Engineering topics

Epstein, S.

Publications and source records attributed to Epstein, S..

At least 19 records

NASA NTRS1994

Isotopic analyses of nitrogenous compounds from the Murchison meteorite: ammonia, amines, amino acids, and polar hydrocarbons

The combined volatile bases (ammonia, aliphatic amines, and possibly other bases), ammonia, amino acids, and polar hydrocarbons were prepared from the Murchison meteorite for isotopic analyses. The volatile bases were obtained by cryogenic transfer after acid-hydrolysis of a hot-water extract and analyzed by combined gas chromatography-mass spectrometry of pentafluoropropionyl derivatives. The aliphatic amines present in this preparation comprise a mixture that includes both primary and secondary isomers through C5 at a total concentration of > or = 100 nmoles g-1. As commonly observed for meteoritic organic compounds, almost all isomers through C5 are present, and the concentrations within homologous series decrease with increasing chain length. Ammonia was chromatographically separated from the other volatile bases and found at a concentration of 1.1-1.3 micromoles g-1 meteorite. The ammonia analyzed includes contributions from ammonium salts and the hydrolysis of extractable organic compounds, e.g., carboxamides. Stable isotope analyses showed the volatile bases to be substantially enriched in the heavier isotopes, relative to comparable terrestrial compounds delta D < or = +1221%; delta 13C = +22%; delta 15N = +93%). Ammonia, per se, was found to have a somewhat lower delta 15N value (+69%) than the total volatile bases; consequently, a higher delta 15N (>93%) can be inferred for the other bases, which include the amines. Solvent-extractable polar hydrocarbons obtained separately were found to be enriched in 15N (delta 15N = +104%). Total amino acids, prepared from a hydrolyzed hot-water extract by cation exchange chromatography, gave a delta 15N of +94%, a value in good agreement with that obtained previously. Nitrogen isotopic data are also given for amino acid fractions separated chromatographically. The delta 15N values of the Murchison soluble organic compounds analyzed to date fall within a rather narrow range (delta 15N = +94 +/- 8%), an observation consistent with their formation, or formation of their precursors, by interstellar chemistry.

Non-NASA Center↗

NASA NTRS1993

Sources of Na for the Io atmosphere

The physics and geology of Io have been extensively studied, but there has been little discussion of the chemistry. Relatively little is known about Io chemistry, but there are constraints. Further, it will be a long time before improvements will result from direct observation, given the severe difficulties with the Galileo mission. Via laboratory simulation experiments, plausible thermochemical and photochemical processes which determine the nature and amounts of surface constituents of Io are explored. The well-known density of Io shows that the planet overall is rocky. Because the orbit of Io is well within the magnetosphere of Jupiter and because Io only has a thin, transient SO2 atmosphere, the surface is continually sputtered with magnetospheric ions. Complex processes ionize and accelerate the Io surface atoms to keV and MeV energies. Remarkably, only S, O, and Na ions were found by Voyager. Sputtering also produces an atomic cloud of Na and S (O not observable) with a trace of K. Both gaseous and solid SO2 are known from spectroscopic studies. A trace of H2S and possibly CO2 are present. Geologic features are interpreted in terms of elemental S, but there is no direct evidence for this constituent. We thus have a rocky planet which does not have rocks on the surface. Our general goal is to understand the cycling of Na, S, and O through the crust and atmosphere on present-day Io and to understand how Io evolved to this state. A specific objective was to determine the phases on the surface which are the source of the Na in the atmosphere of Io.

Burnett, D. S.↗

NASA NTRS1993

High D/H ratios of water in magmatic amphiboles in Chassigny: Possible constraints on the isotopic composition of magmatic water on Mars

The D/H ratios of kaersutitic amphiboles contained in magmatic inclusions in the Shergottites Nakhlites Chassignites (SNC) meteorite Chassigny using the ion microprobe were measured. A lower limit on the delta(D(sub SMOW)) of the amphiboles is +1420 +/- 47 percent. Assuming Chassigny comes from Mars and the amphiboles have not been subject to alteration after their crystallization, this result implies either that recycling of D-enriched Martian atmosphere-derived waters into the planetary interior has taken place, or that the primordial hydrogen isotopic composition of the interior of Mars differs significantly from that of the Earth (delta(D(sub SMOW)) approximately 0 percent). In addition, the measurements indicate that the amphiboles contain less than 0.3 wt. percent water. This is much lower than published estimates, and indicates a less-hydrous Chassigny parent magma than previously suggested.

