SETI

The Search for Extraterrestrial Intelligence. The first practical proposals in SETI were made in the 19th and early 20th centuries, but were aimed only at interplanetary communication (see communication, with the Moon and planets). The roots of SETI in its modern form, as a search for artificial signals over interstellar and even intergalactic distances, can be traced back to the 1930s with the discovery by Karl Jansky of radio waves coming from a source outside the Solar System. This led, in time, to the birth of radio astronomy and to the construction, in the late 1950s, of the first large radio telescopes such as those at Jodrell Bank and Green Bank. Only with such powerful instruments was it feasible to start looking for Earth-type signals from nearby stars.

The dawn of SETI

As a serious scientific enterprise, SETI began in 1959 with two independent events. The first was the publication of a paper in which Cornell researchers Philip Morrison and Guiseppe Cocconi discussed the suitability of radio waves as a communication medium, man's newly-acquired ability to eavesdrop on interstellar radio conversations, and the optimum frequency at which to conduct a search (see Morrison and Cocconi Conjecture). They argued that:

If signals are present, the means of detecting them is now at hand. Few will deny the profound importance, practical and philosophical, which the detection of interstellar communications will have. We therefore feel that a discriminating search for signals deserves a considerable effort. The probability of success is difficult to estimate; but if we never search, the chance of success is zero.

Meanwhile, at the National Radio Astronomy Observatory, Green Bank, Frank Drake had independently arrived at the same conclusion. Indeed, Drake had already begun to assemble the equipment he would use in Project Ozma, the first observational SETI program, carried out in 1960. Despite Ozma's failure to detect any extraterrestrial transmissions from its two target stars, it served to stimulate widespread public interest and lively (often critical) scientific debate. In 1961, an informal conference, sponsored by the Space Science Board, was held at Green Bank (see Green Bank conference). A dozen scientists and engineers deeply interested in the possibility of extraterrestrial life were invited to attend, including Drake himself, Morrison, Cocconi, Carl Sagan, Su-Shu Huang, Melvin Calvin, John Lilly, Bernard Oliver, Dana Atchley, and J. P. T. Pearman. At the conference, the now famous Drake Equation was discussed for the first time.

SETI strategies

The dawn of the SETI era stimulated scientists to consider the pros and cons of searching at all, the best strategy involving radio wave searches, and alternative approaches to finding evidence of extraterrestrial intelligence.¹ Into the last category came the suggestions of Dyson spheres and Bracewell probes. The feasibility of interstellar travel was also considered around this time by Robert Bussard, Freeman Dyson, Sebastian von Hoerner, John Pierce, Edward Purcell, and Carl Sagan.

In the Soviet Union, SETI was seen as a natural outcome of communist philosophy and, partly for this reason, became quickly established as a respectable field of research. Interest there was initially sparked by the writings of Iosef Shklovskii and tended to focus on the possibility of civilizations far in advance of our own. In 1963, a radio wave search was carried out for Kardashev civilizations, though at a different frequency to that employed by Project Ozma.

Within the radio search paradigm, which by the mid-1960s was well-established as the standard approach to SETI, much debate focused on methodology. An artificial signal, unlike one of natural origin, would be expected to have a narrow bandwidth so that it could only be detected by an antenna tuned to one particular frequency. The question was which frequency offered the best chance of success. Morrison and Cocconi had argued for 1,420 MHz, corresponding to the ubiquitous 21-centimeter line of neutral hydrogen, but the subsequent discovery of other common natural radio frequencies (see waterhole) complicated the decision. Moreover, the merits of targeted searches had to be weighed against those of all-sky surveys. In the decades following Project Ozma, many different approaches were tried.

In 1970, NASA,s involvement with SETI began through some preliminary work carried out by John Billingham. This led, in 1973, to an ambitious proposal by Billingham and Bernard Oliver, known as Project Cyclops, to detect extraterrestrial civilizations by eavesdropping on their stray electromagnetic signals. Although the proposal failed, it served to stimulate interest in a NASA SETI program of more modest scale. This eventually led to the High Resolution Microwave Survey and, when this had to be abandoned because of budget cuts, its privately-funded successor, Project Phoenix.

In 1973, what was to become the longest-running SETI program to date, began at the Ohio State University Radio Observatory. Its most dramatic moment came in 1977 with the detection of the mysterious Wow! signal. Meanwhile, Drake and Sagan employed the giant Arecibo radio telescope to search for emissions from advanced civilizations in other galaxies. The mid 1970s also saw the very foundations of SETI challenged by a revival of interest in the Fermi Paradox.

