Spanish network science to understand how molecular complexity arose in space

Science of complex networks for astrochemistry and astrophysics

Illustrating the science of complex networks for astrochemistry. // Marina Fernandez Ruiz / PNAS

SINC Agency
| 07/31/2022 – 12:00

The origin of chemical complexity in space is, in addition to an open question, a fundamental aspect to understand the first steps that gave rise to the origin of life. Today, an international study, led by researchers from the Center for Astrobiology (CAB, CSIC-INTA), offers a new approach to the origin of molecular complexity in space, using complex network theory.

The authors, who publish their work in the journal PNASexplain the appearance of complex molecules in the clouds of the interstellar medium from a novel point of view: as an emergent process typical of the complexity theoryused in fields such as sociology or computer science and which explains collective phenomena as diverse as traffic jams or avalanches.

The team created a theoretical and computational environment, called NetWorldwhere the interaction between complex networks that can represent any simple structure, whether chemical, biological or social, is simulated.

The results show that, in “wild” environments, only the simplest pieces of this type of LEGO are created. However, when the environment softens, these building blocks actively interact, drastically giving rise to an enormous diversity of compounds, which would later represent the fundamental building blocks of structures on a larger scale and in increasingly larger systems. complex.

This system does not attempt to simulate the rules of real chemistry and does not use real data, but as the lead author points out, James Aguire of the CAB, “what is surprising is that if we understand the nodes of our networks as atoms and each network as a molecule, NetWorld is able to describe the starting point in the process of the origin of life : the emergence of complexity in the evolution of chemical diversity in the interstellar medium.

The link between the extreme simplicity of the model and its ability to describe the real phenomenology of astrobiological relevancesuggests that many basic properties on the long road from chemistry in space to prebiotic chemistry and ultimately to life as we know it might show simple, universal patterns.

NetWorld and game theory

The NetWorld environment models the evolution of complex network structures (nodes linked by connections) towards complexity. The rules of interaction between these networks, which allow them to grow and evolve, are very simple and have been taken from game theory: each node competes with the others to be well connected in the network thanks to the ‘interaction.

Therefore, the rules have nothing to do with real chemistry or biology, but rather a “network chemistry” abstract. NetWorld predicts an abrupt transition from a simple “biodiversity” network (a few different networks of small size) to a much more complex network (thousands of different networks of very different size and complexity) when the parameter representing the environment reaches a critical value.

This transition is observed in different areas of astrobiology, so NetWorld is able to describe this fundamental property of the chemistry of the origin of life from a truly new perspective, the authors insist.

Similar astrophysical and computing environment

Indeed, in this astrophysical environment, the phenomenology is similar to that of the Networld computing environment: when the interstellar clouds condense, the interstellar dust shields the ultraviolet light that hampers many chemical reactions, and the molecules created up at this time interact, giving rise to dozens of new, much more complex molecules.

“There is a drastic transition to complexity in both systems, and the properties of these two transitions are equivalent,” says the co-author Fernando Puente Sanchezresearcher at the Swedish University of Agricultural Sciences.

According to the computer model, the abundance of structures created is proportional to the number of paths that give rise to each structure. So we found previously unknown proportionality relationship between the actual molecular abundances of the different molecules in dark clouds (such as hydrocyanic acid –HCN–, ammonia –NH3– and others) and the potential number of chemical reactions that generate them as a product.

Therefore, “NetWorld promises to be a new bridge between astrochemistry and complexity theory”, concludes the CAB astrochemist Izaskun Jimenez-Serraalso co-author of the article.

Reference: M. García-Sánchez, J. Aguirre et al. “The emergence of interstellar molecular complexity explained by interacting networks”. revista Proceedings of the National Academy of Sciences (PNAS), 2022 | DO I: 10.1073/pnas.2119734119.

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