The isotopic composition of Te has been measured in a purified sample of interstellar microdiamonds from the Allende meteorite. Small positive anomalies were only found in Te-128 (4.0 +/- 0.3 parts per thousand) and Te-130 (9.3 +/- 2.0 parts per thousand) from three analyses of the Allende microdiamond sample EB#2. The magnitude of the anomalies are smaller than in the heavy noble gases, although the absolute amount of anomalous Te is greater than that of anomalous Xe in the same sample. The anomalies in Te can be interpreted in terms of standard r-process nucleosynthesis followed by rapid separation of the stable isotopes from their radioactive precursors.

Four density fractions of interstellar graphite were analyzed for isotopically anomalous noble gases by stepped heating. As in SiC, the dominant components show the signature of the s-process and apparently come from AGB- (Asymptotic Giant Branch) stars of 1–3 M⊙. But graphite seems to come from a broader range of stars and conditions, comprising at least three and perhaps all four known sources of carbon stardust. Two extreme types of KrS are present, having high or low (Kr86Kr82)s ratio and occurring in high- or low-density graphite, respectively. [(Kr86Kr82)s = 4.8 in the fraction of 2.15–2.20 g/mL and ≤0.5 in fractions of ≤2.15 g/mL]. These imply two different kinds of AGB-stars, with mean neutron exposures of ≥0.55 mb−1 and ≤0.07 mb−1 . In addition to neon from AGB-star He-shells with its characteristic Ne20Ne22 ∽ 0.09, all graphite fractions also contain monoisotopic Ne22 from the decay of Na22 (t12 = 2.58a). This suggests the presence of material from novae and supernovae. In contrast to the differences in isotopic ratios, the elemental ratios of the anomalous gases resemble those of SiC, with a generally close match to AGB-star He-shells. But Ne is low by 10–100x, presumably due to diffusion loss.

A procedure has been developed for isolating three types of interstellar grains from primitive meteorites, in >90% purity and yields of generally greater-than-or-equal-to 70%, and is here applied to the Murchison C2M meteorite. Silicates are dissolved in HF-HCl kerogen (macromolecular organic matter) is destroyed by Cr2O7=, KOH, and H2O2, and microdiamonds (approximately 400 ppm) are recovered as a colloid. Graphite (<1 ppm) is isolated by density and size separations. Spinel in the residue is dissolved in H2SO4, leaving SiC (approximately 6 ppm), hibonite, and corundum.The size distribution of SiC has been measured in the range 0.2 to 6 mum. Over part of this range, it can be fit either to a power-law or a log-normal distribution, but the deficiency of small grains strongly favors the latter. Statistics are more limited for graphite spherules, but they, too, follow a log-normal distribution, and so does interstellar diamond (LEWis et al., 1989). Apparently the primary condensation process in stellar atmospheres consistently yields a log-normal distribution. The power-law distribution commonly inferred for interstellar grains may have been produced by secondary processes such as fragmentation.

We have analyzed He, Ne, Ar, Kr, and Xe in fourteen size fractions of interstellar SiC, isolated from the Murchison C2 chondrite. All are mixtures of a highly anomalous component bearing the isotopic signature of the astrophysical s-process and a more normal component, generally solar-like but with anomalies of up to 30% in the heavy isotopes. As these two components strikingly resemble predictions for the He-burning shells and envelopes of red giant carbon stars, it appears that the SiC grains are pristine circumstellar condensates from such stars. A number of elemental and isotopic ratios (such as Kr-80/Kr-82 and Kr-86/Kr-82) vary with grain size, suggesting that the SiC comes from carbon stars representing a range of masses, metallicities, temperatures, and neutron densities.The Ne-21-content of the SiC suggests a presolar cosmic-ray irradiation of up to 130 Ma, representing the interval between formation of the grains in a circumstellar shell and arrival in the solar system 4.6 Ga ago. Actually there is evidence that most of the Ne-21 (and Ne-22) is in less-than-or-equal-to 10% of the grains, suggesting that much of the SiC was degassed during or shortly before formation of the solar system. Thus the true cosmic-ray ages may be 7 to 18X longer. Apparently the gas-rich SiC grains predate the solar system by rat least 130 Ma and possibly up to 2000 Ma.

