The Search for Extraterrestrial Intelligence:

A Short Historyby Amir Alexander

Part I: A Signal from the StarsIt was the summer of 1967 and Jocelyn Bell, research student in radio astronomy at Cambridge, was having a bad day. As part of her doctoral dissertation she was monitoring a new radio telescope, scanning the skies for signs of interplanetary scintillation and quasars. But while the research was going well, some unexplained "scruff" kept appearing in her charts. At first, Bell and her advisor, Tony Hewish, thought that the signal must be some sort of Earthly radio interference. Such disturbances are normal in radio astronomy. But try as they might, Bell and Hewish could not eliminate the signal. It was coming from somewhere in the galaxy.

Upon closer analysis they found something even more remarkable about the signal: it pulsated at precise regular intervals, 3 and 2/3 of a second apart. What natural radio source in the galaxy would send a signal with such accuracy and precision? In 1967 nobody knew, and the researchers began to suspect that possibly the source wasn't natural at all. Could it be that they were receiving a transmission from an alien civilization? Only half jokingly they began referring to the source as "LGM," standing for "little green men."

As word of the discovery spread, more and more astronomers began converging on the Cambridge observatory. To satisfy the growing Jocelyn Bell at the Cambridge Radio Telescope.

Credit: Big Ear Observatory

interest, Jocelyn Bell had to spend more and more of her time tracking the strange signal and looking for others like it. She was not pleased: "Here was I" she recalls thinking, "trying to get a Ph.D. out of a new technique, and some silly lot of little green men had to choose my aerial and my frequency to communicate with us!"

The LGM signal turned out to have nothing to do with alien civilizations. Within a year several similarly pulsating objects were detected. Their source, it was widely acknowledged, was rapidly spinning neutron stars, which were appropriately designated "pulsars."

Radioactive neutron stars are very unpromising places to search for intelligent life. Nevertheless, it is not altogether surprising that for a while, Bell and Hewish seriously considered the possibility that their signal was a transmission from an alien world. The 1960s, after all, were the height of the "Space Age." Only a decade removed from the Sputnik, astronauts and cosmonauts were breaking new paths in space, each trying to outdo the other. Unmanned missions were being launched to the planets, and the race for the moon was about to reach its climax. The popular imagination was saturated with space exploration, with television series like "Star Trek" and " Lost in Space" dominating the airwaves. Is it surprising that radio astronomers came to wonder whether the signals they were detecting originated with otherworldly intelligence?

Most significantly, perhaps, the search for alien civilizations was becoming scientifically respectable. Thanks to a small but growing cadre of scientists and engineers devoted to searching the skies for an alien signal, talk of advanced civilizations on other worlds was no longer reserved to science fiction buffs. The Search for Extra-Terrestrial Intelligence (SETI) was turning into a legitimate scientific enterprise, utilizing the most advanced technologies available and supported by some of the leading astronomers in the world.

When Bell and Hewish considered the source of their signal, they did not need to look far: in their very field of radio astronomy, SETI was a significant and growing presence. It would have been surprising if they hadn't wondered whether they had accidentally stumbled upon the alien signal their colleagues were so ardently searching for.

How did this transformation come about? How did the stuff of science fiction become the subject of real "hard" science?

Part II: SETI's Founding Moment

It is, of course, very difficult to pinpoint an exact birth-date for SETI. Fascination with other worlds and their inhabitants has a long history, dating back to antiquity. Even the search for radio signals from space stretches back to experiments by the leading radio pioneers in the earliest days of radio. But the history of modern

SETI does have a clear beginning. In 1959 Philip Morrison and Giuseppe Cocconi were young physicists at Cornell University interested in gamma rays. "One spring day in 1959," recalls Morrison, "my ingenious friend Giuseppe Cocconi came into my office and posed an unlikely question: would not gamma rays, he asked, be the very medium of communication between the stars?" Morrison agreed that gamma rays would work, but suggested they should consider the entire electromagnetic spectrum for its possibilities.

The result of this brainstorming was a short two-page article, which was published in Nature magazine on September 19, 1959. Entitled "Searching for Interstellar Communications," it is rightly considered the founding document of modern SETI.

In the article Morrison and Cocconi freely admit that it is impossible to estimate the probability of the existence of alien civilizations on planets orbiting distant stars. But based on the only example available - that of humans on Earth - they argue that one cannot rule out that there may be very many alien technological societies out there. Many of them, they argue, may be much older than human societies and far more technologically advanced.

The aliens, furthermore, would in all likelihood consider our Sun to be a likely candidate for the formation of a technologically advanced civilization, and would seek to make contact with it. The main question, according to Morrison and Cocconi, is what means would they choose?

Electromagnetic waves (radio waves, light waves, etc.) they argue are the obvious choice. Only these, traveling at the speed of light, can cross the fantastic distances involved without dispersing and in anything resembling a practical amount of time. This leads to the next crucial question: at what frequency will the aliens transmit their signal?

The most rational frequencies for communication between the stars, Morrison and Cocconi argued, were between 1 and 10,000 MHz. Those are the frequencies in which the planetary atmosphere interferes the least with electromagnetic signals, and where radiation noise from our galaxy is also at a minimum. Several years later it was discovered that those were also frequencies in which there was little interference from Cosmic Background Radiation, but this was not known in 1959.

Dr. Philip Morrison

The first page of Cocconi and Morrison's classical article in Nature, September 19, 1959.Image: Nature Magazine.

