Project Cyclops, A Design... - Department of Earth and Planetary ...

hadbeendiscovered, it couldbegina series of
transmissions
conveying information about the sending civilization,
and about how to contact it.
Bracewell also suggests we be alert for such probes in
our own solar system. Villard (ref. 4) has suggested that
long delayed echoes, which are in fact occasionally
heard, conceivably could originate from such a probe.
Until the source of such echoes can be definitely
ascribed to some mechanism such as slow propagation in
the ionosphere near the plasma cutoff frequency, this
will continue to be an intriguing, albeit an unlikely,
possibility. The phenomenon deserves further study.
An interstellar monitor probe could be much smaller
than a spaceship and could take longer in flight. But
although there would be no crew to face the psychological
barriers or physiological problems of generations
spent in space, there are still good reasons to require a
short transit time. If the probe were to require a
thousand years (or even only a century) to reach its
destination, serious doubt would exist that it would not
be obsolete before arrival. Thus even probes should be
capable of velocities on the order of that of light. With
this in mind probe weights in excess of a ton would
almost certainly be needed.
To "bug" all the likely stars within 1000 light-years
would require about 10 6 probes. If we launched one a
day this would take about 3,000 years and an overall
expenditure on the order of well over $10 trillion.
Interstellar probes are appealing as long as someone else
sends them, but not when we face the task ourselves.
The simple fact is that it will be enormously
expensive, even with any technological advance we can
realistically forecast, to send sizable masses of matter
over interstellar distances in large numbers.
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We cannot rule out the possibility that we might
stumble onto some evidence of extraterrestrial intelligence
while engaged in traditional archeological or
astronomical research, but we feel that the probability
of this happening is extremely small. Not everyone shares
this view. Dyson, for example, has suggested (refs. 5, 6)
that very advanced civilizations may have such powerful
technologies that they can engage in engineering efforts
on a planetary or stellar scale. He visualizes civilizations
rebuilding their planetary systems to create additional
habitable planets, planetoids, or huge orbiting space
stations and thus provide more lebensraum. (See Appendix
B.) Noting that this would increase the surface area
at which radiation was occurring at temperatures on the
order of 300 ° K, he suggests that such civilizations might
be detectable as a result of the excess radiation in the
lO/a range, and concludes that a rational approach to the
search for extraterrestrial intelligence is indistinguishable
from an expanded program in infrared astronomy. While
we admire Dyson's imagination we cannot agree with
this conclusion, much as we might like to see more
infrared astronomy for its own sake.
In the first place we would argue that Dyson's
premises are far more speculative than our conclusions.
It is one thing to admit the possibility of Dyson's
civilizations; it is quite another thing to consider them
probable enough to base our entire search strategy on
their existence. We submit that, to a civilization capable
of the feats he describes, the construction of an
extremely powerful beacon and interstellar search system
would be child's play and that Dyson's civilizations
would have pursued this course long before engaging in
the remodeling of their planetary systems. (Further
discussion of the motivations for, problems associated
with, and detectability of Dyson's civilizations is given in
Appendix B.)
However, let us assume that a super-civilization does
rebuild its planetary system, not into the artificial
structures Dyson describes, but into replicas of the home
planet. These at least would offer living conditions to
which the species was already adapted. Would such
systems be detectable? The Sun radiates about 500,000
times as much energy in the 10/a region as the Earth and
about 100,000 times as much as all the planets combined.
If all the heavy elements in the Sun's planets were
reassembled at about 1 AU from the Sun, about nine
more Earthlike planets could be constructed and the
present planetary 10# radiation would be doubled to
become only 50,000 times less than that of the Sun.
This is still a long way from being a detectable increase.
Let us further assume that on each of these new
earths the civilization releases one thousand times as
much energy as we do. Earth traps about 1017 watts of
sunlight, which it must then re-radiate. Geothermal and
tidal heat is negligible by comparison. At present our
world-wide rate of release of energy from coal, oil,
natural gas and nuclear sources totals about 6X 10 _2
watts, or about one sixteen thousandth part of the
sunlight we receive. Even a thousandfold increase in this
rate on each of the one old and nine new earths would
raise their total infrared radiation only 6% leaving it still
negligible compared with the Sun.
Finally, even if we were to detect a star with more
than twice as much 10# radiation as we would expect
from the visible light output, would we not conclude
merely that it was surrounded by a lot of dust, instead
of a super civilization? The excess IR radiation lacks the
hallmark of intelligence which combines a high degree of
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