SETI today

Today, interest in SETI has never been greater. A number of programs are active, including the SETI Institute's Project Phoenix, Harvard's BETA, Berkeley's SERENDIP, and the SETI League's Project Argus, this last one unique in that it relies upon data gathered worldwide by a growing army of amateur observers. The public's interest in SETI has been heightened by the suggestion of possible life on Mars and the giant moons of Jupiter, as well as by fictional portrayals, such as Sagan's Contact.² Finally, there is a sense in which SETI, in addition to being a scientific quest, answers a modern spiritual need (see SETI, religious dimensions of).

See also SETA (Search for Extraterrestrial Artifacts) and SETV (Search for Extraterrestrial Visitation) and the list of SETI observing programs after the references below.^{2,
3, 4}

References

Bracewell, R. N. "Communications from Superior Galactic Communities," Nature, 186, 670-671 (1960). Reprinted in A.G. Cameron (ed.), Interstellar Communication, W. A. Benjamin, Inc., New York, pp. 243-248 (1963).
Introductory paragraph: Since Morrison and Cocconi published the suggestion that there might be advanced societies elsewhere in the Galaxy, superior to ourselves in technological development, who are beaming transmissions at us on a frequency of 1,420 MHz/s., Drake has described equipment under construction to look for such transmissions. The confidence necessary to commence actual observations is based on an opinion that planets are a common by-product of the formation of starts. One argument among others is that stars of spectral type later than F5 have low angular momenta, just as the Sun has; and in the case of the Sun we know that it is because the momentum (98 per cent of it) resides in planets. Of the thousands of millions of planets in the Galaxy likely to be situated similarly to the Earth in relation to their star, it is hard to dismiss the possibility that some have more advanced civilizations than ours. In view of the acceleration with which technology develops, advanced societies could be incredibly more advanced.
Sagan, Carl. Contact. New York: Simon & Schuster (1985).
Bova, Ben, and Preiss, Byron. First Contact: The Search for Extraterrestrial Intelligence. New York: NAL Books (1990).
Cameron, A. G. W. Interstellar Communication. New York: W. A. Benjamin (1963).

