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-years 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.
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).