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NASA NTRS2005

Neutral Mass Spectrometry for Venus Atmosphere and Surface

The assignment is to make precise (better than 1 %) measurements of isotope ratios and accurate (5-10%) measurements of abundances of noble gas and to obtain vertical profiles of trace chemically active gases from above the clouds all the way down to the surface. Science measurement objectives are as follows: 1) Determine the composition of Venus atmosphere, including trace gas species and light stable isotopes; 2) Accurately measure noble-gas isotopic abundance in the atmosphere; 3) Provide descent, surface, and ascent meteorological data; 4) Measure zonal cloud-level winds over several Earth days; 5) Obtain near-IR descent images of the surface from 10-km altitude to the surface; 6) Accurately measure elemental abundances & mineralogy of a core from the surface; and 7) Evaluate the texture of surface materials to constrain weathering environment.

Mahaffy, Paul↗
NASA NTRS1981

Observational data needs useful for modeling the coma

A computer model of comet comae is described; results from assumed composition of frozen gases are summarized and compared to coma observations. Restrictions on relative abundance of some frozen constituents are illustrated. Modeling, when tightly coupled to observational data, can be important for comprehensive analysis of observations, for predicting undetected molecular species and for improved understanding of coma and nucleus. To accomplish this, total gas production rates and relative elemental abundances of H:C:N:O:S are needed as a function of heliocentric distance of the comet. Also needed are relative column densitites and column density profiles with well defined diaphragm range and pointing position on the coma. Production rates are less desirable since they are model dependent. Total number (or upper limits) of molecules in the coma and analysis of unidentified spectral lines are needed also.

Huebner, W. F.↗
NASA NTRS1983

Survey of chondrule average properties in H-, L-, and LL-group chondrites - Are chondrules the same in all unequilibrated ordinary chondrites?

The petrogenetic properties of chondrules in different unequilibrated ordinary chondrites (UOCs) are compared to averaged chondrule-suite values obtained from recent analyses of several H-group, L-group, and LL-group chondrites. The purpose of the study was to develop a data base for future statistical analyses of chondrite characteristics. Mean end-member compositions of olivine (mol percent Fa) and pyroxene (mol percent Fs) were used as indices of the relative degree of 'equilibration' of each chondrule suite. It is found that the bulk chondrule geometric-mean abundances of Na, Mg, and Ni are the same from one UOC to another, and show no major systematic trends related to the H-group, L-group, of LL-group parentage of the host chondrites. The patterns of rare-earth element abundances in the chondrules are also examined, and the results are compared with statistical analyses. It is concluded that multivariate statistical analysis of pooled UOC chondrule data is justified for chondrule bulk compositions, as long as the statistical results are not misinterpreted as the primary petrogenetic features of chondrules.

Gooding, J. L.↗
NASA NTRS1994

Noble gases in presolar diamonds I: Three distinct components and their implications for diamond origins

High-purity separates of presolar diamond were prepared from 14 primitive chondrites from 7 compositional groups. Their noble gases were measured using stepped pyrolysis. Three distinct noble gas components are present in diamonds, HL, P3, and P6, each of which is found to consist of five noble gases. P3, released between 200 C and 900 C, has a 'planetary' elemental abundance pattern and roughly 'normal' isotopic ratios. HL, consisting of isotopically anomalous Xe-HL and Kr-H, Ar with high Ar-38/Ar-36, and most of the gas making up Ne-A2 and He-A, is released between 1100 C and 1600 C. HL has 'planetary' elemental ratios, except that it has much more He and Ne than other known 'planetary' components. HL gases are carried in the bulk diamonds, not in some trace phase. P6 has a slightly higher median release temperature than HL and is not cleanly separated from HL by stepped pyrolysis. Our data suggest that P6 has roughly 'normal' isotopic compositions and 'planetary' elemental ratios. Both P3 and P6 seem to be isotopically distinct from P1, the dominant 'planetary' noble-gas component in primitive chondrites. Release characteristics suggest that HL and P6 are sited in different carriers within the diamond fractions, while P3 may be sited near the surfaces of the diamonds. We find no evidence of separability of Xe-H and Xe-L or other isotopic variations in the HL component. However, because approximately 10(exp 10) diamonds are required to measure a Xe composition, a lack of isotopic variability does not constrain diamonds to come from a single source. In fact, the high abundance of diamonds in primitive chondrites and the presence of at least three distinct noble-gas components strongly suggest that diamonds originated in many sources. Relative abundances of noble-gas components in diamonds correlate with degree of thermal processing, indicating that all meteorites sampled essentially the same mixture of diamonds. That mixture was probably inherited from the Sun's parent molecular cloud.

