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Terraforming and SETI – The Search for Extraterrestrial Intelligence

Chapter prepared for ‘Where Are They? Implications of Our Failure to Detect Extraterrestrials’, by Hart and Zimmermann, 1984 (updated, 1992).


Earth is unique in the Solar System -- it is the only planet that seems to
support life. Its hospitable ecosphere stands in stark contrast to the empty,
lifeless landscapes of the Moon, Mars, Venus, Mercury, and other worlds probed
by our spacecraft. Recent arguments suggest that while planets may be common
in the Universe, habitable worlds may not be. Internally, a candidate planet's
proper composition, tectonic dynamics, and very narrow but extremely long-
period thermal stability may be rare. External biosphere-destroying natural
processes, from interstellar dust clouds to sterilizing radiation sources, may
periodically rid vast regions of a galaxy of planet-bound life forms.
Such a severe limitation on life-supporting worlds significantly impacts
discussions of the Search for Extraterrestrial Intelligence at both ends of the
question, the search for causes and the search for consequences. On the former
issue, it seriously reduces the stage on which the formation and evolution of life
may take its chances against the odds: few candidate planets means even fewer
ultimate successes. At the other end of the question, it suggests strategies for
searching for the successful technologies that do evolve, by identifying
potential technological activities they would choose to engage in, activities that
may have very long range of detectability. The significance to human searches
for ETI may be profound.
The issues of 'probability of intelligence arising' are dealt with in other
papers in this collection. My purpose is to address the question of final
consequences. What kind of technological activity would be attractive to a
civilization on a rare habitable planet? Our sample size is one, which makes us
'average'. But we have the imagination to hypothesize alternatives and
variations. What do they suggest?
The hypothesized rarity and brevity of Earth-like worlds may be subject to
technological redress. Even if Earth is unique and alone and threatened with
future external assault, it doesn't have to stay that way. Future terrestrial tool-
users (human or otherwise) may someday be able to increase the number of life-
supporting worlds in this solar system from one, as at present, to a dozen or
more. Instead of just being a freak accident of biology, Earth could serve as a
blueprint for the transformation of her sterile sister worlds into earthlike
biospheres. There's no need to passively hope and wait for this metamorphosis
to come about through billions of years of random, rare accidents. It can be made
to happen in just a few centuries of deliberate technological manipulation.
The term for this awesome concept is terraforming. The word was coined
50 years ago in a science-fiction story, but the concept of purposeful world
shaping goes back much further in human literature, to the creation myths of all
cultures. How far it may still be ahead of its time is unknown. But it is not an alien.
unthinkable idea.
Advocates of terraforming conjure up idyllic visions of reshaped planets
made fit for human settlements. They ask incredulous listeners to imagine red-
skied Mars watered and in bloom, to imagine choking Venus tamed and cooled.
to imagine even Earth's sterile, airless Moon transformed into a smaller replica of
And how could such planetary remodeling be accomplished? The
transformations, it turns out, do not really require magic but only extrapolation
from what we know today. Colossal energies would be needed, but in a few
centuries such forces should be available. Intimate knowledge of climatology
would be needed, but those lessons must be learned on earth in any case.
Manipulations of biology and ecology are still far beyond present scientific
capabilities, but they lie along the directions in which modern science and
technology are moving.
Each candidate planet would require a different combination of these
techniques, although many of the tools would be common from world to world.
The major obstacle is not technological but conceptual: Humanity does not yet
realize that it has the capability to transform whole planets, not only for worse (as
we are often warned by the doomsday prophets) but also for better.
A good first candidate is the planet Venus, once though to be a twin of the
earth but now known to be a closer analog of medieval visions of hell. The planet
gets too much sunlight, has too much carbon dioxide and sulfuric acid. and has a
day-night cycle far too long.
Imagine what would happen to a human being placed on the surface of
Venus. Immense atmospheric pressures would instantly crush the soft body
tissues, while ovenlike temperatures would convert body water to steam. Layers
of charring flesh would peel off explosively. An expanding cloud of soot would
surround a pile of crumbling bones as the acidic vapors of Venus turned a human
body to dust.
Terraformers call for a physical assault on such hostile conditions. Carbon
dioxide and other chemicals in the atmosphere of Venus would be transformed
biologically by clouds of algae, suitably tailored in genetics laboratories to thrive
under Venusian conditions. Artificial dust clouds or thousand-kilometer wide
parasols would shade the planet. in orbits that mimicked a near-24-hour day-
night cycle. The excess mass of oxygen in the atmosphere (about sixty bars
worth) would have to be physically ejected or -- better yet -- combined with
hydrogen imported from the icy asteroids beyond Jupiter, to form water oceans
and limestone.
