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	Presolar grains - Wikipedia, the free encyclopedia
		Presolar grains are tiny crystalline grains found in the fine-grained matrix of primitive meteorites, and are assumed to be older than the solar system.
		Because presolar grains consist of refractory minerals, they survived the collapse of the solar nebula, and also the subsequent formation of planetesimals.
		Presolar grains are investigated using scanning or transmission electron microscopes (SEM/TEM), and mass spectrometric methods (noble gas mass spectrometry, resonance ionization mass spectrometry (RIMS), secondary ion mass spectrometry (SIMS, NanoSIMS)).
	en.wikipedia.org /wiki/Presolar_grains (409 words)

	PSR Discoveries: Hot Idea: Stardust in the Lab
		The presolar nature of the dust grains is revealed in the relative abundances of the isotopes of the common elements.
		SEM micrograph of presolar graphite grain, 5 micrometers in diameter, from the Murchison meteorite.
		Ratios of silicon isotopes in presolar grains from the Murchison carbonaceous chondrite.
	www.psrd.hawaii.edu /July97/Stardust.html (2156 words)

	PSRD:: Silicate Stardust in Meteorites
		Presolar grains, also called stardust, are exotic compounds such as diamond, graphite, aluminum oxide, and silicon carbide.
		One explanation is that until recently presolar grains were found by using strong acids to dissolve 99.9% of the meteorite, leaving a residue of acid-resistant grains.
		In contrast, all silicon carbide grains are presolar.
	www.psrd.hawaii.edu /June04/silicatesMeteorites.html (2081 words)

	[No title] (Site not responding. Last check: 2007-10-29)
		Since presolar diamond and SiC were discovered eleven years ago, presolar grains have revitalized the study of stellar nucleosynthesis and have precipitated a radical change in the way meteoriticists and cosmochemists think about the origin of the solar system.
		Presolar grains also potentially provide information on the relative rates of early and late nucleosynthesis in the galaxy, the rate of galactic mixing, the degree to which isotopic composition tracks metallicity, and whether the sun has a composition that is average for its age and location or is somehow anomalous.
		Presolar Grains as Probes of Nebular Processing: The presence of presolar grains in all classes of chondrites [19, 20] challenges the notion that the presolar history was erased by vaporization of dust in the solar nebula [e.g., 21].
	www.uark.edu /campus-resources/metsoc/huss.htm (1192 words)

	Presolar Grains in Meteorites (Site not responding. Last check: 2007-10-29)
		Presolar grains are tiny dust particles that are literally bits of stars we can study in the laboratory.
		These dust grains became swept up in the interstellar medium and eventually made their way into the cloud of gas and dust ("molecular cloud") from which the Sun, Earth and planets formed 4.6 billion years ago.
		Because the atoms in the grains are the original atoms from the parent stars, by studying this dust we can probe processes that occur inside stars and in the interstellar medium.
	www.dtm.ciw.edu /lrn/psg_main.html (265 words)

	Ernst K. Zinner
		Note that the numbers of grains of different types in the plot do not correspond to their observed frequencies but that grains from rare classes have been selectively located by ion imaging and are thus over-represented in the graph.
		Corundum and most of the SiC grains are believed to come from red giant stars, stars that lose a large part of their atmosphere at the end of their lives, corundum from oxygen-rich stars, SiC from carbon stars.
		Zinner E. (1998) Stellar nucleosynthesis and the isotopic composition of presolar grains from primitive meteorites.
	epsc.wustl.edu /admin/people/zinner.html (919 words)

	[No title] (Site not responding. Last check: 2007-10-29)
		Presolar grain studies have thus far led to rudimentary, but significant, improvements in understanding, a few of which I mention for purposes of illustration.
		While fluffy and fractal condensates seem plausible and, indeed, may describe as yet undiscovered presolar grains (silicates?), the known presolar phases are generally dense, compact and often euhedral solids (e.g., presolar SiC and corundum), appearing in crystal and electronic structure to be simply miniature versions of their macroscopic counterparts.
		There are two forms of presolar carbon (graphite and nanodiamonds), but we do not have a clear idea of the provenance of the latter or of the denser forms of the former, nor do we know what factors control whether graphite or diamond is produced.
	www.uark.edu /campus-resources/metsoc/bernatow.htm (1423 words)