Huss, Gary R.↗
NASA NTRS1991

He-3 and other lunar volatiles

Constraints are considered and estimates are given for the abundances of He-3, other noble gases, and chemically reactive volatiles (e.g., H, C, N, S, F, Cl) on the Moon. For the case of surface inventories, solar wind particles implanted into grains on the surface of the Moon provide an accessible, though not necessarily abundant, source of H, C, N and the noble gases. Solar wind implanted species are concentrated in the infest grain sized, and are only found in the upper few meters of the regolith, where there are grains that have been directly exposed to the Sun. Elemental abundances in surface soils are typically 10s of mg/g, and vary according to the exposure history of the soil. The abundance of the rare, but possibly economically important, isotope He-3 is typically a few mg/g. The largest uncertainty in estimates of the total lunar abundance of solar wind implanted species comes from the lack of knowledge of their distribution with depth below the upper meter or two. For the case of bulk inventories, constraints resulting from lunar sample analyses and from physical chemical models of volatile behavior during the hypothesized giant impact origin of the Moon is used to give estimated abundances.

Fegley, B., Jr.↗
NASA NTRS1991

Geochemistry and petrogenesis of proterozoic mafic dykes in north Kerala, southwestern Indian Shield - Preliminary results

Mafic dyke intrusions occur in three distinct orientations ( NNW-SSE and NW-SE and NE-SW) in north Kerala regions, the southwestern part of the Indian Shield. Dating of two NNW-SSE trending dykes by K-Ar method has yielded Middle Proterozoic ages (ca. 1660 Ma and ca. 1420 Ma respectively). Our initial geochemical results on these dyke rocks (0.65-0.15 wt pct K2O, 0.37-0.38 wt pct P2O5, 3.30-1.00 wt pct TiO2, 11-1 p.p.m. Rb, 250-90 p.p.m. Sr, 230-40 p.p.m. Ba, 160-40 p.p.m. Zr, and 30-10 x chondrite rare earth elemental abundances) indicate a transitional character between abyssal and plateau tholeiites. Petrogenetic modelling suggests that the dyke compositions have been derived by different degrees of partial melting of a heterogenous source mantle. The mantle sources with accessory amphibole and/or garnet, variably enriched in LREE and LIL elements, are compatible with the observed geochemical data.

Radhakrishna, T.↗
NASA NTRS1999

An Abundance Analysis of Two Carbon-Rich Proto-Planetary Nebulae: IRAS Z02229+6208 And IRAS 07430+1115

In this paper, we present an LTE abundance analysis of two new proto-planetary nebulae, IRAS Z02229 + 6208 and IRAS 07430 + 1115, based on high-resolution (R approximately equal 55,000) optical echelle spectra. Results show that both stars are metal-poor ([Fe/H] = -0.5) and overabundant in C, N, and s-process elements. The average elemental abundances are [C/Fe] = +0.8, [N/Fe] = +1.2, and [s-process/Fe] = +1.4 for IRAS Z02229 + 6208, and [C/Fe] = +0.6, [N/Fe] = +0.4, and [s-process/Fe] = +1.6 for IRAS 07430+ 1115. These abundances suggest that the stars have experienced nucleo-synthesis on the asymptotic giant branch (AGB), and the resultant products of CNO, 3alpha, and s-process reactions were brought to the photosphere during shell flashes and deep mixing episodes during the AGB phase of their evolution. Of major significance is the measurement of a high Li abundance in both stars, log epsilon(Li) approximately equal 2.3 and 2.4 for IRAS Z02229 + 6208 and IRAS 07430 + 1115, respectively. This may be the result of hot bottom burning, below the deep convective zone. We also present an analysis of the circumstellar molecular (C2 and CN) and atomic (Na I and K I) absorption spectra of both stars. We derive rotational temperatures, column densities, and envelope expansion velocities using molecular C2 Phillips and CN Red system bands. The values derived for expansion velocities, 8-14 km/s, are typical of the values found for post-AGB stars. IRAS 07430+ 1115 is unusual in that it shows P Cygni-shaped C2 emission profiles in the spectra of the circumstellar envelope. A minimum distance for IRAS Z02229+6208, determined from interstellar Na I lines, suggests that it is evolved from an intermediate-mass star. Including these two stars, the number of post-AGB stars for which clear C, N, and s-process elemental overabundances are found rises to eight. IRAS Z02229 + 6208 is known to possess the 21 micron emission feature in its mid-infrared spectrum; these results support the idea that all 21 micron emission stars are carbon-rich post-AGB stars.

