Meteoritic organics

Artificial hydrothermal vents might be constructed and supplied with plausible concentrations of simple reactants such as CO, H2, NH3, and H2S. Appropriate levels of amino adds induding a small chiral excess, along with the sorts of amphiphilic molecules described above, can be rationalized by the findings from the Murchison meteorite. Organic molecules such as found in irradiated interstellar ice models, including HMT, can also be induded. The system should indude weathered feldspars, which can be modified to indude the reduced transition-metal minerals that they are known to contain. [134] Such minerals as Fe,Ni sulfides are likely to have been both present and stable in the environment of early Earth and are known [153, 155] to catalyze formation of organic molecules from simpler precursors. 

In several previous chapters, we have discussed element volatility. Here we focus on some of the most volatile constituents in meteorites - organic compounds, noble gases, and ices. Each of these actually constitutes a voluminous subject of its own in cosmochemistry, and we can only provide overviews of these interesting components. 

The above results are interpreted as indicating the presence of diverse chirality in unknown meteorite organics. 

It appears that conditions in the solar nebula were appropriate for the FTT but not the Miller-Urey reaction. Kinetic calculations (Lewis and Prinn, 1980) as well as observations on comets (Delsemme, 1977) show that CO and COj, not CH, were the principal forms of carbon. And the dust-laden solar nebula was opaque to UV, precluding any photochemical reactions. It seems best, however, to approach the problem empirically, by examining the meteoritic organic compounds themselves for clues to their formation. We shall review these compounds class by class, looking for the signatures of the FTT or Miller-Urey reactions. 

Vdovykin, G. P. Carbonaceous Matter of Meteorites (Organic Compounds, Diamonds, Graphite), Nauka Publishing Office, Moscow (1967) English translation, NASA TT F-582, Washington, D.C., (1970). 

The principal focus of this review is on the analysis of the organic matter in the Murchison CM2 chondrite, together with data from other meteorites, where it can be shown that they have not been compromised by terrestrial contamination. It primarily covers work undertaken since 1980, a period that has seen the increasing use of stable-isotopic techniques to elucidate the sources of meteoritic organic matter, improved methods to study the structure of organic matter such as NMR, and the first in situ examinations of organic matter in meteorites these approaches have provided significant advances in our... 

Hypotheses for the origin of meteoritic organic matter must account for its molecular and isotopic composition and be consistent with models of meteorite petrogenesis consequently, a number of potential environments have been considered (Table 9). Until the early 1990s, the favored hypothesis involved the catalytic hydrogenation of CO in the solar nebula. However, a characteristic of such catalytic reactions is their structural selectivity. FTT synthesis, in particular, produces a structurally selective suite of hydrocarbons and other compounds that, initially, were believed to... 

Table 9 Sources and processes potentially involved in the production of meteoritic organic matter.

Hayatsu R. (1964) Orgeuil meteorite organic nitrogen contents. Science 146, 1291-1293. 

Early studies involved pyrolysis of this residue and revealed the presence of aromatic ring systems such as benzene, naphthalene, their alkyl derivatives as well as higher aromatic hydrocarbons. Today, GC-MS analyses of super-critical fluid extracts of hydrous pyrolysates (77), Ha-pyrolysis products (72) as well as solid-state C-NMR spectroscopy (75) of meteorite organic residues are applied to provide insight into the structure of the macromolecular carbon. Most recent, hydrothermal treatment (300 °C at 10 MPa) of demineralized lOM of the Murray meteorite has yielded in the release of a wide variety of carboxylic acids and heteroaromatic compounds including C3-C17 alkyl carboxylic acids and N-, O-and S-containing hydroaromatic and aromatic compounds (74). 

The organic material in carbonaceous chondrites is of more direct interest with regard to the problem of the origin of life on the Earth, not only because of the possible participation of similar material in the formation of the Earth, but because of the possibility that the mechanisms of formation of terrestrial and meteoritic organic compounds may be related. It has been suggested by Anders et al. (1974) that many of the organic compounds in meteorites may have been formed by Fischer—Tropsch-type reactions. There is reasonable agreement, for example, between certain hydrocarbon isomers... 

The identification of the individual molecular constituents isolated from meteorites using solvent extraction, chemical degradation, or pyrolytic techniques, which may also include isolation and derivatization, commonly culminates in analysis by GC-MS and/or liquid chromatography-mass spectrometry (LC-MS). However, with the high isomeric diversity present in meteoritic organic material, it is not often possible to unambiguously resolve individual components. 

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