Terraforming or Planetary Protection

Human space exploration, resource extraction or the construction of future settlements are activities destined to produce profound environmental changes on other celestial bodies. The most drastic alteration, however, is the transformation of a planet to make it more Earth-like, a process known as planetary engineering or “terraforming.”

According to the definition of planetary scientist Christopher McKay, planetary engineering aims to permanently transform an entire world with interventions that are " stable over long time scales without requiring continuous technological interventions... ". After the fundamental initial transformation, achieved thanks to a significant input of energy, materials and technologies, the terraformed celestial body should function as a natural environment of the Earth and maintain its balance indefinitely.

We have been talking about “terraforming” for over half a century. Already in the early 1960s, astrophysicist Carl Sagan hypothesized the possibility of “microbiological reengineering” of Venus by introducing blue-green algae into its atmosphere. The algae would have used photosynthesis to convert the planet's abundant carbon dioxide into oxygen, substantially reducing the greenhouse effect and lowering Venus's surface temperature. Sagan later turned his attention to “redesigning” Mars, considered the best candidate for successful terraforming.

If Venus is covered by a dense and toxic atmosphere, responsible for an uncontrolled greenhouse effect with intolerable temperatures and pressures on its surface, Mars has the opposite problem. Billions of years ago, its magnetic field disappeared and the solar wind blew away much of the atmosphere. With extremely low atmospheric pressure, surface water evaporated, leaving only ice deposits beneath the surface. To terraform Mars, planetary engineers would need to increase its surface temperature and atmospheric pressure, while protecting the planet from solar wind. Sagan suggested scattering a dark material, transported by the two satellites Phobos and Deimos which are among the darkest objects in the solar system, to absorb a greater amount of solar heat and increase surface temperature. In this way, the water vapor and carbon dioxide released into the atmosphere would contribute to generating a greenhouse effect which, in turn, would facilitate a further increase in temperature and the creation of a denser atmosphere.

Today, also thanks to the data obtained from the probes sent to the red planet, we can better define the multidisciplinary interventions that would be necessary to transform Mars into a habitable environment for humans:

· The first step would be warming the planet to allow for a more temperate climate. For this purpose, orbital mirrors could be used, capable of concentrating sunlight and significantly increasing the average temperature of the planet which is now around -60 °C.

· At the same time, the density of the atmosphere should be increased, which is just one hundredth of that of the Earth. This would allow the presence of liquid water on the surface and would contribute to warming the planet. To increase the atmospheric pressure of Mars, it is thought to concentrate the heating on the polar ice caps, which are mainly composed of dry ice (solid CO₂), the sublimation of which would release large quantities of greenhouse gases.

· Furthermore, it would be necessary to introduce oxygen into the atmosphere to make it suitable for humans, who could then breathe without the need for pressure suits. For this purpose, devices powered by solar energy have been tested, which imitate photosynthesis and are capable of converting CO₂ into oxygen and glucose. In addition, cyanobacteria, known for their ability to transform CO₂ into oxygen even in extreme environments, or genetically modified plants could be used to optimize the photosynthesis cycle in the changed environmental conditions of Mars.

· Water management will also be important to create the reserves necessary for human life and agriculture. Part of it may be produced by the thawing of permafrost, but it may also be necessary to capture frozen comets or asteroids to make them impact Mars and thus release water on its surface.

· Finally, the creation of artificial magnetic fields will be fundamental to create a sort of "magnetosphere" capable of deflecting charged particles coming from the solar wind and to protect human beings from cosmic radiation.

Each of these interventions will require advanced research and technologies as well as enormous quantities of materials and economic resources. Terraforming is an example of long-term planning, because it will take many decades of patient effort before a human can walk unprotected on the surface of Mars.

If the combination of these strategies could, at least theoretically, transform Mars into an environment more suitable for the life of future Earth colonists, it inevitably raises ethical questions. Such massive interventions, in fact, can damage or even wipe out potential life forms present on the planet. Any Martian microbes would probably not be able to survive in an environment more similar to Earth and therefore the process of "terraforming" could make species or entire ecosystems disappear before their existence has even been detected.

According to astrobiology experts, we may miss the opportunity to make the most important scientific discovery in human history: finding life forms that evolved outside our planet. Even if there is currently no life on Mars, changes to the Martian environment would introduce physical processes - such as precipitation and new chemical reactions related to flowing water - that could easily erase or contaminate any evidence that extraterrestrial life has ever existed on its surface .

In this sense, the ethical dilemma of “terraforming” far surpasses planetary protection concerns related to contamination created by the landing of a terrestrial vehicle or the construction of human settlements. As planetary engineering aims to modify Mars on a global scale, it could destroy any pre-existing ecosystem, even before it has been determined with certainty whether indigenous life forms exist or have ever existed.

On the other hand, if we discovered evidence of microbial life on the red planet, would that be enough to prevent terraforming and limit settlement on Mars? Carl Sagan, in his book “Cosmos”, supported precisely this position: « If there is life on Mars, I think we shouldn't do anything with Mars. Mars therefore belongs to the Martians, even if the Martians are only microbes. The existence of independent biology on a neighboring planet is a treasure beyond all valuation, and the preservation of that life must, in my opinion, supersede any other possible use ..."

Sagan's space ethic, according to which humans should avoid worlds where indigenous life forms exist, appears difficult to implement. Human history has amply demonstrated how our evolution has too often occurred at the cost of the extermination of entire species. Can we think that the extinction of some Martian microbe could hinder our expansion outside the Earth, especially if this became vital for the human species?

It may seem premature to discuss the risks of destroying the Martian ecosystem, which may not exist at all, due to the use of technologies we do not yet have, but I believe this is precisely the point of the matter. For centuries we have acted without thinking about the consequences and the damage caused is there for all to see and is jeopardizing our very future on Earth.

Perhaps it is appropriate to reflect on the mistakes made and start evaluating the risks of destroying entire ecosystems even before developing the technologies to terraform other worlds. An ethical reflection towards other forms of life, even extraterrestrial ones, is also a way to measure the level of civilization of a species that aspires to reach the stars.