Reddy, Bacham E.↗
NASA NTRS1974

Modeling the evolution of Sm and Eu abundances during lunar igneous differentiation

The current work presents models for the evolution of europium and samarium abundances during lunar igneous processes. The effect of probable variations in lunar temperature and oxygen fugacity, mineral-liquid distribution coefficients, and the crystallization or melting progression are considered in the model calculations. Changes in the proportions of crystallizing phases strongly influence the evolution of trace element abundances during fractional crystallization, and models must include realistic estimates of the major phase equilibria during crystallization. The results are applied to evaluating the possibility of generating KREEP-rich materials by lunar igneous processes.

Weill, D. F.↗
NASA NTRS2012

Using the Fe/Mn Ratio of FeO-Rich Olivine In WILD 2, Chondrite Matrix, and Type IIA Chondrules to Disentangle Their Histories

The Stardust Mission returned a large abundance of impactors from Comet 81P/Wild2 in the 5-30 m range. The preliminary examination of just a limited number of these particles showed that the collection captured abundant crystalline grains with a diverse mineralogy [1,2]. Many of these grains resemble those found in chondrite matrix and even contain fragments of chondrules and CAIs [1-3]. In particular, the olivine found in Wild 2 exhibits a wide compositional range (Fa0-97) with minor element abundances similar to the matrix olivine found in many carbonaceous chondrites (CCs) and unequilibrated ordinary chondrites (UOCs). Despite the wide distribution of Fa content, the olivine found in the matrices of CCs, UOCs, and Wild 2 can be roughly lumped into two types based solely on fayalite content. In fact, in some cases, a distinct bi-modal distribution is observed.

Frank, David R.↗
NASA NTRS1987

On the chemical homogeneity of the 30 Doradus H II region and a local enrichment by Wolf-Rayet stars

Emission-line strengths have been obtained at 10 positions in the outer regions of the 30 Dor nebula and analyzed in the standard way. There are two major results: (1) the elemental abundances for nine of the outer regions are remarkably similar to those previously measured in the core. This result implies the spectra of the cores and halos of giant H II regions (subject to the different ionizing radiation fields) are analyzed correctly by the standard methods. Hence measurements of extragalactic H II regions with poor spatial resolution correctly represent the abundances of the whole nebula. The O/H ratio in 30 Dor, by number, is 0.30 solar. The Ne/O, S/O, Ar/O, and Cl/O are close to solar. The gas-phase Fe/O is about 0.2 solar, which probably implies that most of the iron is within solid grains. The He/H is 0.0810 as shown by each of the three strong lines available. One region is cool and rich in helium and all other heavy elements except nitrogen. The spectrum of the region does not resemble that of a supernova remnant in that the forbidden O I and S II lines are not nearly strong enough. The abundances can be explained fairly well as over 10 solar masses of H-poor material ejected during the evolution of a single massive (about 80 solar masses) star during its late O-star and Wolf-Rayet phases.

