© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm

24.2.5  SETI:  Yesterday and Today

As it has developed over the past two decades, the science of SETI -- Search for Extraterrestrial Intelligence -- today entails a passive listening strategy in hopes of detecting alien beacons or other transmissions. The older acronym CETI (Communication with Extraterrestrial Intelligence), still in use in the Soviet Union, implies a more active strategy in which humankind might actually converse with ETs. Because "communication" connotes a two-way exchange -- which may people fear -- NASA officials and American scientists engaged in this work on a professional basis prefer the isolationist connotations of "search." This, this believe, helps to avoid heated popular controversy and to reassure an anxious public that the intention is only to listen quietly, never to transmit.

Actually, SETI research of sorts has been underway since before the turn of the century. Nikola Tesla, native Croatian by birth and inventor of the induction motor, perhaps may be credited as the first SETI worker in history. Tesla believed that the Earth possessed a gigantic electric field that could be set aquiver if a sufficiently high voltage could be made to jump a large enough spark gap. In 1899, using money furnished by wealthy industrialist J.P. Morgan, Tesla erected a 70-meter-high transmission tower at a site in Colorado Springs, Colorado. One night when he was alone in his laboratory, the inventor observed "electrical actions" which he later interpreted as possible messages from Mars:

The changes I noted were taking place periodically, and with such a clear suggestion of number and order that they were not traceable to any cause then known to me. I was familiar, of course, with such electrical disturbances as are produced by the sun, Aurora Borealis and earth currents, and I was as sure as I could be of any fact that these variations were due to none of these causes.... It was some time thereafter when the thought flashed upon my mind that the disturbances I had observed might be due to intelligent control.....The feeling is constantly growing on me that I had been the first to hear the greeting of one planet to another.¹⁴⁶

Italian physicist and inventor of the radio Guglielmo Marconi reported in 1920 that his company’s radio stations had been picking up mysterious signals for the better part of a decade. Some of these sounded like a code, but were otherwise meaningless. Occasionally Marconi heard three dots and a dash -- Morse code for the letter "V" -- at frequencies ten times lower than were then in common use in man-made transmitters. When asked if these signals might be messages from another planet, Marconi answered in the affirmative.³²⁹¹

The next early SETI venturer was David Todd, chairman of the Astronomy Department at Amherst College in Massachusetts. Todd, excited by the prospect of the mysterious Marconi messages, tried to persuade all radio stations in the country to shut down during the closest approach of Mars to Earth in 1924 so he could listen for alien signals. While not entirely convincing, he managed to persuade the Chief of Naval Operations of the United States Navy to go along with his scheme. On 21 August 1924, the Chief sent word to the twenty most powerful military stations under his command to avoid unnecessary transmissions and to listen for strange signals from space. Army stations received similar orders, and in one instance a cryptologist from the Signal Corps was present to provide on-the-spot translations, if need be. But nothing substantive was detected, and the entire project died a quiet death. It was to be nearly 37 years before humanity once again would turn its ear to the stars.

It is useful to pause at this point and ask what is the likelihood of success of such a search. Many writers have pointed out that continuous transmissions into space would have a fairly low expectation of success in any given year, yet at the same time would be inordinately expensive. Also, first contact could bring unexpected trouble. Why announce our presence to the universe, these critics ask? Why invite danger and unnecessary risk? Hearing this, many SETI researchers have wondered out loud: "What if all alien civilizations were listening and no one was sending?"

At least three requirements should be satisfied if a society is to convert from a passive listening culture to an active transmitting one:

1. The civilization must have sufficient energy on hand that a 10¹⁵ watt continuous transmitter represents a negligible cost to the transmitting society;

2. The civilization should command a technology and energy re sources sufficiently powerful to defend itself against invasion or other military threats from any star system to which it directs its signals; and

3. The civilization should have great political and cultural longevity, in order to ensure continuity of operation and support of the beacon system.

It would appear that at least a Type II stellar culture may be necessary to fulfill all three preconditions of a transmitting society.^1285,28

Using the Drake Equation (see Chapter 23) and assuming various values for cultural longevity, it is possible to estimate how deeply into space we must carry our search in order to achieve a specified probability of success. From the figures in Table 24.2, it appears that the most likely search ranges are from 100-1000 light years, a volume of space which encloses some 10⁴-10⁶ stars. If we spend just 1000 seconds examining each one, then the expected search time required to achieve a high probability of success on a modern, fully-dedicated radiotelescope with full computer guidance and tracking capability is on the order of several decades. Because of this somewhat encouraging result, growing numbers of xenologists are entering the SETI sweepstakes in hopes of becoming the first to detect messages from an extraterrestrial civilization.

