescopes, Uranus was found in 1781, Neptune in 1843, and not until 1930 was Pluto finally foundcaptured in this telescopic photographa speck of light moving against a stationary background of stars. So distant was this small, frozen world, it would take another fifty years to discover its moononly clearly visible in this 1990 Hubble Space Telescope photograph. Faced with the task of looking beyond our solar system for evidence of other worlds, astronomers in this century hit a technological brick wall. But now, that wall is tumbling down. A new breed of planet hunter has come upon the scene with better telescopes, faster computers and new ideas of what to look for. The first problem to overcome in detecting distant planets is that you can't see them, so astronomers have come up with techniques to get around this. At Allegheny Observatory in Pittsburgh, George Gatewood. GEORGE GATEWOOD: Well, you can't just simply image a planet. An ideal thing would be to just simply take the telescope and look at the star and see the planets moving around it. The difficulty is that planets do not give out much light. It's entirely reflected light. A good analogy of the difficulty is to consider 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: Because they cannot see what they are searching for, planet hunters must look instead for the very subtle effect a planet's gravity has on the star it orbits. Here, the Hammer Thrower represents a star, like our sun, being pulled at by the gravity of a planet. Every time the planet circles, the star wobbles from side to side. In space, we cannot see the planet, but we can, in theory, detect the influence it has on its parent star. In this scaled- down version of a solar system, we watch as the planet orbits the star. Each time it circles, the star is pulled. Much exaggerated in this demonstration, astronomers must strain to see these subtle shifts. Detecting wobbling stars is the main technique astronomers have for finding planets. It was established earlier this century. But as optics and data collection have improved, so have its chances for success. 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 though they were put together in a single movie, to see if the stars motion is linear or if it has that very small, wavy pattern that we're seeking. NARRATOR: The wobbles these observers are trying to find are minute. Even a giant planet like Jupiter, a thousand times the size of earth, would have a barely discernible effect on a star. It's like trying to see a man waving on the moon. The problem is made even worse by the swirling atmosphere of the earth. It causes starlight to twinkle, and even those tiny variations are enough to obscure the wobbles caused by orbiting planets. Observing stars from space helps eliminate the problem. FRITZ BENEDICT: Well, we're using a space-based device, the fine guidance sensors on Hubble Space Telescope, to do roughly the same kind of work, looking for the wobbles. 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 get perhaps slightly better results. Yeah, we're down to a third of a Jupiter for a six hundred-day period. NARRATOR: Fritz Benedict started using the Hubble Space Telescope three years ago. It's the most expensive telescope ever built, and orbiting high above the atmosphere, it should give him the edge in planet detection. FRITZ BENEDICT: The problem is you don't get a lot of time with the Hubble Space Telescope. I can't go to a Telescope Time Allocation Committee and say, "I want to look for little green men." But I sure can go to a Telescope Time Allocation Committee and ask to look for planets. And even though the planets that I may find aren't habitable, they would be examples of solar systems, and if they're solar systems like ours, they'll have planets like the earth. The chemistry on the surface of that planet will be the same chemistry as on the surface of our planet. It's a start. It really is a start. NARRATOR: But Fritz Benedict's efforts are frustrated. The Hubble is much in demand and planet hunting is not its main priority. To date, the Hubble has studied only two stars for signs of wobbles. Because of these time constraints, Fritz Benedict has seen no more success than his counterparts on the ground, despite his unencumbered view. FRITZ BENEDICT: 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: Working from the Lick Observatory near San Francisco, astronomers are perfecting another technique less vulnerable to atmospheric distortions. Instead of photographing a star to look for changes in its position, the Lick astronomers measure variations in the color of the star. Changes in color would indicate that the star is in motion, wobbling from the gravitational pull of an orbiting planet. 