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