The first scientist to attempt to pick up interstellar signals was Dr. Frank D. Drake.¹⁶¹⁹ Despite the many technical difficulties at the time, Drake initiated mankind’s first systematic search for messages from intelligent beings on other worlds in the late evening of 11 April 1960. His equipment had been set up at the newly built National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia. Drake named his effort Project Ozma after the queen of the mythical land of Oz, a place very far away, difficult to reach, and populated by strange and exotic beings.¹⁵³⁵

The Ozma apparatus was operated at the hydrogen frequency of 1.42 GHz with a narrow bandwidth of 100 Hz. Two receiving horns were placed close together at the focus of the 26-meter-wide radio dish, so that the target star and the adjacent empty space could be monitored simultaneously. By subtracting one signal from the other electronically, stray emissions and background noise could be eliminated. Drake pointed the receiver at each of two target stars -- Tau Ceti and Epsilon Eridani.

Early in the investigation a strong signal was picked up, while the equipment was pointing at Epsilon Eridani. A series of high-speed pulses, roughly eight per second, were detected "so regularly spaced that they could only be the product of intelligent beings."⁷⁰² There was, as Drake later described the scene, "a moderate amount of pandemonium" in the control room. The strange signals were heard several more times over a period of several months. Eventually it was discovered that they were the product of a secret military experiment in radar countermeasures using airborne transmitters.

Listening continued through July 1960. Some 150 hours of total observational time were logged for the two target stars. Though Project Ozma did not detect any messages. from extraterrestrial civilizations, it cannot in fairness be reckoned a failure. Only two stars out of billions were sampled, and only in one narrow frequency band with only very poor (by modern standards) receiver sensitivity. The chance that alien signals had been overlooked was great. But perhaps the most significant achievement of Project Ozma was purely symbolic: Drake had proven that it was technically possible to perform scientifically valid SETI experiments.

Ozma was the first but certainly not the last. In the two decades since Drake’s initial pioneering effort nearly two dozen SETI searches have been conducted at observatories around the world (Table 24.3). Nearly 1000 nearby stars have now been at least briefly checked for intelligent transmissions, both in ultraviolet and in a variety of radio frequency bands. Individual whole galaxies have been monitored for evidence of emissions of the sort expected if Type III civilizations were present. Other searches have included simple sky surveys and sweeps of the entire sky for telltale pulsed signals. (Many highly unusual receiver systems have been proposed, including the Luneherg lens,¹⁵⁷⁰ Siforov’s isotropic scanner,²⁸ and Berger’s "celestial iconospherics" lenses.¹⁶⁶)

So far, none of these searches has yielded unambiguously positive results. The most comprehensive search undertaken to date, completed in 1976 at Green Bank by Zuckerman and Palmer in a survey of 659 stars, turned up a number of peculiar signals. According to one writer:

Ten stars which had shown "glitches" (i.e., unexplained spikes of energy) were carefully resurveyed. Several of the glitches were traced to terrestrial sources of interference, such as aircraft, while others remained a mystery; however, since none of the spikes were repeated, they were unlikely to be due to beacon transmissions from other civilizations.³²⁵⁷

It is certainly possible that a beacon once trained on Sol, perhaps for years or even decades, has continued on in its signaling schedule to other stars and will not return to our direction for thousands of years hence. As Edward Fitzgerald once wrote: "The Moving Finger writes; and, having writ, moves on."

Although several searches are still in progress at the present time, many xenologists are convinced that SETI searches are doomed to failure so long as they depend solely upon individual initiative and random funding. What is needed, they argue, is a major long-term commitment to SETI in which major radiotelescope equipment is dedicated in part or in whole to the search for communicative societies. To implement such systematic, far-reaching schemes, a new generation of ultrasensitive apparatuses may be required.

In 1971 NASA/Ames Research Center and Stanford University conducted a joint summer study to design one such integrated system. Co-directed by Dr. John Billingham of NASA/Ames and Dr. Bernard M. Oliver, Project Cyclops was a design study for a giant array of radiotelescopes whose performance would imitate that of a single radio dish many kilometers in diameter (Figure 24.6).* The Cyclops system would consist of more than a thousand fully steerable paraboloid radio antennae, each 100 meters in diameter (about the size of the largest contemporary steerables). The output from each of the antennae would be carried into a large central computer facility using a sophisticated system of phased transmission lines. The computer would coordinate and synchronize the movements of the many radio dishes and would employ special signal enhancement techniques to try to dig alien messages out of the incoming data. From the air, the final Cyclops system "would be seen as a large central headquarters building surrounded by an orchard of antennas about 10 kilometers in diameter."⁵⁷

