The matter we are made of was literally created either during the birth of the universe itself or by the stars, during or at the end of their lives in the case of the most massive. Human beings are therefore children of the stars. In addition, we now know that it mostly contains planetary systems. Its extraordinary diversity allows us to question the presence of life outside Earth and consider the possibility of expanding beyond the confines of our ancestral home. However, colonizing other stars also involves numerous unknowns: Is it really feasible and, if so, appropriate? What cultural implications would it have? How would it affect our species?
Potential ecosystems of the Solar System
The Sun has a cohort of eight planets and dozens of dwarf planets and trans-Neptunian objects. It also contains a huge amount of comets and asteroids. The latter are of great interest for their mineralogy and in fact, the first steps have already been taken to begin commercial exploitation. Apart from Ceres, a dwarf planet a little less than 1000 km in diameter, which is located between the orbits of Mars and Jupiter that is being explored by the American probe Dawn, the other dwarf planets are too far from the Sun and too cold. Mercury and Venus are unsuitable. due to the opposite factor: high temperatures and, in the case of Venus, very high atmospheric pressure with an extraordinarily hostile chemical composition. The evidence for liquid water, a chemical compound that is still assumed to be essential for life to be present, on the current surface of Mars, an Earth analog in several respects, is controversial according to some studies. Uranus and Neptune, gaseous giants dominated by lightweight chemical compounds, are also a huge distance from our star and thus have low temperatures. What potentially suitable environments for life are left within the Solar System?
Jupiter and Saturn, although gaseous and dominated by the two lighter chemical elements, hydrogen and helium, have extremely varied satellite cohorts with very different characteristics and some of which show great astrobiological potential. Thus, Europa and Enceladus have ice sheaths and possibly immense oceans beneath their surfaces. The European mission Jupiter Icy Moon Explorer (JUICE), which is scheduled to be launched in 2022, and the American one Europa Clipper plan to continue exploring three of Jupiter’s most massive comrades, focusing on Europa, although they will not reach there until after 2030. There are several proposals for space missions to Saturn and its satellite Enceladus, but none of them have gone beyond conceptual designs. Therefore, we will have to wait more than a decade to get additional evidence on the internal structure of Europa and its potential to support life. In any case, as far as we know, it seems to be that the only celestial body in our planetary system that harbors life or is suitable for its development is Earth.
The plethora of planets outside the solar system
In the last two decades, since 1995, a number of different factors have been identified thousands of planetary systems in the vicinity of the Sun. Given that in the Milky Way, our galaxy, there are more than 200 billion stars and that it is believed that most of them could host planets, the possibilities have multiplied exponentially since the enunciation of the renowned Drake Equation. Among other reasons, this increase is due to the extraordinary planetary diversity, some of which are truly exotic.
As examples: the existence of planets orbiting around three stars, others that have atmospheres of metallic compounds and even planets that have formed from the material provided by the destruction of their central star and that revolve around a neutron star. Plus, Red dwarf stars, the most common stars in the universe, have shown great complexity in their planetary systems. Trappist-1 has become a prime target, as has GJ1132 b, whose planet orbits around it in just 1.6 days compared to more than 365 days of the Earth’s year and yet its gaseous cover has been detected, or LHS 1140 b, a planet composed essentially of ferric compounds and situated in the habitability zone of its star. The nearest, Proxima Centauri, is also home to a planet in an adjacent star that could have insolation compatible with the presence of liquid water, although the star is very active. Ross 128 b could possibly be even more interesting. This is extremely inactive and would therefore lack that intense bombardment of particles and highly energetic radiation which could be a real obstacle to the presence of life in the planetary system of Proxima.
In addition, a significant number of Earth-like, high-density, rocky planets have also been discovered. In fact, some of them are in orbits that allow enough energy to arrive so that the water, if it exists, is in a liquid state, in the so-called Habitability Zone. In any case, the presence of liquid water, even if it suggests the possibility of harboring life, is not a sufficient (and perhaps not even necessary) condition. Additional features are required, such as: Star stability (the so-called space weather), plate tectonics (allowing for the presence of orography and the presence of orography and the water and carbon cycle), and isolation from other stars (the nearest star is farther away, so that there are no dynamic interactions that change the orbits of the planets).