Watson, L. L.↗

NASA NTRS1992

Isotopic and molecular analyses of hydrocarbons and monocarboxylic acids of the Murchison meteorite

The monocarboxylic acids and hydrocarbons of the Murchison meteorite (CM2) were isolated for isotropic analysis. The nonvolatile hydrocarbons were analyzed as crude methanol and benzene-methanol extracts and also after separation by silica gel chromatography into predominantly aliphatic, aromatic, and polar hydrocarbon fractions. The volatile hydrocarbons were obtained after progressive decomposition of the meteorite matrix by freeze-thaw, hot water, and acid treatment. Molecular analyses of the aromatic hydrocarbons showed them to comprise a complex suite of compounds in which pyrene, fluoranthene, phenanthrene, and acenaphthene were the most abundant components, a result similar to earlier analyses. The polar hydrocarbons also comprise a very complex mixture in which aromatic ketones, nitrogen, and sulfur heterocycles were identified. The monocarboxylic acids, aliphatic, aromatic, and polar hydrocarbons, and the indigenous volatile hydrocarbons were found to be D-rich. The deuterium enrichment observed in these compounds is suggestive. In two separate analyses, the delta-D values of the nonvolatile hydrocarbons were observed to increase in the following order: aliphatic-aromatic-polar. This finding is consistent with an early solar system or parent body conversion of aromatic to aliphatic compounds as well as the suggestion of pyrolytic formation of aromatic from aliphatic compounds.

Krishnamurthy, R. V.↗

NASA NTRS1992

Hydrogen and carbon isotopic composition of volatiles in Nakhla: Implications for weathering on Mars

Gases were collected at 120, 200, 300, 415, and 600 and 850 C. Hydrogen yields for the 600 and 850 C aliquots were measured separately and then the gases were combined for isotopic analysis. CO2 samples collected at the two lowest temperature steps amounted to less than 0.5 mu mole and were not analyzed isotopically. Excluding the 120 C temperature step, the bulk delta D of the sample was + 187 percent. Delta D values increase from -91 percent in the 120 C step to +518 percent in the 315 to 850 C step. The hydrogen content is greatest in the 120 C step and is roughly constant in the 200, 300, and 415 C aliquots. Between 415 C and 850 C, the yield drops off considerably. From 850 C to 950 C, virtually no H2 and only minor CO2 (less than 1 mu mole) were extracted. Using the isotopic analysis from the 300, 415, 600, and 850 C temperature collections, the bulk delta C-13 sub (PDB) is 0.0 percent. The heaviest component (delta C-13 sub (PDB) of +29 percent) was collected between 300 and 415 C. The release of hydrogen at the low temperatures reported here is consistent with the breakdown of the phases that constitute the alteration product between approx. 250 and 650 C. Although not as high as the present Martian atmosphere, the high delta D values are consistent with a Martian origin for the meteorites in question.

Watson, L. L.↗

NASA NTRS1991

Correlated Si isotope anomalies and large C-13 enrichments in a family of exotic SiC grains

A hypothesis is presented to the effect that the distinctive morphological characteristics and comparatively simple Si isotope systematics identify the platy SiC crystals as a genetically related family, formed around a single isotopically heterogeneous presolar star on an association of related stars. The enrichments in C-13 and the Si isotope systematics of the platy SiC are broadly consistent with theoretical models of nucleosynthesis in low-mass, carbon stars on the ASG. The Si isotope array most plausibly reflects mixing between (Si-28)-rich material, inherited from a previous generation of stars, and material enriched in Si-29 and Si-30, produced in intershell regions by neutron capture during He-burning. The absence of a correlation between the Si and C isotopic compositions of the SiC suggests either episodic condensation of SiC, extending over several thermal pulses, in the atmosphere of a single star, or the derivation of the SiC from several stars characterized by different rates of C-13 production.

Stone, J.↗

NASA NTRS1991

Implanted He-3, He-4, and Xe in further studies of diamonds from Western Australia

In measurements of the noble gases in additional samples of diamonds from the Argyle and Ellendale lamproites in Western Australia, no neon-rich stones were encountered. No neon was detected above the relatively high blank levels in the glass apparatus. White and brown diamonds showed no differences in noble gas content, nor did samples segregated by the color of long-wave UF fluorescence. The rare gas patterns in the 1.2 Ga Argyle pipe are largely consistent with implanted He-3, He-4, and fissiogenic Xe from U/Th in the matrix rock in which the diamonds have been stored for so long. These implanted species are absent in diamonds from the much younger (about 20 Ma) Ellendale pipe. Implantation formulas for several models of inhomogeneously distributed U/Th are given. Differences in He-3 content between pipe and alluvial Argyle samples are consistent with expected cosmogenic production in the latter. An expanded data base for helium and carbon isotopic data on the same samples supports a negative (He-4)-delta(C-13) correlation seen in earlier work.

