Educator's Guide to Life Beyond Earth|
Courtesy of the Jet Propulsion Laboratory
Table of Contents
Searching for Signs of Intelligence
In 1992, the Jet Propulsion Laboratory
launched a survey of the sky using radio telescopes.
The High Resolution Microwave Survey (HRMS) was designed
to map the entire sky over the next several years. Part of the survey
was the search
for extraterrestrial intelligence, also known as SETI. This was
not a wild-eyed search for the type of "aliens" that routinely
turn up in supermarket tabloids. It was a careful examination of
space around us. In fact, HRMS was designed to just "listen;"
no signals were transmitted.
The HRMS was managed from the Ames Research Center in the San
Francisco Bay area. JPL was a collaborating center. The JPL part
of the project used radio telescopes of the Deep Space
Network in California and Australia. Ames headed a search of
selected targets with a huge 300-meter (1,000-foot) radio
telescope in Puerto Rico. The extremely sensitive receivers
began the search on Columbus Day, October 12, 1992.
However, Congress killed the program in October 1993
because of budgetary pressures. The SETI (Search
for Extraterrestrial Intelligence) Institute, a privately-funded,
non-profit organization that had been working on the HRMS,
took over part of the effort aimed at discovering
exterrestrial signals. The new effort is called Project Phoenix.
NASA made its sophisticated equipment and facilities
available to the SETI Institute's scientists and engineers.
We already know that the sky is filled with radio energy. But
Project Phoenix will also be listening for non-natural sources.
Scientists have determined that the radio portion of the
electromagnetic spectrum is one of the best places to search for
signs of extra-terrestrial life. Radio waves, especially at some
frequencies, appear much more powerful compared to the natural
background of the sky. Visible light signals would have to be
extremely strong at their source in order to be detected over
even short distances. After all, stars are huge balls of glowing
gas but none, except our own Sun, is even bright enough to cast a
Radio signals can travel through dust and gas clouds that would
block out or scatter visible light. But this does not mean that
our radio and television broadcasts would be detectable by an
alien civilization or that we can expect to eavesdrop on their
equivalent of soap operas or athletic shoe advertisements. Our
radio, TV and radar transmitters send energy out in all
directions. The signals get weaker as they get farther and
farther from the transmitter.
The energy falls off by the square of the distance. If one
receiver is twice the distance from a transmitter than another,
the energy is not 1/2 but only 1/4! At three times the distance,
it is 1/9, at four times it is 1/16 and so on.
Very quickly, the
signals get too weak to be casually detected.
But, an alien
intelligence that was interested in communicating would send out
a focused beacon, perhaps like a lighthouse. The signal would be
able to travel at the speed of light for many years. Of course,
in order for their beacon to be detected, someone would have to
Searching is exactly what Project Phoenix
will be doing. Using radio telescopes, the entire sky will be
scanned. Unexpected or unusual signals will automatically be
extracted from the data by computer. Scientists will then
examine that data. If something intriguing turns up, a more
detailed examination can be made.
Detecting a Signal
What will happen if signals suspected to be of extra-terrestrial
origin are detected? Will the scientists keep it quiet? The
project has given these questions careful consideration. The
technical information will be given to independent observers so
that they can confirm the findings. This will avoid
embarrassment and confusion over misinterpretation. Then, the
information will be released to the public.
Most likely, the finding will be that we have found something
like a lighthouse beacon. The distance to the source is likely
to be so great that conversations will be impossible. To
communicate with a civilization on a planet 50 light years from
Earth (right next door by astronomical standards) would take a
century round trip. The signal we receive would already be 50
years old. Do the senders live longer than we? Did they send out
a signal knowing that only their children and grandchildren might
get a reply? Can we even hope to ever understand each other?
Project Phoenix will only cover a
comparatively small portion of our galaxy. Our galaxy is only
one of hundreds of billions of galaxies. Galaxies contain tens
to hundreds of billions of stars. Project scientists might find
signs of intelligent life, they might find interesting new
natural objects, or they might find nothing at all. There might
be life elsewhere in the Universe, or we might be completely
alone. We will never know unless we take a look. It is a search
for a golden needle in a cosmic haystack.
