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The Dawn of Organic Chemistry

Periodic Reporting for period 3 - DOC (The Dawn of Organic Chemistry)

Reporting period: 2020-10-01 to 2022-03-31

From a “simple” chemical point of view, all terrestrial living organisms, from microbes to humans, are made up of the same basic components: amino acids, fatty acids, sugars, nucleobases, etc. In total, we are referring to about 50 “small” molecules containing less than 100 atoms of carbon, with hydrogen, oxygen, nitrogen and other elements in smaller quantities: as we know, terrestrial life is based on organic chemistry.
Of course, this is not by chance, because the electronic structure of carbon makes it the element that constitutes the backbone of the terrestrial life “small” molecules. However, this would not be enough if carbon was not also available for making these molecules. Luckily for us, carbon atoms form molecules relatively complex also in space and, particularly important, in regions where future Solar-like planetary systems are born. Astronomers call these molecules iCOMs, for interstellar Complex Organic Molecules. During the formation of the Solar System, iCOMs could have been transmitted to the small bodies, such as comets and asteroids (whose small fragments are called meteorites when reach Earth). Indeed, we see organic molecules in cometary and meteoritic material, even amino acids.
This led the Nobel laureate C. De Duve to affirm: “the chemical seeds of life are universal” and “life is an obligatory manifestation of matter, written into the fabric of the Universe”.
The objective of the DOC project is to understand the dawn of organic chemistry, namely the start of organic chemistry in systems similar to the progenitor of the Solar System, with the ultimate goal to understand how organic chemistry builds up and evolves in these systems and, consequently, to understand how universal the chemical seeds of life are.
To do that, we need a reliable theory for the organic chemistry in nascent Solar type systems and obtaining it is the immediate goal of DOC.
In the first half of the DOC project, we paved the route for achieving the DOC goal.
We started several systematic studies to observe and measure the organic content during the first phases of the formation of a Solar-like planetary system: from the very beginning, when the future system is only a dense clump in the interstellar molecular clouds of the Milky Way and is known with the name of Prestellar Core, to the youngest known protostars, called Class 0 protostars, and then the slightly more evolved sisters, named Class I protostars, and finally the youngest protoplanetary disks, where the planet formation starts taking place.
So far, we do not see any evidence that organic chemistry loses momentum when the system evolves from a Class 0 protostar, where a plethora of iCOMs are detected in the regions that will eventually form planets, comets and asteroids, to a young protoplanetary disk, where the exiguity of the material in these objects make extremely difficult to observe iCOMs.
In parallel, we started a systematic theoretical study of the chemistry that can take place in these regions. Two major possibilities exist: either iCOMs form by reactions of smaller molecules in the gas-phase or they are formed on the interstellar grain icy surfaces by reactions of small frozen radicals.
Exploring all the possibilities is out of the capacity of a single group, as the theoretical study of one single system takes months of computing time on the largest computers. We started focusing on the simplest routes on the grain icy surfaces, the combination of radicals, and found that they are impervious routes, with large mountains to overcome and no much energy for doing that. We also imagined new routes on the gas-phase and found that some are actually efficient, as in the case of the formation of glycolaldehyde, the interstellar molecule closest to a terrestrial sugar.
The chemical theoretical calculations and astrophysical observations are used to tune the theory of the organic chemistry at the naissance of a planetary system similar to our own, as in an orchestra to obtain the best final sound of the music.
As it is often the case, progresses do not increase linearly with time but rather exponentially. At the beginning of a project, one has to set the basis for a new construction: they have to be solid for the rest not to collapse later. We have so far built our solid basis and in the second half of the project we will build the upper part of the construction with, hopefully, windows, towers and all the beautiful ornaments that make a new building reliable and good.
By the end of the project, we expect a much more complete understanding of how organic chemistry is born, grows and evolves while a planetary system like our Solar System forms. We will hopefully be able to answer the question in which nascent planetary systems the small molecules that may have triggered life on Earth are present and, ultimately, how much the Solar System is peculiar when it comes to organic chemistry.