High molecular weight organic matter in martian meteorites

We have performed an investigation to detect high molecular weight organic matter in martian meteorites. Solvent-extracted samples of two Antarctic finds (ALH 84001, sub-sample 106 and EET A79001, sub-sample 351) and one non-Antarctic fall (Nakhla) were analysed by flash pyrolysis-gas chromatography-mass spectrometry. Results suggest that our sub-sample of ALH 84001 contains no pyrolysable organic matter. In contrast, our samples of EET A79001 and Nakhla contain organic matter of high molecular weight, which releases aromatic and alkylaromatic hydrocarbons, phenol and benzonitrile as major compounds upon pyrolysis. The detection of similar pyrolysis products from Nakhla and EET A79001 indicates that these martian meteorites may have a common high molecular weight organic phase. Carbon isotopic measurements of individual molecules in the Nakhla pyrolysate, by flash pyrolysis-gas chromatography-isotope ratio mass spectrometry, reveal that this high molecular weight organic matter has some similarities to that found in carbonaceous chondrites. At this point, an origin by terrestrial contamination cannot be unequivocally ruled out, but the data seem to support proposals that martian samples contain organic matter originating from meteoritic infall on Mars. The results suggest that a wider, pyrolysis-based study of martian meteorites would be a justifiable use of these precious samples. (C) 2002 Elsevier Science Ltd. All rights reserved.