Related categories

   • SETI, ALL ENTRIES
   • EXTRATERRESTRIAL AND NON-HUMAN INTELLIGENCE
   • ASTROBIOLOGY

SETI OBSERVING PROGRAMS: 1960–1999
date	investigator(s)	location	antenna diameter (m)	search freq (Hz)	resolution (Hz)	targets	comments
1960	Drake	Green Bank	26	1420 M	100	ε Eridani, τ Ceti	Project Ozma
1963-64	Kardashev, Sholomitskii	Crimea Deep Space Station	16 × 8 ant.	923 M	10 M	2 quasars	CTA 102 - initial report of type III civilization
1966	Kellerman	Parkes	64	350-5,000 M	full bandwidth	1 galaxy (1934-63)
1968-69	Troitskii, Rakhlin, Gershtejin, Starodubstev	Zimenkie	5	926-8, 1421-3 M	13	11 stars and M31
1968-82	Troitskii	Gorky	dipole	1, 1.875, 3.75, 10 G		all-sky
1969-83	Troitskii, Bondar, Starodubstev	Gorky, Crimea, Murmansk, Primorskij	dipoles	600, 927, 1863 M		all-sky	search for pulsed signals
1970-72	Slysh, Pashchenko, Rudnitskii, Lekht	Nancay	40 × 240 antennas	1665, 1667 M	4 k	5 OH masers	search for unnatural emission characteristics
1970-72	Slysh	Nancay	40 × 240 antennas	1665, 1667 M	4 k	10 nearest stars
1971, 1972	Verschuur	Green Bank	91, 43	1420-1, 1410-30 M	490, 6.9 k	9 stars	Project Ozpa
1972	Kardashev, Popov, Soglasnov, et al	Crimea, RT-22	22	8570 M		galactic center	search for statistical anomalies
1972-74	Kardashev, Gindilis, Popov, Soglasnov, Spangenburg, et al	Caucasus, Pamir, Kamchatka, Mars 7	38, 60	371, 408, 458, 535 M	5 M	omnidirectional	"eavesdropping" search for pulses
1972-76	Zuckerman, Palmer	Green Bank	91	1413-25, 1420-1 M	6.4 × 10⁴, 4 k	674 stars	Project Ozma II
1972-6	Bridle, Feldman	Algonquin	46	22,235 M	30 k	70 stars	first search at the water wavelength
1973-74	Shvartsman, et al	Special Astrophys. Observatory, MANIA	0.6	optical		21 peculiar objects	optical search for short pulses and laser lines
1973-1998	Dixon, Ehman, Raub, Kraus	Ohio State	53	1420 M	10 k	all-sky	Wow! signal in 1977
1974	Wishnia	Copernicus	1	UV		nearby stars	search for UV lasers lines
1975	Drake, Sagan	Arecibo	305	1420, 1667, 2380 M	1 k	4 galaxies	search for type II civilizations
1975-79	Israel, de Ruiter	WRST	1500	1415 M	4×10⁶	50 star fields
1976	Wielebinski, Seiradakis	Max Planck Institute	100	1420 M	20 M	various nearby stars	search for pulsed signals with periods of 0.3-1.5 s
1976	Black, Cuzzi, Clark, Tarter	Green Bank	43	8522-3 M	5	4 stars
1977	Black, Cuzzi, Clark, Tarter	Green Bank	91	1665, 1667 M	5	200 stars
1977	Drake, Stull	Arecibo	305	1664-8 M	0.5	6 stars
1978	Shvartsman, et al	Special Astrophys. Observatory, MANIA	6	optical			optical search of 30 radio objects for pulses from Kardashev II or III civiliz.
1978	Horowitz	Arecibo	305	1420 M	0.015	185 stars
1978	Cohen, Malkan, Dickey	Arecibo, HRO, Parkes	305, 36, 64	1665-7, 22235, 1612M	9.5 k, 65 k, 4.5 k	25 globular clusters	passive search for type II and III civilizations
1978	Knowles, Sullivan	Arecibo	305	130-500 M	1	2 stars
1978	Makovetskij, Gindilis, et al	Zelenchukskaya, RATAN-600	7.4×450			Barnard's Star
1978-80	Harris	Pioneer Venus, Venera 11 and 12		20 keV - 1 MeV		54 gamma-ray bursters	search for 3 linear events as sign of i/s spacecraft
1979	Cole, Ekers	Parkes	64	5000 M	10 M, 1 M	nearby FGK stars
1979	Freitas, Valdes	Leuschner Observatory	0.76	optical		Lagrangian points	Bracewell probes
1979-81	Tarter, Clark, Cuquet, Lesyna	Arecibo	305	1420, 1666 M	5, 600	200 stars
1979-85	Bowyer et al	Hat Creek	26	917-937, 1410-30, 1602-5 M, etc	2×500	all-sky	SERENDIP piggyback
1980	Witteborn	NASA-Univ. of Arizona, Mt Lemon	1.5	infrared		20 stars	infrared excess from Dyson spheres
1980-81	Suchkin, Tokarev, et al	Nirfi, Gorkii, Gaish, Moscow		9.3 M	1.5 k	Lagrangian points	Bracewell probes
1981	Lord, O'Dea	Univ. of Mass.	14	115 G	20 k, 125 k	N. galactic rot. axis
1981	Israel, Tarter	WRST	3000 max. baseline	1420 M	4 M, 10 M	85 star fields	parasitic search
1981-82	Biraud, Tarter	Nancay	40×240	1420 M, 1665-7 M	49	343 stars
1981	Shostak, Tarter	WRST	3000 max. baseline	1420 M	1.2 k	galactic center	interferometer search for pulsed signals
1981	Talent	Kitt Peak	2.1	optical		3 stars	search for enhanced stellar lines of rare earth elements as evidence of ET nuclear waste disposal
1981-2	Valdes, Freitas	Kitt Peak	0.61	optical		Langrangian points	Project SETA. Search for Bracewell probes
1982	Horowitz, Teague,Linscott, Chen, Backus	Arecibo	305	2841 M / 1420 M	0.03	250 stars / 150 stars	Suitcase SETI
