A SEARCH FOR EXTRATERRESTRIAL AMINO-ACIDS IN CARBONACEOUS ANTARCTIC MICROMETEORITES

Antarctic micrometeorites (AMMs) in the 100-400 mu m size range are th e dominant mass fraction of extraterrestrial material accreted by the Earth today. A high performance Liquid chromatography (HPLC) based tec hnique exploited at the limits of sensitivity has been used to search for the extraterrestrial amino acids alpha-aminoisobutyric acid (AIB) and isovaline in AMMs. Five samples, each containing about 30 to 35 gr ains, were analyzed. All the samples possess a terrestrial amino acid component, indicated by the excess of the L-enantiomers of common prot ein amino acids. In only one sample (A91) was AIB found to be present at a level significantly above the background blanks. The concentratio n of AIB (similar to 280 ppm), and the AIB/isovaline ratio (greater th an or equal to 10), in this sample are both much higher than in CM cho ndrites. The apparently large variation in the AIB concentrations of t he samples suggests that AIB may be concentrated in rare subset of mic rometeorites. Because the AIB/isovaline ratio in sample A91 is much la rger than in CM chondrites, the synthesis of amino acids in the microm eteorite parent bodies might have involved a different process requiri ng an HCN-rich environment, such as that found in comets. If the prese nt day characteristics of the meteorite acid micrometeorite fluxes can be extrapolated back in time, then the flux of large carbonaceous mic rometeorites could have contributed to the inventory of prebiotic mole cules on the early Earth.