| Of all the problems facing mankind, perhaps the most|
intriguing is: Can there be life on other worlds? Are we
alone in the universe, or is life likely to be widespread?
Let us admit at once that we do not yet have the slightest
evidence of the existence of life anywhere except on the
Earth. Moreover, we must confine ourselves to discussing
life of the kind we can understand. All our science tells us
that life must be based upon carbon; if this is wrong, then
the rest of our science is wrong too, which does not seem
very likely. Rather reluctantly, we must reject the weird
and wonderful beings so beloved of science-fiction writers,
and which are usually classed as BEMs or Bug-Eyed
Monsters. Life-forms on other worlds need not necessarily
look like us, but they will be made up of the same ingredients
– and after all, there is not much outward resemblance
between a man, a cat and an earwig.
A planet is very small compared with a normal star,
and has no light of its own; so far, no extra-solar planets
have been directly observed. Luckily, there are other ways
of detecting them. A massive planet orbiting a normal star
will make the parent star ‘wobble’ very slightly, and these
tiny wobbles can be detected. The first success came in
1995, when two Swiss astronomers, Michel Mayor and
Didier Queloz, tracked down a planet orbiting the star
51 Pegasi, 54 light-years away. The mass of the planet was
a little more than half that of Jupiter, so that it was clearly
a gas-giant; also it was very close to the star, and had a
period of only 4.2 days. Since then many other extra-solar
planets have been detected, and by 2003 the grand total
had exceeded 100.
Multi-planet systems also exist. Upsilon Andromedae,
44 light-years away, is twice as luminous as the Sun, and
rather hotter; three planets have been found, all gas-giants,
although the innermost, only about 9 million kilometres
(5 million miles) from the star, is less massive than Jupiter.
One particularly important case is that of Epsilon
Eridani, one of our nearest stellar neighbours (10.7 lightyears)
and not too unlike the Sun, though considerably
cooler and less massive. It had long been regarded as a
suitable candidate for a planetary centre, and a planet has
indeed been found, with a mass 0.9 that of Jupiter and a
separation of 494 million kilometres (307 million miles).
The period is 2502 days.
The ‘wobble’ technique can trace only giant planets
orbiting normal stars, but it seems inevitable that planets
of Earth-type mass must also exist. It is now clear that
planetary systems are very common in the Galaxy.
Other techniques can also be used; a large planet passing
in front of a star will cause a slight drop in the star’s
apparent brilliancy. Also, some stars are known to be asso-
ciated with clouds of cool, possibly planet-forming material.
In the case of the southern star Beta Pictoris, such a cloud
has been photographed directly.
Can any of these extra-solar planets support life? This
is a question which is not too easy to answer, because we
are unsure of the origin of life even on Earth. (Suggestions
that life did not originate here, but was brought to Earth by
way of a comet or a meteorite, seem to raise more problems
than they solve.) All we can really say is that if we
could locate a planet similar to the Earth, moving round a
star similar to the Sun, it would be reasonable to expect
life not unlike ours.
So far as communication is concerned, we must concede
that in our present state of technology interstellar
travel is impossible; even if we could travel at the speed of
light it would take a spacecraft years to reach even the
nearest star. When we consider ‘exotic’ forms of travel –
teleportation, thought-travel and the like – we are back in
the realms of science fiction. It may happen one day, but
at the moment we cannot even begin to speculate as to
how it might be done.
Therefore, the only hope is to use radio, and various
attempts have already been made. The first dates back to
1960, when the powerful telescope at Green Bank, in West
Virginia, was used to ‘listen out’ for signals rhythmical
enough to be interpreted as artificial. The wavelength
selected was 21.1 centimetres, because emissions at this
wavelength are emitted by the clouds of cold hydrogen
spread through the Galaxy and radio astronomers anywhere
would presumably be on watch. The two stars
singled out for special attention were Tau Ceti and Epsilon
Eridani, which are the nearest stars which are sufficiently
like the Sun to be regarded as possible centres of planetary
systems. The experiment – officially known as Project
Ozma, but more generally as Project Little Green Men –
produced nothing positive, but further surveys have been
made since, and the International Astronomical Union has
set up a special Commission to concentrate upon SETI, the
Search for Extra-Terrestrial Intelligence. At the General
Assembly in 1991 it even published a Declaration giving
instructions as to the procedure to be followed in the event
of an alien contact.
Of course, there is the time-delay factor. Send out a
message to, say, Epsilon Eridani in 2004 and it will reach its
destination in 2015; if some obliging operator on an Epsilon
Eridanian planet hears it and replies immediately, we would
expect an answer in 2026. This means a delay of 22 years,
which makes quick-fire repartee difficult. However, no
doubt mathematical codes could be devised, because mathematics
is universal, and we did not invent it; we merely discovered
it. The real significance would be in establishing
that ETI does exist. The effect upon our thinking – scientific,
religious, political – would indeed be profound.
It has been argued that we really are alone, and that
there are no other living things anywhere in the universe.
On the other hand it has also been argued that there may
be civilizations in all parts of stages of development.
It is also possible that there are planets upon which the
inhabitants have wiped themselves out in war – as we are
ourselves in danger of doing; we have the ability to turn
the whole of the Earth into a barren, radioactive waste, and
our technology has far outstripped our actual intelligence.
The search goes on; our radio telescopes are used to
listen out, and even to send messages in the hope that
someone, somewhere, will hear them. The chances of success
may be slight, and it is a measure of our changing
attitudes that experiments such as SETI are considered
worth carrying out at all.
PHILIP'S A T L A S O F T H E U N I V E R S E