Skip to main content Skip to Search Box

Definition: SETI from The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide

In astronomy, any of various attempts to search the skies for extraterrestrial signals using powerful radio telescopes or optical telescopes. Although serious SETI projects date from 1960, the name is specifically associated with a programme originally launched by NASA in 1992. NASA cancelled its project in 1993, but other privately funded SETI programmes continue.


Search for Extraterrestrial Life and SETI

SETI Institute

SETI League: Searching for Extraterrestrial Intelligence

Summary Article: Search for Extraterrestrial Intelligence
From Encyclopedia of Science and Technology Communication

The search for extraterrestrial intelligence (SETI) is a scientific endeavor that draws widespread and constant public attention. Media coverage of SETI has been plentiful since scientists first began to talk about it, and SETI scientists pay close attention to what journalists say about their work.

In the 19th century, astronomers first learned to record the spectra of celestial objects and found that they were made of the same stuff as things on Earth, including the elements of which life is made. Charles Darwin's theory of evolution gave further weight to the idea of life as originating as a result of natural processes. In the mid-20th century, radio astronomy was invented. Ever since, SETI scientists have been searching for signals of extraterrestrial technological origin.

The standard SETI technique is to use ground-based radio telescopes coupled with specially developed multichannel signal processors to listen for and identify signals originating from extraterrestrial technology. The two standard modes of searching for radio signals are targeting stars identified as good candidates for having planets and surveying sections of the sky for prominent signals. Other SETI methods include looking for optical (involving visible light) or infrared evidence of the presence of technology on a planet.

The scientific search for evidence of extraterrestrial (ET) intelligent life got its start with the publication of a paper in the British journal Nature on September 19, 1959, describing a concept for “searching for interstellar communications.” This paper, authored by physicists Giuseppe Cocconi and Philip Morrison (then affiliated with Cornell University), offered a scientific and technical rationale for searching for evidence of extraterrestrial intelligent life by using radio telescopes to listen for signals generated by ET technology. At that time, the scientific community knew enough about the origin, evolution, and nature of galaxies, stars, and planets and enough about radio astronomy techniques to make Cocconi and Morrison's proposal seem plausible, and a community of SETI scientists began to organize.

In 1960, astronomer Frank Drake conducted the first radio-telescope search for signals of extraterrestrial intelligent origin at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia. Drake's Project Ozma observed two nearby sunlike stars, Tau Ceti and Epsilon Eridani, listening for signals in a narrow band of the radio spectrum. In 1961, in collaboration with the Space Science Board of the National Research Council, Drake organized the first scientific conference on SETI, held at the NRAO. One product of this conference was the so-called Drake equation, named for its creator Frank Drake.

The Drake equation—N = N∗ fp ne fl fi fc fL—is not actually an equation. It is a heuristic tool, a technique for guesstimating how many planets in the Milky Way galaxy might host intelligent life. This technique rests on a number of assumptions, so its product, the estimated number of communicating civilizations in our galaxy, is by no means a precise quantity, with possible answers ranging from zero to millions or more.

N∗ is the number of stars in our galaxy (estimates range from 100 billion to 400 billion, including tens of billions of sunlike stars), fp is the proportion of those stars that might have planets, ne is the proportion of those planets that might be habitable, fl is the proportion of those habitable planets where life might have evolved, fi is the proportion of those planets with life where intelligent life actually has evolved, fc is the proportion of intelligent life forms on those planets that are willing and able to communicate by radio signals, and fL is the fraction of the life of those planets with intelligent radio-communicating life during which the communicating civilizations exist (or existed). Creating values for each of these variables is more a speculative than a mathematical exercise.

In addition to the United States, a few other countries, including Argentina, Australia, India, and Russia/Soviet Union, have engaged in SETI research. In 1961, the first international SETI symposium was held in the Soviet Union, and in 1964, astronomer Nikolai Kardashev conducted the first Soviet SETI search. The U.S. National Aeronautics and Space Administration (NASA) pursued some SETI studies in the 1970s, and in the 1980s it established a 10-year SETI research and development program culminating in an operational SETI project. NASA's High-Resolution Microwave Survey started operations in October 1992 at the Arecibo Observatory in Puerto Rico and at NASA's Deep Space Network station in southern California. In 1993, Congress canceled the project, and NASA has not had a SETI program since.