Rosa, Michael↗
NASA NTRS2001

Abundances in the Planetary Nebula IC 5217

High resolution optical wavelength spectroscopic data were secured in the optical wavelengths, 3700A - 10,050A, for the planetary nebula IC 5217 with the Hamilton Echelle Spectrograph at Lick Observatory. These optical spectra have been analyzed along with the near-UV and UV archive data. Diagnostic analyses indicate a nebular physical condition with electron temperature of about 10,700 K (from the [O III] lines) and the density of N(sub epsilon) = 5000/cm. Ionic concentrations have been derived with the representative diagnostics, and with the aid of a photoionization model construction, we derived the elemental abundances. Contrary to the previous studies found in the literature, He and C appear to be depleted compared to the average planetary nebula and to the Sun (and S marginally so), while the remaining elements appear to be close to the average value. IC 5217 may have evolved from an O-rich progenitor and the central star temperature of IC 5217 is likely to be 92,000 K.

Hyung, Siek↗
NASA NTRS2006

Siderophile-element Anomalies in CK Carbonaceous Chondrites: Implications for Parent-body Aqueous Alteration and Terrestrial Weathering of Sulfides

CK chondrites constitute the most oxidized anhydrous carbonaceous chondrite group; most of the Fe occurs in magnetite and in FeO-rich mafic silicates. The two observed CK falls (Karoonda and Kobe), along with thirteen relatively unweathered CK finds, have unfractionated siderophile-element abundance patterns. In contrast, a sizable fraction of CK finds (9 of 24 investigated) shows fractionated siderophile abundance patterns including low abundances of Ni, Co, Se and Au; the most extreme depletions are in Ni (0.24 of normal CK) and Au (0.14 of normal CK). This depletion pattern has not been found in other chondrite groups. Out of the 74 CK chondrites listed in the Meteoritical Bulletin Database (2006; excluded considerably paired specimens; see http://tin.er.usgs.gov/meteor/ metbull.php) we analyzed 24 and subclassified the CK chondrites in terms of their chemical composition and sulfide mineralogy: sL (siderophiles low; six samples) for large depletions in Ni, Co, Se and Au (>50% of sulfides lost); sM (siderophiles medium; two CKs) for moderately low Ni and Co abundances (sulfides are highly altered or partly lost); sH (siderophiles high; one specimen) for enrichments in Ni, Co, Se and Au; 'normal' for unfractionated samples (13 samples). The sole sH sample may have obtained additional sulfide from impact redistribution in the parent asteroid. We infer that these elements became incorporated into sulfides after asteroidal aqueous processes oxidized nebular metal; thermal metamorphism probably also played a role in their mineral siting. The siderophile losses in the SL and sM samples are mainly the result of oxidation of pentlandite, pyrite and violarite by terrestrial alteration followed by leaching of the resulting phases. Some Antarctic CK chondrites have lost most of their sulfides but retained Ni, Co, Se and Au, presumably as insoluble weathering products.

Huber, Heinz↗
NASA NTRS1993

Chemical composition of new Acapulcoites and Lodranites

The bulk compositions of two Antarctic Lodranites, MAC 88177 and FRO 90011, and two Acapulcoites, ALH 81261 and Monument Draw, were determined with instrumental neutron activation analysis. Acapulcoites have essentially chondritic major and trace element abundances but achondritic texture. They consist of entirely recrystallized, fine grained mineral assemblages. Chondrules are extremely rare; one relict radiating pyroxene chondrule was described in Monument Draw (MD). The coarse grained Lodranites also have achondritic textures, but they are different compositionally with depletions in Al, Na, and incompatible elements probably a result of separation of partial, feldspar-rich melt. MAC 88177 is significantly more depleted in incompatible elements than FRO 90011 suggesting a higher degree of partial melting for the MAC-Lodranite. The chemical data support a genetic relationship between Lodranites and Acapulcoites inferred earlier from oxygen isotopes, petrology, and mineral composition.

Zipfel, J.↗
NASA NTRS1976

On the calculation of cosmic-ray exposure ages of stone meteorites

Abundances of cosmic ray-produced noble gases and Al-26, including some new measurements, have been compiled for some 23 stone meteorites with exposure ages less than 3,000,000 yr. Concentrations of cosmogenic He, Ne, and Ar in these meteorites have been corrected for differences in target element abundances by normalization to L-chondrite chemistry. Combined noble gas measurements in depth samples of the Keyes and St. Severin chondrites are utilized to derive equations for normalizing the production rates of cosmogenic He-3, Ne-21, and Ar-38 in chondrites to an adopted 'average' shielding. The measured unsaturated AL-26 concentrations and the calculated equilibrium Al-26 for these meteorites are combined to estimate exposure ages. These exposure ages are statistically compared with chemistry- and shielding-corrected concentrations of cosmogenic He, Ne, and Ar to derive absolute production rates for these nuclides, which are found to be roughly 25% higher than production rates used in the past. From these production rates and relative chemical correction factors, production rates for other classes of stone meteorites are derived.