A range of frequencies of 10,000 MHz is still far too wide for conducting a systematic search. Morrison and Cocconi therefore hazarded a guess that has shaped the course of SETI research to this day: The aliens, they argued, are most likely to be broadcasting at a frequency of 1420 MHz (wavelength of 21 cm). That is the emission frequency of the atom of the most common element in the universe - hydrogen. This frequency would suggest itself because it would be known to any observer in the universe. Any systematic search should begin here.

The authors then made another observation, which has had a profound impact on the way SETI searches are conducted: any signal sent from a the aliens' orbiting planet to our orbiting planet would necessarily drift away from its original frequency. This is the result of the Doppler shift, familiar to anybody who has heard the change of pitch of a train's whistle as it passes by. Because the speed at which the planets are moving relative to each other constantly changes, the frequency of the transmission will inevitably drift over time. A search for an alien signal would have to take this drift into account, and search for a transmission whose frequency slowly changes.

Morrison and Cocconi concluded their article with a challenge to skeptical readers. Many, they admitted, would argue that this kind of speculation belongs in science fiction rather than science. This is not so: their argument, they claimed, shows that the presence of an alien signal is consistent with all that is presently known. They concluded with a challenge that has become the rallying cry for all SETI enthusiasts since: "The probability of success is difficult to estimate; but if we never search, the probability of success is zero."

Part III: A Blueprint for SETIMorrison and Cocconi's short article became the blueprint for most of the SETI projects conducted in the past 40 years. The suggestion that electromagnetic signals were the most promising means for interstellar communications became the underlying assumption of all the searches, including the optical ones. The assumption that any alien signal would exhibit a Doppler drift has also been incorporated into all subsequent SETI projects, which invariably check for signals at drifting frequencies.But most important of all was their suggestion of a "universal" frequency that the aliens would most likely use for their transmissions. 1420 MHz has remained the most popular frequency used by SETI projects to this day.

The Water Hole.

In later years another SETI pioneer, Hewlett Packard Vice President Bernard Oliver, added another magic frequency, 1662 KHz, the emission frequency of another very common molecule - OH, or hydroxyl. Hydrogen and hydroxyl combine to form H2O - water - the basic component of life, as we know it. Since 1662 KHz shares the advantages of 1420 MHz in being in a relatively "quiet" region of the spectrum, Oliver came to believe that the band between them held some unique promise for detecting an alien signal: "Surely the band lying between the resonances of the disassociation products of water is ideally situated and an uncannily poetic place for water-based life to seek its kind," Oliver wrote in 1971. "Where shall we meet? At the water-hole, of course!" Since then, the term "water hole" has been used to refer to searches at or around the hydrogen emission frequency.

Morrison and Cocconi's article was a call for action, and they hoped to put their theory to the test. Cocconi contacted Sir Bernard Lovell at the Jodrell Bank radio observatory, the largest dish in the world at the time, and suggested devoting telescope time to search for an extraterrestrial signal. Sir Bernard was, however, skeptical, and nothing came of the venture. The launch of the first radio search for an alien signal was left to others.

Part IV: The Origins of Project OzmaAt around the same time that Morrison and Cocconi were speculating about alien signals, a young astronomer named Frank Drake was pursuing his own investigations into interstellar communications. Drake was a staff member at the National Radio Astronomy Observatory at Green Bank, West Virginia. At the time, the newly established NRAO was in the odd position of being a radio observatory without a radio telescope. The 140-foot dish panned for the site was in the early stages of what turned out to be a very troublesome construction. It would not be completed until years later. As a stopgap measure, the NRAO purchased an 85-foot radio telescope, which became operational in April of 1959.

As a junior staff member in Green Bank, Drake had a part in many of the radio-astronomy projects at NRAO. His fascination, however, was with the search for alien civilizations. As a graduate student in radio astronomy at Cornell, Drake had once detected a strong seemingly artificial radio signal coming from the direction of the Pleiades. After weeks of analysis, Drake had concluded that the signal in fact originated on Earth, but the possibility of detecting an alien radio signal remained very much on his mind.

In March of 1959 Drake calculated that if a strong radio signal would be sent from Earth, using existing technology,

it could be detected at a distance of 10 light years by an 85-foot dish. In other words, the new radio telescope at Green Bank should be capable of detecting signals as far as 10 light years away, even if they are sent by transmitters no more powerful than the ones then available on Earth. Drake noted that there were several sun-like stars within a distance of 10 light years from Earth. These, he reasoned, were good candidates for beginning the search for alien intelligence.

One day, during lunch at a greasy spoon diner not far from the observatory, Drake broached the topics with his colleagues. Would it be possible to use the new radio telescope then being built at Green Bank to search for extraterrestrials? It was, undoubtedly, Drake's good fortune that unlike the Jodrell Bank radio observatory, which had rejected Morison and Cocconi, the Green Bank dish was not yet operational and therefore could be flexible about its future schedule. He was also fortunate that Lloyd Berckner, acting director of NRAO, was present at the lunch that day, and gave Drake's proposal the go-ahead. Drake dubbed the venture "Project Ozma," after Princess Ozma of Oz, from Frank L. Baum's classic tale.

The months that followed were a busy time in Green Bank. But even while the new radio telescope went on-line and began collecting data, Drake and his colleagues kept up work

Dr. Frank Drake in the 1990's

on Project Ozma. For cost-saving reasons, they decided to concentrate on the hydrogen 1420 MHz band. That was the frequency at which radio telescopes most commonly operate, and it would therefore require the least alterations in the existing equipment. In the end, the price tag for parts unique to Ozma amounted to no more than $2000.

