Protocol for Future Amino Acid Analyses of Samples Returned by the Stardust Mission

Introduction: The delivery of amino acids to the early Earth by interplanetary dust particles, comets, and carbonaceous meteorites could have been a significant source of the early Earth's prebiotic organic inventory [1]. Amino acids are central to modern terrestrial biochemistry as major components of proteins and enzymes and were probably pivotal in the origin of life. A variety of amino acids have been detected in the CM carbonaceous meteorite Murchison [2], many of which are exceptionally rare in the terrestrial bio-sphere including α-aminoisobutyric acid (AIB) and isovaline. AIB has also been detected in a small percentage of Antarctic micrometeorite grains believed to be related to the CM meteorites [3]. One problem associated with the analysis of mi-crometeorites is that these particles can be heated to very high temperatures (1000 to 1500ºC) during atmospheric entry [4], causing some of the amino acids originally present in the grains to decompose or evaporate into the cold atmosphere [5]. In contrast to large micrometeorites, particles returned from comet 81P/Wild 2 by Stardust provide an opportunity to investigate the amino acid content in grains that likely did not experience as extensive heating between their departure from the comet and their delivery to Earth. We have recently optimized a new liquid chromatography time of flight-mass spectrometry (LC-ToF-MS) technique coupled with OPA/NAC derivatization in order to detect amino acids in meteorite grain extracts by UV fluorescence and exact mass simultaneously [6]. To validate our technique for amino acid analyses of Stardust material, we analyzed 20 µm sized grains from the Murchison meteorite and 36 different Stardust quality aerogels from both the comet and interstellar collection surfaces. Preliminary results from these analyses are reported here. Murchison meteorite (USNM 6650.2) was crushed with an annealed (500ºC overnight) mortar and pestle and fifteen meteorite grains (20 µm dia., total mass ~ 0.15 µg) were hand-picked under an optical microscope and transferred to a clean test tube. Olivine grains (20 µm) from a crushed sample that had been heated at 500°C for several hours were used as a procedural blank. In addition, 36 aerogel samples and soil and water samples collected from the Genesis crash site in the Utah Test and Training Range (UTTR) were analyzed in parallel. The UTTR soil and aerogel samples were crushed with a glass rod inside a clean test tube. Each sample was sealed in a glass test tube with 1 ml of double-distilled water for …