The large-scale organization of chemical reaction networks in astrophysics

– The large-scale organization of complex networks, both natural and artificial, has shown the existence of highly heterogeneous patterns of organization. Such patterns typically involve scale-free degree distributions and small world, modular architectures. One example is provided by chemical reaction networks, such as the metabolic pathways. The chemical reactions of the Earth’s atmosphere have also been shown to give rise to a scale-free network. Here we present novel data analysis on the structure of several astrophysical networks including the chemistry of the planetary atmospheres and the interstellar medium. Our work reveals that Earth’s atmosphere displays a hierarchical organization, close to the one observed in cellular webs. Instead, the other astrophysical reaction networks reveal a much simpler pattern consistent with an equilibrium state. The implications for large-scale regulation of the planetary dynamics are outlined. Introduction. – The interstellar medium (ISM) – gas and micron-sized dust particles between the stars – is the raw material for the formation of future generations of stars which may develop planetary systems like our own. Astronomical observations of interstellar and circumstellar regions have lead to the identification of well over one hundred different molecules, most of them being organic in nature [1]. Motivated by these discoveries, astrochemistry – the chemistry of the interstellar gas – has developed into an active research area of astrophysics and detailed chemical models can now be constructed which reconstruct the history and role of the ISM in the evolutionary cycle of the galaxy [2]. Crucial to modeling chemical kinetics in the interstellar medium, the UMIST kinetic database [3] consists in the chemical reactions relevant to astrochemistry. In view of the increasing data on the chemical composition of the solar system’s planets from latest planetary missions, there is growing interest in the astrophysical community for modeling the weather and atmospheric chemistry of the neighboring planets. Such modeling provided extensive chemical reaction networks (CRN) [4] that expect confirmation from future (∗) E-mail :[email protected] (∗∗) E-mail :[email protected]