	Presolar Grains in Meteorites: An Overview
		An overview of the various types of presolar grains identified so far in primitive meteorites, including their physical properties and a list of the elements for which isotopic abundance anomalies have been detected is given in Table 1.
		Grains larger than ~0.5 µm have been individually analyzed for the isotopic composition of the structural and several of the more abundant trace elements and show isotope abundance anomalies in many elements (Table 1).
		C observed in individual mainstream grains is similar to the range observed in the atmospheres of such stars (Alexander, 1993; Hoppe and Ott, 1997), is one of the strong arguments for the carbon star origin of most SiC grains.
	ecf.hq.eso.org /~ralbrech/amico/intabs/ottu.html (2430 words)

	[No title] (Site not responding. Last check: 2007-10-29)
		Primitive meteorites contain small concentrations (ppb to ppm) of presolar dust grains that have survived largely unaltered the processes that led to the formation of the solar system.
		The presolar dust grains preserve memories of both nucleosynthesis in the parent stars and galactic chemical evolution.
		The other types of presolar grains are larger and range from about 0.2 to 20 micrometer.
	www.agu.org /pubs/gap/1999JA900194/1999JA900194.html (247 words)

	American Scientist Online - Stardust Memories (Site not responding. Last check: 2007-10-29)
		These presolar grains are indeed from a heaven, one much older and in a different place from the one we see in the night sky.
		Once the grains have been isolated and identified—"tedious work, requiring a great deal of care," says Lewis—the next step is to deduce the type of star that could synthesize the various isotopes in the grain and produce the grain itself.
		The theorists' calculations have shown that many of the presolar grains were made by stars at or near the end of their lives.
	www.americanscientist.org /template/AssetDetail/assetid/15747 (799 words)

	First silicate stardust found in a meteorite
		Nine grains, with diameters from 0.1 to 0.5 micrometers, had unusual oxygen isotope ratios and were highly enriched in silicon.
		Five grains were enriched in 17O and slightly depleted in 18O, suggesting that deep mixing in red giant or asymptotic giant branch stars was responsible for their oxygen isotopic compositions.
		One grain was very depleted in 18O and therefore was likely produced in a low-mass star when surface material descended into areas hot enough to support nuclear reactions.
	www.eurekalert.org /pub_releases/2004-03/wuis-fss030304.php (946 words)

	Encyclopedia: Meteorite (Site not responding. Last check: 2007-10-29)
		79% of meteorites are chondrites - balls of mafic minerals with small grain size indicative of rapid cooling.
		Also, presolar grains are identified in carbonaceous chondrites.
		The isotope ratios of carbonaceous chondrites are similar to those of the Sun.
	www.nationmaster.com /encyclopedia/Meteorite (2028 words)

	Geological Sciences at ASU: Gary R. Huss (Site not responding. Last check: 2007-10-29)
		Topics of my current research include presolar grains (grains that formed before the solar system existed) which we recover from primitive meteorites, short-lived radionuclides and chronology of the early solar system, and the origin of the various components of chondritic meteorites (matrix, chondrules, calcium-aluminum inclusions (CAIs), metal grains).
		Most of the known types of presolar grains apparently formed as direct condensates from gas ejected from dying stars.
		Presolar grains have now been found in the most primitive member of all chondrite classes that have been studied.
	geology.asu.edu /people/scientists/huss (1739 words)