The 85 foot radio telescope at Green Bank used by Project Ozma as it appears today.Image: NRAO/AUI.

Two events combined to speed up project Ozma in late 1959. One was the appointment of Otto Struve as the first permanent director of NRAO. Struve was famous for his work on the measurement of stellar rotation, which he argued could indicate the presence of planets orbiting distant stars. In Struve's mind, it was only a short leap from extrasolar planets to extraterrestrial intelligence: he supported Ozma wholeheartedly. Furthermore, he brought to the effort his extensive connections and his flair for public relations. Whereas Drake and his colleagues, fearing for their academic respectability and their peace of mind chose to keep the project a secret, Struve went public immediately in a lecture at MIT. "The cat was out of the bag," Drake recalled years later. "Looking back now, only good came from letting it out." While the dreaded wave of publicity did indeed follow, so did public support and valuable donations in money and equipment.

The other event was the publication of Morrison and Cocconi's article in Nature in September of 1959. Drake was pleased that such prominent researchers were working along similar lines to his own. In particular, Morrison and Cocconi provided theoretical support for searching at the very same frequency that Drake chose for cost-saving reasons - 1420 MHz. Struve, however, was concerned that the Ozma team would be robbed of their due credit, and he urged Drake to begin the search as soon as possible.

Part V: Project Ozma - The SearchFor its time, Ozma was on the cutting edge of technology. It utilized an experimental parametric amplifier, donated by Microwave Associates, and the novel maser technology. By combining these with an 85 ft dish, Drake and his team were able to achieve a degree of sensitivity a thousand times greater than anything previously possible. The output mechanism was conventional - a simple chart recorder and a tape recorder. At the last minute the Ozma crew added a loudspeaker as well, just in case…

Ozma began operations on April 8, 1960, with the aim of searching for signals from the two closest sun-like stars - Tau Ceti and Epsilon Eridani. Throughout the first morning the 85-foot dish tracked Tau Ceti and recorded radio emissions that seemed to be coming from its direction at or about the hydrogen line. Despite the early excitement, not meaningful signal was detected. In the afternoon the radio telescope was shifted to Epsilon Eridani.

In a 1981 interview Drake recalled what happened next: "A few minutes went by. Then it happened. Wham! Suddenly the chart recorder started banging off the scale. We heard bursts of noise coming out of the loudspeaker eight times a second, and the chart recorder was banging against its pin eight times a second . . . We all looked at each other wide-eyed. Could it be this easy?"

It was not to be that easy. The signal disappeared, and would not be heard for several more days. When it did suddenly reappear ten days later, the Ozma team was ready: the signal, they found, was just

as strong on a simple antenna rigged through the window, as it was on the big radio telescope. It was clearly of Earthly origin, most likely the emissions of a military electronic warfare plane on an exercise run.

Tau Ceti as it appears in NASA's star catalogue. Image: NASA.

Project Ozma operated for a month, rested for another month, and then returned for another (final) month of observations. In all, it devoted 200 hours of observation to its two targets, Tau Ceti and Epsilon Eridani. It scanned 7200 channels divided equally between the 2 stars, each with a bandwidth of 100 Hz. The entire search was conducted around the central frequency of 1420 MHz, with deviations to both sides to look for Doppler drifts in the transmission frequency due to the relative motions of the Earth and the supposed source planet. While Ozma did not find a signal from an extraterrestrial society, it did become the model for most future SETI projects.

Part VI: The Dolphins Meet at Green BankIn November of 1960, a highly select group of physical scientists and engineers made its way to the remote hills of West Virginia for a small informal conference. The meeting was convened in Green Bank under the auspices of the National Academy of Science, to discuss a question that was only just gaining scientific respectability: what are the prospects of establishing contact with other worlds? It is a measure of just how risky the topic was considered, that it was decided not to announce the conference, and no official publication followed the meeting.

The conference was organized by J.P.T. Pearman of the Science Board of the National Academy of Science. The other ten attendees included Dana Atcheley, president of Microwave Associates, who donated the parametric amplifier to Project Ozma; Melvin Calvin, a world renowned biochemist who studied the origins of life; Bernard Oliver, Vice President for Research and Development at Hewlett-Packard; Carl Sagan, then a young astronomer at Cornell; Phillip Morrison, author with Giuseppe Cocconi of the

Nature article which launched modern SETI; Giuseppe Cocconi; Frank Drake, of Ozma Project fame; Su Shu Huang, astronomer and expert on extrasolar planets, and his former teacher, Otto Struve, director of the Green Bank observatory and host of the conference; and John Lilly, who had recently published his controversial Man and Dolphin arguing that dolphins are an intelligent species. It was in a jesting tribute to Lilly's celebrated work that the conference attendees styled themselves "The Order of the Dolphins."

For the development of SETI, the meeting was a momentous event. For the first time, the possibility of communication with alien civilizations was being seriously discussed by some of the world's most prominent scientists. So prominent, in fact, that one of them, Melvin Calvin, was awarded the Nobel Prize in Chemistry during the course of the conference. "It was wonderful," Sagan recalled in a 1993 interview, " . . . these good scientists all saying that it wasn't nonsense to think about the subject. There was such a heady sense in the air that finally we've penetrated the ridicule barrier . . . It was like this 180 degree flip of this dark secret, this embarrassment. It suddenly became respectable."

