Interstellar ices meteorite

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. 

Fig. 8 Phase and fluorescence micrographs of membranous vesicular structures formed from a Murchison meteorite extract (left) compared to vesicles formed by a 20 mM de-canoic acid-decanol mixture [72] (center) and a vesicular structure produced by the photoproduct of an interstellar-ice analog [31]. The vesicles produced by the photochemical ice analog product were allowed to capture pyranine, a fluorescent anionic dye, to demonstrate that a true membrane was present. Scale bars show 20, 10, and 5 pm, from left to right...

As for meteorite analysis, amino acids from such interstellar ice analogues are usually detected after (often acidic) hydrolysis of crude reaction products, and subject to the same interpretation restrictions. Pointing out the formation of peptides [85] (without further arguments) to explain the detection of amino acids in such acid-hydrolyzed irradiated ices is at least questionable since many other precursors can be involved. 

Sandford S. A., Bernstein M. P., and Swindle T. D. (1998) The trapping of noble gases by by the irradiation and warming of interstellar ice analogs. Meteorit. Planet. Sci. 33, A135. 

Figure 6 shows the HPLC chromatogram of one of the residues compared to the chromatogram of a soluble extract from the primitive meteorite Murchison. There are two conclusions to be drawn from this figure. First, since each peak represents a different compound, or more likely a different family of compounds, both the laboratory residue and meteoritic extract are complex chemical mixtures. Second, the similarity in peak distributions between the two samples indicates that the kinds of chemicals present in each sample are similar. This similarity raises the interesting question, "Do the families of compounds in carbonaceous meteorites have an interstellar ice/cometary heritage "... 

The detection of diamino acids in the Murchison meteorite (41) has stirred up the speculation that these compounds are perhaps direct products of interstellar synthesis processes. In particular, laboratory experiments aimed at the ultraviolet (UV)-irradiation of interstellar ice analogs leads to the formation of refractory material which, after hydrolysis with 6 M HCl, has been shown to contain mono-amino acids as well as diamino acids (42). Although it is evident that some organic compounds that were formed in the interstellar medium, either in the gas phase or in interstellar grains, survived exposure to the interstellar... 

Laboratory experiments have shown that radiation processing of simulated presolar ices leads to more complex molecular species [25-27]. Hundreds of new compounds are synthesized, although the starting ices contain only a few simple common interstellar molecules. Many of the compounds formed in these experiments are also present in meteorites and cometary and asteroidal dust (interplanetary dust particles - IDPs), and some are presumably relevant to the origin of life, including amino acids [28,29], quinines [30], and amphiphilic material [31]. 

Naphthalene, anthracene, and similar hydrocarbons are termed polycyclic aromatic hydrocarbons (PAHs) because they are composed of multiple aromatic rings. PAHs have been found in meteorites and identified in the material surrounding dying stars. Scientists have mixed PAHs with water ice in a vacuum at -260°C to simulate the conditions found in interstellar clouds. To simulate radiation emitted by nearby stars, they shined ultraviolet light on the mixture. About ten percent of the PAHs were converted to alcohols, ketones, and esters— molecules that can be used to form compounds that are important in biological systems. 

Plate 7. (A) Fluorescence micrograph of the water insoluble droplets formed from a Murchison meteorite extract (67) compared to (B) the fluorescent droplets producedfrom the photolysis residue of the interstellar/precometary ice analog H20 CHsOH NH3 CO (100 50 1 1) at 10 K (40). The similarity between these vesicles is another indication of similarity between the laboratory ice residue and extraterrestrial organics in meteorites. 

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