Terraforming Mars: will we ever make it?
Many of the people interested in the human exploration of space are ready to accept the
idea that sooner or later we can go to Mars to build a permanent base, and even large
settlements; but to the same people, the prospect of transforming the planet's environment to adapt
it to the needs of us on earth seems instead pure fantasy or, at best, a technological challenge to
be projected into a very distant future. But are things really like that?
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A point of view, that of these people, completely shared and worthy of respect...
But although it is currently a cold, dry and probably lifeless planet,
according to many other experts, Mars has all the elements necessary to sustain life: water,
carbon, oxygen and nitrogen. Not to mention that several of its physical characteristics,
such as gravity, rotational speed and axial tilt, are virtually identical
to those of the Earth and make it the ideal candidate for a future terraforming attempt.
The concept of "global modification of a hostile planetary environment to make it habitable" is
due to the literary inventiveness of William Olaf Stapledon (1886-1950),
an English writer known above all for his science fiction novels. In fact,
it is mentioned for the first time in his 1930 novel, Last and First Men, a monumental fresco
(which has recently also become a movie!) which tells of humanity's space epic over two
billion years... And in which it is said, among other things, that to purify Neptune's poisoned
atmosphere and make it breathable, humans release genetically modified plants on its surface,
capable of absorbing harmful molecules and injecting those of oxygen in their place.
Ten years later, in a short story entitled Collision Ship and published in 1942, the American
writer Jack Williamson (1908-2006) baptized that same concept with the term "terraforming",
that is the set of operations necessary to transform a planet into another Earth.
For several years terraforming was considered a typical narrative device of science fiction,
on a par with hyperspace travel. But scientists soon started talking about it too. The first to
do so was the famous American astronomer Carl Sagan (1934-1996), who in 1961 proposed a way
to make the planet Venus more welcoming to hypothetical terrestrial colonizers.
Venus, as we well know, is a real hell. On the surface, the temperature is about
460°C and the atmospheric pressure is 92 times that of the earth; which is like being here on
Earth under a thousand meters of water... Any organism deposited on the surface of Venus is
then immediately "roasted" and crushed (and the Soviet Venera probes know something about it).
The high temperature is due to a large amount of greenhouse gases present in the Venusian
atmosphere (CO2 and water vapor). Sagan's idea was therefore to seed the atmosphere of Venus
with algae of the genus Nostocacae, which thanks to their photosynthetic
activity would have absorbed CO2 and produced carbohydrates, releasing oxygen as a bonus.
Although attractive, this scenario would not have had much chance of leading to a
radical transformation of the climate of Venus as Sagan wrote the article when the prohibitive
value of atmospheric pressure was not yet known, which he estimated at only 4 bars.
The 1970s were the years in which the concept of terraforming began to circulate extensively
in scientific circles. During that time, several articles were written and the first
conferences were held. In the context of more conservative scientific groups,
the term was still considered non-serious and speculative. But now it was no longer
just science fiction writers and "eccentric" scientists (like Sagan) who wrote on the subject.
The idea of ​​being able to change the face of another planet had now made its way,
and immediately it was applied to Mars, which to many seemed much more promising than Venus.
Even Mars is nowadays a decidedly hostile planet to life: it is very cold (-53°C on average,
with excursions between -140°C and +20°C), its atmospheric pressure is very low (6%
than the terrestrial one), on the surface there is never water in a liquid state except in very
particular conditions and the atmosphere is unbreathable for a man (96% CO2). Also,
the surface is constantly bombarded by cosmic and ultraviolet rays,
radiations that make life almost impossible to establish.
So why is it believed that Mars is the most suitable planet for early terraforming?
The main reason is that, according to what we know today, the red planet is the only one on which
liquid water once flowed. It is also likely that it even possessed a large ocean in the northern
hemisphere, a dense atmosphere composed mainly of carbon dioxide and significant quantities
of water in lakes and rivers. These conditions are assumed to have existed in the first billion years
of the solar system. Subsequently, for still partially unknown causes, there was a gradual
absorption of the atmosphere into the soil and a partial dispersion into space. The atmosphere
became so thin that a self-reinforcing cooling phase began for the planet.
To bring Mars back to life, according to some, it will only take him back to his youth!
Scientists are in fact in agreement on the fact that the first level of terraforming can be said
to be reached when: 1) the atmospheric mass is increased to significantly reduce the amount of
radiation reaching the ground; 2) liquid water will be available on the surface;
3) the ground temperature will be increased by about 60 degrees. In practice, when the
conditions of Mars will resemble those of the Earth in the pre-Cambrian period:
a complete and autonomous biosphere, capable of supporting the life of anaerobic microorganisms.
To arrive at this scenario, the first step will be
to increase the concentration of CO2 in the atmosphere, to exploit the greenhouse
effect. This will cause a gradual rise in temperature and set off a chain reaction.