Carl Sagan in the 1960s

Part VII: The Birth of the Drake EquationThe Green Bank meeting was also remarkable because it featured the first use of the famous formula that came to be known as the "Drake Equation". When Drake came up with this formula, he had no notion that it would become a staple of SETI theorists for decades to come. In fact, he thought of it as an organizational tool - a way to order the different issues to be discussed at the Green Bank conference, and bring them to bear on the central question of intelligent life in the universe.

The grand question of the number of communicating civilizations in our galaxy could, in Drake's view, be reduced to seven smaller issues:

The rate of star formation in our galaxy at the time our Solar System was formed (R*);

The fraction of stars that have planets around them (fp);

The number of planets per star that are capable of sustaining life (ne);

The fraction of planets in ne where life evolves (fl);

The fraction of fl where intelligent life evolves (fi);

The fraction of fi that communicate (fc);

The lifetime of a communicating civilization (L);

Denoting the number of communicating civilization in our galaxy by N, and multiplying the different elements, we get the famous Drake Equation:

N= R* fp ne fl fi fc L

Image taken by the Hubble Space Telescope of star formation in nebula NGC 604 in galaxy M33. The formation of stars was, and still is, one of the only components of the Drake Equation for which empirical evidence is available.Image: Space Telescope Science Institute, Hui Yang (U. IL), and NASA

The equation served its purpose well at the Green Bank conference. It provided a framework that enabled the different researchers, who had very different backgrounds and specialties, draw upon their specialized knowledge, and at the same time contribute to the general question of the meeting.

Soon, however, to Drake's surprise, it became much more than that. The short mathematical formula proved irresistible to SETI promoters: it reduced a huge and almost unmanageable speculative question to a neat series of seemingly specific questions. While the larger question seemed too large and speculative, its seven components appeared to lend themselves to scientific inquiry. No less important, posed as a formula, the question seemed mathematical and quantitative. What better way of gaining scientific respectability than formulating a mathematical equation?

The Green Bank meeting weighed in on each of the elements in the equation, and came up with generally optimistic estimates. The rate of star formation (R*) was the only element in the equation about which some reliable information existed, and the conference settled on a conservative estimate of about one star per year. Otto Struve was the resident expert on extrasolar planets (fp), and he suggested that planets orbiting distant stars were, in fact, very common. Su-Shu Huang gave an optimistic assessment about the likelihood of planets having life supporting environments (ne), and Calvin and Sagan suggested that on suitable planets life would ultimately emerge (fl). Lilly gave an optimistic assessment on the likelihood of intelligence emerging on a life-bearing planet (fi), based on his work on dolphins. If at least two intelligent species emerged on Earth, doesn't that suggest that intelligence is common? Lilly's views, however, were highly controversial, and often dismissed by mainstream biologists. Even the sympathetic audience at Green Bank was quick to note that dolphins were not a technological species, and would be unlikely to send radio beams into space.

The final two elements in the equation were in the field of social science: how likely are intelligent beings to communicate with other civilizations (fc), and how long do civilizations last (L)? Significantly, there were no social scientists at Green Bank. But while lamenting their absence, Morrison also pointed out that even specialists were unlikely to have the answers for such grand questions. In their absence, he suggested that based on Earthly experience civilizations were likely to develop advanced technology, and that curiosity and the urge to communicate appear to be universal. Furthermore, he suggested, if civilizations are able to overcome the dangers of nuclear self-destruction, they can probably sustain themselves for very long periods of time.

In summarizing their discussions, the conference members concluded that the number of communicating planets could range from fewer than 1000 to more than a billion. Most of them thought the higher number a more likely estimate. On this basis they called for a vigorous radio search for extraterrestrial intelligence, using a 300-foot dish, very large computers, and patience to search for at least 30 years.

Part VIII: The New SearchesIt is one of the oddities of SETI history that in spite of increasing public interest in extraterrestrials, and despite a growing literature on the subject, a full decade passed before the Green Bank conference's call for action was answered. While a few SETI searches were launched in the Soviet Union under the leadership of radio astronomer Iosif S. Shklovskii, no immediate successor to project Ozma emerged in the West. Though the members of the Order of the Dolphins, veterans of the Green Bank conference, continued lobbying intensely for a sustained radio search, it was 1971 before a new search was finally launched.

The 1960s were a decade of intellectual brainstorming for SETI researchers. During this time SETI ideas progressively gained ground in the scientific community, and lively debates took place on the most basic issues of the emerging field: what kind of civilizations might be contacted, what kind of signal we should look for, where to search, and how. The exchanges were lively and fruitful, but they did not produce actual searches. An actual SETI program required a strong conviction about the type of alien intelligence one is searching for, and a commitment to a specific search strategy, In the 1960s the field was still groping towards a suitable and widely acceptable approach.

What emerged from the debates was what physicist Freeman Dyson called "The orthodox view" on life in the universe:

Life is common in the universe. There are many habitable planets, each sheltering its brood of living creatures. Many of the inhabited worlds develop intelligence, and an interest in communicating with other intelligent creatures. It makes sense then to listen for radio messages from out there, and to transmit messages in return. It makes no sense to think of visiting alien societies beyond the solar system, or to think of being visited by them. The maximum contact between alien societies is a slow and benign exchange of messages, a contact carrying only information and wisdom around the galaxy, not conflict and turmoil. (Quoted in Steven Dick, The Biological Universe (Cambridge: Cambridge University Press, 1996), 438.

