Interstellar grains

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. 

Ruffle D. P. and E. Herbst (2001). New models of interstellar grain chemistry - II. Surface chemistry in quiescent cores. Monthly Notices of the Royal Astronomical Society 322 770-778. 

Amari S, Lewis RS, Anders E (1994) Interstellar grains in meteorites I. Isolation of SiC, graphite, and diamond size distributions of SiC and graphite. Geochim Cosmochim Acta 58 459-470... 

Anders E, Zinner E (1993) Interstellar grains in primitive meteorites diamond, silicon carbide, and graphite. Meteoritics 28 490-514... 

Jeffery PM, Reynolds JH (1961) Origin of excess Xe in stone meteorites. J Geophys Res 66 3582-3583 Jones AP, Tielens AGGM, Hollenbach DJ, McKee CF (1997) The propagation and survival of interstellar grains. In Astrophysical Implications of the Laboratory Study of Presolar Materials. Bematowicz TJ, Zinner E (eds) AIP, New York, p 595-613... 

Chondrites are the oldest and most primitive rocks in the solar system. They are hosts for interstellar grains that predate solar system formation. Most chondrites have experienced a complex history, which includes primary formation processes and secondary processes that inclnde thermal metamorphism and aqneons alteration. It is generally very difficult to distinguish between the effects of primary and secondary processes on the basis of isotope composition. Chondrites display a wide diversity of isotopic compositions including large variations in oxygen isotopes. 

Onuma N, Clayton RN, Mayeda TK (1970) Oxygen isotope fractionation between minerals and an estimate of the temperature of formation. Science 167 536-538 Ott U (1993) Interstellar grains in meteorites. Nature 364 25-33... 

From these considerations we conclude that the failure of the emission spectrum of interstellar dust to vary as 1/A2 in the far infrared, which is predicted for small crystalline spheres, may be the result of either noncrystallinity or nonsphericity (or both). Therefore, the infrared emission spectrum may not prove to be as uniquely diagnostic of interstellar grain characteristics as it once was thought to be. 

Coyne, G. V., T. Gehrels, and K. Serkowski, 1974. Wavelength dependence of polarization XXVI. The wavelength of maximum polarization as a characteristic parameter of interstellar grains, Astron. J., 79, 581-589. 

Huffman, D. R., 1977. Interstellar grains the interaction of light with a small-particle system, Adv. Phys., 26, 129-230. 

Seki, J., and T. Yamamoto, 1980. Amorphous interstellar grains wavelength dependence of far-infrared emission efficiency, Astrophys. Space Sci., 72, 79-86. 

Wickramasinghe, N. C., and K. Nandy, 1972. Recent work on interstellar grains, Rep. Prog. Phys., 35, 157-234. 

As noted previously, most of the presolar grains so far identified are circumstellar condensates (stardust), but some grains formed in interstellar space. The interstellar grains are not likely to contain large isotopic anomalies. So how can we recognize these interstellar grains in meteorites ... 

What are the important differences between circumstellar condensates and interstellar grains ... 

Ice mantles are important constituents of interstellar grains in molecular clouds, and icy bodies dominate the outer reaches of the solar system. The region of the solar system where ices were stable increased with time as the solar system formed, as accretion rates of materials to the disk waned and the disk cooled. The giant planets and their satellites formed, in part, from these ices, and probably also from the nebular gas itself. 

Interstellar grains with ice mantles probably comprised a significant amount of the material that collapsed to form the solar nebula. Heating of this material caused the icy mantles to sublimate, producing a vapor that subsequently condensed as crystalline ices as the nebula cooled. By mass, H20 ice rivals rock in terms of potentially condensable matter from a gas of cosmic composition. The amount of water ice depends, of course, on the extent to which oxygen is otherwise tied up with carbon as CO and/or C02 (Prinn,... 

Sephton, M. and Gilmour, I. (2000) Aromatic moieties in meteorites relicts of interstellar grain processes Astrophysical Journal, 540, 588-591. 

Indeed, the actual carbon fraction in fullerenes depend of the proper mixture of these molecules in the interstellar medium. It is likely that the number density of fullerenes and buckyonions will decrease with increasing radius (R). A distribution of the type N(full) a R m has been frequently considered in the literature on interstellar grain populations (Mathis et al. 1977). A mixture of fullerenes and buckyonions following such size distribution may reproduce the observed UV bump. The best fits to the shape, peak energy and width of the bump are obtained for m values in the range 2.5 4.5 (Fig. 1.6b). 

The first steps in any new discipline are always slow and tentative but once they have been made, growth of the subject is almost always exponential. Such has been the case for C60 and the discovery of interstellar grains in meteorites. Both these subjects are new areas of science involving carbon, demonstrating the spectacular scope in the chemistry of this unique element. 

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