We report new chemical analyses for up to 26 trace elements, including seldom-determined highly siderophile elements Ir, Os, Re, Au, Pd, and Ge, for 59 lunar samples. Most of these samples are polymict breccias from Apollo 16. Remarkably few have Group 7 (extremely low Au/Ir) meteoritic components. Several samples have uncommonly high Au/(Ir + Re) ratios, even higher than group IL. Volatile-element enrichments are found in several fragments from "rusty rock" 66095. A matrix sample from fragmental breccia 60639 shows Cd and In enrichments, also observed previously in samples of anorthosite and mare basalt from the same breccia. Evidently, for these highly labile elements, chemical exchange has affected clasts that for most other elements are pristine. Interesting pristine samples analyzed include the sodic ferrogabbro component of 67915, which has an extraordinarily high Re concentration, by pristine rock standards; KREEP basalt 15386, which has extremely low Ir, but (in common with most other pristine KREEP rocks) a relatively high Ge concentration; and FAS anorthosite 65315, which has probably the lowest REE levels of any lunar anorthosite.

Noble gases in several HF/HCL resistant residues of the CM2 chondrite Murchison were measured by closed-system stepped etching, in order to study the planetary gases in their major carrier "Q"-an ill-defined minor phase, perhaps merely a set of adsorption sites. Neon, Ar, Kr, Xe, and probably also He in "Q" of Murchison have the same isotopic and nearly the same elemental abundances as their counterparts in Allende (CV3). The isotopic composition of Ne-Q is consistent with mass-dependent fractionation of either solar wind Ne or Ne from solar energetic particles. Unlike Allende, Murchison during HNO3 attack releases, besides Q-gases, large amounts of two other Ne-components, Ne-E and Ne-A3, a third subcomponent of Ne-A. This work confirms that Q-gases of well-defined composition were an important noble gas component in the early solar system and are now found in various classes of meteorites, such as carbonaceous chondrites, ureilites, and ordinary chondrites. Ne-Q may have played a role in the formation of noble gas reservoirs in terrestrial planets.

Forty-one large SiC grains from the Murchison CM2 chondrite, ranging up to 15 x 26-mu-m, were analyzed by ion probe mass spectrometry for the isotopic compositions of C, N, Mg, and Si, and the concentrations of Al, Ti, V, Fe, Zr and Ba. Most grains were also examined by Raman spectroscopy. The majority have large isotopic anomalies, with C-13/C-12 and N-14/N-15 up to 30x and 9x solar, and Si-29,Si-30 enriched by up to 102 parts per thousand. Only two grains, characterized by extremely heavy carbon (delta-C-13 = 28,582 and 18,883 parts per thousand) give evidence for fossil Mg-26, with (Al-26/Al-27)0 ratios of 2.1 x 10(-3) and 3.9 x 10(-3).On the basis of C and Si isotopic composition, twenty-nine of the grains fall into three compact clusters, presumably from three discrete sources. Two of these clusters are anomalous and comprise only grains of cubic structure (according to their Raman spectra). The third, isotopically, normal cluster contains only anhedral, noncubic grains; and although contamination cannot be categorically excluded, an origin in a reducing environment in the early solar system is a viable possibility. The reality of these clusters is further supported by differences in morphology, size, N-content, and Al/N. This clustering of coarse-grained (> 6-mu-m) SiC stands in sharp contrast to the quasicontinuous distribution of finer grained SiC and suggests that the top approximately 0.1% of the mass distribution is a distinct population.A few conclusions can be reached about the astrophysical origin of the coarse-grained SiC. The C and N isotopic compositions of the anomalous grains are not very diagnostic, being consistent with H-burning in the CNO cycle. The very existence of SiC requires C-rich stars, of C/O > 1. The Si-isotopic compositions qualitatively show the signature of neutron capture in He-burning shells of highly evolved stars, narrowing the choice to asymptotic giant branch (AGB) or Wolf-Rayet stars. AGB stars are the more likely candidates, as only they can (during their final, planetary nebula phase) provide high mass loss rates and hence the high gas densities required for growth of large SiC grains.

INTERSTELLAR graphite and silicon carbide grains recovered from the Murchison CM2 chondritic meteorite are known to show large anomalies in the isotopic abundances of neon, xenon, carbon, nitrogen and silicon1-3. These anomalies provide clues to the nucleosynthetic origin of the material from which the grains formed. Here we report that both types of grain also have large abundances of Mg-26 from the decay of extinct Al-26 (half-life 705,000 years). The deduced initial Al-26/Al-27 ratios range up to 0.06 in graphite and 0.2 in SiC-1,200 and 4,000 times the maximum values found in refractory inclusions in primitive meteorites. All proposed stellar sources of carbonaceous dust (red giants, novae, Wolf-Rayet stars and supernovae) also produce Al-26, but the highest Al-26/Al-27 ratios found in these grains seem to rule out Wolf-Rayet stars and supernovae. The aluminium abundance correlates with that of nitrogen, suggesting that the aluminium condensed as aluminium nitride.