In addition, a growing consensus emerged that searches should be conducted close to the hydrogen emission frequency (1420 MHz, or 21 cm) and perhaps in the water hole - the band between 1420 and 1660 MHz. Most - though not all - of the searches conducted since that time have accepted these basic assumptions and followed some version of this basic strategy.

Part IX: Ozpa - A Skeptic's SearchThe lingering questions about how to conduct a search were still very much in evidence in the first post-Ozma SETI project in the United States. So much so that the search leader himself, G. L. Verschuur of the NRAO, expressed serious doubts about the purpose of the enterprise: "It is the author's belief," he wrote in an article describing the project, "that any detection of signal from another civilization will most likely be an accidental one in the sense that we will pick up signals not meant for us. For this reason it is unlikely . . . that a wavelength around 21 cm is the wavelength at which to search." These are indeed serious misgivings, coming from the very person who was to conduct the search.

Nevertheless, Verschuur went ahead with his program. Conceived as a direct continuation of Drake's 1960 project, it was based, like Ozma, in Green Bank,

West Virginia. Whereas Drake had to content himself with the use of an 85-foot radio telescope, Verschuur had the use of a 300-foot dish and a 140-foot dish, as well as far more advanced sensitive equipment. Over the course of 1971 and 1972 Verschuur pointed his instruments at nine nearby stars, including the ones targeted by Ozma, listening at the hydrogen line frequency and correcting for Doppler shifts. In some respects it was an expanded and improved "Ozma," but in other respects it was a much smaller project: whereas Drake's team devoted 150 hours to their observations over three months, Verschuur and his colleagues spent only 13 hours observing over the span of two years. Nevertheless the similarities were such that Verschuur's search became popularly known as "Ozpa."

The 140 foot radio telescope at Green Bank, West Virginia, used in Project Ozpa. Image: NRAO/AUI

Ozpa was followed by a larger and more sustained NRAO search designated "Ozma II," which surveyed 674 stars over 500 hours between 1972 and 1976. Over the next three decades, many searches followed. Most of them were small and limited in scope, depending on available telescope time at established observatories, and designed to test a researcher's particular hypothesis. Some, however, were larger and more sustained and a few of those will be mentioned here.

Part X: "Wow!"The longest running as well as one of the most famous searches was conducted with the use of the giant "Big Ear" radio telescope at Ohio State University. "Big Ear" was no ordinary radio-telescope: instead of the familiar "dish," it was composed of a flat aluminum surface the size of three football fields, with a giant reflector at each end - one flat and one parabolic. Its sensitivity was equivalent to that of a 175-foot dish. From 1973 up to its dismantling in 1998 (to make room for a golf course), its most important mission was a continuous dedicated hydrogen-line SETI search.

The most famous moment in the history of Big Ear, which earned it a place of honor in the annals of SETI, came on the night of August 15, 1977. As on every other night, as Big Ear was searching the skies for an alien signal, its observations were being recorded on a printout sheet: a long list of letters and numbers was continuously being churned out, one long list for every one of the fifty channels scanned by the telescope. A list of characters appeared recording an unusual transmission at the frequency of channel 2: "6EQUJ5" the list read. This startled Big Ear volunteer Jerry Ehman, a professor at Franklin University in Columbus, who was monitoring the readings that night. He circled the code for later reference and added a single comment in the margins" "Wow!"

The Big Ear Radio Telescope at Ohio State University, as it appeared before its demolition in 1998. Credit: The Big Ear Observatory.

This was, of course, the famous "Wow!" signal, which immediately entered SETI lore. The series "6EQUJ5" described the strength of the received signal over a short time-span. In the system used at the time at Big Ear, each number from 1 to 9 represented the signal level above the background noise. In order to extend the scale, the staff added letters, with each one from A to Z representing increasingly stronger signal levels. 6EQUJ5 represented a signal that grew in strength to level "U," and then gradually subsides. In more familiar notation, the signal increased from zero to level 30 "sigmas" above the background noise, and then decreased again to zero, all in the span of 37 seconds.

Two aspects of this signal immediately caught the attention of Ehman and project director John Kraus, who saw the results the following morning. First of all, 37 seconds was precisely the time it takes the Big Ear scanning beam to survey a given point in the heavens. Because of this, any signal coming from space would follow precisely the "Wow!" signal's pattern - increasing and then decreasing over 37 seconds. This practically ruled out the possibility that the signal was the result of Earthly radio interference.

Secondly, the signal was not continuous, but intermittent. Kraus and Ehman knew that, because Big Ear has two separate beams that scan the same area of the sky in succession, several minutes apart. But the signal appeared on only on of the beams and not on the other, indicating that it had been "turned off" between the two scans. A strong, focused and intermittent signal coming from outer space: Could it be that Big Ear had detected an alien signal?

The computer printout of the "Wow!" signal, along with Jerry Ehman's famous comment.Credit: The Big Ear Observatory.

Since 1977 several attempts had been made to find the "Wow!" signal once more - to no avail. To this day we do not know the source of the strongest and clearest signal ever to come through on a SETI search. Since it was undoubtedly artificial, and almost certainly of celestial origin, Jerry Kraus speculates that it may have come from a space probe (human space probe, that is…) that he and the Big Ear staff were not aware of. That would certainly make it an intelligent celestial signal, but not an alien one. And still, there is always the possibility that it was something else - a true signal from an alien civilization. Unless the signal is detected again, we may never know for sure.

