166 lines
8.3 KiB
Plaintext
166 lines
8.3 KiB
Plaintext
|
|
|
|
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.
|
|
|
|
|
|
|
|
|
|
----------------------------------------------------------------------
|
|
|
|
S E T I SEARCH SUMMARY
|
|
______________________________________________________________________
|
|
|
|
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
|
|
______________________________________________________________________
|
|
|
|
|
|
---
|
|
SETI, THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE, NASA/JPL
|
|
400-265, 9/85
|
|
|
|
|