Organic interstellar

Herbst E, van Dishoeck EF (2009) Complex organic interstellar molecules. Ann Rev Astron Astrophys 47 427-480... 

Carbonaceous solids also reach Earth in the form of organic and icy materials that condensed in the cold outer regions of the solar nebula and also as organic materials preserved in interstellar grains. 

A second major class of ion-molecule reactions that is relatively poorly studied consists of systems involving very unsaturated hydrocarbon neutrals, especially radicals. The unsaturated nature of the organic chemistry in interstellar clouds leads to sizeable abundances of very unsaturated hydrocarbons such as the polyacetylenes HC H, the carbenes H2C , the radicals C H, and the clusters Cn. Although some work has been done on the chemistry of such species, much of the relevant ion-molecule chemistry involving ions such as C+, CH3, and even C2H2 must be guessed at from generalizations based on a small number of studied systems. 

Fig. 3.12 Model of an agglomerate consisting of many small interstellar dust particles. Each of the rod-shaped particles consists of a silicate nucleus surrounded by yellowish organic material. A further coating consists of ice formed from condensed gases, such as water, ammonia, methanol, carbon dioxide and carbon monoxide. Photograph Gisela Kruger, University of Bremen...

Ehrenfreund, P. and Charnley, S.B. (2000). Organic molecules in the interstellar medium, comets and meteorites. Annu. Rev. Astron. Astrophy., 38, 427-483... 

As far as acyclic allene hydrocarbon intermediates are concerned, these begin with a C3H2 species, 254, about which there has been considerable discussion since it has also been detected in radioastronomy studies to belong to the (growing) number of organic compounds present in interstellar and circumstellar space [105]. 

The circumstances producing an e.e. on the early Earth could well have been capture and amplification of one of the fluctuational mechanisms outlined above, although present evidence favors the meteoric infall of chiral molecules synthesized in interstellar dust douds. The total flux of organics on the early Earth, delivered to Earth both by way of comets and other bolides, and synthesized by terrestrial mechanisms... 

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. 

Two mechanisms have been proposed to account for the deuterium enrichment (1) for organic molecules, high D/H ratios can be explained by ion molecule reactions that occur in interstellar space and (2) for the phyllosilicates the enrichment can be produced via isotope exchange between water and hydrogen (Robert et al. 2000). 

Fig. 3.2 Different carbon compounds in primitive meteorites. Species classified as interstellar on the basis of C-isotopes are shaded. Only a minor fraction of organic carbon is interstellar, (after Ming et al. 1989)...

Kerridge JF (1983) Isotopic composition of carbonaceous-chondrite kerogen evidence for an interstellar origin of organic matter in meteorites. Earth Planet Sci Lett 64 186-200 Kerridge JF, Haymon RM, Kastner M (1983) Sulfur isotope systematics at the 21°N site. East Pacific Rise. Earth Planet Sci Lett 66 91-100... 

A hundred or so different molecular species have been spotted in molecular or circumstellar clouds. Most interstellar molecules are organic molecules, that is, they are carbon-based. This indicates that chemical evolution does occur on a cosmic scale. What is more, many molecules on the interstellar list are fundamental building-blocks for the construction of biological structures. 

Star formation and the formation of star systems with planets around them, constantly takes place in dense interstellar clouds. The material present in these clouds is incorporated into the objects that are formed during this process. Pristine or slightly altered organic matter from the cloud from which our solar-system was formed is therefore present in the most primitive objects in the solar system comets, asteroids, and outer solar-system satellites. Pieces of asteroids (and perhaps comets) can be investigated with regards to these components through the analyses of meteorites (and eventually in samples returned from these bodies by spacecraft) in laboratories on Earth. The infall of asteroid and comet material from space may have contributed to the inventory of organic compounds on primordial Earth. 

In cosmochemistry, we use stable-isotope fractionations to study evaporation and condensation in the solar nebula, aqueous processes on asteroids, and even ion-molecule reactions to form organic molecules in interstellar clouds. The oxygen isotopes also show large mass-independent shifts that may be related either to chemical or physical processes or to incomplete mixing of the products of nucleosynthesis. These topics will be covered in detail in later chapters. 

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