Cressy, P. J., Jr.↗
NASA NTRS1993

Trace element content of chondritic cosmic dust: Volatile enrichments, thermal alterations, and the possibility of contamination

Trace element abundances in 51 chondritic Interplanetary Dust Particles (IDP's) were measured by Synchrotron X-Ray Fluorescence (SXRF). The data allow us to determine an average composition of chondritic IDP's and to examine the questions of volatile loss during the heating pulse experienced on atmospheric entry and possible element addition due to contamination during atmospheric entry, stratospheric residence, and curation.

Flynn, G. J.↗
NASA NTRS2001

The X-Ray Spectrometer for Mercury MESSENGER

Mercury is the closest planet to the Sun and because it is so close, it is difficult to study from Earth-based observatories. Its proximity to the Sun has also limited the number of spacecraft to visit this tiny planet to just one, Mariner 10, which flew by Mercury twice in 1974 and once in 1975. Mariner 10 provided a wealth of new information about Mercury, yet much still remains unknown about Mercury's geologic history and the processes that led to its formation. The origin of Mercury's metal-rich composition is just one area of investigation awaiting more and improved data to sort between competing hypotheses. Mercury plays an important role in comparative planetology, and many of the processes that were important during its formation are relevant to the Earth's early history. MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) is a Discovery mission that has been designed to fly by and orbit Mercury. It will launch in March 2004, flyby Mercury in 2007 and 2008 and enter an elliptical orbit in April 2009. During the one-year orbital phase, a suite of instruments on board the MESSENGER spacecraft will study the exosphere, magnetosphere, surface, and interior of Mercury. One of these instruments will be an X-Ray Spectrometer (XRS) that will measure surface elemental abundances. Remote X-ray spectroscopy has been accomplished before on the Apollo 15 and 16 missions, and more recently on NEAR Shoemaker. The MESSENGER XRS will measure characteristic X-ray emissions induced in the surface of Mercury by the incident solar flux. The Ka lines for the elements Mg, Al, Si, S, Ca, Ti, and Fe will be detected with spatial resolution on the order of 40 km when counting statistics are not a limiting factor. These measurements can be used to obtain quantitative information on elemental composition.

Starr, R. D.↗
NASA NTRS1978

Chemical condensation sequences in supernova ejecta

Equilibrium condensation is investigated for composition and pressures representative of supernova (SN) ejecta. The results are compared with those obtained for the solar nebula, and the distribution of elements among the various gaseous species and solid phases is computed for solar and SN-shell condensation sequences. The data are applied to problems concerning the observed mass fractionations of Si, Mg, and O in Allende, as well as to the strong depletion of heavy-element abundances in the interstellar medium. The results indicate that dust grains from a SN could have introduced isotopic anomalies into the solar nebula, that many minerals produced in SN ejecta are the same as those predicted to be stable in the solar nebula, and that the observed depletion of heavy elements in the interstellar gas could be due to dust formation in SN ejecta.

Lattimer, J. M.↗
NASA NTRS1989

Chemical stratification in white dwarf atmospheres and envelopes

Theoretical arguments supporting a new mechanism maintaining a homogeneously mixed composition in white dwarf atmospheres with traces of helium are presented. Diffusion time scales, meridional circulation, mass loss, accretion of interstellar matter, convection, and radiative levitation are discussed. Theoretically, layered envelopes, with hydrogen on top of helium and an abundance profile in the transition layer determined by diffusion equilibrium, are expected. In cases with observed helium and hydrogen in the atmosphere this means that the total hydrogen mass must be very small. The empirical evidence for such atmospheres are assessed, using a new grid of model atmospheres with stratified element abundances and applying it to typical mixed abundance cases at the hot end of the white dwarf temperature sequence.

Koester, D.↗