The Search for Extraterrestrial Intelligence, SETI, An Introduction

The Searches

Assuming that there are technological civilisations out there at our level or beyond, then we really have two basic options in devising a search strategy:

A targeted search of nearby sun-like stars,
An all-sky survey for interesting signals of unknown origin.

The former, which involves aiming at likely candidate stars for long periods of time, is well suited to large, steerable dishes with their narrow beamwidths and high sensitivities. If we guess right as to which stars constitute likely candidates, the targeted search will provide us with the greatest likelihood of immediate success. But since only a limited number of relatively nearby candidate stars is known to us, concentrating our search in their direction may cause us to miss an equally good star of which we happen to be unaware.
An all-sky survey, on the other hand, makes no a priori assumptions as to the most likely direction to explore. The survey attempts to sweep out the entire sky which can be seen from a given location. No antenna tracking is required - sky survey radiotelescopes are operated in what's called meridian transit mode, they rotate with the Earth.

Kardashev’s classification of civilisation types allows rationalisation of search strategies. In looking for Type I civilisations we must adopt a targeted search concentrating on nearby Sun-type stars using sensitive directional detectors. Type II civilisations would be able to broadcast their presence over a much greater distance and over wide areas, so all-sky surveys within our own galaxy, coupled with targeted searches of clusters of stars will suffice to catch any signal. Type III civilisations would be able to advertise their presence from way outside our galaxy, and an all sky survey would reveal their presence adequately.

What to look for ?

Initial searches concentrated on direct evidence of communication via microwave band radio. In the last ten years, the emphasis has changed to the detection of technological phenomena, in particular the ability of any technical species to modify its local environment in ways that can be detected over interstellar distances. Suggestions have been made to search for the following:

Enhancement of rare earth elements resulting from dumping fissile waste into a parent star.
Enhanced emission at 1.516701 GHz due to tritium leaking from orbital fusion reactors or propulsion systems (Valdez, Freitas 1986)
Infrared excess resulting from re-radiation from a Dyson sphere.
Gamma ray bursts from interstellar propulsion systems based on matter/antimatter annihilation.
The presence of companion craft to asteroids and moons, especially von Neumann probes.
The presence of orbital craft around planets (specifically at the Lagrangian points), or about the Sun

The last two are local searches based on assumptions of colonisation by a technical species, nevertheless the technology for detection is similar to that used for the other more distant searches.

On a basic level, the search for any evidence of biological activity would give us more information on the "life" terms in the Drake Equation, whether intelligence had developed or not. Discovery of enhanced oxygen lines in planetary atmospheres is one such example (especially if in co-existence with reactive gases e.g. methane)

The sheer scale of activity needed to confirm or deny the existence of ETI has never been adequately satisfied in any search so far, but in comparison to the early searches, even amateur SETI projects these days offer a far better chance than the brave first steps of the professional pioneers.

The simple truth is that there are 100 billion frequencies to monitor in the SETI window, and a signal could come in at any time from anywhere on any one of these channels, and last from a few thousandths of a second to thousands of years. In the words of Jill Tartar, formerly of NASA’s High Resolution Microwave Survey, the analogy of searching for a needle in a haystack is woefully inadequate. Imagine searching through all the haystacks in the world for a single needle – but you don’t even know what this needle looks like (is it bone, plastic, knitting, sewing etc ?) Given 50 years to find it, on your own, you would have about 0.04s to search each haystack. Conceivably, with a large enough labour force, human beings could achieve this very difficult feat in the time allowed. This situation pales into insignificance when compared with the cosmic haystack, where an individual would need billions of years to complete such a search, with the additional complication that the needle might only be transient. Clearly this is not a job for human beings, but requires massive computing power to analyse multiple channels simultaneously. It is no surprise that information technology has only recently advanced to a point where this computers are fast and cheap enough to begin to make a dent in SETI. There is still a long way to go, even at this rate of progress.

Since 1959 there have been a total of 80 searches world-wide, both targeted and all-sky. These have been conducted by individuals, small groups, universities and national institutions.
These are the highlights of those attempts:

Project Ozma

In 1960, radioastronomer Frank D. Drake (the current director of the SETI Institute), then at the National Radio Astronomy Observatory in Green Bank, West Virginia, carried out humanity's first attempt to detect interstellar radio transmissions. Project Ozma was named after the queen of L. Frank Baum's imaginary land of Oz - a place:

"very far away, difficult to reach, and populated by strange and exotic beings."