	ScienceWeek
		Surprisingly, circumstellar silicate grains were absent from the collection of identified presolar grains despite attempts to isolate them from meteorites.
		Two grains are identified as pyroxene, two as olivine, one as a glass with embedded metal and sulfides (GEMS), and one as an Al-rich silicate.
		These grains of circumstellar dust predate the solar system and provide a new and powerful way to investigate stellar evolution and nucleosynthesis with a level of detail and precision almost unheard of in nuclear astrophysics.
	scienceweek.com /2004/sc040709-2.htm (1420 words)

	Reprints (Site not responding. Last check: 2007-10-29)
		Presolar Grains From Meteorites: Remnants From the Early Times of the Solar System.
		Presolar SiC Grains of Type A and B: Their Isotopic Compositions and Stellar Origins.
		Boron in Presolar Silicon Carbide Grains from Supernovae, Astrophys.
	solarsystem.wustl.edu /reprints.htm (2357 words)

	[meteorite-list] Silicate Stardust in Meteorites (Site not responding. Last check: 2007-10-29)
		Written by G. Jeffrey Taylor Hawai'i Institute of Geophysics and Planetology One of the most exciting discoveries in cosmochemistry during the past 15 years is the presence of presolar grains in meteorites.
		By analyzing oxygen isotopes (16O, 17O, and 18O), the rare presolar grains will be conspicuous in a sea of grains with normal solar system oxygen isotopic composition, like supernovae in the normal starry sky.
		The grain identified with the red circle, however, stands out by being enriched in 17O and depleted in 18O compared to solar values; it is a presolar grain.
	six.pairlist.net /pipermail/meteorite-list/2004-June/161865.html (2257 words)

	Megan O'Grady Abstract (Site not responding. Last check: 2007-10-29)
		Typically, presolar SiC grains are isolated from meteorites by dissolving 99.9% of these meteorites in acid solutions — a method analogous to "burning down the haystack to find the needle." A mixture of HCl and HF is primarily used to dissolve meteorites, yet any presolar SiC grains within the meteorites are able to remain intact.
		The thin section from this SiC presolar grain was subsequently examined under a transmission electron microscope (TEM), allowing for further observation of its structure and composition.
		This was the first occasion in which a presolar grain that was not exposed to acid solutions could feasibly be examined under a TEM.
	www.gl.ciw.edu /interns/2001/OGrady_abstract.html (292 words)

	STARDUST FROM METEORITES
		The study of presolar meteoritic grains is a new inter-disciplinary field that brings together topics from nuclear physics to astronomy and chemistry.
		However, with the recent discovery that some dust grains extracted from primitive meteorites were produced in stellar environments, we now have the opportunity to gather information about stars and our Galaxy from the laboratory analysis of tiny pieces of stardust.
		While a number of specialized reviews exist on the topic, this book is the first work that brings together in a unified and accessible manner the background knowledge necessary for the study of presolar grains together with up-to-date discoveries in the field.
	www.worldscibooks.com /physics/5705.html (350 words)

	Researchers discover carriers of astronomical 2175 extinction line in presolar grains
		Floss said that Bradley's discovery is significant because organic carbon and amorphous silicates are abundant in interstellar dust clouds and abundant carriers are needed to account for the fact that the 2175 Å feature is so commonly observed by astronomers.
		The Washington University contribution is important because the NanoSIMS measurements prove that these grains in the IDPs are actually presolar.
		The presolar grains in IDPs range from 100 nanometers to 500 nanometers.
	www.eurekalert.org /pub_releases/2005-01/wuis-rdc011005.php (719 words)

	[151.01] Isotopic heterogeneity in the interstellar medium: constraints from presolar dust grains (Site not responding. Last check: 2007-10-29)
		The Si isotopic composition of presolar SiC grains from meteorites is believedto largely reflect the initial variability of the grains' parent AGB stars, but it is unknown how much of this variability is due to mean chemical evolution and how much to incomplete mixing of material from distinct supernovae.
		This suggests that either the circumstellar oxide grains and SiC grains formed in very different stellar populations or that local enrichment of molecular clouds is not the correct explanation for isotopic variability in presolar grains.
		Monte Carlo modeling of inhomogeneous chemical evolution is in progress and should help quantify the level of allowed isotopic heterogeneity in the interstellar medium and aid in the interpretation of the presolar grain isotopic data.
	www.aas.org /publications/baas/v33n4/aas199/883.htm (330 words)

