LPS XXVI 1269 CARBON ISOTOPIC MEASUREMENTS OF FRAGMENTS OF METEORITIC

Abstract- Meteorites provide us with an excellent opportunity for studying extraterrestrial organic compounds and constitute our only practically available record of pre-biotic evolution and the state of matter 4.5 billion years ago [I]. It now appears that the organic components in meteorites originated from more than one environment and possible source regions include dense interstellar clouds, the solar nebula, planetissimals [2 and refs. therein] and stellar atmospheres [3]. During its complex history the organic fraction has possibly been affected by the hydrothermal alteration that is believed to have created the hydrated silicates in the carbonaceous meteorites[4]. Clues to the origin, synthetic pathways and evidence of aqueous alteration can be found in the structures of organic compounds but more conclusive information is potentially forthcoming from the measurement of isotopic ratios [I]. The majority of the organic matter in meteorites is in the form of a macromolecule which is insoluble in common organic solvents [4]. It is primarily this property which has repulsed attempts at structural elucidation so that it is still only poorly characterised [5]. The macromolecule is believed to be similar to coal and approximates to a condensed aromatic framework with various functional and heteroatomic bridging groups attached [5]. One method, developed over the last 20 years to analyse macromolecules, is hydrous pyrolysis, which involves heating samples at 250 to 360°C for several days under pressure in the presence of water (a hydrogen donor) and an inert atmosphere [6]. The technique relies on components within the macromolecule attempting to attain a more stable molecula