Experimental shock chemistry of aqueous amino acid solutions and the cometary delivery of prebiotic compounds

A series of shock experiments were conducted to assess the feasibility of t he delivery of organic compounds to the Earth via cometary impacts. Aqueous solutions containing near-saturation levels of amino acids (lysine, norval ine, aminobutyric acid, proline, and phenylalanine) were sealed inside stai nless steel capsules and shocked by ballistic impact with a steel projectil e plate accelerated along a 12-m-long gun barrel to velocities of 0.5-1.9 k m sec(-1). Pressure-temperature-time histories of the shocked fluids were c alculated using 1D hydrodynamical simulations. Maximum conditions experienc ed by the solutions lasted 0.85-2.7 mus and ranged from 5.1-21 GPa and 412- 870 K. Recovered sample capsules were milled open and liquid was extracted. Samples were analyzed using high performance liquid chromatography (HPLC) and mass spectrometry (MS). In all experiments, a large fraction of the ami no acids survived. We observed differences in kinetic behavior and the degr ee of survivability among the amino acids. Aminobutyric acid appeared to be the least reactive, and phenylalanine appeared to be the most reactive of the amino acids. The impact process resulted in the formation of peptide bo nds; new compounds included amino acid dimers and cyclic diketopiperazines. In our experiments, and in certain naturally occurring impacts, pressure h as a greater influence than temperature in determining reaction pathways. O ur results support the hypothesis that significant concentrations of organi c material could survive a natural impact process.