Presolar grains graphite

The carriers of anomalous Ne-E (two forms of which were now known) and Xe-S were quickly identified. Neon-E(H), which is released at temperatures above 1200 °C in stepped heating experiments, and Xe-S were found to be carried in presolar silicon carbide (Tang and Anders, 1988). Neon-E(L), which is released below 900 °C, was found to be carried by presolar graphite (Amari et al., 1990). Once these presolar compounds were shown to be present in meteorites, studies were carried out to identify all of the different types of meteorites that carry presolar grains. Concentrated searches for other presolar phases were also initiated, and many new types of presolar grains have been found. This work is just beginning, however, and we cannot yet account for the majority of the presolar components that must have been present in the Sun s parent molecular cloud. 

Silicon is one of the most important elements in astronomical studies based upon the anomalous isotopic compositions of presolar grains. These include not only the presolar grains containing silicon (as SiC), but also presolar graphite particles containing trace Si compositions. These isotopic variations have helped define physically distinct families of presolar grains and helped to identify their stars of origin. 

Presolar grains Supernova condensates, called SUNOCONs, are presolar grains that condensed from the expanding supernova interior gas. Graphite and SiC... 

Figure 2.5 Presolar grains from primitive meteorites. Left presolar SiC from the Murchison meteorite scale bar is 200 nm. Middle presolar graphite from Murchison scale bar is 1 pm. Right presolar silicate grain (within the white circle) in the matrix of the Acfer 094 meteorite scale bar is 500 nm. Photo credit Max Planck Institute for Chemistry.

Compared to carbonaceous presolar grains much less isotope information, mostly for the major elements, is available for O-rich presolar dust (Lodders Amari 2005 Zinner 2007). This has several reasons. Other than presolar SiC and graphite, presolar oxides have only low trace-element concentrations. Moreover, it is not possible to produce chemical separates that consist mostly of presolar oxide grains. Presolar silicates can be found only in situ by ion imaging (see Appendix 2), a time-consuming task. The O-isotopic data of refractory oxides (corundum and other... 

Chondrite matrices are also the carriers of presolar grains. These phases cover a broad mineralogy and include diamonds and graphite, silicon carbide (SiC), titanium carbide (TiC), silicon nitride (SisN, ), corundum, spinel, silicates, and even rare metal grains. 

Graphite, the third type of carbonaceous presolar grains, was isolated because it is the carrier of Ne-E(L) (Amari et al., 1990 Amari et al., 1995b). Subsequent isotopic measurements of individual grains revealed anomalies in many different elements. 

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