Exobiology and Evolutionary Biology

Characterization of Organic Matter in Interplanetary Dust Particles: Analysis of Organic Grain Coatings to Constrain the Production Mechanisms of Early Solar System Organic Matter

PI: George Flynn

Chondritic, porous interplanetary dust particles (CP IDPs) are the most primitive samples of the Solar Nebula available for laboratory analysis [Ishii et al., Science, 2008]. The ~10 micron CP IDPs are unequilibrated aggregates of mostly submicron grains, including olivine, pyroxene, glass, and sulfide. We have found that the individual grains are coated by ~100 nm thick layers of organic matter. This implies an assembly sequence: grain formation, emplacement of the organic coating, and finally assembly of CP IDPs. Thus, these organic grain coatings appear to be the earliest surviving organic matter produced in our Solar System. We have performed a preliminary analysis of the grain coatings in several CP IDPs by Carbon X-ray Absorption Near-Edge Structure (C-XANES) spectroscopy. The similarity of coating thickness and XANES spectra for coatings on all grains, independent of mineralogy, indicates that mineral specific catalysis, one widely accepted model for organic formation in the early Solar System, was not the production mechanism for this organic matter. Our observations are consistent with the alternative model, production by irradiation of carbon-bearing ices that condensed onto grain surfaces. We propose to continue our analyses of these grain coatings by C-XANES, and expand the analyses to include O-, and N-XANES, which will provide a more complete characterization of the primitive organic coatings on the grains. Combined C-, N- and O-XANES on the same grain coatings is especially important since work by other investigators indicates that higher O:C and N:C ratios correlate with higher primitiveness (i.e., less thermal modification). In addition, we will compare the C, N-, and O-XANES spectra of organic matter produced in laboratory simulations of early Solar Nebula processes in an effort to better understand the processes that resulted in early, pre-biotic organic matter in our solar system. Anders [Nature, 1989] noted that IDPs delivered a significant amount of organic matter to the surface of the early Earth, and proposed that this organic matter might have been important for the origin of life on Earth. Because IDPs experience less severe heating during deceleration in the atmosphere of Mars, larger IDPs are accreted onto Mars with their organic matter unpyrolized, resulting in a larger surface density (mass/area) of IDP organic matter on Mars than on Earth (Flynn, Earth, Moon and Planets, 1996). Our determination of the types and relative abundances of organic functional groups present in the IDPs provides an inventory of the pre-biotic organic matter delivered to the surfaces of Earth and Mars by IDPs. One group of IDPs that we will study, from a special collection that the NASA Johnson Space Center Curatorial facility specifically timed to coincide with a significantly enhanced dust flux from a recent outburst on Comet 26P/Grigg-Skjellerup, is particularly interesting because modeling and measurements indicate these comet dust particles were not severely heated during atmospheric deceleration. Thus they provide the opportunity to analyze cometary organic matter, preserved at low temperature in the comet since the formation of the Solar System.