Figure 24.6 Advanced SETI Systems: Project Cyclops

PROJECT CYCLOPS SYSTEM: At above left is an artist’s conception of a high aerial view of the entire Cyclops array of 100-meter radiotelescopes. Diameter of the entire antenna system is about 16 kilometers. At above right is an artist’s impression of the ground level view of the Project Cyclops installation, showing the central control and processing building nestled within the radiotelescope "orchard," and a small shuttlebus on tracks. (Photos courtesy of NASA/Ames Research Center)

The Cyclops array as originally proposed would be assembled piecemeal over a 25 year period, for a total cost of $10-25 billion. This is about the same level of commitment as was required for the Apollo Moon Program a decade ago. (Or, as one observer has wryly noted, 22 days of Defense Department spending would support Cyclops for a quarter-century of development.) The Project, covering 65 km² in some remote desert wilderness area, would be sensitive enough to conduct searches for 1000 megawatt beacons out to 1000 light-years or to eavesdrop on the electromagnetic "garbage" of technical societies out to about 100 light-years.

The NASA SETI Advisory Panel recently considered a number of alternatives to the Cyclops system.²⁸⁶⁵ One major proposal under consideration is the concept of an orbital SETI installation (Figure 24.7). A giant spherical radio dish could be placed in Earth orbit at lunar distance, perhaps at one of the semistable Lagrangian points of Luna’s orbit. A shield would be erected to blot out all radio interference from transmitters on Earth. When fully implemented the system might measure 3 kilometers in diameter, but early test models could probably be flown with diameters of 30-300 meters.

Figure 24.7 Advanced SETI Systems: Orbital Telescope Facility

This giant dish would sweep the entire sky once during each orbital period, so any target could be observed at least once every 28 days. Since the telescope is spherical rather than parabolic in shape, the feed horn at the focus may be moved to tune in on distant objects so that the entire dish does not have to be reoriented. Since the feed horn can move a full 180^o across the surface of the collecting dish, this means that any target theoretically may be observed for a continuous 14-day period if so desired.

An additional advantage of an orbital SETI system is that multiple feed horns may be used without sacrifice of accuracy or sensitivity. This should permit the simultaneous observation of many different target stars within a given hemisphere of the celestial sphere. Finally, from a structural engineering aspect the orbital system would be much easier to build than a ground-based Cyclops network.³¹⁵⁵

Lunar Farside systems (Figure 24.8) were also under serious consideration by the SETI specialists.³¹⁴² NASA has considered the relative merits of Cyclops-type arrays [many small dishes) and Arecibo-type arrays (few large dishes) if constructed on the far side of the Moon. Since this side always faces away from Earth, any SETI system located there would be entirely free of terrestrial radio interference because of the shielding effects of 3000 kilometers of solid rock. The abundance of lunar craters of all sizes makes an Arecibo-type array especially attractive, which one study found to be significantly cheaper than Cyclops type setups on the moon. (SETI enthusiasts often refer to such an installation as "Lunarcibo."³¹⁴⁹) A large expense common to both proposals is the sizeable lunar colony which would be necessary to support the project, A countervailing advantage is that building materials should be close at hand.

Figure 24.8 Advanced SETI Systems: Lunar Farside Systems

Cyclops-type Array (at left): Artist’s impression of Lunar Cyclops array, showing central control and procuring building and lunar base in left middle distance. Arecibo-type Array (at right): A large dish could besited in a lunar crater on the far side of the Moon, to provide a large collection area with complete shielding from Earth.

During 1975-1976, NASA commissioned systems analysts at Stanford Research Institute to perform a cost-benefit analysis of sixteen different antenna concepts intended for use in the search for extraterrestrial signals of intelligent origin.³²⁶² The study showed that the orbital SETI system compared quite favorably with a ground-based Cyclops network in terms of cost. Quite unexpectedly, the critical parameter turned out to be N, the total number of communicative civilizations in the Galaxy. If N is very high and we only need to search a few hundred light-years out into space to achieve success, then Cyclops is cheaper because of the lower levels of R&D required. But if we must listen out to 500 light-years and beyond (N is very small), then the space-based system is cheaper to build and to operate. The price of the Lunar Farside scheme was deemed significantly higher than either of these two options.³²⁹²

SETI systems, once constructed, should prove enormously useful in basic research in radioastronomy. SETI detection networks can make major contributions during off-time to the following areas of scientific investigation: Cosmology, external galaxies, quasars and radio galaxies, the intergalactic medium, kinematics and structure of the Milky Way, stellar evolution, super novae and pulsars, composition of the interstellar medium, and solar system studies including surface mapping of terrestrial planets, jovian moons, asteroids and meteorites.²⁸⁶⁵