Part XI: NASA Steps InWhile most SETI searches were modest, local affairs, this was not always the case. The most ambitious of all SETI searches was conducted by NASA, which had access to funding and resources on a completely different scale than any of the other searches. Indeed - NASA involvement in SETI was decisive, both in gaining mainstream respectability for the extraterrestrial search and in advancing the search technology to levels undreamt of by the Ozma pioneers. At the same time, the NASA search also demonstrated the risks of dependence on

government funding: during times of budget cuts in Washington, the SETI project turned out to be extremely vulnerable to changing political winds.

In 1970 John Billingham of NASA's Ames Research Center in Mountain View, California, convinced Ames director Henry Mark to start a small study of SETI strategies and the likelihood of contacting an alien civilization. The result was "Project Cyclops," a 1971 summer faculty fellowship program sponsored by Stanford University and NASA Ames.

The moving spirit behind the study was Bernard M. Oliver, the Hewlett Packard VP who we've already met at the 1961 Green Bank conference. The proposal that emerged from the study, under Bernard's leadership, was ambitious indeed. It envisioned a forest of about one thousand 100-meter (about 300 ft) dishes, occupying an area of about 10 kilometers in diameter. If we remember that ten years earlier project Ozma was conducted with a single 85 ft telescope, we might get an

idea of the scale of the project Oliver and his colleagues were proposing. Ozma cost $2000; Cyclops called for an investment of $10 billion!

The scale of the project was well beyond anything NASA would or could sanction. Its primary mission was launching spacecraft, and a SETI search would always be a sideshow for NASA. But even a small NASA program could command resources far in excess of anything available for SETI previously.

Over the next ten years, NASA continued to sponsor workshops and studies on the feasibility of SETI. Gradually, two main search strategies emerged. One approach, sponsored by NASA Ames, favored the traditional, "targeted" search. As with most (though not all) previous searches, the idea was to select certain stars, which were similar to our sun and relatively nearby, and listen carefully to any signals emanating from them. These stars, the argument went, offered the best chance of establishing contact with an alien civilization.

The other approach advocated a "full sky survey," and it was championed by Bruce Murray, director of the Jet Propulsion laboratory (JPL) in Pasadena. According to Murray it was futile to speculate where alien civilizations would be found. It was also useless to make any assumptions as to what frequency they would be transmitting in. The fact is, Murray insisted, that we just don't know. The

The cover of the Project Cyclops report. Click on the image for a full-size version.Image: The SETI League

Dr. Bruce Murray, Director of the JPL 1976-1982, and currently Chairman of the Board of The Planetary Society.Image: The Planetary Society

only reasonable route is to systematically search the entire sky for a signal on the widest band of frequencies possible. Such a search would not be as sensitive as a targeted search, but it would make up for that by its breadth and scope.

By 1979 NASA had in place the outlines of a coherent SETI plan. Instead of choosing between the competing approaches, NASA decided to pursue them both. A targeted search would be based at NASA Ames, while an all-sky survey would be headquartered at JPL. An official NASA project named the "Microwave Observing Program" (MOP) was established to conduct the search, following a period of research and development.

An artist's rendition of a Cyclops SETI telescope array on the dark side of the moon.Image: NASA.

 

Part XII: SETI Goes to WashingtonFrom the begining, MOP faced a bumpy ride. As early as 1979 Senator William Proxmire awarded the program his infamous Golden Fleece Award," given to wasteful programs sponsored by the Federal government. In 1982 Proxmire actually managed to cut all federal funding for MOP through a legislative amendment, threatening to put an end to the entire effort. The threat was averted through the timely intervention of Carl Sagan, who met personally with the Senator and convinced him that SETI was a worthwhile pursuit. Sagan then introduced a petition in support of SETI signed by many of the world's leading scientists, including seven Nobel laureates. The publicity and prestige Sagan generated kept

the NASA SETI program on track for another decade.

On October 12, 1992, 500 years to the day after Columbus landed in the New World, the two NASA searches were finally launched. The Ames search began to scan its 800-1000 targeted stars from the 305-meter (1000-foot) radio telescope in Arecibo, Puerto Rico, the largest dish in the world. The JPL program began mapping the skies using the 34-meter dish at the Deep Space Communications Complex in Goldstone in the Mohave Desert. The searches were also given a new NASA designation - High Resolution Microwave Survey (HRMS).

The Radio Telescope at Arecibo, Puerto Rico

Both searches utilized the most advanced technology available. The targeted search would analyze the spectrum between 1 and 3 GHz looking for narrow band signals. To accomplish this, its Multi Channel Spectrum Analyzer would analyze a 20 MHz wide band at any given moment, parse it into 20 million 1 Hz channels, and look for signals at bandwidths of between 1 and 28 Hz.

The JPL search was designed to map the entire sky at frequencies ranging from 1 GHz to 10 GHz. This enormous 9 GHz band would be analyzed by the Wide

Carl Sagan, 1934-1996

Band Spectrum Analyzer, designed to scan a bandwidth of 320 MHz simultaneously, and parse it out into sixteen million 20 Hz-wide channels. It would create a mosaic of 25,000 frames making up the entire night's sky. If we consider that 15 years earlier Big Ear was searching a mere 50 channels, we get a sense of the magnitude of the technological achievement involved.

But less than one year after their launch, both searches were suddenly and irrevocably terminated, victims of a new wave of Congressional budget cuts. This time it was Senator Richard Bryan of Nevada who led the charge against governmental expenditures on SETI. "The Great Martian Chase," he said, "may finally come to an end. As of today millions have been spent and we have yet to bag a single little green fellow. Not a single Martian has said take me to your leader, and not a single flying saucer has applied for FAA approval."

