Worlds of David Darling > Children's
Encyclopedia of Science > Could You Ever Meet an Alien? > 3. E.T. Phone
COULD YOU EVER MEET AN ALIEN?
a book in the Could You Ever? series by David Darling
3. E.T. Phone Home!
It will be many years before we can send a spacecraft to a nearby star to
search for life around it. The closest star to the Sun, a red dwarf called
Proxima Centaur, is about 25 trillion miles away. Even our fastest robot
probes, at present, would take around 100,000 years to cover that enormous
| In the future, spacecraft may be able to
travel to other stars in reasonably short times. Beam-propelled laser
sails such as the one shown here are one form such spacecraft may
Scientists know of ways to make spacecraft go much faster. But it is unlikely
that any high-speed starship will be launched for at least another century.
The next best method is to try to make contact with intelligent aliens by
radio waves. Here on Earth, we regularly make se of telephones to call people
rather tan visit them in person. It would make sense for any alien race
that knew how to send and receive radio messages to do the same. Perhaps
inhabited planets in our region of space are exchanging such messages at
this very moment. If so, then all we need to do is set up the right equipment
and tune in!
Listening to alien conversations, though, even assuming any are taking place,
is not that simple. First, just as an ordinary radio has to be tuned to
pick up a particular station, so astronomers have to choose the precise
wavelength at which they are going to listen for an alien signal. The wavelength
is the distance between the top of one wave at the next. Radio waves may
be anywhere from less than a tenth of an inch to hundreds of yards long.
The second problem is deciding where to point the receiver. There are an
enormous number of stars to choose from – billions and billions in
our area of space alone. Unless a receiver is trained exactly on the place
from which a radio message is coming, nothing will be heard.
In 1960, American astronomer Frank Drake began the first serious attempt
to pick up radio signals from intelligent beings around another star. The
project was named Ozma, after the queen of the land of Oz in Frank Baum's
famous series of stories.
|The radio dish used in Project Ozma
Drake knew there were billions of wavelengths, as well as billions of targets,
from which to choose. But he was helped by a suggestion that had been made
by two scientists, Giuseppe Cocconi and Philip Morrison, a year earlier.
Cocconi and Morrison pointed out that one wavelength, about eight inches,
was very useful for studying the Universe. It is the one at which atoms
of cold hydrogen – the most common substance in space – give
off radio waves. According to these scientists, this wavelength would be
known by all intelligent beings everywhere. As a result, it might be used
as a standard for sending and receiving signals.
Acting upon this idea, Drake built a receiver tuned to the special hydrogen
wavelength. Then he fitted the receiver to the 85-foot radio telescope –
a large, bowl-shaped instrument for collecting radio waves from space –
at the National Radio Astronomy Observatory in Green Bank, West Virginia.
As his first target, he chose Tau Ceti, a nearby star that is similar to
For eight hours, Drake heard nothing but crackles. Then, a signal came in
at precisely eight pulses a second! Could it be a race of Tau Cetians trying
to communicate? After checking his equipment thoroughly, Drake pointed the
telescope at another star. The signal stopped. Then he directed the instrument
back toward Tau Ceti. But the signals were gone, never to be heard again.
Later, it turned out that what Drake had probably picked up were radio signals
from a passing plane.
|The Warm Glow of a Super Race
One of the problems our civilization is likely to face is a shortage
of energy. One way to solve this, according to astronomer Freeman
Dyson, would be to build a thin, round shell of material all the way
around the Sun. Thousands of years from now, human beings may be able
to take apart a whole planet, such as Jupiter, in order to build such
a "Dyson sphere." The inside of the shell would capture almost all
the energy given off by the Sun, making it available for useful purposes.
From the outside the Dyson sphere would give off a strong infrared
glow, since it would be much warmer than the surrounding space. Other
intelligent beings, more advanced than us, may already have built
such enormous structures around their own stars. If so, suggested
Dyson, we ought to be able to detect their infrared glows from Earth.
|A Dyson sphere is an artificial hollow
ball built around a star by an advanced, intelligent race. This
imaginary Dyson sphere around the Sun has been made by taking
apart the planet Jupiter.
A year after he began Project Ozma, Frank Drake helped organize the first
large meeting of scientists to discuss the search for extraterrestrial intelligence,
or SETI. Extraterrestrial means "outside the Earth."
|The Andromeda Galaxy is a spiral galaxy similar
to our own. The Drake equation predicts how many intelligent races
there may be in our galaxy.
While making plans for the meeting, Drake wrote down a formula for determining
the chances of finding advanced extraterrestrial life. The so-called Drake
equation has become the most popular way of calculating the chances that
intelligent life exists in space.
Our Sun is one of about 200 billion stars making up a huge collection known
as the Milky Way Galaxy. The Drake equation predicts how many races of intelligent
beings, capable of communicating with each other, the Galaxy may contain.
It states that this number depends on the following items:
The Drake equation identifies the key requirements for intelligent beings
in space. To begin with, it requires the right star, the right planet, and
the right kind of life. Put these estimates into the equation, multiply
them together, and there is the answer – the number of communicating
civilizations in the Galaxy.
- the rate at which stars are being made in the Galaxy;
- the fraction of stars with planets;
- the fraction of planets capable of supporting life;
- the fraction of planets where life actually arises;
- the fraction of life that evolves into intelligent creatures
- the fraction of intelligent creatures with the desire and ability
to communicate; and
- the average lifetime of a race of such creatures
Yet, some scientists have suggested that Jupiter may have life – or,
at least, the beginnings of life. The mixture of gases in Jupiter's atmosphere,
which includes hydrogen, methane, ammonia, and water vapor, is quite similar
to that on our own planet billions of years ago. What is more, Jupiter's
atmosphere is almost certainly warmer at great depths. Far below the cloud-tops,
there may be a layer in which conditions are not greatly different from
those that existed long ago on Earth. It is here, say some researchers,
hat the chemicals needed for life may have been, and may still be, formed.
The multiplication is easy. Making the estimates is the hard part. And the
answer is only as correct as the estimates that are used.
For example, how many stars in the Galaxy are capable of supporting life
as we know it? Very old stars are probably not suitable, since they formed
at a time when there was very little carbon in the Universe. Any planets
of old star would not contain much carbon, either, so the chemicals of life
that we think are necessary could not build up. Stars that circle around
one another are probably out of the question, too. Any planets they had
would follow unsteady paths, making conditions on them swing wildly from
one extreme to another. In this way, we can rule out perhaps three-fourths
of all the stars in the Galaxy.
We can also rule out certain types of planets. If they circle too close
to their parent star they will probably be too hot to support life. On the
other hand, if they are too far away, their surfaces will be too cold. According
to some scientists, there is only a narrow zone around any given star in
which a planet can move if it is to support life. In the case of the Sun,
the Earth falls in the middle of this zone. All of the other planets of
the Solar System probably move outside it.
Today, no one can give an exact answer to the question of life on other
worlds. Different scientists put different estimates into the Drake equation.
The answers that come out, as a result, range all the way from hundreds
of millions of planets with intelligent life to just one – the Earth!