There is growing interest in SETI in the astronomical community generally. A questionnaire sent to radioastronomy observatories around the world asked the question: "Have you ever engaged in any search for coherent or "intelligent" signals at your facilities?" Approximately 50% of the observatories responding answered in the affirmative.²⁸⁶⁵ Scientists in the United States and the Soviet Union are excited by the prospects.⁸⁸⁰ In America, a five-year program was proposed in 1978 that involves a search of specific stars by a team at NASA/Ames in Mountain View, California,³¹²⁹ and a complementary search in the manner of a sky survey by a team at the Jet Propulsion Laboratory (JPL) in Pasadena, California.**³¹³⁰ In Russia, two overlapping ten-year plans were advanced by SETI scientists in 1975 which offer a combination of ground-based and satellite listening posts capable of continuous monitoring of the entire sky, nearby galaxies, and other selected objects of interest.^1480,3681

One final sticky issue remains for discussion. Will we -- should we -- transmit?¹²⁰ At present there exist no laws in national or international legal systems to prevent this, so there is nothing to stop any private or public organization from doing it if they want. It is common knowledge among working astronomers that many minutes of valuable radiotelescope research time are sometimes diverted (between regularly scheduled astronomical observations) to take a quick listen to Tau Ceti or Epsilon Eridani from time to time. The temptation to transmit is equally great, and one writer about six years ago reported that "Tau Ceti has signals periodically transmitted to it by the Arecibo dish in Puerto Rico."¹¹³⁹ The writer later recanted, acknowledging that "I have now been informed that the information quoted was unofficial and that the big dish has not been used to transmit signals to Tau Ceti."¹¹⁴⁰ Nevertheless, it is likely that at least a small amount of unofficial broadcasting has occurred from time to time.

Further, we already know about one official "message to the stars" that has been sent out into space (Figure 24.9).

Figure 24.9 The Arecibo Pictogram Transmitted to M13 on 16 November 1974

ARECIBO MESSAGE IN BINARY CODE was transmitted in 1974 toward the Great Cluster in Hercules (M13) from the 1,000-foot antenna at Arecibo. The message is decoded by breaking up the characters into 73 consecutive groups of 23 characters each and arranging the groups in sequence one under the other, reading right to left and then top to bottom. The result In a visual message (see below) that can be more easily interpreted by making each 0 of binary code represent a white square and each 1 a black square.

ARECIBO MESSAGE IN PICTURES and accompanying translation shows the binary version of the message decoded. Each number that is used is marked with a label that indicates its start. When all the digits of a number cannot be fitted into one line, the digits for which there is no room are written under the least significant digit. (The message must be oriented in three different ways for all the numbers shown to be read.) The chemical formulas are those for the components of the DNA molecule: the phosphate group, the deoxyribose sugar and the organic bases thymine, adenine, guanine and cytosine. Both the height of the human being and the diameter of the telescope are given in units of the wavelength that is used to transmit the messages: 13.6 centimeters.

At 1700 GMT on 16 November 1974, the giant Arecibo radiotelescope (equivalent isotropic power output 2 x 10¹³ watts) was used to transmit mankind’s first deliberate radio message "for possible reception by other intelligent creatures."¹⁵⁷¹ The transmission was made at 2.38 GHz by Frank Drake and Carl Sagan, and consisted of 1679 bits of information arranged in a 23 x 73 pictogram as shown in Figure 24.9. The simple message took 169 seconds to send, and was aimed at the globular cluster M13 which is 24,000 light-years away. At this distance the Arecibo beam just covers the 300,000 stars in the cluster. Theoretically we may receive a reply no sooner than 49,974 A.D. -- the round trip transit time at the speed of light. However, it is now reported that there are between 20-100 stars of the red giant and orange giant variety in the path between here and M13, and that literally thousands of stars may have been fanned by the Arecibo beam while it was being tuned up to send the actual message. Communicative civilizations at any of these sites may have an earlier chance to intercept the message or at least parts of it. We may get an answer sooner than we expect.***

* Cyclops appears to be the working out of ideas earlier put forward by Oliver. On 27 July 1965 at an AIAA Conference in San Francisco, Oliver suggested that by building between 1-10 thousand radiotelescopes, each about 30 meters in diameter, in a 6-kilometer-square of flat terrain in certain areas such as Texas, we could "detect the unintended radiation from another intelligent race."

** Jill Tarter at NASA/Ames has informed the author that the survey team would be happy to include any specific star in one of their SETI sky searches, upon request from scientists of from members of the general public.³¹⁴⁹

*** Less than a year after Drake and Sagan sent the Arecibo signal, the following reply was received at Cornell University: "Message received. Help is on the way -- M13." This was printed out on a teletype machine that serves as a data hotline linking Cornell with the facilities at Arecibo. Since the response was 47,999 years too early, Drake suspects a somewhat closer source -- a staff member with a sense of humor.⁴¹⁸

Last updated on 6 July 2013