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     ÄÄÄÄÄÄÄÄÄÄÄ *                                         * ÄÄÄÄÄÄÄÄÄÄÄ
                 *    L I T E R A R Y   F R E E W A R E    *
                 *                                         *
                 *           F O U N D A T I O N           *
     ÄÄÄÄÄÄÄÄÄÄÄ *                                         * ÄÄÄÄÄÄÄÄÄÄÄ
                 * * * * * * * * * * * * * * * * * * * * * *
                  -=ð P R O U D L Y  í  P R E S E N T S ð=-
                                     (S E T I)
 Our Milky Way Galaxy is only one of 10 billion galaxies in the
 presently observable universe. Our Sun is just one of some 300
 billion stars in our galaxy alone. Astronomers have confirmed that
 the Sun and the galaxy, which make our existence possible, are not
 unusual or basically different from other galaxies and stars.
 A few generations ago, astronomers believed that planetary systems
 were extremely rare--that our solar system and our Earth with its
 life-supporting environment might well be unique. Chemists and
 biologists knew little if anything about the processes that led to
 the origin of life. In the last fifteen years, however, a number
 of important discoveries have strongly suggested that there is a
 fundamental relationship between the origin and evolution of life
 and the origin and evolution of the universe.
 Advances in astronomy and physics have given renewed support to the
 concept that planets are not rare exceptions, but are a natural
 part of the star formation process and may number in the hundreds
 of millions in our galaxy alone. [In December 1984, the National
 Science Foundation announced that a team of Arizona astronomers had
 detected a possible solar system around Beta Pictoris, a star 53
 light years from Earth.] Recent biological experiments applying
 natural energy sources to molecules have produced some of the
 organic building blocks that make up the chemistry of life. Radio
 astronomers have discovered that many organic molecules exist even
 in the depths of interstellar space. Elements identified in these
 molecules include hydrogen, nitrogen, oxygen, carbon, silicon, and
 phosphorus. Earth has been without life only a small fraction of
 its age, which leads many scientists to look upon the formation of
 life on other suitable planets as very likely. Once begun, and
 given billions of years of relative stability, life may achieve
 intelligence and, in some cases, may evolve into a technological
 One direct way of testing whether intelligent life exists beyond
 our solar system is to search for an artificially generated radio
 signal coming from interstellar space. As an example, ultrahigh
 frequency and microwave radio signals emanating from Earth are
 expanding into space at the speed of light. This radio, radar, and
 television "leakage" of ours currently fills a sphere nearly 100
 light-years in diameter.  The same phenomenon would serve to
 announce the presence of other intelligent life. Moreover, advanced
 civilizations might be operating radio beacons, possibly to attract
 the attention of emerging societies and bring them into contact
 with a community of long-established intelligent societies existing
 throughout the galaxy.
 Either type of signal (leakage or beacon) would be easiest to
 detect at frequencies where the background radio noise is minimal.
 One of the quietest regions of the electromagnetic spectrum is the
 "microwave window" that lies in the frequency band between 1000 and
 10,000 megahertz (MHz). It is reasonable to assume that others
 wishing to establish interstellar contact by radio might choose
 this band.
 The search for extraterrestrial intelligence (SETI) is not new,
 having first been proposed by U.S. scientists in 1959. Since that
 time, numerous scientific and technical studies have been made on
 an international scale, and more than 30 radio searches have been
 attempted, covering only a minute area of search space. What is new
 today is the available technology. Radio telescopes on Earth are
 sufficiently sensitive to detect signals no stronger than some
 leaving Earth at distances of a thousand light-years or more. The
 305 meter (1000-ft) diameter radio telescope at Arecibo, Puerto
 Rico, could detect transmissions from nearby stars that are less
 powerful but similar to our own television and radars. Advances in
 computers and data processing techniques now make it possible to
 search automatically through millions of incoming radio signals
 each second and, if it is present, to identify a signal transmitted
 by an intelligent society.
 The NASA SETI Program is nearing the end of a 5-year research and
 development phase, using existing radio telescopes and advanced
 electronic techniques to develop prototype SETI instrumentation.
 The program is being jointly carried out by the Jet Propulsion
 Laboratory (JPL) at Pasadena, California, and the NASA Ames
 Research Center at Moffet Field, California. Leading radio
 scientists from the national laboratories and academic community
 have also joined together in the SETI Science Working Group to
 assist the JPL-Ames team in developing the instrumentation and the
 search strategy.
 The proposed plan involves two complementary search modes that are
 designed to cover a range of possibilities. One mode is an all-sky
 survey that will search the entire celestial sphere over a wide
 frequency range (1200 to 10,000 MHz plus spot bands up to 25,000
 MHz) to cover the possibility that there may be a few civilizations
 transmitting strong signals, possibly as interstellar beacons.
 Longer observing times may be allocated to directions that include
 a large number of stars, especially the galactic plane. The radio
 telescopes employed will be the 34-meter (112-ft) diameter antennas
 that are part of NASA's Deep Space Network. The survey will be
 conducted by moving the telescope across the sky at a constant
 rate. It will cover at least 10,000 times more frequency space than
 all previous survey attempts, will be about 300 times more
 sensitive, and will take about 5 years to complete.
 The second mode is a high-sensitivity targeted search that will
 look for weak signals originating near solar-type stars within 80
 light-years distance from Earth. The objective is to examine the
 possibility that nearby civilizations may have radio transmitters
 no more powerful than our own. Some stellar clusters and nearby
 galaxies will also be observed. The frequency range covered will
 be 1200 to 3000 MHz plus spot bands between 3000 and 10,000 MHz.
 To achieve very high sensitivity, the targeted search will use some
 of the largest radio telescopes available, including the 305-meter
 (1000-ft) diameter antenna at Arecibo, Puerto Rico, and the Deep
 Space Network's 64-meter (210-ft) diameter antennas. The number of
 targets covered will be much larger than previous searches and the
 range of frequencies covered will be thousands of times greater.
 The targeted search is expected to take about 3 years to complete.
 Current astrophysical knowledge and the available technology make
 the SETI observing program both timely and feasible. Timeliness
 also relates to the rapidly-increasing sources of radio frequency
 interference (RFI) in the microwave band. Portions of the microwave
 spectrum that directly concern SETI ar subject to allocation to
 numerous users worldwide, emphasizing the need to proceed with SETI
 while it remains economically possible with our current technology.
 If the use of the microwave spectrum continues to increase at its
 present rate, the greatest exploration opportunity in the history
 of mankind may be placed economically and technologically beyond
 our reach for the foreseeable future.
                        S E T I  SEARCH SUMMARY
 Area Coverage                All directions       1000 stars,
 Signal search                Continuous Wave       Pulses, drifting
 Frequency coverage           1200-10,000 MHz +    1200-3000 MHz +
                              spot bands           bands
 Frequency resolution         1000, 32 Hz          1000, 32, 1 Hz
 Receiver bandwidth           Wide (~250 MHz)      Narrow (~10 MHz)
 Observing time per
 direction at each            0.3 - 3 sec          100-1000 sec
 frequency setting
 Channels analyzed            ~10 million          ~10 million
 per second
 Antenna diameter            34 meters             305 and 64 meters
 Search duration             ~5 years              ~3 years
 400-265, 9/85

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