The stars chosen by Drake for the first SETI search were t ceti in the constellation Cetus (the Whale) and e eridani in the constellation Eridanus (the River), some eleven light years (66 trillion miles) away. Both stars are about the same age as our Sun.

From April to July 1960, for six hours a day, Project Ozma's 26m NRAO radio telescope was tuned to the 21-centimeter "hydrogen line" (1.420 GHz). A single 100 Hz channel receiver scanned 400 kHz of bandwidth. The astronomers analysed the tapes for a repeated series of uniformly patterned pulses that would indicate an intelligent message or a series of prime numbers such as 1, 2, 3, 5 or 7.

t ceti proved to be a disappointment, but the minute Drake and his team turned the telescope onto e eridani, a loud burst of noise emerged from the speaker 8 times a second, matched by a pen trace that went off the scale! The initial surge of adrenalin was muted when they turned the telescope away from the star and returned to find the signal had disappeared. Despite local press reports of a government conspiracy to cover up the first "contact", Drake’s research indicated the source of this signal to be a high flying U2 spyplane taking part in a secret military experiment. Beyond this, the only sound that came from the loudspeaker was static and no meaningful signals turned up on the recording paper.

Despite its crudity by todays’ standards, Project OZMA was a ground breaking first step towards serious SETI research.

Pulsars

It is important to note that the scientific community has always been receptive to the idea of ETI, even if not involved in a direct search. One classic example is the discovery made by Jocelyn Bell in 1967. She was working as a Ph.D. student at the Cambridge University radioastronomy labs using a large array of receivers. She observed a regular pulsing radio signal with a period of 1/30^th second that returned every sidereal day (showing that it was not of terrestrial origin) and alerted her supervisor, Anthony Hewish. He withheld from publishing this finding for a few months, during which the source was tentatively ascribed to LGM (Little Green Men). After following the pulses for some time, it was realised that there was no wandering of frequency that would be expected to arise from Doppler shifting of a source in planetary orbit. The discovery of more of these periodic sources pointed to a physical origin, which turned out to be rapidly rotating neutron stars left behind after catastrophic supernovæ explosions – so called pulsars.

Russian searches

In the 1960's, the Soviet Union dominated SETI, and it frequently adopted bold strategies. Rather than searching the vicinities of nearby stars, the Soviets used nearly-omnidirectional antennas to observe large chunks of sky, counting on the existence of at least a few very advanced civilisations capable of radiating enormous amounts of transmitter power. This was a result of a paper published by Kardashev in 1963 proposing that the maximum amount of information transfer was more likely to be transmitted over a broad spectrum in the decimetric window and varying on very short time scales (this was in antithesis to the American expectation that there would be a simple beacon alert on a narrow band to signal "here we are"). In particular the analysis of two radio sources, CTA 21 and CTA 102 (from the California Institute of Technology catalogue) over a year (1964-65) showed all the characteristics Kardashev had proposed, including regular intensity fluctuations with a period of 100 days. TASS reported this Soviet discovery of ETI in 1965, just after the discovery by an American team that CTA 102 was an example of a very distant quasar. More a footnote to Cold War politics than objective scientific analysis.

Project Cyclops

At the beginning of the 1970's, NASA's Ames Research Centre in Mountain View, California began to consider the technology required for an effective search. A team of outside experts, under the direction of Bernard Oliver, on leave from the Hewlett-Packard Corporation, produced a comprehensive study for NASA known as Project Cyclops. The Cyclops report provided an analysis of SETI science and technology issues that is the foundation upon which much subsequent work is based.

As the perception grew that SETI had a reasonable prospect for success, the Americans once again began to observe. During the 1970's, many radio astronomers conducted searches, using existing antennas and receivers. Some of the efforts, employing improved technology, have continued to the present time.