Twenty-six A12O3 grains from the Murchison CM2 chondrite have been analyzed by ion microprobe mass spectrometry for the isotopes of O, Mg, and Ti and the abundances of Mg, Ca, Sc, Ti, V, Sr, Y, Zr, La, and Ce. Being the most refractory major phase in solar matter, A12O3 retains a particularly durable record of the early solar system. 26Mg24Mg ranges up to 56× the solar-system ratio, owing to decay of extinct 26A1, but the initial 26Al24Al ratios do not exceed the canonical maximum of 5 × 10−5 established in earlier work. There is no evidence for fossil radiogenic 26Mg surviving from presolar times. Oxygen isotope compositions cluster mainly near δ18O = −50%. (lighter than bulk spinel), but range from −94 to −11%.. The grains divide into three groups on the basis of 26A1, 16O, Ti, and V content, and 26Al and O show distinctive correlations (in contrast to all previous studies), suggesting an origin from the following components. Group 1 (high 26A1, Ti, V): mixture of material with 26Al24Al = 5 × 10−5 and δ18O = −45%. with dead Al of δ18O ≈ −100%.. Group 2 (low 26A1, Ti, V): mixture of material with 26Al27Al = 5 × 10−6 with dead Al, with complex fractionation and exchange of O resembling that of FUN inclusions. Group 3 (no 26A1; high Ti, V): dead Al from various sources. In terms of this model, the corundum formed from two components with live 26Al and a mass fraction of 43% dead Al, but we do not know whether this figure is typical of carbonaceous chondrites in toto, let alone the entire solar nebula. Trace element abundances in corundum are generally at less than Cl levels relative to Al, and decline with increasing volatility, from Zr to Ca.

Twenty-six corundum (Al2O3) grains from the Murchison C2 chondrite have been studied by ion probe mass spectrometry, to determine the isotopic record of this highly refractory phase. Mg-26/Mg-24 ranges up to 56 times the solar system ratio, owing to decay of extinct Al-26, but the initial Al-26/Al-27 ratios (= R0) do not exceed the canonical maximum of 5 x 10(-5) in other meteoritic samples. We conclude that this ratio represents the abundance of live Al-26 in the early solar system, not fossil radiogenic Mg-26 surviving from presolar times. The grains divide into three groups on the basis of Al-26, O-16, Ti, and V content, and Al-26 and O-16 show distinctive correlations (in contrast to all previous studies). This suggests an origin from at least three discrete components, two of which contained live Al-26 (R0 = 5 x 10(-5) and 5 x 10(-6)). Variable R0 values in primitive meteorites apparently reflect mixing of these components rather than decay of Al-26 over a protracted interval and thus are consistent with a short time scale (< 10(6) yr) for the solar nebula.

The IMS-HIS double-focusing mass spectrometer that flew on the Giotto spacecraft covered the mass per charge range from 12 to 56 (amu/e). By comparing flight data, calibration data and results of model calculations of the ion population in the inner coma, the absolute mass scale is established, and ions in the mass range 25 to 35 are identified. Ions resulting from protonation of molecules with high proton affinity are relatively abundant, enabling us to estimate relative source strengths for H2CO, CH3OH, HCN, and H2S, providing for the first time a positive in situ measurement of methanol. Also upper limits for NO and some hydrocarbons are derived.

Nature 348, 293-302 (1990) IN this article, the second affiliation for Edward Anders was omitted. In addition to the Chicago address, he is attached to the Physikalisches Institut der Universitat, CH-3012 Bern, Switzerland.

We have measured carbon at the marine K/T boundary site SM-4 at the Sumbar river in Turkmenia, USSR, which has an undisturbed Ir profile and the largest known Ir anomaly (580 ng/cm2). Twenty samples, ranging from −100 to +100 cm, were analyzed to determine the concentration and δ13C of elemental carbon and kerogen, using a Cr2O7 oxidation method (Wolbach and Anders, 1989) to resolve these components. The samples were unusually complex, containing 3 kerogen components of distinctive IR spectra and half-lives in Cr2O7 (~200, ~100, and ⪡60 h), in addition to soot and charcoal from the K/T fire. The elemental C has δ13C = −25.96 ± 0.6 l%o, close to the mean for 11 K/T sites (-25.8 ± 0.6%; 11 mg/cm2). The first of the 2 kerogen components (δ13C = −22.8%), which dominates in the Cretaceous, appears to come from detrital carbonaceous shale; the second (δ13C = −27.7%o) occurs only in the boundary clay and may come from land plant material swept to sea, or phytoplankton grown in the presence of excess, light CO2 from fires on land.