A century or two after this transformation, human beings would walk in the
upland regions of Venus without backpack refrigerators and perhaps even find it
pleasant. Along the newly formed coasts of the Aphrodite and Lakhshmi
continents, the climate could resemble that of Samoa or Curaçao or the Côte
Mars offers different problems. A human body placed on Mars would exhale
all of its internal gases in a great rush out of body orifices. Consciousness
would fade through anoxia as the thin Martian air provided no breath. The cold of
the sand would freeze the fallen body within minutes, but it might take millions of
years for the mummified flesh to erode. In the end, one patch of red sand might
have a lighter coloration; beyond that, the visitor would leave no trace.
Mars has neither enough air nor enough sunlight, although its day is
nearly earthlike. To attract more sunlight, dark soot could be mined from the two
small moonlets in orbit around Mars, and spread on the surface of the planet. If
permafrost (giant dust-covered glaciers) exists, it might melt, flooding the surface
after a billion years of drought; in cases where enough such native water does
not exist, asteroidal water would have to be imported. Biological activities could
be instigated, perhaps in miles-deep oasis valleys gouged out of the landscape
by the ice melt or by the impact of incoming asteroids (which also would heat
these wide 'oasis craters'). Additional heating could be provided by giant space
mirrors, a thousand kilometers on a side, concentrating sunlight onto the planet.
As the Martian air thickens to breathable levels, and as temperatures rise
to above the freezing point of water, a new climate could be formed that would
approximate that of the Andes or the Caucasus or Kashmir. It such conditions on
the new planet seem unattractive, recall the persistent stories of longevity and
happiness among mountain people here on earth.
Earth's own Moon need not remain forever barren. Even as human mining
activities bring it a measure of life in the coming decades, it too could hold an
atmosphere, either baked from its own rocks or imported from Saturn and beyond
(a 200-kilometer ice cube would provide an adequate atmosphere that lunar
gravity could hold for thousands of years). Other rocky worlds such as Mercury
and various moons of the outer planets such as Ganymede, Titan, and Triton
could similarly be engineered into habitable home worlds.
There is a new candidate whose qualifications have only recently been
recognized: Io, innermost of the Galilean worlds circling Jupiter. Its sulfur
volcanoes blasted their way into human consciousness via the Voyager probes,
driving home the lesson that in space one can only dare expect the unexpected.
It is in keeping with this still-unfaded sense of wonder, elicited by the Voyager
vistas, that I want to nominate Io for terraforming - and at the top of the heap, as
Io has several advantages over more classical candidates. First, it has an
internal heat source generated by tidal stresses induced by Jupiter (most of the
surface is cold because in a vacuum the outflowing heat leaks away quickly).
Second, its 42 1/2-hour day is not grossly different from that of Earth. Third, it is
deep within the magnetic field of Jupiter. a factor which has biochemical
advantages lacking on all other solid planets beyond Earth.
But of course Io has some powerful drawbacks, at present. First is the
killing radiation belt which surrounds Jupiter. Second is the lack of water or, for
that matter, any atmosphere worth sneezing into. Third is the surface enrichment
of sulfur compounds spewed forth from underground lakes of molten sulfur. Each
of these problems by itself might seem to veto any consideration of terraforming
Io and appear to counterbalance the substantial advantages enumerated above.
Well, maybe not. Radiation belts are swept out by rings of rocky debris -
as we learned during Saturn flyby missions. The Jovian radiation in the
neighborhood of Io could thus be decontaminated by pulverizing a large fraction
of the small inner carbonaceous moon. Amalthea (or the even smaller moons
discovered inside Amalthea's orbit), forming an artificial ring extending out to and
enveloping Io.
Next, water would have to be imported, either from ice-rich, sibling-worlds
Ganymede and Callisto or by impacting some outer Jovian moons or nearby
asteroids onto Io (comets are too small and too unpredictable to be worth
chasing). Note that the sulfur, while plentiful on the surface due to differentiation,
should not be more abundant in proportion to the whole mass of the planet than it
is on Earth. The surface sulfur could be buried using dirt excavated by the impact
force of the 'ice-teroids' carrying the components of the future atmosphere and
ocean. Subsequently, biological tailoring could begin, lasting many decades --
then spacesuits on Io would become obsolete. Io could be made a habitable
world by the end of the next century.
This vision is at present unconstrained by harsh reality. Perhaps its thermal
state is too active to support a stable crust (then we can turn our attention to
cooler, wetter Europa). Perhaps the asteroidal engineering needed to 'short
circuit' the Jovian radiation belts is too ambitious or unreliable. Perhaps some
form of carbon-sulfur life exists in the hot springs or. even more bizarre, swims in
the liquid sulfur ocean beneath the crust.