Excitement at Ohio

The Ohio State Radio telescope ("Big Ear") was larger than three football fields in size and equivalent in sensitivity to a circular dish 52.5 meters in diameter. The beam of the telescope was elliptical, being forty minutes of arc in the declination (vertical) direction and eight minutes of arc in the right ascension (horizontal) direction at 1.4 GHz. This may be visualised by comparing it with the size of the Moon, which is a thirty minutes of arc diameter circle in Earth's sky. The telescope surveyed the sky by remaining stationary and allowing the rotation of Earth to sweep its beam in a narrow circular path through the sky once each day. After a few days of observation, the beam is moved slightly up or down and the pattern is repeated. It takes several years to thoroughly search the sky. A SETI search began in 1973.

The bandwidths of the channels ranged from ten to fifty kilohertz (kHz), depending on their distance from the centre frequency. The output of the eight channels was plotted using pen recorders. The charts were laboriously searched for unusual signals by graduate students. The search strategy chosen at the time was to explore the vicinity of the 21-cm hydrogen line, Doppler correlated to the Galactic Standard of Rest. Due to the random motions of the stars and the rotation of our Milky Way galaxy, signals transmitted at the hydrogen line frequency would be received at somewhat different frequencies. To avoid this ambiguity, the deliberate assumption was made that any civilisation transmitting at the hydrogen line would offset their transmission frequency in just the right way to remove all their motions with respect to the centre of the galaxy, which is the only unique reference point shared by all the galactic inhabitants. It was then up to the operators to offset their receiver frequency to compensate for Earth's motions to arrive at this unique galactic frequency. Because of humankind's uncertainty about the galactic rotation velocity (measured by observing the motions of the stars and gas in our stellar neighbourhood), they still had to search a total bandwidth of several hundred kHz. A lot of chart paper was generated during the two years this effort continued, but no recognised signals of intelligent origin were found. The system was upgraded in 1976 for a new search.

Two types of unexplained signals were detected during this search. The first kind is quite rare, with the best example being the "Wow!" signal found in 1977. This name was unintentionally applied from Jerry Ehman's comments in the margin of the computer printout when he noticed the signal. In his own words he describes this event:

"I came across the strangest signal I had ever seen, and I immediately scribbled 'Wow!' next to it," Ehman explained. "At first, I thought it was an Earth signal reflected from space debris, but after I studied it further, I found that couldn't be the case."

The signal was unmistakably strong and had all the characteristics of an extraterrestrial signal. It was narrowband and matched the antenna pattern exactly, indicating it had to be at least at lunar distance. A signal from a nearer object would show a wider pattern.
A check of artificial satellite data showed that no publicly known Earth satellites were anywhere near the position of the signal source. Furthermore, the frequency of the signal was near the 1.420 GHz hydrogen line, where all radio transmissions are prohibited everywhere on and off Earth by international agreement. Searches were made in the direction of the Wow signal hundreds of times after its discovery and over a very wide frequency range. The signal was never found again. In fact, whilst receiving this signal the first time, it turned off during monitoring.
What was the "Wow!" signal? We will probably never know. Conceivably it could have been a secret military satellite in solar orbit, transmitting on an illegal frequency. Military transmitters often ignore civilian agreements. Its characteristics rule out any terrestrial transmitter, near-Earth satellite, reflection from space debris, or equipment malfunction. Perhaps it was a transmission from some other civilisation. If so, it seems that they were not trying very hard to attract our attention, since the signal disappeared before anyone could really find out what it was.

The other kind of unexplained signals received are much more numerous. These are narrowband pulses (lasting less than ten seconds) which go "bump in the night". There have been thousands of such signals received, apparently from all over the sky, and never from exactly the same direction more than once. Clearly these signals are not from any single source (intelligent or otherwise), but they are very interesting in their own right. They could be some form of previously unknown astrophysical phenomenon.

The Harvard SETI Group

The first high resolution SETI began in 1978 with a search, at the Arecibo 305m dish, of 200 interesting candidate objects. That project used off-line long Fourier transforms to search 1 kHz instantaneous bandwidth (IBW) segments centred on the 21 cm line of neutral hydrogen, with a resolution bandwidth (RBW) of 0.015 Hz (the highest resolution and sensitivity ever achieved in SETI). The tiny bandwidth of the search (1 kHz at 1.4 GHz: one part in a million) required a transmitting civilisation to precompensate their carrier beacon for their motion relative to the Sun. The project organisers felt this to be a rather restrictive scenario, although a task an advanced civilisation could accomplish, if they so desired. The search produced no conclusive results.

