SETI


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SETI

(sĕt`ē) [Search for ExtraTerrestrial Intelligence], name given to a series of independent programs to detect radio signals from civilizations beyond the solar system. Modern SETI efforts can be dated from 1959 when Cornell physicists Giuseppi Cocconi and Philip Morrison pointed out the potential for using microwave radio signals to communicate with extraterrestrial civilizations. They suggested that a frequency of 1420 MHz be utilized as a communication channel since that corresponded to the signal emitted by neutral hydrogen, the most abundant element in the universe; that frequency, by international agreement, is now prohibited in all radio transmissions everywhere on and off the earth.

In 1960 the first such program, Project Ozma, led by American astronomer Frank Drake at the National Radio Astronomy Observatory in Green Bank, W.Va., focused on the nearby stars Epsilon Eridani and Tau Ceti. Since then other searches, most of limited duration and concentrating on stars similar to the sun, have been conducted without success. In 1992 the High Resolution Microwave Survey (HRMS) was initiated. Using radio telescopes around the world in a planned ten-year search, HRMS envisioned a two-pronged approach. One group was to focus on solar-type stars within 100 light-yearslight-year,
in astronomy, unit of length equal to the distance light travels in one sidereal year. It is 9.461 × 1012 km (about 6 million million mi). Alpha Centauri and Proxima Centauri, the stars nearest our solar system, are about 4.3 light-years distant.
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 of Earth; the other was to conduct an all-sky survey. HRMS was halted by a funding cutback in 1993, but privately raised funds were used by the SETI Institute from 1995 to 2004 to conduct a search of nearby solar-type stars. Project Phoenix, as it was called, monitored only microwave frequencies because there are few natural sources of emissions in that range and researchers hoped that extraterrestrials would recognize that range as a quiet region of the electromagnetic spectrum suited to sending a message. The Allen Telescope Array, which uses a large number of small radio antenna dishes began operations in 2007 with 42 dishes (with an ultimate total of 350 planned). Located in the Cascade Mts. at Hat Creek, Calif., this joint project of the SETI Institute and the Univ. of California, Berkeley, is a broad sky survey over a wide portion of the radio spectrum in a search for evidence of extraterrestrial life; other astronomical research also is conducted. Mothballed during much of 2011 due to funding shortfalls, the array is now also used by the U.S. air force to track objects in orbit.

In addition to the listening efforts of the radio astronomers, other forms of contact have been attempted. Various coded messages have been broadcast in the hope that an extraterrestrial civilization might also have a SETI program. Gambling on a chance encounter with an extraterrestrial civilization, the U.S. space probes Pioneer 10 and 11 each carry an engraved plaque with a message from the earth, and Voyager 1 and 2 each have a recorded message of words and music. All four of these space probes have moved beyond the orbits of the planets and will travel in interstellar space indefinitely.

Bibliography

See also E. Ashpole, The Search for Extraterrestrial Intelligence (1990); D. Swift, SETI Pioneers (1990); F. Drake and D. Sobel, Is Anyone Out There? (1992); P. Davies, The Eerie Silence (2010).

SETI

(set-ee) Abbrev. for search for extraterrestrial intelligence. Any of many searches in which neighboring stars, and sometimes more distant stars, have been studied primarily by means of radio telescopes for signals indicative of life (see exobiology). The SETI hypothesis is that the Universe holds many examples of intelligence of the human type – creatures with the power of abstract thought who can construct models of the external world and can use their skills to build things, including large radio telescopes and transmitters.

The pioneering program was Frank Drake's Ozma project of 1960. It was unsuccessful, as were subsequent projects using more sophisticated equipment and targeting more stars. Microwave frequencies (1–10 GHz, i.e. wavelengths of 3–30 cm) are thought to be the most favorable to study: natural sources of noise in our atmosphere and in the interstellar medium are at a minimum in this waveband and some common molecules have strong microwave emissions. These include neutral hydrogen at 1.42 GHz and the hydroxyl radical at 1.7 GHz. The longest full-time search was started in 1970 by Robert Dixon of Ohio State University and now covers the frequency range 1.4 to 1.7 GHz. Another long-term search began in 1983 under Paul Horowitz; assuming that artificial signals cover only a very narrow frequency band compared with natural radio emissions, highly sensitive receivers have been used to tune into particular frequencies, which are split into narrow bands (at present 0.05 Hz in width).

The latest and most ambitious SETI is NASA's 10-year Microwave Observing Program, which began in Oct. 1992. The targeted search, by the Ames Research Center, is examining at high sensitivity about 1000 nearby sunlike stars. The specially designed receiver is being used with radio telescopes at Arecibo (305 meter dish), Parkes (64 m), and Green Bank (43 m); the equipment analyzes the frequency range 1–3 GHz, splitting it into two billion channels each 1 Hz wide, while software searches for different patterns of artificial signals. The other part of the program, the sky survey, which is undertaken by a team at the Jet Propulsion Laboratory, is systematically scanning the entire sky at lower sensitivities. The two receivers for this part of the project will be used with a 34-m telescope at Goldstone and a similar NASA telescope in the southern hemisphere; from 1996, the final systems covered the frequencies 1–10 GHz, and analyzed 32 million channels.

SETI

[′sed·ē]

SETI

(Search for ExtraTerrestrial Intelligence) A huge grid computing project on the Internet that takes advantage of unused processing time in users' computers to analyze radio telescope data. The purpose of SETI@home, which is administered by the University of California at Berkeley, is to pick up communications from other planets. If narrow-bandwidth radio signals were to be detected, scientists maintain that these unnaturally occurring communications would be evidence of extraterrestrial sources.

Get Involved!
You can participate by downloading a screen saver that converts idle time into computations. Data are saved every couple of minutes and sent back to the SETI website at periodic intervals. Initiated in 1999, millions of enthusiastic users have since generated well over a billion results. For more information, visit www.setiathome.ssl.berkeley.edu. See grid computing.
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So Dominik is right: we do need to have an international discussion about whether we should make our existence known, should the intensified SETI research yield a positive result.
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Cabrol of the SETI Institute and NASA Ames Research Centre.
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Fifty years after it beganAuand 18 years since Congress voted to strip taxpayer money from the effortAuthe nationAAEs search for extraterrestrial intelligence is alive and growing.AoI think thereAAEs been a real sea change in how the public views life in the universe and the search for intelligent life,Ao said Jill Tarter, a founder of the nonprofit SETI Institute and the person on whom Carl SaganAAEs book AoContactAo, and the movie that followed, were loosely based.AoWeAAEre finding new extra-solar planets every week,Ao she said.
I'm an astronomer at the Search for Extraterrestrial Intelligence (SETI) Institute in California.