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presolar grains
Presolar grains are interstellar solid matter in the form of tiny solid grains, each thought to originate in a single star, and all originating at a time before the Sun was formed (presolar: before the Sun).
Presolar stardust grains formed within outflowing and cooling gases from earlier (pre-Sol) stars. The stellar nucleosynthesis that took place within the presolar star gives each granule an isotopic composition unique to that star, which differs from the isotopic composition of our solar system's matter as well as from the galactic average. These isotopic signatures often fingerprint very specific astrophysical nuclear processes〔Ernst Zinner (1998) Stellar nucleosynthesis and the isotopic composition of presolar grains from primitive meteorites, ''Annual Review of Earth and Planetary Sciences'' 26:147-188.〕 that took place within the parent star and prove their extra-Sol origin.〔T. J. Bernatowicz and R. M Walker (1997) Ancient stardust in the laboratory, ''Physics Today'' 50:1212, 26-32〕〔D.D. Clayton and L.R. Nittler, Astrophysics with presolar stardust, ''Ann. Review of astron. Astrophys.'' 42, 39-78 (2004)〕
==History==
In the 1960s, the noble gases neon〔D. C. Black and R. O. Pepin (1969) Trapped neon in meteorites. II., ''Earth Planet. Sci. Lett.'' 36, 377-394〕 and xenon〔J. H. Reynolds and G. Turner (1964) Rare gases in the chondrite Renazzo, ''J. Geo. Phys. Res.'' 69, 3263-3281〕 were discovered to have unusual isotopic ratios in primitive meteorites. Their origin and the type of matter they contained was a mystery. In the mid-1970s, Donald D. Clayton predicted that unusual isotopic compositions would be found within thermally condensed grains produced during mass loss from stars of differing types, and argued that such grains exist throughout the interstellar medium.〔D. D. Clayton, Precondensed Matter: Key to the Early Solar System. ''Moon and Planets'' 19, 109-137 (1978)〕〔D.D. Clayton and R.A. Ward, s-process studies: xenon and krypton isotopic abundances, ''Astrophys.J.'' 224, 1000-1006 (1978)〕 He defined several different types of presolar grains that might be found: stardust from red giant stars, sunocons from supernovae, nebcons from nebular accretion, and novacons from novae. His suggestions lay dormant for a decade until such grains were discovered within meteorites. The first unambiguous demonstration of the existence of stardust within meteorites came from the laboratory of Edward Anders in Chicago,〔B. Srinivasan and E. Anders, ''Science'' 201, 51-56 (1978)〕 who found that the xenon isotopic abundances contained within an insoluble carbonaceous residue that remained after the meteorite bulk matched almost exactly the predictions for red-giant stardust.〔 There followed a decade of intense experimental searching to isolate single grains of those xenon carriers.
In 1987 diamond〔Lewis R.S., Tang M., Wacker J.F., Anders E. and Steel E. (1987) ''Interstellar diamonds in meteorites'', Nature 326, 160-162〕 and silicon carbide〔Bernatowicz, T., Fraundorf, G., Ming, T., Anders, E., Wopenka, B., Zinner, E., and Fraundorf, P. (1987) ''Evidence for interstellar SiC in the Murray carbonaceous meteorite'', Nature 330, 728.〕 grains were found to contain noble gases. Significant isotopic anomalies were in turn measured within the structural chemical elements of these grains.〔Ernst Zinner (1996) Stardust in the laboratory, ''Science'' 271:5245, 41-42〕
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