With support from NASA and The Planetary Society, Paul Horowitz spent a year building a high-resolution hardware spectrometer that could handle the kind of signal processing that was used in the earlier Arecibo search, but in real time. It came to be known as "suitcase SETI". Suitcase SETI travelled to Arecibo in March 1982, where it searched 250 candidates (stellar and other), mostly at the second harmonic of HI, at 2.84 GHz. Although the radio interference rejection was impressive; once again, no confirmed signals were detected.

SENTINEL

With sponsorship by The Planetary Society, and with the permission of NASA, a reconfigured Suitcase SETI was attached to the 26m steerable Cassegrain radiotelescope at Harvard, Massachusetts between 1983 and 1985. This search, known as Sentinel, was the first dedicated high-resolution SETI, covering the northern sky in a transit mode at the 21 cm line. Unlike the earlier targeted searches at Arecibo, an all-sky transit search was chosen because the larger beam size (30 arc minutes, compared with 3 arc minutes at Arecibo) corresponds to a full search of the visible sky in about 200 days. Once again, the system was sensitive only to precompensated carrier transmissions to our heliocentric frame. No confirmed signal sources were observed.

BETA

The experience of META showed that the next search system should incorporate means for

rapid and automatic re-observation of candidate events,
better discrimination of interference, through a simultaneous 3 beam configuration,
coverage of the full 1.4-1.7 GHz "waterhole" band of frequencies.

Thus was born "BETA" (Billion channel ExtraTerrestrial Assay), the current search of the Harvard SETI group, which was switched on in October 1995. BETA took four years to design and build, with support from The Planetary Society, NASA, the Bosack/Kruger Foundation, and the Shulsky Foundation. It uses the 26-meter dish to feed a 240 million channel Fourier spectrometer (80 million channels of 0.5 Hz resolution and 40 MHz instantaneous bandwidth for each feed) whose outputs feed an array of programmable "feature recognisers." Each potential source is visited 8 times at each frequency hop, in each sky beam. A good candidate triggers the antenna to leapfrog a few beamwidths to the west, inviting the source to perform an encore. If that ever happens, the antenna will break off its survey and go into star tracking mode, repeatedly moving on and off the candidate source, archiving all integrated spectra.

SERENDIP

(Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) is an ongoing scientific research effort undertaken at the University of California, Berkeley.
SERENDIP has been in operation for 18 years, beginning with SERENDIP I in 1979. The SERENDIP I instrument consisted of a 100-channel spectrum analyser which was located at UC Berkeley's Hat Creek Observatory. Since that time, SERENDIP has undergone a series of sequential improvements.
SERENDIP II, which ran from 1986 to 1988, was thousands of times more powerful than its predecessor. The second-generation instrument was able to observe 65,000 channels per second and was primarily located at the 42m NRAO radio telescope at Green Bank and to a lesser extent on four other high-quality telescopes around the world.
SERENDIP III began operations at Arecibo in April 15, 1992. The end of its 4 year survey coincided with the beginning of a major upgrade at Arecibo. The upgrade is now complete, and SERENDIP IV was installed at Arecibo in June 1997. It greatly enhances the SERENDIP search; and will collect 168 million channels worth of data every 1.7 seconds.
SERENDIP IV, like SERENDIP III, is piggybacking on the Arecibo telescope. Dedicated telescope time will be used to look back at the most interesting candidates from this and previous searches.

In addition to the new SERENDIP IV systems under construction for the groups in Australia and Italy, other SETI groups have adopted all or part of the SERENDIP III system in their search efforts. The SERENDIP III design is at the heart of the Harvard BETA system.

Ohio State University has been using a 4 million-channel version of SERENDIP IV for conducting SETI observations at OSU radio observatory.
The data gathered by the instrument is transferred across the Internet to the SERENDIP lab at Berkeley. There the data is run through a series of algorithms designed to reject radio frequency interference and detect signals that have some possibility of being both artificial and extraterrestrial.

Current results - The 4 year SERENDIP III sky survey at Arecibo Observatory was completed in 1998, logging a total of 10,000 hours of observation time. The project has observed 93 percent of the sky visible from Arecibo at least once, and has searched 43 percent of the Arecibo sky at least 5 times. Along the way, SERENDIP has probed more than 100 trillion radio channels at very high sensitivity. Final SERENDIP III data analysis is currently under way. So far, no signal has merited re-observation, but the entire run of data is getting a fresh look. When all of the data are considered together, some candidates, such as those in which strong signals recur several times, become more interesting.

