Definition of General Habitability (for life)

It is a dynamic and complex phenomenon, whose origin and existence depend on the interactions and feedback between life (conceived as a possible universal phenomenon) and the stellar, planetary, climatic, physicochemical and energetic conditions of certain places in the Universe.

Quote (APA)

Sandro Cervantes Nunez | Jul. 2022
Cand. Doctor in Earth Sciences and Astrobiology

A universal phenomenon, or science fiction?

Is there life on other planets or moons? What is that life like and what are the conditions in which it lives? Is new life originating or dying out somewhere in the universe? These are just some of the questions that have haunted humanity for millennia (Leucippus and Democritus V century BC. C.) and have inspired, to date, a whole range of artistic and commercial productions in the area of ​​scientific fiction. This is a very controversial topic, which causes immediate rejection in some, and the greatest astonishment and interest in others. However, beyond fiction and our preferences, these are issues that are currently being studied from science (see ESA), and have allowed us to understand from another perspective and in a more complete way, to the life that we know and to appreciate it even more, realizing (in all what we have studied of the universe), of how singular and unique they seem to be, the planetological and habitability conditions of our Land.

Although our technical capabilities are not yet sufficient to fully resolve these enigmas, it is essential to create and strengthen a theoretical framework conceptual and methodological approach that allows us to get closer to this goal. For this reason, since the end of the last century, a new field was designed (and continues to improve and grow to this day). multidisciplinary science, called Astrobiology or Exobiology, whose main objective is the study of life more beyond the Earth. This is a great objective that implies not only discovering and studying the possible life that has originated or colonized another planet or moon, our solar system and other stars, but also to study and propose, what may be the future of life on Earth and beyond is.

Scope of the study of astrobiology and habitability

Perhaps at some point in the coming decades or centuries, through the research carried out in this field of knowledge, we will be able to find vestiges of extinct and even active life, with one of our robotic or manned exploration missions, on nearby planets and moons, or through perception remote in some of the nearby stars, and we will have to redefine part of the biological theory. For the time being, the theory of general habitability may allow us to better study and understand the conditions in which it lives, evolves, and settles. extinguishes (or could extinguish), terrestrial and human life, as well as those in which they will survive or proliferate, both on Earth and outside of it, in case we or some catastrophic natural event, endanger the conditions of terrestrial and human habitability current.

And it is that we cannot ignore that due to the possible consequences, in the short, medium and long term, of the climate change and environmental degradation, or due to the explosion of a supervolcano, the impact of some meteorite or comet, to a terrible pandemic or a nuclear war, certain extensions of the Earth, or all of it, could become uninhabitable for most life, including human life, and we may not be able to restore them even with all our scientific and technological. Nor can we ignore the exploratory restlessness and the desire to conquer of our species, which by themselves, or in combination with the problematic climatic-environmental and human greed, could attract or force us to colonize and/or terraform new sites outside the Earth, seeking from simple entertainment, use of new means, a new development as a galactic species, or worse still, seeking to survive in the long term, in the face of the dangers of humanity and the universe.

Habitability Classification

In order to strengthen the conceptual theoretical framework, we need to study the possible life that could have originated beyond the Earth, or to prepare for the creation of habitable conditions that humanity might require or seek in the future, I have proposed the following classification for the theory of general habitability, encompassing the different manifestations of it, both on Earth and possible outside it.

Table 1. Proposal for the classification of the types of habitability.

Life factors that make the Earth unique

In our solar system it is and in the search for exoplanets, so far, we have not found a planet equal to or similar to ours (see NASA), which is capable of support terrestrial life, that is, a planet to which we can take an ark ship and calmly descend to inhabit it, together with the millions of species terrestrial. We will never find that planet in the entire universe, although as a consolation, it is most likely that we will find planets with certain similar conditions, that we will have to modify or adapt our life to them, to be able to inhabit them in a way close to how we inhabit this planet. Why does this happen? Again, general habitability theory can help us better understand this point.

Given the evolution In the normal universe, each planet and moon originally have a particular mass, size, density and orbital conditions, as well as an atmospheric composition and structure. also particular, which can be altered by cosmic events of great magnitude (gravitational waves, supernovae or super-massive black holes, stars or planets wandering, etc.); by own or nearby stellar events (origin, development and final stage of the stars); due to gravitational or physical interactions between planets, moons and remnants of planetary nebulae (meteorites, comets and dwarf planets); and finally by volcanism and plate tectonics. All these factors, together with the chemical composition, size and energetic environment of the protoplanetary disk where planets originate, makes each planet and moon unique, something similar to what happens with our footprints fingerprints

And to top it off, as we well know, the atmosphere of our planet did not have the current concentrations of oxygen and nitrogen when it originated. Life over billions of years modified the atmosphere and the availability of nutrients on the surface terrestrial, interacting with the factors mentioned above, to originate the environmental and climatic conditions current. Therefore, even if we could find a planet with life, and extremely similar to ours at a stellar, planetological and physicochemical level, the abundance, diversity and biological evolution of that life, would make it different from ours, since biological evolution is not a mechanism that always follows the same path.

Even if we could go back in evolutionary time on our planet, to those moments when life came out of the sea and colonized the land, there is no guarantee that our species would originate again, not even turning back the clock to the moments of the extinction of the dinosaurs, moreover, not even going back to the origin of the hominids. So, the role that life plays in the atmospheric and physicochemical evolution of your planet, makes it practically impossible to find an Earth 2.0.

A challenging new term for biology

Biology is the science that studies life, and even so, it does not have a definition of terrestrial habitability, much less one of general or universal habitability. From its origin to date, all the attention of this science has been focused on the study of the origin, nutrition, metabolism, growth, diversity, relationships, evolution and other processes of living beings. To fulfill its objectives, biology has not needed to elaborate these definitions, because for practical purposes, we only know life and furthermore, we tend to consider the entire Earth to be habitable (although we precisely know that only a tiny bit of it is habitable). layer of the Earth, called the Biosphere), so we don't normally question whether certain places on it were, are, or will be livable. In this way, biology studies and explains habitability, in terms of relationships between habitat and ecological niche.

However, considering everything that has been detailed in the previous paragraphs, the general habitability or universal, could (or perhaps should), become a subject of study and protection, important also for the biology.