THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE

 

 

                  THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE

                                  (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 civilization.

 

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.

 

 

 

 

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                       S E T I  SEARCH SUMMARY

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SEARCH PARTICULARS            SKY SURVEY              TARGET SEARCH

______________________________________________________________________

 

Area Coverage                All directions       1000 stars, regions

 

Signal search                Continuous Wave       Pulses, drifting CW

 

Frequency coverage           1200-10,000 MHz +    1200-3000 MHz + spot

                             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

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SETI, THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE, NASA/JPL

400-265, 9/85