Southern SERENDIP was first connected to the Parkes Radio Telescope on 20 March, 1998 with the ability to scan eight million channels at once. This has now been upgraded to 58 million channels.

The High Resolution Microwave Survey

By the late-1970's, SETI programs had been established at NASA's Ames Research Centre and at the Jet Propulsion Laboratory (JPL) in Pasadena, California. These groups arrived at a dual-mode strategy for a large-scale SETI project.

The Targeted Search, proposed by Ames Research Centre, was a high sensitivity search that looked for weak signals originating near stars like our Sun that are within 100 light-years distance from Earth. The objective was to test the hypothesis that advanced technologies are using microwave frequencies, and that our largest, present day radio telescopes and the Targeted Search receiver are sensitive enough to detect these signals. Star clusters and some nearby galaxies were also to be observed. The search frequency range was 1.0 to 3.0 GHz. Some of the large radio telescopes used were the National Science Foundation's 305m diameter antenna at Arecibo, the Australian 64m diameter antenna at Parkes, Australia, and the National Radio Astronomy Observatory's 42m diameter antenna at Green Bank, West Virginia. The prototype 74 000 channel receiver was updated to an 8 million channel cascaded Fourier transform receiver designed to observe for 1000 seconds per star and respond to a signal of the bleep bleep or whistle variety.

JPL would use the same technology but systematically sweep all directions. This All-Sky Survey was designed to observe the entire celestial sphere over the 1.0 to 10.0 GHz frequency range, plus spot bands up to 0.25 GHz, to explore the possibility that there may be civilisations transmitting strong signals, possibly as interstellar beacons. The sky survey initiated operations using the 34-meter diameter antennas of the Deep Space Network.

In 1988, after a decade of study and preliminary design, NASA Headquarters formally adopted this strategy, and funded the program. The HRMS inaugurated its observational phase at 19:00 hours Universal Time on 12 October 1992. In a co-ordinated program, the Arecibo antenna pointed at the star Gliese 615.1A and the Goldstone antenna began to scan a small area of sky that included the position of the target star. During the following year, the Sky Survey team continued observations at Goldstone on a part-time basis with a prototype system while continuing to build the operational system with sixteen times the capability. The Targeted Search team returned from Arecibo after the scheduled two month observing session and immediately disassembled the system for upgrades and expansion.
In October 1993, both HRMS teams were making good progress toward completing their operational observing systems. Meanwhile in Washington, Congress was not making progress in trimming the budget. After voting for the Space Station and the Advanced Solid Rocket Motor, they voted against the HRMS (about $12 million) thus cutting nearly 0.1% of NASA's budget. The project was formally terminated a year after its inauguration.

Project Phoenix

The aptly named Phoenix project sought to rise from the ashes of the HRMS and to continue the work begun by NASA with private funding under the umbrella of the SETI Institute. Project Phoenix concentrates efforts on that component of the HRMS known as the Targeted Search. Its strategy is to carefully examine the regions around 1,000 nearby Sun-like stars. The world's largest antennas are being used, and these have committed observing time for SETI. Phoenix will also commit to a search before radio interference from terrestrial sources grows to render detection of weak signals impossible. Project Phoenix is orders of magnitude more comprehensive than any experiment yet performed in this arena.
The characteristics of the Targeted Search System (TSS) are determined by the following observational requirements. The TSS must:

search for artificial signals that have a narrow bandwidth (<300 Hz, the narrowest natural maser lines), may be highly polarised, drift in frequency by less than 10-9 Hz/sec and may be continuously present or pulsed
search the "Microwave Window" from 1 GHz to 3 GHz
use the largest available radio telescopes to achieve high sensitivity
observe each frequency band for at least 300 seconds
observe approximately 1000 sun-like stars within a distance of 150 light years
conduct the search with near real time processing so that candidate signals may be tested immediately
be highly automated to minimise operator interaction and increase the quality and uniformity of the search.

