Impact-induced Formation of Prebiotic Molecules on Terrestrial Planets

New chemical species can form from reactions induced by shock-heating upon formation of an impact vapor plume and its interaction with the background atmosphere of a rocky planet. Previous studies have assumed chemical equilibrium in computing the abundance of chemical species: such a simplified model can underestimate those concentrations by a factor of 10 in high temperature shock conditions. A more accurate description of the plume/atmosphere interaction demands a coupled hydrodynamics and kinetics calculation. We present a new model extending the work of Ishimaru et al. (2010) by considering an atmosphere on the target planet. We assess the production of prebiotic molecules (HCN, CH4, NH3) for different impact scenarios, varying kinetic energy of the impactor, atmospheric surface density and composition. We find that prebiotic species are produced on Earth-like planets with a N2-CH4 atmosphere, with increasing abundance when: i) the atmospheric surface density increases; ii) the impact energy decreases; iii) the amount of methane in the pre-existing atmosphere increases. The presence of oxygen in today's inner solar system planets prevents the production of HCN. On Titan, impacts can constitute an additional sink for methane. Our findings provide necessary but not sufficient conditions for prebiotic chemistry to start, to assess the astrobiological potential of impacts on terrestrial worlds.