Oxidation of carbon compounds by silica-derived oxygen within impact-induced vapor plumes

Impact-induced vapor plumes produce a variety of chemical species, which may play an important role in the evolution of planetary surface environments. In most previous theoretical studies on chemical reactions within impact-induced vapor plumes, only volatile components are considered. Chemical reactions between silicates and volatile components have been neglected. In particular, silica (SiO2) is important because it is the dominant component of silicates. Reactions between silica and carbon under static and carbon-rich “metallurgic” conditions (C/SiO2 ≫ 1) are known to occur to produce CO and SiC. Actual impact vapor plumes, however, cool dynamically and have carbon-poor “meteoritic” composition (C/SiO2 ≪ 1). Reactions under such conditions have not been investigated, and final products in such reaction systems are not known well. Although CO and SiO are thermodynamically stable at high temperatures under carbon-poor conditions, C and SiO2 are stable at low temperatures. Thus, CO may not be able to survive the rapidly cooling process of vapor plumes. In this study, we conduct laser pulse vaporization (LPV) experiments and thermodynamic calculations to examine whether interactions between carbon and silica occur in rapidly cooling vapor plumes with meteoritic chemical compositions. The experimental results indicate that even in rapidly cooling vapor plumes with meteoritic compounds are rather efficiently oxidized by silica-derived oxygen and that substantial amounts of both CO2 and CO are produced. The calculation results also suggest that those oxidation reactions seen in LPV experiments might occur in planetary-scale vapor plumes regardless of impact velocity as long as silicates vaporize.