The TSS is a transportable SETI system that is used in conjunction with existing radio telescopes for high sensitivity SETI observations. The channels in the Multi Channel Spectrum Analyser (MCSA) overlap each other slightly in frequency, providing near-optimum response to both Continuous Wave and pulsed signals whether they remain in a channel or drift in frequency by as much as one channel per spectrum. The MCSA has a sustained computation rate of approximately 75 GFLOPS (75 billion floating point operations per second).

In order to have immediate independent testing of candidate signals that does not waste telescope time, a stand-alone subsystem has been developed. The so-called Follow-up Detection Device (FUDD) applies intensive signal processing to a relatively narrow frequency band around a candidate signal. Given the basic characteristics of a candidate signal (frequency, frequency drift rate, power) the FUDD can use higher resolution to achieve higher sensitivity and accuracy. When the characteristics are known with sufficient accuracy, the FUDD can form a matched filter for the signal for even higher sensitivity. The sensitivity gain from the matched filter allows a relatively small antenna to be used to confirm a detection made on a large antenna. Confirmation of a signal by an independent observatory is considered essential for classifying a signal as of extraterrestrial origin.

In practice, this process is carried out simultaneously on FUDDs at two antenna sites. When the SCS determines that a signal reported by the SDS cannot be ruled out as interference, the signal characteristics are reported to both FUDDs. While the main TSS subsystems go on to a new observing frequency on the target star, the FUDDs tune to the frequency of the candidate signal and observe simultaneously. If the signal is persistent, the FUDD at the main antenna can quickly detect and improve the measurements of the signal characteristics. The improved parameters for the signal and the geometric transformation factors between the two sites are reported to the FUDD at the remote antenna site and used to form a matched filter for that signal. The filter is applied to the data that were collected simultaneously with the main site FUDD. If the signal is detected by both FUDDs, it is a very convincing candidate extraterrestrial signal.

The TSS was transported to the Parkes Observatory, NSW, Australia at the end of 1994. A dedicated observing session using the 64-m telescope at Parkes and the 22-m telescope at Mopra began Feb. 2, 1995. With only a few interruptions for time-critical radio astronomy, the Phoenix observations continued full-time until June 6. During that time more than 23,000 observations were conducted (an observation is defined as successfully searching a 10 MHz bandwidth).

Observations resumed in October 1996 at the 42m Telescope of the National Radio Astronomy Observatory in Green Bank, West Virginia. Later the TSS visited the upgraded Nançay telescope in France and other large northern hemisphere observatories. These sites allowed observations of stars that are beyond the declination limits of Arecibo and Parkes.

By mid-1999, Phoenix had examined about half of the stars on its "hit list." So far, no clearly extraterrestrial transmissions have been found. Observations are currently being made during two three-week sessions each year using the Arecibo 305m dish. During the observing sessions, the astronomer on duty posts reports.

The SETI Institute's current fundraising focus is a $12 million campaign to build and deploy the real-time signal detection equipment it has recently designed and prototyped. The New Search System (NSS) will complete the ongoing Project Phoenix observations at Arecibo and Jodrell Bank Observatories through the years 2003 and 2004. The NSS will expand detection ability five-fold in processing bandwidth (speed) by the spring of 2004, and through a final reconfiguration will mate with the Allen Telescope Array (ATA) in 2005.

The Allen Telescope Array

The Allen Telescope Array (ATA) is a joint project between the SETI Institute and the University of California at Berkeley Radio Astronomy Lab (RAL).
The ATA will consist of approximately 350 6.1-meter offset Gregorian dishes arrayed at the Hat Creek Radio Observatory site. Given the number of antennas and large size of the primary beam (approximately 2.5 degrees at 21 cm wavelength), this array will have an unprecedented amount of flexibility in observing. Several individual users may simultaneously use the array to observe a different part of the sky at an independent frequency, or image the sky at one or more frequencies.
It is scheduled for completion in 2005 and hopefully will go on to be part of a much larger array - the SKA or Square Kilometer Array
Users will be able to access the array through a secure internet connection. Due mainly to the benevolence of two founder members of Microsoft this will be the first dedicated SETI antenna that can take part in targetted and global searches. It is hoped to expand Phoenix's targeted search from 1000 stars to hundreds of thousands.