After an investment of around $60 million over 23 years, and less than one year of operation, NASA's SETI project was unexpectedly dead. Nevertheless, despite the crushing disappointment to SETI enthusiasts caused by the cancellation of the most ambitious search ever attempted, it can now be said that HRMS did not die in vain. The enormous resources available to NASA supported remarkable technological advances, which would have been very difficult to achieve without such backing. Furthermore, the equipment used in the Ames targeted search did not go to waste, but was passed on to the privately funded SETI Institute. The Institute then used to launch its own targeted search, the ongoing and aptly named "Project Phoenix."

Although the NASA searches were incomplete and short-lived, they completely transformed the face of SETI. Compared to the relatively amateurish efforts of previous searches, SETI became a professional enterprise conducted by experts using the most advanced technologies available. The scope and sophistication of the searches has also been increased by an order of magnitude through NASA's involvement. And though NASA is no longer an active participant in SETI, the existing SETI programs all took shape under the influence of its impressive effort.

Part XIII: SETI after NASAThe cancellation of NASA's SETI program in 1993 was a severe shock to the SETI community. For although HRMS was a very small project by NASA standards, it dwarfed all other SETI efforts combined. As long as NASA was a part of SETI, it was clearly the dominant player, and its demise left a void that was difficult to fill.

NASA, nevertheless, was never the sole sponsor of SETI. In the shadow of HRMS grew a variety of private groups that devoted their resources to SETI, and sometimes joined forces with NASA. When HRMS was unexpectedly cancelled,

Senator Richard Bryan, Democrat of Nevada

these groups stepped forward to save what they could and preserve SETI research. Two of these private organizations stand out in particular for their leadership role in preserving SETI in difficult times: The SETI Institute, headquartered in Northern California's Silicon Valley, and The Planetary Society, based in Pasadena.

The SETI Institute was founded in 1984 to sponsor and conduct research on SETI and life in the universe. The Institute included among its founders and sponsors SETI veterans such as Frank Drake of Project Ozma fame, and fellow "Dolphin" Bernard Oliver. But it also included a new generation of investigators such as Jill Tarter and Seth Shostak. Most of the Institute's earlier projects were funded by NASA, and it played a significant role in the targeted search program that was based at NASA Ames in nearby Moffett Field.

When HRMS was cancelled in 1993, the SETI Institute stepped in to save the targeted search, and became its main sponsor. It quickly acquired much of the NASA Ames' SETI equipment, and set about establishing its own privately funded project. In February 1995 it launched Project Phoenix, a highly advanced targeted search based on the defunct NASA program.

For their search, Phoenix scientists compiled a list of 1000 stars that seemed the most likely to be homes of alien civilizations. They are mostly solar-type stars at a distance of no more than 200 light years from Earth and older than 3 billion years, as well as the very closest stars regardless of type. When stars are discovered to have planets, they are also added to the list. Each targeted star can be monitored for signals at any wavelength between 1000 and 3000 MHz. For comparison, the now popular SETI@home monitors a frequency band of only 2.5 megahertz, which is just over one-thousandth of Phoenix's capabilities. Phoenix computers then analyze this enormous bandwidth with razor-thin resolution, and can recognize a signal with a width of only 0.7 Hz. This is crucial for recognizing intelligent signals, because no known naturally occurring signal is

less than 300 Hz wide.

Project Phoenix is a mobile operation. Its advanced custom-made electronics hardware is packed into a truck trailer, which can pitch camp at any of the major radio observatories around the world. Its first stop was the 64 meter (210 foot) dish at the Parkes Observatory in Australia, and in September 1996 it moved to the National Radio Astronomy Observatory in Green Bank, West Virginia. There it shared time for a year and a half on the 43 meter (140 foot) dish, only a short distance

Dr. Jill Tarter, SETI Director at the SETI Institute.Credit: The SETI Institute.

The 64 meter dish at the Parkes Observatory in New South Wales, Australia.Credit: CSRIO and Seth Shostak.

from the 85 foot dish used by Frank Drake in the pioneering Project Ozma. Since 1998 Project Phoenix has been camped at Arecibo in Puerto Rico, where it makes use of the 305 meter (1000 foot) radio telescope, the largest in the world.

As a targeted search, Phoenix can monitor particular stars with remarkable precision and breadth, unmatched by other searches. Working at "real time" with other observatories around the world, it can offer almost immediate verification of any signal it may detect. This is important both because it helps eliminate the possibility of Earthly interference, and because signals from deep space can disappear quickly due to interstellar scintillation. Its main limitation is that is has to share observing time with other radio-astronomy projects at the major radio observatories. At Arecibo, for example, it can only run 20 observing sessions of 12 hours each every six months, meaning that it is "on the air only a fraction of the time. Nevertheless, after almost seven years of operation, Project Phoenix is going strong, and gearing up for a receiver upgrade sometime in 2002.

Whereas the SETI Institute continued the HRMS targeted search, The Planetary Society took a different approach to SETI in the post-NASA years. Even before the cancellation of HRMS, The Planetary Society had shown a marked preference for "all sky surveys" in preference to targeted searches. This approach reflected the views of Bruce Murray, the future president of The Planetary Society, who consistently argued that we should not make any assumption about the nature of an alien civilization, and that we should therefore not limit our search to stars that appear hospitable to our human sensibilities. As director of the Jet Propulsion Laboratory from 1976 to 1982 Murray was largely responsible for establishing the "all sky survey" element of NASA's SETI project at JPL.

