Hydrous Chondrites under Shock

Abstract We examine the shock response of a chondrule-like multicomponent silicate melt enriched with 2 wt% H 2 O, representative of hydrous chondrites, using ab initio molecular dynamics. We calculate Hugoniot equations of state (HEOS) and evaluate how hydration affects transport, structural, and thermodynamic features under shock compression. Under the same initial conditions, our results show that water has a minimal direct effect on HEOS. However, the corresponding decrease in initial density significantly shifts the pressure–temperature trajectory. At constant shock pressures, hydration raises peak temperatures, altering volatile loss and melting behavior. The enhanced heating and melting caused by the presence of water implies that hydrated materials could have played a role in shaping the evolution of planetesimals. This challenges previous assumptions constructed on dry silicate models and suggests that volatile-rich bodies may have differentiated more efficiently. In shocked melts, the fast diffusion of hydrogen, compared to the cations, indicates its weak integration into the silicate network. Accordingly, we find that Si–H forms only transiently. Furthermore, analysis of the electron localization function supports the presence of bonded Si–H and Fe–H species along the HEOS, identified from a geometrical approach. The proportions of hydrides depend on the shock conditions and could affect the redox state of the melt, even when they are rare. Our results suggest that even a small amount of water in silicates influences the thermodynamics and chemical behavior during planetesimal impacts. These transformations should be considered in models of core formation and volatile depletion of early planetary bodies.