Modeling the Chemical Evolution of Cosmic-Ray Irradiated H₂O: CO₂ Ices with PROCODA: Implications for Protostars and Trans-Neptunian Objects

Abstract The understanding of the physicochemical processes that occur in astrophysical ices under irradiation is fundamental to elucidate the mechanisms of molecular species formation in cold environments of the interstellar medium and the outer Solar System. In this study, we investigate the chemical evolution of an H₂O: CO₂ (10:1) mixture irradiated by heavy ions (⁵⁸Ni¹³⁺, 52 MeV) taken from literature, using the computational code PROCODA to model reactions kinetics and column densities in the solid phase (and radiation induced desorption processes) through coupled differential equations. The model accurately reproduced the evolution of relative abundances of molecules such as H₂O₂, CO₂, CO, and other minor species, indicating the relevance of radiolysis and cosmic ray induced desorption processes. The good agreement between the simulated data and astronomical observations (e.g. trans-Neptunian object Charon and some protostars W33A and IRAS 2A) suggests that the modeled mechanisms are representative of conditions found in cold and irradiated astrophysical environments. Furthermore, the study points out potential molecular candidates that, although not detected in recent observations of Charon, are chemically plausible to occur in its surface regolith. The obtained results reinforce the importance of integrated approaches among experimentation, modeling, and observation for constructing consistent scenarios of chemical evolution in space.