Chemical production by Pulse-Laser Irradiation on Ices: Simulation of impact shock-induced chemistry

Abstract

Chemical changes and synthesis occurring on icy satellites are generally explained by the influence of UV photons and high-energy charged particles on ices. Nonetheless, impact process onto ices could be especially advantageous and efficient as a local or global endogenic energy source for driving interesting surface chemistry. Impacts can ensure that ices are eventually exposed, for a limited period of time, to aqueous melt in impact craters and ejecta, allowing impurities included in the ice to undergo hydrolysis and other reactions. Upon impact, the kinetic energy of the bolide is transferred to the ground liberating a great deal of stress energy which could initiate in situ a diverse series of chemical reactions in the fracture zone beneath the crater.

In the present work, we report the experimental results of a new approach testing in laboratory the chemistry conducted by impacts into planetary ices. Mixtures of pure water ices containing impurities like CO2, Na2CO3, CH3OH and CH3OH / (NH4)2SO4 were irradiated at 77K by a pulsed Nd-YAG laser beam (1064 nm). GC-MS and FTIR analyses show that hydrogen peroxide, carbon monoxide and methanol are formed in irradiated H2O / CO2 ices. Ice containing sodium carbonate generates under laser radiation CO and CO2 which are also products of the irradiated H2O / CH3OH and H2O / CH3OH / (NH4)2SO4 ices. Besides, methane and more complex molecules are produced after irradiating ices containing methanol and, adding ammonium sulfate to the methanol induces the production of nitrogen compounds such as N2O, HCN and CH3CN.