The process of formation of molecules and the origin of life

Where do we come from? This simple question has probably always fascinated humanity, and it is in fact one of those that even the most ancient of cosmologies and religions had to answer, in order to satisfy the thirst for knowledge about it. Today, downstream of all the modern scientific knowledge and technological developments that have gone so far as to make dedicated services available on the market, we can go back many generations both through the analysis of archival documents and even further back through the analysis of our DNA; this is how, for example, some roots of my family have been documented back to the Italy of the Lombards, and this is how I can identify my kinship in the form of shared DNA with some victim of the Vesuvius eruption or even more back in time, going back to single individuals who lived in the Neolithic. Again thanks to DNA and the science of evolution, we can go back even further, going back to incredibly distant eras in the history of life on Earth and tracing ancestors in very remote creatures. But while all of this certainly captures my imagination as a biologist, the opening question can be understood even more radically: Where do the atoms and molecules we are made of come from? Incredible as it may seem, today we are beginning to answer this question directly, and not just by experimentally verifying theories on the mechanisms of the original formation of atoms and molecules.

Thanks to modern astronomy, equipped with gigantic and very powerful instruments, we can in fact turn our gaze to the abyss of the cosmic space that surrounds us; and this, as we well know, is equivalent to look into the abyss of time since the formation of the universe. To our surprise, in some cases, the ancient processes that led to the formation in the universe of atoms or molecules fundamental to our own physical constitution are still active, and for this reason they are visible at relatively small distances from us, i.e. by looking relatively recently.

It is the case of water formation of which we ourselves and every living organism on our planet are composed. We have known for some time that, on our planet, water may have been brought by numerous comets, engulfed during its initial accretion phase. But when and where was the water present in comets formed? A team of researchers has used the ALMA interferometer to measure chemical signals in the disc of leftover materials from the formation of a young star 1300 light-years away, called V883 Orionis, by detecting water vapor there, a recent article in Nature reported. . The disc is the seat where, successively, bodies such as planets and comets originate; as a result, it became critical to establish whether the water vapor found in the disk itself was similar to the water found in comets and planets like ours. To do this, it is possible to reveal the relationship between “normal” water – i.e. water consisting of two atoms of hydrogen and one of oxygen (H2O) – and “semi-heavy” water, i.e. containing one of deuterium (Hdo). Well, the Hdo:H2O ratio indicates that the water inside the disk of V883 Orionis is directly inherited from the phases in which the matter that gave rise to the star thickened. In fact, the ratio of semi-heavy water to normal water in the accretion disk of V883 Orionis matches the ratio that other astronomers have measured in clouds of material around protostars, i.e. much younger objects. And the same ratio of semi-heavy water to normal water is found in comets from the outer reaches of our solar system. This is proof that the water molecules in our solar system could have originated in the cold interstellar medium before the formation of the Sun.

Therefore, water and its deuterated species are formed on grains of frozen dust, starting from molecules that are inherited from the prestellar phase in what is called the half prestellar, where organic molecules are also formed at the base of the compounds necessary for life; during the accretion of a disk and its collapse around a nascent star and then during the formation of comets, no significant chemical changes occur, and the water that is ubiquitously present in the cosmos is therefore that formed in the frigid space, before that that the Sun was born, on grains of dust and in clouds of rarefied gas where the molecular building blocks of life on our planet were also formed.