Mcconville, P.↗

NASA NTRS1991

Isotopic analyses of amino acids from the Murchison meteorite

An account is given of the results of H-2, C-13 isotopic analyses of the Murchison meteorite incorporating an ultrafiltration step to exclude the possibility of fine particulate contaminants. The meteorite's amino acids were chromatographically separated in order to preclude isotopic enrichment by basic compounds other than the amino acids. The results indicate that the Murchison amino acids are isotopically highly unusual; delta-C-13 is elevated by about 40 percent, and delta-D by fully 2500 percent. This high D content of the meteorite's alpha-amino acids may be due to the synthesis of their molecular precursors by low-temperature ion-molecule reactions in an interstellar cloud.

Pizzarello, S.↗

NASA NTRS1991

Stable hydrogen and carbon isotope ratios of extractable hydrocarbons in the Murchison meteorite

A fairly fool-proof method to ensure that the compounds isolated from meteorites are truly part of the meteorites and not an artifact introduced by exposure to the terrestrial environment, storage, or handling is presented. The stable carbon and hydrogen isotope ratios in several of the chemical compounds extracted from the Murchison meteorite were measured. The results obtained by studying the amino acids in this meteorite gave very unusual hydrogen and carbon isotope ratios. The technique was extended to the different classes of hydrocarbons and the hydrocarbons were isolated using a variety of separation techniques. The results and methods used in this investigation are described in this two page paper.

Krishnamurthy, R. V.↗

NASA NTRS1991

Isotopic composition of hydrogen in insoluble organic matter from cherts

Robert (1989) reported the presence of unusually enriched hydrogen in the insoluble HF-HCl residue extracted from two chert samples of Eocene and Pliocene ages. Since the presence of heavy hydrogen might be due to the incorporation of extraterrestrial materials, we desired to reexamine the same samples to isolate the D-rich components. Our experiments did not reveal any D-rich components, but the hydrogen isotope composition of the insoluble residue of the two chert samples was well within the range expected for terrestrial organic matter. We also describe a protocol that needs to be followed in the hydrogen isotope analysis of any insoluble organic matter.

Non-NASA Center↗

NASA NTRS1991

Implanted 3He, 4He, and Xe in further studies of diamonds from Western Australia

In measurements of the noble gases in additional samples of diamonds from the Argyle and Ellendale lamproites in Western Australia we have failed to encounter any neon-rich stones such as showed solar-like isotopic compositions in earlier work. No neon was detected above the relatively high blank levels in our glass apparatus. White and brown diamonds showed no differences in noble gas content, nor did samples segregated by the color of long-wave UF fluorescence. The rare gas patterns in the 1.2 Ga Argyle pipe are largely consistent with implanted 3He, 4He, and fissiogenic Xe from U/Th in the matrix rock in which the diamonds have been stored for so long. These implanted species are absent in diamonds from the much younger (approximately 20 Ma) Ellendale pipe. We give implantation formulae for several models of inhomogeneously distributed U/Th. Differences in 3He content between pipe and alluvial Argyle samples are consistent with expected cosmogenic production in the latter. An expanded data base for helium and carbon isotopic data on the same samples supports a negative [4He]-delta 13C correlation seen earlier in work from our group, but if the Argyle samples, which contain light carbon, are corrected for implanted 4He, the correlation is considerably weakened. We no longer see an earlier 3He/4He-delta 13C correlation.

NASA Discipline Number 52-10↗

NASA NTRS1987

Noble gases in diamonds - Occurrences of solarlike helium and neon

Seventeen diamond samples from diverse locations were analyzed for the contents of He, Ar, Kr, and Xe, and of their isotopes, using a Reynolds (1956) type glass mass spectrometer. The results disclosed a large spread in the He-3/He-4 ratios, ranging from values below atmospheric to close to the solar ratio. In particular, solarlike He-3/He-4 ratios were seen for an Australian colorless diamond composite and an Arkansas diamond, which also displayed solarlike neon isotopic ratios. Wide variation was also observed in the He-4/Ar-40 ratios, suggesting a complex history for the source regions and the diamond crystallization processes.

Honda, M.↗

NASA NTRS1987

Unusual stable isotope ratios in amino acid and carboxylic acid extracts from the Murchison meteorite

The isotopic composition of hydrogen, nitrogen, and carbon in amino acid and monocarboxylic acid extracts from the Murchison meteorite has been determined. The unusually high D/H and N-15/N-14 ratios in the amino acid fraction are uniquely characteristic of known interstellar organic materials. The delta D value of the monocarboxylic acid fraction is lower but still consistent with an interstellar origin. These results confirm the extraterrestrial origin of both classes of compound and provide the first evidence suggesting a direct relationship between the massive organosynthesis occurring in interstellar clouds and the presence of prebiotic compounds in primitive planetary bodies.