	[49.06] Observational Evidence for Presolar Grains around Oxygen-rich Evolved Stars (Site not responding. Last check: 2007-10-29)
		Many presolar grain types have been found in meteorites since the discovery of presolar silicon carbide (SiC) grains in the Murray meteorite.
		There is very little observational evidence for most of these presolar grains around AGB stars, and what little evidence does exist is generally misinterpreted.
		We present the observational evidence (or lack thereof) for these oxide grains, and discuss the discrepancies between meteoritic and astronomical results, as well as the problems of interpreting dust features in astronomical spectra.
	www.aas.org /publications/baas/v35n5/aas203/682.htm (193 words)

	Universe Today - Silicate Found in a Meteorite
		This is an important discovery, because it tells researchers that the early solar system formed from gas and dust, and not in a hot solar nebula - until now, these silicate particles had only been found in interplanetary dust.
		The team used a special mass spectrometer to analyze the composition of individual grains in the meteorite, searching for particles which had to be formed in stars.
		In the March 5 issue of Science, Nguyen and her advisor, Ernst K. Zinner, Ph.D., research professor of physics and of earth and planetary sciences, both in Arts and Sciences, describe nine specks of silicate stardust — presolar silicate grains — from one of the most primitive meteorites known.
	www.universetoday.com /am/publish/silicate_found_meteorite.html?532004 (1191 words)

	Ernst K. Zinner
		Bio: The research interests of Ernst Zinner are centered on the study of primitive meteorites and interplanetary dust, particularly their record of the nucleosynthesis of elements in stars and the formation of the solar system.
		The most important information is contained in presolar grains that condensed in the expanding atmospheres and the explosions of stars and survived the formation of the solar system and in refractory solids that formed in the solar system but carry a presolar isotopic signature.
		In recent years, Zinner and co-workers have identified four types of presolar dust in meteorites: silicon carbide, graphite, corundum and silicon nitride.
	news-info.wustl.edu /sb/page/normal/486.html (1359 words)

	Energy Citations Database (ECD) - Energy and Energy-Related Bibliographic Citations
		The imprint of nova nucleosynthesis in presolar grains
		Five silicon carbide and two graphite presolar grains, whose isotopic signatures point toward a nova origin, are described.
		In addition, theoretical isotopic ratios of several nuclear species, ranging from C to Si, computed with hydrodynamic models of nova outbursts, are shown.
	www.osti.gov /energycitations/product.biblio.jsp?osti_id=20519411 (183 words)

	Record: Researchers find carriers of astronomical extinction line in presolar grains
		Last year, Frank Stadermann, Ph.D., senior research scientist in physics, and Christine Floss, Ph.D., senior research scientist in earth and planetary sciences and physics, both in Arts and Sciences, reported that some grains within IDPs are presolar in origin.
		Bradley used a state-of-the-art transmission electron microscope equipped with a monochromator and a high-resolution electron energy-loss spectrometer, allowing him to analyze in the 2175 Å range, to get exactly the same type of absorption feature in these dust particles.
		The WUSTL contribution is important because the Nano-SIMS measurements prove that these grains in the IDPs are presolar.
	record.wustl.edu /news/page/normal/5082.html (781 words)

	Newly discovered presolar grain phases
		A new type of presolar grain, namely titanium carbide/iron composite grains, was recently discovered (in 4 different SN graphites).
		These composite grains consist of a TiC with an iron-nickel grain (either BCC kamacite or FCC taenite) epitaxially grown onto one of the TiC faces.
		The diffraction patterns next to the images can be used to determine the crystal structure of both phases (TiC and iron) and to see exactly how one grows on the other.
	www.physics.wustl.edu /~tkc/SNgraphites/newphases.htm (209 words)

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