SETI in Europe

Dr. Stelio Montebugnoli of the Bologna Radio Astronomy Institute has developed a spectrum analyser system that will be used for SETI observations with both the 33m antenna and the "Northern Cross" antenna. The SETI programme will include targeted observations of solar type stars at 1.42, 4.8, 22, 23 GHz. A sky survey program could be done at 40.8 MHz with the Cross telescope. The SETI group will soon develop a 4 million channel spectrum analyser.

Results so far: 24 Target Stars observed in 35 frequency bands each 8 MHz wide, dual polarisation. Observations lasted 299 or 92 seconds, 436 successful observing sequences completed in 200 hours observing. 15 candidate signals passed ON OFF ON test. None of these signals survived additional confirmation observations.

Optical SETI

Since 1998 there has been a large increase in Optical SETI (OSETI) where telescopes are looking for short (nanosecond) pulses from nearby sunlike stars. Columbus University, Ohio and Princeton have active OSETI programmes and more recently OSETI has been pursued at Harvard, Berkeley and the Lick Telescope, California.

Since the Princeton OSETI project began in 2001, through 2002 October 14, they have made 2435 observations of 1397 different stars. Similar numbers of observations have been made in other programmes but no candidate signals have been detected yet.

Amateur Searches

There are many amateur collaborations that are organised nationally, or internationally and can be seen as adjuncts to the professional searches, although most of these projects sacrifice multichannel analysis for a host of narrowband stations all linked into a network (via the internet). One of the most advanced of these is Project Argus (organised by the SETI-League) whose philosophy is described below:

Individual research grade radiotelescopes can view only a small fraction of the sky at a given time, typically on the order of one part in a million. All-sky coverage with these instruments would thus require a million telescopes, each at a cost of several million dollars. Project Argus will employ much smaller, quite inexpensive amateur radiotelescopes, built and operated by SETI League members at their individual expense.

A typical amateur radiotelescope can be built for from a few hundred to a few thousand dollars, depending upon the expertise of the builder. Only five thousand of these smaller instruments are necessary to provide full sky coverage. The equipment, although of modest sensitivity, will still be capable of detecting microwave radiation from technologically advanced civilisations out to a distance of several hundred light years.

Perhaps the most ambitious radio astronomy project ever undertaken without Government equipment or funding, Project Argus is an effort to deploy and co-ordinate roughly 5,000 small radiotelescopes around the world, in an all-sky survey for microwave signals of possible intelligent extra-terrestrial origin. When fully operational, Project Argus will provide the first ever continuous monitoring of the entire sky, in all directions in real time.
Project Argus, named after the all-seeing Greek guard-being with 100 eyes, is a key effort of The SETI League, Inc., a membership supported, non-profit educational and scientific corporation. The League was established in 1994 to further the scientific Search for Extra-Terrestrial Intelligence (SETI). The SETI League is currently developing the necessary hardware, software, protocols and procedures for distribution to its members world-wide. The search phase of Project Argus began with five operational radiotelescopes on Earth Day, April 21, 1996.

The most recent development in using amateur resources connected via the internet has been the trial of a computer screen saver program that displays a sample of data collected by SERENDIP at the Arecibo telescope.
Since SETI@home was launched in 1999, over four million people have downloaded the screensaver onto their personal computer. When they are not using the machine, the program crunches the data it has been sent by SETI. Each data packet is a 100 second segment of noise collected as the Arecibo radio telescope sweeps the sky. The program sifts through this to look for any signals that stand out from the background static. SETI is notified whenever someone detects a signal that appears to have been emitted from a single point, such as a planet. Such signals last about 12 seconds and have a "bell curve" shape. The characteristic shape is due to the telescope sweeping towards and then away from the source of the signal, with the peak being when the telescope points straight at the source.
Over 350 million such signals have been spotted in the radio data. But in the limited time available, the astronomers will be able to revisit a maximum of 150 interesting signals.
It is now possible that an ETI signal may well be detected first by an amateur enthusiast (cf comets and supernovae where the amateur contribution always has been significant, and is now growing due to affordable advance in CCD and computer technology).

[As an interesting corollary of this, in October ‘98 a flurry of interest was generated by a British amateur claiming detection of a signal from the star system EQ Pegasi. This was announced on the internet and subsequently reported by the BBC. Investigation has shown that this has all the hallmarks of a hoax (see the SETI institute’s report on their web site), but the false excitement may well be matched by the genuine article in the future!]