Children of the stars

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Human expansion beyond the Earth

The matter of which we are made was created, literally, either during the birth of the universe itself or by the stars, during their lifetime or at the end of it in the case of the most massive stars. Human beings are, therefore, children of the stars. On the other hand, we now know that most of them contain planetary systems. Their extraordinary diversity allows us to question the presence of life outside the Earth and to consider the possibility of an expansion beyond the confines of our ancestral home. However, the colonization of other stars also involves many unknowns: Is it really feasible and, if so, desirable? What cultural implications would it have? How would it affect our species?


The Sun has a cohort of eight planets and dozens of dwarf planets and trans-Neptunian objects, in addition to containing a huge number of comets and asteroids. The latter are of great interest for their mineralogy and in fact the first steps have already been taken to initiate commercial exploitation. Except for Ceres, a dwarf planet just under 1000 km in diameter, which is located between the orbits of Mars and Jupiter and is being explored by the American Dawn probe, the other dwarf planets are too far from the Sun and are too cold bodies. Mercury and Venus are not suitable because of 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 the presence of life, on the present surface of Mars, a terrestrial analogue in several respects, is controversial according to some studies. Uranus and Neptune, gas giants dominated by light chemical compounds, are also at a great distance from our star and therefore at low temperature. What potentially suitable environments for life are left within the Solar System?

daawIllustration 1: Updated version of the Drake formula, which allows estimating the possible number of technological civilizations in our galaxy. Most of the parameters suffer from extraordinary uncertainty. Credit: University of Rochester.

Jupiter and Saturn, although gaseous and dominated by the two lightest chemical elements, hydrogen and helium, have cohorts of satellites with very varied characteristics, some of which show great astrobiological potential. Thus, Europa and Enceladus have ice envelopes and possibly immense oceans beneath their surfaces. The European Jupiter Icy Moon Explorer (JUICE) mission, scheduled for launch in 2022, and the American Europa Clipper plan to continue exploration of three of Jupiter's most massive companions, focusing on Europa, although they will not arrive there until after 2030. Regarding Saturn and its satellite Enceladus, there are several proposals for space missions, but none have gone beyond conceptual designs. Therefore, we will have to wait more than a decade to get additional evidence about Europa's internal structure and its potential to harbor life. In any case, from what we know, it appears that the only celestial body in our planetary system that harbors life or is suitable for its development is Earth.


In the last two decades, since 1995, several thousand planetary systems have been identified in the vicinity of the Sun. Given that there are more than 200 billion stars in the Milky Way, our galaxy, and that it is believed that most of them could harbor planets, the possibilities have multiplied exponentially since the enunciation of the well-known Drake formula. Among other reasons, this increase is due to the extraordinary planetary diversity, some of which are truly exotic.

As examples: the existence of planets that orbit 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. In addition, red dwarf stars, the most common 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 only 1.6 days compared to more than 365 days in the Earth's year, yet its gaseous envelope has been detected, or LHS 1140 b, a planet composed essentially of ferric compounds and located in the habitability zone of its star. The closest, Proxima Centauri, also harbors an adjacent planet that could have insolation compatible with the presence of liquid water, although the star is very active. Even more interesting could be Ross 128 b, which is not very active and therefore lacks the intense bombardment of particles and highly energetic radiation that could be a real obstacle to the presence of life in Proxima's planetary system.

sdawThis artist's conception shows the closest known planetary system to our own, called Epsilon Eridani. Observations from NASA's Spitzer Space Telescope show that the system hosts two asteroid belts. Image: Spitzer Space Telescope / NASA

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 reach them so that water, if it exists, is in a liquid state, in the so-called Habitability Zone. In any case, the presence of water in a liquid state, even if it suggests the possibility of harboring life, is not a sufficient (and perhaps not even necessary) condition. Other additional characteristics are required, such as: stability of the star (the so-called space weather), plate tectonics (which allows the presence of orography and the water and carbon cycle), or isolation from other stars (that the nearest star is far away, so that no dynamic interactions occur that change the orbits of the planets).


Exploration outside the boundaries of the Solar System is now a reality. The American probes Voyager 1 and 2, launched more than 40 years ago, are now entering interstellar space (the status can be checked at this link). However, they will not cross paths with other stars. The Starshot proposal, from breakthrough initiatives, aims at sending thousands of micro-spacecraft to start the exploration of the nearest star systems, which would be the first step of a colonization process that will take hundreds of years in the future when we have enough technology to perform such an act.

A possible justification can be found in the following statement by the well-known physicist and popularizer Stephen Hawking:

"Expansion into space will completely change the future of humanity... We are running out of space and the only places to go are other worlds... Expansion is the only thing that can save us from ourselves. I am convinced that we humans need to leave Earth... We have no other choice."

However, expansion within the Solar System or even interstellar expansion would not be a solution to overpopulation due to the billions of human beings inhabiting our planet or the overexploitation of resources, since, if it were technically possible, the amount of resources required 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 would probably far exceed any possible advantages.


Emerging technologies, which are highly disruptive, will to a large extent make this possible colonization possible. Detailed knowledge of our own nature at the 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 into our biological part, the possibility of becoming cyborgs, which would allow us to adapt to much more hostile environments. Technology, therefore, opens up multiple opportunities, but also dangers.

A possible colonization process would require a series of well-defined stages, lasting hundreds of years at best: i) remote search and exploration, ii) in situ exploration, iii) adaptation of the environment, iv) occupation.

  • The first phase consists of identifying suitable planetary systems remotely, both with ground-based instrumentation and space-based telescopes.

  • The next step would be analogous to the Starshot program, in order to obtain detailed information on a small number of planets in the solar neighborhood.

  • The third step would have a much longer duration and would involve a large investment of resources, as it would include the dispatch of nano-robots to prepare the appropriate infrastructure, including the search for mineral deposits, development of nano-factories, energy facilities and even the construction of a laser to deaccelerate subsequent micro-ships in a reverse process to their departure from Earth, which would considerably shorten the transit times between the two planets. It would also require the implementation of geo-engineering processes, in order to terra-form the planet, making it more suitable for the presence of human beings.

  • The last step would be the transfer of information to create human beings in situ. That is, no population transfer, which is impractical and even unfeasible.

ESO video about Ross 128 b in:

Seen from a historical point of view, the investment in time does not seem excessive. The evolution of humanity is characterized by a permanent transhumance, 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 come at a cost: a great deal of environmental pollution and a great loss of biodiversity.

Thus, this process involves considerable technological and scientific challenges, but above all ethical ones. What social and political changes would be necessary? What social elements, including family or government, would be irreversibly affected? Would it necessarily require the acceptance of mechanical implants that "augment" our capabilities? Should changes be allowed to be implemented at the genetic level, possibly leading to the creation of another species?

Reflecting a little further and based on previous experience, what right do we humans have to adapt another planet to our needs? This question, which may seem purely academic now, would be essential if biological activity were identified in any environment suitable for colonization. Is it licit to change the ecology of a planet to satisfy our expansive impulse? In fact, it is not necessary to go outside the Solar System: if we were to identify the presence of life on Mars, Europa, or Enceladus, should we continue exploration, risking very likely biological contamination and mega-extinction of the weaker ecology?

We are on the threshold of a new era of space exploration and possibly of humanity as a species. It is necessary, therefore, a deep reflection on how, where and why. Nothing less than our future and perhaps that of others is at stake.....

well so far my article about astronomy since I will take the whole month of January for me the astronomical month all related to space and the cosmos space among other things the different planets of our solar system and its characteristics and curiosities ....

and happy new year 2022

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