Epstein, S.↗

NASA NTRS1985

A search for presolar organic matter in meteorite

The D/H ratios and the C-13/C-12 ratios of acid-insoluble organic matter of 4 meteorites, Ochansk (H4), Plainview (H5), Gladstone (H6) and Odessa (IA), were measured. delta-D values for hydrogen extracted by stepwise combustion were negative, down to -280 deg/infinity. delta-C-13 values were also negative except in the case of the carbon coming off at the highest temperature steps for Plainview and Odessa meteorites. The concentrations of C-13-rich carbon were 3-5 orders of magnitude smaller than those found in Murchison meteorite, suggesting that relic grains of stellar condensates were mostly destroyed in the meteorites examined.

Yang, J.↗

NASA NTRS1984

Relic interstellar grains in Murchison meteorite

It is shown that, in the Murchison meteorite, the D/H ratios of hydrogen are unusually high in several separates and in one case up to 30 times the cosmic value of 2 x 10 to the -5th. Many phases show high C-13/C-12 ratios, up to 2.5 times the terrestrial value of 0.011. These C-13-rich and D-rich components of the two chemical elements are not correlated. They are heterogeneously distributed, suggesting that different components in the meteorite originated from different astrophysical sites and at different times. The D-rich hydrogen in the meteorite is probably due to molecules formed by ion-molecule reactions in interstellar clouds while the tiny amount of C-13-rich carbon is probably due to nucleosynthesis in red giant stars as suggested by Swart et al. (1983). Both of these heavy-isotope enriched components survived homogenization in the accumulation and subsequent history of the meteorites.

Yang, J.↗

NASA NTRS1983

Interstellar organic matter in meteorites

Deuterium-enriched hydrogen is present in organic matter in such meteorites as noncarbonaceous chondrites. The majority of the unequilibrated primitive meteorites contain hydrogen whose D/H ratios are greater than 0.0003, requiring enrichment (relative to cosmic hydrogen) by isotope exchange reactions taking place below 150 K. The D/H values presented are the lower limits for the organic compounds derived from interstellar molecules, since all processes subsequent to their formation, including terrestrial contamination, decrease their D/H ratios. In contrast, the D/H ratios of hydrogen associated with hydrated silicates are relatively uniform for the meteorites analyzed. The C-13/C-12 ratios of organic matter, irrespective of D/H ratio, lie well within those observed for the earth. Present findings suggest that other interstellar material, in addition to organic matter, is preserved and is present in high D/H ratio meteorites.

Yang, J.↗

NASA NTRS1982

Shock-induced devolatilization of calcite

Experimental measurements of the release adiabats by Vizgirda (1981) indicate that substantial vaporization takes place upon release from shock pressures of 37 GPa for calcite and 14 GPa for aragonite. The present investigation includes the first controlled partial vaporization experiments on calcite. The experiments were conducted to test the predictions of the release adiabat experiments. The quantities of the gaseous species produced from shocked calcite and their carbon and oxygen isotopic compositions were determined, and the shock-induced effect on the Mn(2+) electron spin resonance spectrum in the shock-recovered calcite was observed. On the basis of the obtained results, it is concluded that shock stresses at the 17-18 GPa level give rise to volatilization of 0.03-0.3 (mole) percent of calcite to CO2 and CO. The devolatilization of calcite occurs at low pressure at significantly lower entropy densities than predicted on the basis of thermodynamic continuum models.

Boslough, M. B.↗

NASA NTRS1982

The concentration and isotopic composition of hydrogen, carbon and nitrogen in carbonaceous meteorites

Stepwise pyrolysis was used to extract H2, N2 and C from powdered meteorites and from meteorite residues resulting from partial dissolution in aqueous HF or from reaction with HF-HCl solutions. Concentrations and isotopic compositions were determined for the cases of the carbonaceous chondrites Orgueil, Murray, Murchison, Renazzo and Cold Bokkeveld. Acidification of the meteorites removed the organic sources of H2, so that H2 in the HF-HCl acid residues came mostly from the insoluble organic matter making up 70-80% of the total carbon in carbonaceous meteorites. Good correlation is found between delta-D and the concentration of H2 in the acid residues, but no correlation exists between the delta-D, delta-C-13 and delta-N-15 in them. A model is proposed for both the high delta-D values and the relationship between those values and the H2 concentration.

Robert, F.↗