The possible human expansion beyond the borders of the Solar System
Exploration beyond the limits of the Solar System is already a reality. The American probes Voyager 1 and 2, launched more than 40 years ago, are entering interstellar space (the status can be checked at this link). However, they will not cross with other stars. The Starshot proposal, by breakthrough initiatives, is aimed at sending thousands of nanocrafts to start exploring the closest stellar systems, which would be the first step in a colonization process.
A possible justification can be found in the following statement by the renowned physicist and commentator Stephen Hawking:
“Spreading out into space will completely change the future of humanity… We are running out of space and the only places to go to are other worlds… Spreading out may be the only thing that saves us from ourselves. I am convinced that humans need to leave Earth… We have no other choice.“
However, spreading out within the Solar System or even interstellar would not be a solution for overpopulation due to the billions of human beings inhabiting our planet or the overexploitation of resources, given that, if technically possible, the amount of resources needed to move even a small fraction of the population would be enormous. Thus, the impact of such a process would be entirely excessive and the negative consequences are likely to far exceed any possible advantages.
Other alternatives to direct star colonization
Emerging, highly disruptive technologies will, to a large extent, enable this possible colonization. Detailed knowledge of our own nature at a genetic level and the ability to alter it to adapt to new environments represents a change in the rules of the game. There is also the ability to incorporate mechanical elements to our biological part, the possibility of becoming cyborgs, which would allow us to adapt to much more hostile environments. Technology, therefore, opens up many opportunities, but also risks.
A possible colonization process would require a number of well-defined stages, which would last hundreds of years at best: (i) remote search and exploration, (ii) in situ exploration, (iii) adapting the environment, (iv) occupation.
- The first phase consists of identifying suitable planetary systems remotely, both with terrestrial instrumentation and with space-based telescopes.
- The next step would be similar to the Starshot program, in order to obtain detailed information on a small number of planets in the solar neighborhood.
- The third step would last much longer and would entail a large investment in terms of resources, as it would involve sending nano-robots to prepare the right infrastructure, including searching for mineral deposits, developing nano-factories, energy installations and even building a laser launching subsequent micro spacecraft ships, in an inverted process to their departure from the Earth, which would considerably shorten transit times between the two planets. It would also require the implementation of geo-engineering processes in order to terra-formar the planet, making it more suitable for the presence of human beings.
- The final step would be the transfer of information to create human beings in situ. That is, not to transfer the population at all, which is impractical and even unfeasible.
Vídeo de ESO sobre Ross 128 b en:
From a historical point of view, the investment in terms of time does not seem excessive. The future of humanity is characterized by a permanent migration, by a colonizing process that has taken us from the African savannah to the most inhospitable places on the planet, such as the Lut desert in Iran, where some of the highest temperatures have been recorded, to Antarctica, in a colonization that has lasted tens of thousands of years. It is true that the process has had a cost: high environmental pollution and a great loss of biodiversity.
This process therefore involves considerable technological and scientific, but above all ethical, challenges. What social and political changes would be needed? What social elements, including family- or government-related, would be irreversibly affected? Would it necessarily require the accepting mechanical implants that would “enhance” our capabilities? Should changes at the genetic level be allowed to take place, possibly leading to the creation of another species?
Reflecting a little further and based on previous experience, what right do humans have to adapt another planet to our needs? This question, which may seem purely academic at the moment, would be essential if biological activity were identified in any suitable environment for colonization. Is it licit to change the ecology of a planet to satisfy our expansive impulse? In fact, there is no need to go outside the Solar System: if we identify the presence of life on Mars, Europa or Enceladus, should we continue with the exploration, risking a very probable biological contamination and a mega-extinguishing of the weakest ecology?
We find ourselves on the threshold of a new era of space exploration and possibly humanity as a species. It is therefore necessary to reflect deeply on the how, where and why. We risk nothing less than our future and perhaps that of others.
David Barrado Navascués
European Space Astronomy Center (ESAC, Madrid)