There is no assurance that Project Phoenix
will find evidence of extraterrestrial intelligence, but the
search itself is certainly thought provoking. The SETI Institute
is developing educational materials for elementary students.
The Drake Equation
One important aspect of the search is that it encompasses a very
wide range of subjects and can be taught across the curriculum.
A broad view of the topic can be found in the cornerstone of
SETI, the "Drake Equation." Developed by astronomer Dr. Frank
Drake in 1961, it is a way of organizing information to try to
estimate the number of civilizations that might be emitting
detectable radio signals. None of the values are really known
now and estimates can vary by many orders of magnitude! Indeed,
each one of the terms also raises thought provoking questions
about nature and ourselves.
(Computer formatting prevents the use of subscripting. In the
following equation and definitions the letter(s) following the
first letter should actually be subscripts; R(subscript)star,
N = Rstar x fp x ne x fl x fi x fc x L
- N =
- the (estimated) Number of civilizations in our galaxy
currently capable of communicating with others. "N" is an
estimate since it is the product of estimates.
- Rstar =
- the Rate of star formation during the period when our
solar system was born. (How are stars born?
How long do they live? How do they die?)
- fp =
- the fraction of stars with planets. (Are planets routinely
formed with stars or is our system a fluke?)
- ne =
- the number of planets, per solar system, with an environment
suitable for life. (Why are conditions on Earth
suitable for life like ours? Why are conditions
on other planets in our solar
system so hostile?)
- fl =
- the fraction of suitable planets on which life actually
appears. (Are fertile conditions enough to allow life to get a
- fi =
- the fraction of life bearing planets on which intelligence
emerges. (Life has been present on Earth for billions of years, but
why is intelligence such a recent development?)
- fc =
- the fraction of intelligent societies that develop the
ability and desire to communicate with other worlds. (We have only
had radio communications technology for a few decades. Is the
desire to know about the universe a natural outgrowth of
- L =
- the Longevity of each technological society in the
communicative state. (Do societies develop the ability to destroy
themselves or their environment soon after they develop
The product "N" might be a very large number or a very small one.
All that we know for certain is that the value is
greater-than-or-equal-to 1; after all, we are here and the fact
that we can contemplate this is evidence of intelligence.
Without quite a bit more information, it would be totally
unrealistic to try to discuss each element of the equation in
detail. But each variable can generally be used to point out
important points about our Universe. Even defining terms like
"galaxy" or "intelligence" will broaden student's views.
For classroom activities, students can be encouraged to make
drawings of "aliens" and their worlds. They can write essays
about what the impact of a detection of intelligent life would
have on society or themselves, or on what message they would send
to aliens. Research in astronomy, biology, geology, sociology,
ecology, among a great many other sciences, can be given a SETI
Most science fiction stories deal with interactions with aliens.
Television and movies often do as well--for example: Star
Trek's four series, seven movies, and countless books and
short stories. Often the plots involve current social issues.
Even most of the cinematographic works featuring Arnold
Schwarzenegger deal with interactions with aliens, although the
sociological angles are often secondary.
Please remember that, although "N" may be greater than 1, the
distances between stars is so great that it might very well be
impossible to ever actually visit with aliens. After all, it
took Voyager 2 twelve years to reach Neptune. Neptune is four
hours away at the speed of light. The nearest star is over four
years away at that speed! We may have to be satisfied with radio
communications where decades pass between questions and
Few children are disinterested by the idea of extraterrestrial
intelligence. Many have had their views distorted by their
exposure to supermarket tabloids. It is appropriate to harness
their enthusiasm to the constructive use of science and the
humanities. For more information,
contact the SETI Institute at: 2035 Landings Drive,
Mountain View, CA 94043 Tel.: (415) 961-6633.