Reactivity of meteoritic material in different astrophysical environments

In typical astrophysical environments, where temperatures and densities are very low and radiation fluxes may be high, the transformation of simple molecules in the gas phase is difficult. Consequently, it is widely accepted that the formation of interstellar complex organic molecules (iCOMs) occurs through barrierless reactions or on the surface of dust grains, which are present in all stages of the evolution of a planetary system. Those grains can act as third bodies, absorbing excess energy from reactions, and are also covered in ices (mainly made of water, CO, N2 and other simple organics, such as methanol) which act to concentrate reactants, increase the chances of reactive collisions, and/or protect from radiation newly formed molecules.

However, models generally assume that reactions occur on the ice phase covering the silicate cores, and tend to minimise the chemical role played by
the dust grains themselves. When grains are not covered in ice, interactions between the solid phase and the gas phase are also important. Indeed, dust grains can be a source of reactants and are also rich in metallic components, such as Fe and Ni. These metals are well known on Earth to act as catalysts for the synthesis of organic compounds, such as the Fischer-Tropsch synthesis (FT) to produce hydrocarbons, the Haber-Bosch (HB) for the synthesis of ammonia, and the cyclation of small hydrocarbons in Diels-Alder (DA) type reactions and further formation of aromatics and nanostructures. They also contain FeS phases, such as troilite or pyrrothite, which are also known to be reactive and could be important to the incorporation of S in complex iCOMs.

Different works have already pointed to the importance of bare grain chemistry (Cazaux et al., 2010; Frankland et al., 2016), and in particular, of the catalytic activity of metallic inclusions (Llorca and Casanova, 2000; Ferrante et al., 2000; Tucker et al., 2018; Peters et al., 2023) and their potential role
in the chemical evolution of different astrophysical environments. In this talk, I will discuss the results of our last experiments which are part of our Astrocatalysis project, which aims at investigating relevant catalytic processes that could occur in different astrophysical environments, such as primeval planetary surfaces and atmospheres. I will present our experiments on the reactivity of chondritic material under relevant protoplanetary conditions toward FT synthesis (Cabedo et al., 2021) and towards the formation of H2S (Cabedo et al., 2024). I will also present future experiments regarding the reactivity of the material after ablation with plasma (Cabedo et. al., 2025, in prep.), simulating the potential reactivity of entering material during early stages after planetary formation. Understanding dust grains solid chemistry is important to completely interpret observational data and to have a complete model of the evolution of iCOMS at different stages of star and planetary formation and towards complex organic chemistry.