But where to find the necessary CO2? The Martian atmosphere contains quite a lot of it,
but it is still too small a quantity to do its role well. It will therefore be
necessary to find a way to use that frozen in the polar caps and the Martian regolith.
It has in fact been calculated that the caps would contain enough CO2 to bring the pressure
from the current 6 mbar up to 100 mbar, while the reserves contained in the regolith, which
exist above all at high latitudes, would allow a final pressure of 400-500 mbar to be reached!
But are we really sure? These calculations are based on the most optimistic forecasts,
but in reality, we do not know how much carbon dioxide reserves really are. And it is in this
statement that one of the most serious weaknesses of the terraforming of Mars lies. If too much of
that primal atmosphere has been lost in space, recreating it will be very difficult. Conversely,
if most of it has been absorbed by the regolith or frozen in the polar ice caps,
recreation will be much easier. If the predictions are wrong and
Mars doesn't have enough CO2 to inject into the atmosphere, the task will become
particularly complicated. And this is not just a hypothesis... In 2004, for example,
the European Mars Express orbiter discovered that, contrary to what was previously thought,
the southern polar ice cap is mostly made up of frozen water. And that carbon dioxide would only
be found in a surface layer ten meters thick. If this were the case, its total sublimation
would raise the pressure by only 0.36 mbar, or about 5% of the current atmospheric pressure.
It is also possible, however, that most of the CO2 is found elsewhere,
and that it is chemically bound in carbonates as on Earth. On our planet, CO2 trapped in marine
carbonates returns to the atmosphere thanks to volcanic activity. On Mars, it will be necessary
to vaporize these carbonates using particularly destructive means, which will have important
consequences on the planetary environment, such as nuclear explosions and asteroid impacts,
On the other hand, reassuring data on the consistency of CO2 deposits in the caps come
from the fact that. In a Martian year, atmospheric pressure can increase by 20% when the polar ice
cap melts under the sun's rays in spring, and CO2 changes from a solid to a gaseous state
(sublimation). Likewise, atmospheric pressure drops by 20% as gaseous atmospheric CO2 condenses
to return to a solid-state in the shells during the winter. Which is certainly not a small thing,
since all this happens most naturally. If man can initiate a similar process,
then the system should self-sustain itself according to this mechanism:
by starting the melting of the south polar cap, a small amount of CO2 will be released
which will contribute to increase atmospheric pressure and produce a greenhouse effect. The
heat released will in turn act on the polar cap, which will release more gases, causing a further
increase in the greenhouse effect, and so on... According to the calculations, in fact, an
increase in the temperature of the south polar cap of only 4°C would be enough to start the process.
All good in theory, but how to do it in practice? The choice of the best method to trigger the
greenhouse effect just described is a problem on which there is a great divergence of opinions
among scientists, and therefore many different projects are being studied. It should also be
stressed that none of the technologies set out below are fully available today, but some believe
it is reasonable to think that some will be by the end of the century at the latest. We are therefore
not leaving the scientific method for the world of fantasy, but speculating on the near future of
a young science, still in formation. We should not be surprised, then,
by the audacity of projects such as that of the English astronomer Paul Birch, who to start the
Martian greenhouse effect proposed to build a mirror with a radius of 125 km, capable of
reflecting sunlight towards the South Martian pole to raise its temperature by at least 4°C,
enough to make the carbon dioxide trapped there in the form of dry ice gaseous again.
The mirror, if positioned on the zenith of the south pole at 214,000 km from the planet,
not in orbit, but the so-called "pole-sitter" position (perpendicular to the polar axis of
the planet, kept in place by the balance between the force of gravity and the thrust of sunlight),
could heat the spherical cap of the planet from 70 degrees of latitude.
The huge mirror should be built in 4 microns thick Mylar fabric, like a solar sail,
and coated with aluminum for a total of 200,000 tons. The size and weight of such an object make
its construction on Earth completely unthinkable, so to make it you will have to wait until you
have mining and manufacturing facilities in space, perhaps on the Moon. And given
how the preparations are in full swing for a new “Moon Race”, full of new protagonists
(Chinese, Japanese, Indian, European, private companies), we may not have to wait too long.
However, carbon dioxide is not the only greenhouse gas, nor the most efficient. There is, for
example, the large family of chlorofluorocarbons (CFCs), outlawed in the 1980s because they were
recognized as responsible for the "ozone hole" that hit the atmosphere above Antarctica.
CFCs, as greenhouse gases, are much more efficient than carbon dioxide, and,
thanks to them, the planetary greenhouse effect could be triggered in just 20 years; even if at
costs that are currently impossible, because it would require the construction of factories for
the production of CFCs directly on Martian soil. The industrial effort would be considerable,
and would probably require the support of a work team of several hundred people. And it is
therefore unlikely that such an operation could be carried out before the middle of the 22nd century.
End of Part One In the second part we
will finish by listing the methods proposed to launch the greenhouse effect on Mars and
we will try to give an opinion on the real possibility of making the red planet habitable.