doi:10.1016/j.gca.2003.09.001 The origin of organic matter in the solar system: Evidence from the interplanetary dust particles G. J. FLYNN, 1, * L. P. KELLER, 2 M. FESER, 3 S. WIRICK, 3 and C. JACOBSEN 3 1 Dept. of Physics, SUNY-Plattsburgh, Plattsburgh, NY 12901, USA 2 NASA Johnson Space Center, Houston, TX 77058, USA 3 Dept. of Physics, SUNY-Stony Brook, Stony Brook, NY 11794, USA (Received January 23, 2003; accepted in revised form September 3, 2003) Abstract—The detailed examination of meteorites and interplanetary dust particles provides an opportunity to infer the origin of the organic matter found in primitive Solar System materials. If this organic matter were produced by aqueous alteration of elemental (graphitic or amorphous) carbon on an asteroid, then we would expect to see the organic matter occurring preferentially in interplanetary materials that exhibit evidence of aqueous activity, such as the presence of hydrated silicates. On the other hand, if the organic matter were produced either during the nebula phase of Solar System evolution or in the interstellar medium, we might expect this organic matter to be incorporated into the dust as it formed. In that case pre-biotic organic matter would be present in both the anhydrous and the hydrated interplanetary materials. We have performed carbon X-ray absorption near-edge structure spectroscopy and infrared spectroscopy on primitive anhydrous and hydrated interplanetary dust particles (IDPs) collected by NASA from the Earth’s stratosphere. We find that organic matter is present in similar types and abundances in both the anhydrous and the hydrated IDPs, and, in the anhydrous IDPs some of this organic matter is the “glue” that holds grains together. These measure- ments provide the first direct, experimental evidence from the comparison of extraterrestrial samples that the bulk of the pre-biotic organic matter occurs in similar types and abundances in both hydrated and anhydrous samples. This indicates that the bulk of the pre-biotic organic matter in the Solar System did not form by aqueous processing, but, instead, had already formed at the time that primitive, anhydrous dust was being assembled. Thus, the bulk of the pre-biotic organic matter in the Solar System was formed by non-aqueous processing, occurring in either the Solar nebula or in an interstellar environment. Aqueous processing on asteroids may have altered this pre-existing organic matter, but such processing did not affect in any substantial way the C=O content of the organic matter, the aliphatic C-H abundance, or the mean aliphatic chain length. Copyright © 2003 Elsevier Ltd 1. INTRODUCTION Organic molecules have been detected in extraterrestrial materials by the laboratory analysis of primitive meteorites (Cronin et al., 1988), interplanetary dust particles (Clemett et al., 1993; Flynn, et al., 2000), and a meteorite from Mars (McKay et al., 1996), by spacecraft measurements of dust in the coma of Comet Halley (Kissel and Kruger, 1987), and by astronomical measurements of comets (Knacke et al., 1986), the atmosphere of Titan (Courtin et al., 1991), and grains in interstellar space (Sandford et al., 1991). These organic mole- cules are generally believed to be abiogenic (Cronin et al., 1988: Kerridge, 1999), having been produced by chemical rather than biologic processing. However, the mechanism(s) for the production of the organic molecules observed in interplan- etary and interstellar materials have not been established. The primitive carbonaceous chondrite meteorites deliver to the Earth samples of the pre-biotic organic matter present in our Solar System. About 10% of the organic matter in these prim- itive, hydrated carbonaceous chondrites is present in the form of soluble molecules, which can be easily extracted and stud- ied, while the remaining 90% of the organic matter consists of insoluble macromolecular material that superficially resem- bles terrestrial kerogen (Kerridge, 1999). Some of this macro- molecular organic matter is presumed to be interstellar based on the detection of significant excesses of D, 13 C and 15 N (Kerridge, 1999). A variety of mechanisms for the origin of the pre-biotic Solar System organic matter have been proposed. Kerridge (1993) describes 12 possible mechanisms that may have been involved in the production of this pre-biotic organic matter, and he further notes that the organic synthesis could have taken place in a variety of locations ranging from stellar outflows to aqui- fers on asteroids. No single mechanism or formation location appears capable of fully explaining the diversity of organic compounds and their isotopic composition (see the review by Kerridge, 1999). Current models suggest that many of the organic molecules found in the hydrated carbonaceous chon- drite meteorites were synthesized by aqueous processing of a suite of precursor molecules, some of which were interstellar (Cronin and Chang, 1993; Kerridge, 1999). However, the spe- cific precursor molecules and the degree of modification by aqueous processing are unknown. The comparison of the organic matter in the anhydrous to the hydrated meteorites and interplanetary dust particles provides an opportunity to determine the abundance and the type(s) of precursor molecules and thus the degree of organic complexity in the Solar System before aqueous alteration and to assess the effects of aqueous alteration on these precursor molecules. * Author to whom correspondence should be addressed (george.flynn@plattsburgh.edu). Pergamon Geochimica et Cosmochimica Acta, Vol. 67, No. 24, pp. 4791– 4806, 2003 Copyright © 2003 Elsevier Ltd Printed in the USA. All rights reserved 0016-7037/03 $30.00 + .00 4791