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 colors, blue through red, much like the sun's light is spread into all of its colors in a rainbow. In the star's light, however, we have additional information due to the fact that the star's light must pass through the star's atmosphere on its journey toward us at the earth. NARRATOR: Atoms and molecules in a star's atmosphere absorb part of its light before it passes into space. Each time Geoff Marcy observes a star, he splits the star's light into a spectrum. The wavelengths absorbed by the star's atmosphere show up as lines called absorption lines. By recording the absorption lines, Geoff Marcy can create a kind of fingerprint of the light that can be precisely fixed to one location. And if the star is being pulled by an unseen planet, Geoff Marcy will see this image shift from side to side. This technique is called spectroscopy. Precision is essential, for if the star is wobbling, he must be able to detect a shift plus or minus a handful of atoms. MAN: I think it's going to be about a hundred and fifty to one. 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: Given that giant planets like Jupiter would be, in theory, easier to detect, the odds were great that the first planet found would also be immense, and like Jupiter, lifeless. That did not deter Geoff Marcy, for Jupiter-size planets may be the key to finding inhabited worlds like our own. GEOFF MARCY: Jupiter acts as a sort of cosmic vacuum cleaner. As Jupiter orbits around, it would sweep up the early planetessimals out of which the planets were forming. The comets, the asteroids, would all get gravitationally scattered out or sucked into Jupiter, cleansing the solar system of all of this debris, and the debris, of course, is death for the evolution of organic material, which requires a very quiescent sort of atmosphere and environment. So, it may be that Jupiter itself is a requirement for the development of life. NARRATOR: Despite improvements in technology, planet hunters remain constrained in their search. In order to find a planet, they must look for a wobbling star. And in order to find a planet like our own, they must look for one much larger. Geoff Marcy had been hunting planets for over ten years. George Gatewood had been running his astrometry project in Pittsburgh for even longer. And Fritz Benedict was using the world's most expensive telescope. All together, they studied more than thirty stars. So precisely how many of these giant planets have they uncovered? FRITZ BENEDICT: 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. But they don't have them. 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 planet hunters still believe that out of the billions of stars that surround us, ours cannot be the only sun with planets orbiting around it. Although astronomers have not found these planets, they do have evidence of new planetary systems being born. In 1983, a specially-designed space telescope called IRAS was sent into orbit above the earth's atmosphere. Rather than photographing visible light, IRAS took pictures in the infrared, capturing images of the heat generated by distant stars. One startling discovery was a star surrounded by a strange band of solid particles captured in the star's gravity. It is believed the planets in our solar system were formed from the same kind of star dust. More evidence of young planetary systems followed once IRAS showed us where to look. This is beta pictoris, also surrounded by a ring of dust. But it was the Hubble Space Telescope that later gave us the most vivid images of yet-to-be-born planetary systems. DAVID BLACK: We know that there are stars being formed. We've seen this in ground-based telescopes for many years. We've had it confirmed in a spectacular way recently with the Hubble Telescope. We know that stars are formed in what we call giant molecular clouds. These are immense regions. The average cloud is a thousand to a million times the mass of the sun. But what happens is that some of this material gets together by a process that we, frankly, don't fully understand, becomes unstable to its own gravity and begins to collapse. When it collapses, it has a little bit of rotation. Not much. These clouds would typically take about two hundred million years to go through one revolution. As the collapse proceeds with these clouds, they spin faster and faster, and as they spin, they flatten out into, just like when you make a pizza, it tends to flatten out. And so, we think that that process leads to a disc-like structure. The center ends up making the star, the sun, in our case. And you have a disc out of which the planets get formed. So, this was a natural view, then, that suggested that planetary systems should occur almost every time that a star forms. NARRATOR: These images, taken by the Hubble Space Telescope, look deep into stellar nurseries. The telescope showed evidence of dust discs around young stars. In fact, these tell-tale smudges were found around more than half the stars observed. If stars shrouded in dust are that common, so, the thinking goes, must be the planets they produce. This new evidence confirmed old