An Experimental Study of the Generation and Enantiomeric Enrichment of Sugars and Amino Acids in Cometary Impacts
The discovery of relatively high abundances of organic compounds such as amino acids and sugar derivatives in meteorites, comets, and the interstellar medium implies that there are relatively efficient mechanisms for producing fairly complicated organic compounds in space, supporting the notion that the building blocks of life may have been delivered to Earth by impacting asteroids and comets. Comets are the delivery vehicles of preference because they generate lower pressures and temperatures in an impact and also contain high proportions of organic material and water, the key ingredients for life. The shock chemistry associated with the behavior of organic compounds during impact remains largely unknown, due to the paucity of experimental data for relevant dynamic extreme-condition regimes.
In an earlier NASA-funded project, we conducted "comet impact" experiments in which aqueous fluids containing dissolved amino acids were subjected to hypervelocity impacts and then examined for chemical change. We made several remarkable observations; not only did fractions of the initial amino acids survive shock conditions relevant for an oblique impact, they polymerized to form peptides (rather than other less-biologically-interesting compounds) and there was no tarry, macromolecular material observed as a bi-product.
Here, we outline a 3-year program to expand previous shock chemistry work to include experiments using sugars and sugar derivatives. We propose a series of 6 impact experiments per year to test the following hypotheses: (1 ) that high velocity impacts promote a formose-type reaction to generate sugars (formaldeyde + water --> glycoaldehyde); (2 ) that sugar dimers, trimers, and higher order homologs are produced from an initial mixture of sugar monomers, as was observed with amino acids; and (3) that an initial enantiomeric excess present among amino acids and sugars will be enhanced through shock processing and dimer/polymer formation.
We propose to conduct the impact experiments using an 80-mm-bore gas gun at Los Alamos National Laboratory and a quantitative soft recovery method, already developed. Starting materials( formaldehyde, sugar compounds, amino acids and dipeptides) and recovered products will be analyzed using a combination of liquid and gas chromatography/mass spectrometry. The proposed analytical work capitalizes on procedural methods already developed to distinguish simple sugars, sugar derivatives, amino acids, and small peptides.
The proposed research directly meets a fundamental goal of NASA's Exobiology and Evolutionary Biology program to identify and understand the characteristics of our solar system that may have led to the origin of life. Our results will allow us to assess the role of impact chemistry as a mechanism for generating larger molecules and/or introducing a chiral bias to Earth’s initial inventory of prebiotic compounds.