The Planetary Society, unlike the SETI Institute that concentrated its efforts on one highly sophisticated search, spread its resources among various groups trying out different techniques. Since the early 1980s the Society had been supporting several SETI ventures led by Paul Horowitz of Harvard University. In October of 1995, with Planetary Society funding, Horowitz launched Project BETA - an all-sky radio survey at the "water hole" frequency range. BETA, or the Billion-channel Extra-Terrestrial Assay, is based at the Harvard-Smithsonian Observatory in the town of Harvard, Massachusetts, where it makes use of the 26 meter (85 foot) radio telescope. BETA had completed several surveys of the skies visible from Harvard when the dish was damaged in a storm in March of 1999. With help from The Planetary Society, repairs are under way.

Since 1996 The Planetary Society has also been supporting Project SERENDIP, a radio all-sky survey led by Dan Werthimer of U.C. Berkeley. Like Project

Dr. Bruce Murray, Chairman of the Board of Directors, The Planetary Society.Credit: The Planetary Society.

Phoenix, the SERENDIP receiver is based at the Arecibo Observatory, but unlike Phoenix it doesn't need to wait for highly-prized observation time-slots. Instead, it is permanently perched above the Arecibo dish, scanning whichever part of the sky the dish happens to be pointed at and moving through the sky with the rotation of the Earth. While this approach would not work for a targeted search, it is well suited for an all-sky survey like SERENDIP.

An offshoot of SERENDIP is the wildly successful SETI@home project - the distributed computing venture that sends radio data packets to millions of users around the world. These then use their own personal computers to analyze the data for an alien signal. When SETI@home founders were looking for a sponsor in 1998, The Planetary Society stepped in and provided the needed seed money. The Society has remained the main sponsor for the project ever since. SETI@home uses the data collected by the SERENDIP receiver, but focuses on a narrower bandwidth, centered on the 1420 KHz hydrogen line. With over three million personal computers at its disposal, SETI@home can analyze its data at a depth and detail impossible in more conventional approaches. Like SERENDIP the project is based at U.C. Berkeley and is led by project director David Anderson and chief scientist Dan Werthimer.

The Planetary Society has also branched out beyond radio searches, sponsoring Optical SETI ventures that look for concentrated laser signals from the stars. In 1998 it began supporting two targeted searches, based in Harvard and U.C. Berkeley, which look for very short light bursts coming from candidate stars. Since the end of 2000 The Society has supplemented these projects by funding the construction of the largest dedicated Optical SETI observatory in the world, in Harvard, Massachusetts. When completed ometime in 2002, the observatory will be used for the first all-sky Optical SETI survey.

Part XIV: SETI TodayAs long as NASA was involved in the SETI business, it dwarfed all other ventures by the shear scale of its resources. Even independent groups, like the SETI Institute, were often content to carve a niche within the NASA program rather than branch out on their own. But in the years since the cancellation of HRMS, a wide range of new and innovative projects, such as SETI@home and Optical SETI, have emerged and taken their place in the Sun.

The new Optical SETI observatory under construction in Harvard, Massachusetts, as it appeared in August, 2001.Credit: Paul Horowitz and The Planetary Society.

Some of these projects are the work of The SETI League. Composed of about 1300 enthusiasts, the League is working to set up a network of amateur SETI observers, each working with their own radio dish. Eventually, the SETI League hopes to have no less than 5000 SETI observing stations across the world. With just over 100 observers so far, the venture, known as Project Argus, still has a long way to go. The SETI League is also working on establishing an array of radio dishes in northern New Jersey, which they call "Array2k." When completed, the array will form a new kind of radio telescope, and will be dedicated exclusively to SETI.

One of the best funded and most promising projects for the future of SETI is the Allen Telescope Array, which will be built at the Hat Creek Observatory in northern California's Cascade mountains. The Allen Array is a joint venture of U.C. Berkeley and the SETI Institute, and it is underwritten by a 26 million dollar donation by Microsoft founder Paul Allen. 350 radio dishes, about 6 meters (20 feet) each in diameter, will constitute the Array when completed, giving it a collecting area greater than that of a 100 meter dish.

An artist's conception of the Allen Telescope Array at dusk.Credit: The SETI Insititute.

The Allen Array represents a true breakthrough for radio SETI. As a dedicated observatory, SETI researchers will be using it year-round to search for alien signals, as compared to the several weeks every year, which are allotted to Project Phoenix at Arecibo. In addition, since it is composed of hundreds of separate dishes, the array can be pointed at several points in the sky at the same time, and therefore listen to signals from several stars simultaneously. The latest technology will enable the Array to cover a frequency band 9 gigahertz wide,

more than 3 times wider than project Phoenix, which scans the widest band of any of today's searches. All of this represents a qualitative leap in the capacity of SETI searches, and increases the chances of detecting a "real" signal several-fold.

SETI research suffered a severe blow with the cancellation of the NASA program in 1993, but thanks to the leadership of The SETI Institute and The Planetary Society it recovered quickly. While no longer commanding the scale of resources made available through NASA, SETI programs are also free from the political and funding hazards that come with dependence on government funding. SETI after NASA is perhaps a smaller enterprise, but it is also more diverse, more widely accepted in academic institutions around the world, and - as the phenomenal success of SETI@home has demonstrated - remarkably popular with the public at large. With a broader base and a wider appeal, SETI today is a more viable enterprise than ever before. And although no alien signal has yet been detected, the hope still burns and the search continues...