beliefs. Astronomers have always imagined a universe full of planets, even though they were never able to find one. Some astronomers, in fact, were so sure that other worlds existed, they skipped the planet search entirely and chose instead to listen for signs of intelligent life. Almost forty years ago, SETI was bornthe search for extraterrestrial intelligence. The reasoning behind it was simple: if E.T. did exist, he might be giving us a call. The project started out in 1960. With a single radio telescope, astronomer Frank Drake made the first radio search, scanning the interstellar airwaves for messages from other civilizations. Over the years, the project grew. Steven Spielberg even joined the effort, providing funds to help construct a radio telescope dedicated to finding extraterrestrial life. Eventually, scientists devised ways of listening to thousands of radio frequencies simultaneously. But these advances have yielded only a handful of results, none of which were ever confirmed. No matter how much money or equipment is put into it, SETI has always suffered a major flaw. DAVID BLACK: Part of the argument with SETI is that the absence of evidence is not evidence of absence. We may be out to lunch when the signal comes. We may have picked the wrong channel for the observing. There are whole hosts of things in the chain of assumptions that goes through SETI where a no result doesn't necessarily constrain your understanding. The beauty of the planetary detection problem is that a no result does constrain your understanding. If we don't find the signals down to the level of capability of the telescopes, the planets aren't there, the massive planets, or however low the mass would be based on the technique, just don't exist. And that's the significance. A no result from this technique is truly a no result. DANIEL GOLDIN: We don't even know if in this vast cosmos of ours there is an earth-like planet. We're in 1996, and we still don't know. So, before we even think about people sitting on planets transmitting radio waves, shouldn't we see if there are planets? NARRATOR: Ironically, it was not a planet hunter at all who was the first astronomer this decade to find evidence of a planet beyond our solar system. Andrew Lyne was listening to the heavens, but not for signs of intelligent life. Lyne's interest was in exotic stars known as pulsars. ANDREW LYNE: Here we hear the pulses cross as a beam from the rotating pulsar crosses the line of sight to the earth. In this case, it's about once every .714519 seconds. Very precise rotation. This pulsar is a younger one. This is a pulsar in the Vela Supernova. We can still see the remnants of the explosion in which the pulsar was. . . NARRATOR: Andrew Lyne has found more pulsars than anyone else in the world. These strange astronomical objects are thought to be dead stars, stars that have exploded in a super nova. All that's left behind is a core of material the size of a city spinning up to six hundred times a second. As it spins, the pulsar emits a beam of radio waves that can be detected on earth as regular pulses. It's because of this regularity that pulsars are considered the most accurate clocks in the cosmos, predicable down to the last microsecond. ANDREW LYNE: But one such object, the pulses were arriving earlier and later by a few milliseconds. The natural interpretation here was that this body was moving by a couple of thousand kilometers, or something like that, and it was doing it periodically. About every six months, it moved away, towards us, and back again. NARRATOR: Incredibly, Lyne seemed to have stumbled across evidence of a wobbling pulsar being pulled at by a planet. He published his findings in the journal Nature. The announcement, however, was just too fantastic for some to believe. ANDREW LYNE: Not only people's, but our own reaction, was one of great surprise. On the whole, we would not expect planetary bodies to be around pulsars, certainly normal pulsars, because of the violence of their formation. NARRATOR: In preparation for an upcoming meeting of the American Astronomical Society, Andrew Lyne went back to examine his data to make sure his calculations were correct. ANDREW LYNE: I was doing some more work trying to find ways in which we might be able to confirm or otherwise the hypothesis that it was a planetary body we were looking at. And for some reason, I had a flash of insight as to what might cause this. Unfortunately, my insight was correct, and I found that when appropriate correction was made, the six-month periodicity disappeared, and of course, so did the planet. NARRATOR: Lyne had, indeed, found a wobble, but it was the wobble of the earth as it orbits the sun. A computer error had failed to take this into account. When Lyne made the correction, the wobble in the pulsar disappeared. ANDREW LYNE: I was just completely numb for half an hour, an hour. I just sat there going through everything that I'd said over the l