NATURAL SOLID BITUMENS AS POSSIBLE ANALOGS FOR COMETARY AND ASTEROID ORGANICS - 1 - REFLECTANCE SPECTROSCOPY OF PURE BITUMENS

Natural solid oil bitumens (asphaltites, kerites, arnthraxolites) appe ar to be useful spectral analogs for cometary and asteroid refractory organics. They show color similarities to the surfaces of dark asteroi ds and cometary nuclei, as well as compositional and structural resemb lances to organic components of carbonaceous chondrites, These dark so lids are composed of a variety of organic compounds, most of which are aromatic and aliphatic hydrocarbons, Spectral reflectance measurement s in the range 0.5-16 mu m have been performed on a suite of solid bit umen powders. The samples were also characterized by chemical analyses , solid state C-13-NMR, and X-ray diffractometry, The observed spectra l variations between bitumen samples correlate with their chemical com position and structure. In the near-infrared region spectral parameter s have been found, which make it possible to derive carbon aromaticiti es (f(a)) and the most important elemental ratios (C/(C + H + N + S O) Or H/C). Moreover, these parameters can be used to estimate some st ructural characteristics of the aromatic component tan average interla yer spacing d(002) and vertical crystallite size L-c). The use of the same spectral parameters may help to reveal the presence of mineral ad mixtures when their content in an organic-rich assemblage is too low t o show any distinct absorption bands of the minerals. (C) 1998 Academi c Press.