Terraforming studies consider the conditions needed on habitable planets.
and the tools and techniques which are conceivable today. These topics fill
several chapters in my book, New Earths (Stackpole 1981), the first non-fiction
treatment of the concept of terraforming. Several subsequent issues of the
Journal of the British lnterplanetary Society have been devoted to evolving
concepts. Future lines of inquiry are evident: climatological goals can be
quantified; roadblocks can be identified and areas of current ignorance defined:
strategies can be suggested. The bottom line is that terraforming could well be
possible given enough time and enough money and enough intelligence.
Now turn this futuristic concept toward the problem of SETI. If naturally-
occurring Earth-like worlds are truly rare in the universe, and if star-faring
civilizations (both hypothetical current ETI's, along with our own also hypothetical
descendants) retain a desire to live on (or even just vacation on) planetary
surfaces, they may not be able to find sufficient hospitable planets. in that case
they may have to make their own, and everything so far indicates that such
planetary engineering is feasible.
Engineering planetary surfaces would by only the beginning for such an
advanced technology. Once freed of the boundaries of a single world, every
option would be open. In one direction, multitudes of habitable planets would be
assembled around convenient suns. The end evolution here is the Dyson
Sphere. a spherical structure totally encompassing a star. The entire interior
surface would be available for the biosphere. It is a concept both wildly
imaginative and quaintly limited, as I will explain.
One consequence of this kind of engineering would be the requirement to
maintain very long term narrow thermal and other radiation limits on these
planets or other structures. Olaf Stapledon in the 1930s imagined habitable
worlds being gradually shifted in their solar orbits to account for stellar evolution.
Alternately, the stars themselves would be engineered to promote stability and
inhibit dangerous radiation outbursts. At least by this point, such engineering
activities could become apparent across galactic distances. Whether these
manipulations would be recognizable as artificial is a serious question for
astrophysicists! And this is the key issue for SETI.
The 'signature' of ET terraforming activities and stellar engineering
activities is a worthy topic for speculation. From one direction, currently
conceivable activities for future terrestrial civilizations can be extrapolated until
the applied energies become detectable at galactic distances, and those signals
(an accidental by-product of activities with other intentions) predicted. From the
other direction, observations already made can be compared against
hypothesized artificial causes, such as the 'Little Green Men' suggestion for
pulsars, or the only-half-whimsical suggestion that Seyfert galaxies are alien
mega-Chernobyls. This last suggestion raises the serious observation that once
such energies are harnessed for artificial purposes. they may not always work:
recognizable ET signatures may consist of news that some civilization's greatest
engineering effort has failed spectacularly. Or even more sadly, the traces may
reflect energies released in an unimaginable technological conflict (what we
today would call a 'war') between striving forces whose technical cleverness far
outstripped their wisdom. Extrapolating from our limited sample size, that is not
an inconceivable outgrowth of technological activities.
Furthermore, these signals may only represent a brief phase in the
development of a technological civilization. Somewhere along these lines of
technological development, ET civilizations may dive back under the cloak of
long-range undetectability as they discover and harness even newer discoveries
of physics. True 'artificial gravity' (not circular momentum masquerading as
'weight') may remove the need for using thousands of kilometers of inert rock to
crate a local acceleration field and thereby hold relatively small masses of gas
and liquids. True mastery of nuclear fusion processes may remove the need for
furnaces to be a million kilometers across and too hot to approach within a
hundred million kilometers (a 'Dyson Sphere' thus assumes such a civilization
would have disproportionately vast abilities in one area but be unable to master
stellar fusion control).
For those ET civilizations still depending on biochemical processes,
habitable volumes could then be manufactured on any desired scale. from
kilometers to many millions of kilometers. They need not give off long-range
detectable energies of any kind. But by this stage, or soon thereafter (on a
galactic time scale), the question of detecting them at galactic distances would
become moot, because such evolved, advanced technologies would overcome
all former limitations in original location and speed, and would no longer even
need to be detectable across immense gulfs of space. They would be here. But
their detectability and/or recognizability would be entirely up to them and their
unknowable motives.
Having made full circle back to Earth, we may speculate on the possible
future need for deliberate human climate engineering to repair and enhance our
home planet's habitability, against threats both artificial and natural. But long
before this course of action was recognized, theorists had suggested in their own
metaphors that Earth had already been terraformed by an extraterrestrial culture.
This was the concept of 'directed panspermia', that life is not native to this planet
but was imported for some alien purpose. It is possible that it has already
happened here. It is possible that we ourselves will someday make it happen
These may be the most visible marks that intelligence makes on a
'wild' galaxy, and it is for traces of these activities that, perhaps, we should


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