1982	Vallee, Simard-Normandin	Algonquin	46	10522 M	185 M	galactic center meridian	search for strongly polarized signals
1983-85	Horowitz	Oak Ridge	26	1420 M, 1667 M	0.03	sky survey	Project Sentinel
1983	Damashek	Green Bank	92	390 M	2×10⁶	sky survey	search for single pulses and telemetry
1983	Valdes, Freitas	Hat Creek	26	1516 M	4.9 k / 76 k	80 stars / 12 stars	search for radioactive tritium from ET fusion technology
1983	Gulkis	DSS 43	64	8 G, 2380 M	40 k	southern sky survey
1983-88	Gray	Small SETI Observatory	4	1419-1421 M	1-40	sky survey	amateur meridian transit search
1983-4	Cullers	AMSETI	2	1420, <1000 M			amateur SETI based on satellite TV dishes
1983-8	Stephens	Hay River, NWT	two 18×18	1415-25 M	30 k	northern sky survey	amateur SETI observatory using two 64-ft square dishes
1984	Slysh	satellite radiometer		37 G	400 M	all-sky	Dyson spheres > 1 solar lumunosity within 100 pc
1985-95	Horowitz	Oak Ridge	26	1420, 1665, 1667, 2841 M	0.05	sky survey	META
1986-88	Bowyer, Wertheimer, Lampton	Green Bank	92	400-3,500 M	1	various sky areas	SERENDIP II
1986	Mirabel	Green Bank	43	4,830 M	76	galactic center, 33 stars
1986	Betz	Mount Wilson	1.65	infrared	3.5 M	100 Sun-like stars	search for IR beacons at carbon dioxide laser freq.
1986-	Colomb, Martin, Lemarchand	Argentina	30	1415, 1425, 1667 M	2.5 k	78 Sun-like stars
1987	Tarter, Kardashev, Slysh	VLA	26 × 9 ant.	1,612 M	6.1 k	G357.3-1.3	obs. of IR source near galactic center to check if Dyson sphere
1987	Gray	Oak Ridge	26	1,420 M	0.05	sky positions of Wow! signal	used META system
1988	Bania, Rood	Green Bank	43	8,665 M	305	24 Vega-like stars with IR excess	search for narrow-band signal at freq. of spin-flip of 3He+
1990	Colomb et al.	Argentina	30	1,420 M	0.05	all-sky	META II (southern hemis.)
1990	Blair et al.	Parkes	64	4,462 M	100	100 Sun-like stars	search at pi times 21-cm hydrogen line frequency
1990	Gray	Oak Ridge	26	1,420 M	0.05	M31, M33
1990-	Kingsley	Bexley, Ohio	0.25	optical		nearby stars	COSETI
1992	NASA Ames	Arecibo	305	1.3-2.4 G	1, 7, 28	78 Sun-like stars	HRMS targeted search
1992	JPL	Goldstone	26, 34	1.7 G, 8.3-8.7 G	30	all-sky	HRMS sky survey
1992-96	Bowyer, Wertheimer, Donnelly	Arecibo	305	423-435 M	0.6	all-sky	SERENDIP III
1992-98	Childers	Ohio State	53	1400-1700 M	100 k	all-sky	LOBES (LOw Buget ETI Search)
1993	Steffes, Deboer	NRAO/Tucson	12	203 G	32	40 stars and 3 locations near galactic center	search near positronium line
1995-	SETI Institute	Parkes-Mopra / Arecibo / Jodrell Bank	64 / 305 / 76	1.2-3 G	1	206 stars / 192 stars / 600 stars	Project Phoenix
1995	Gray	VLA	26	1,420 M	381, 6.1 k	"Wow!" signal region
1995	Beskin	Special Astrophysical Observatory	6	optical		several objects
1995	Mauersberger, Wilson, Rood, Bania, Hein, Linhart	IRAM	30	203 G	9.7 k	17 stars and positions	search at spin-flip frequency of positronium
1995-99	Horowitz, et al	Oak Ridge	26	1.4-1.7 G	0.5	northern all-sky	BETA; covered full waterhole (damaged by wind storm)
1996	Blair, Zadnik	Perth, Australia	0.64	optical		nearby stars
1997-	Wertheimer, et al.	Arecibo	305	1.32-1.52 G	0.6	all-sky	SERENDIP IV
1998-99	Gray, Ellingsen	Hobart	26	1.42 G	5	"Wow!" signal region	Search for signals with periods up to 14 hours
1998-	SETI League	amateur dishes (up to 5000)	3-5	1.42 G	10	all directions in real time	Project Argus
1998-	Stootman, et al.	Parkes	64	0.6	1,418-1,420 M	southern random all-sky	Southern SERENDIP; uses 13 beams on sky from focal plane array
1999-	Wertheimer	Leuschner	0.76	optical		nearby stars	search for pulsed signals
1999-	Marcy	Lick and Keck	4 and 10	optical		nearby stars	search for narrowband continuous wave signals in data archive of extrasolar planet search
1999-	Horowitz	Harvard Smithsonian	1.55	optical		nearby stars	search for nanoseccond pulsed signals
1999-	Montebugnoli	Medicina	32	1,415-1,425 M; 4,255-4,256 M	0.6	northern sky survey	SETI Italia; SERENDIP-type ransom sky survey at 21 cm and 7 cm
1999-	Wertheimer, Anderson	Arecibo	305	1.419-1.421 G	0.1	all sky	SETI@home (2.5 MHz of SERENDIP IV data analyzed by screen-savers on home PCs

Based on data compiled by Jill Tarter of the SETI Institute
Thanks to Robert Gray for additional information

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