SETI research in the United States has been privately funded since the cancellation of NASA's program. The Planetary Society, a space exploration advocacy group, has raised private funding for radio and optical SETI projects conducted in the United States and Argentina. The SETI Institute in Mountain View, California, has a Center for SETI Research that is supported by private donations. The center's current SETI project is the Allen Telescope Array (named after its primary donor, Microsoft cofounder Paul Allen) in California. In 2005, NASA awarded a grant to a SETI researcher for a project called “detection of complex, electronic markers of technology.” In 2008, NASA amended its solicitation for space science research proposals to include “detection and characterization of other planetary systems including those that may harbor intelligent life” within the scope of its Origins of Solar Systems research program.

While proponents of UFOlogy—the study of unidentified flying objects—may link SETI with UFOs and alien visitations, there is no relation or collaboration between the two fields. SETI is generally accepted as a legitimate subject of research, recognized by the U.S. National Academy of Sciences, the international Committee on Space Research, and the International Astronomical Union, and conducted by properly credentialed scientists. Nonetheless, a minority of scientists asserts that it is not worthwhile, for reasons scientific or otherwise.

SETI critics have tended to pick at the “ET” in SETI. Cocconi and Morrison cited “interstellar” rather than “extraterrestrial” communications in the title of their seminal paper. SETI scientists tend to avoid the use of certain terms such as “alien.” In 1992, congressional staff persuaded NASA officials to rename their SETI Microwave Observing Project the High Resolution Microwave Survey. Many SETI scientists prefer to describe their target as “extraterrestrial technology” rather than “extraterrestrial intelligence.”

SETI faces other challenges. Extraterrestrial intelligent life (ETI) and the evidence of its technology may not be recognizable to human life. Recognizable or not, it may only exist so far away from Earth that scientists may never be able to detect any signs of it. If scientists do find a signal, they must verify that it is coming from an extraterrestrial technological source, and this procedure is not simple. In addition, there will always be some who will argue that verification of a signal does not equal proof that ETI exists.

The greatest challenge to SETI is the size of the space to be searched. SETI technology—radio and optical telescopes, signal detection equipment, and signal processing systems—has greatly advanced since SETI got its start. Nonetheless, current technology can only search a small fraction of our own Milky Way galaxy. The universe is populated with billions of galaxies (estimates range from 125 billion to 500 billion). While scientists have greatly expanded our knowledge and understanding of the universe over 50 years of study, the universe as a whole remains largely unexplored.

See also

Alien Abduction, Astrobiology, Astronomy, Public Communication of, National Aeronautics and Space Administration, U.S.

Further Readings
  • Bova, B., & Preiss, B. (Eds.). (1990). First contact: The search for extraterrestrial intelligence. New York: NAL Books.
  • Shklovskii, I. S., & Sagan, C. (1966). Intelligent life in the universe (P. Fern, Trans.). San Francisco: Holden Day.
  • Swift, D. W. (1990). SETI pioneers: Scientists talk about their search for extraterrestrial intelligence. Tucson: University of Arizona Press.
  • Billings, Linda
    Copyright © 2010 by SAGE Publications, Inc.

    Related Articles

    Full text Article Search for Extraterrestrial Intelligence
    Encyclopedia of Science and Technology Communication

    The search for extraterrestrial intelligence (SETI) is a scientific endeavor that draws widespread and constant public attention. Media...

    Full text Article SETI
    Astronomy Encyclopedia

    Acronym for Search for Extraterrestrial Intelligence, the umbrella term for all endeavours, especially those using radio telescopes, to find...

    Full text Article BETA
    Dictionary of Astronomy, Peter Collin Publishing

    The Billion-Channel Extraterrestrial Assay, a US project using a radio telescope in Massachusetts to search the sky for signals from...

    See more from Credo