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NASA NTRS1986

Galactic cosmic ray composition

An assessment is given of the galactic cosmic ray source (GCRS) elemental composition and its correlation with first ionization potential. The isotopic composition of heavy nuclei; spallation cross sections; energy spectra of primary nuclei; electrons; positrons; local galactic reference abundances; comparison of solar energetic particles and solar coronal compositions; the hydrogen; lead; nitrogen; helium; and germanium deficiency problems; and the excess of elements are among the topics covered.

Meyer, J. P.↗

NASA NTRS2000

MOD: An Instrument for the 2005 Mars Explorer Program HEDS Payload

The Mars Organic Detector (MOD) was recently selected for the definition phase of the HEDS '05 (originally scheduled for '03) lander instrument package for fundamental biology and in situ resource utilization. MOD is designed to detect organic compounds in rock and soil samples directly on the surface of Mars in order to assess the biological potential of the planet. In addition, a MOD Tunable Diode Laser Spectrometer (TDLS) will provide information on desorption and decomposition temperatures, as well as the release rates and quantities of water and carbon dioxide that can be liberated from regolith samples, thereby providing the parameters needed for the design of systems for the future large-scale in situ extraction of valuable consumable resources. A MOD TDLS will also measure the atmospheric water and carbon dioxide content, as well as the atmospheric carbon dioxide isotopic composition, in order to determine whether there is an isotopic offset between atmospheric and surface carbon.

Bada, J. L.↗

NASA NTRS2010

Search for Organic Nanoglobules in Carbonaceous Chondrites Using Microtomography

Primitive solar materials have various organic matters. In recent years, novel organic materials called organic nanoglobules of a few hundred micrometers in typical size were discovered in carbonaceous chondrites, IDPs, and comet 81P/Wild 2. The organic globules are spherical shape and in many cases with hollow structures. Composition of the globules are mainly aromatic carbon. The isotopic anomalies of SD and 6N 15 observed in the globules indicate that they were formed from photochemical reaction to ice particles at very low temperature environment, such as molecular clouds or outer protosolar disk. Aqueous alteration of organic matters and the gamma-ray irradiation to PAH are also suggested as alternative possible formation processes. If the globules are made from organic ice particles, the hollow regions of the globules are suggested to be once filled with volatile H20-rich organic ices, while if they were formed by aqueous alteration, the hollow regions should be filled with a fluid which caused the aqueous alteration. However, fluids in the globules have not been detected so far in the previous studies. If fluids were originally preserved in the hollows, they might be lost during destructive processes of sample separation or preparation for TEM observation. X-ray computed tomography (CT) is a nondestructive method which can determine 3-D internal structures of objects. SR (synchrotron radiation)-based imaging microtomography can give submicron spatial resolution [8] and was applied to micro textures in extraterrestrial materials, such as cometary grains captured by the Stardust mission [9]. If organic globules are observed non-destructively in carbonaceous chondrites by tomography, we can check the presence of fluids in the hollows. If fluids are preserved, we may analyze chemical and isotopic compositions of the fluids. The purpose of this study is to observe organic nanoglobules using imaging tomography for future analysis.

Matsumoto, T.↗

NASA NTRS2014

Identification of a Compound Spinel and Silicate Presolar Grain in a Chondritic Interplanetary Dust Particle

Anhydrous chondritic porous interplanetary dust particles (CP IDPs) have undergone minimal parent body alteration and contain an assemblage of highly primitive materials, including molecular cloud material, presolar grains, and material that formed in the early solar nebula [1-3]. The exact parent bodies of individual IDPs are not known, but IDPs that have extremely high abundances of presolar silicates (up to 1.5%) most likely have cometary origins [1, 4]. The presolar grain abundance among these minimally altered CP IDPs varies widely. "Isotopically primitive" IDPs distinguished by anomalous bulk N isotopic compositions, numerous 15N-rich hotspots, and some C isotopic anomalies have higher average abundances of presolar grains (~375 ppm) than IDPs with isotopically normal bulk N (<10 ppm) [5]. Some D and N isotopic anomalies have been linked to carbonaceous matter, though this material is only rarely isotopically anomalous in C [1, 5, 6]. Previous studies of the bulk chemistry and, in some samples, the mineralogy of select anhydrous CP IDPs indicate a link between high C abundance and pyroxene-dominated mineralogy [7]. In this study, we conduct coordinated mineralogical and isotopic analyses of samples that were analyzed by [7] to characterize isotopically anomalous materials and to establish possible correlations with C abundance.

Nguyen, A. N.↗

NASA NTRS1978

A local proton irradiation model for isotopic anomalies in the solar system

An attempt is made to explain the O-16 and Al-26 anomalies observed in solar-system bodies in the framework of a local irradiation model wherein a small amount of solar system matter of normal isotopic composition was irradiated by energetic protons from the primeval sun. Several isotopic constraints are summarized with which the model should be consistent, and a proton energy distribution and fluence and a target elemental composition are chosen such that the extraordinary component produced by irradiation satisfies the constraints. Detailed attention is given to the relevant oxygen reactions, Al-26 production, and effects of proton irradiation on isotopes of Mg, Ca, and Ba. A scenario is outlined which satisfies all the constraints. Consequences of the model are discussed with respect to the isotopic anomalies observed in Allende inclusions.

Lee, T.↗

NASA NTRS2013

Timescale of Petrogenetic Processes Recorded in the Mount Perkins Magma System, Northern Colorado River Extension Corridor, Arizona

The Miocene Mt. Perkins Pluton is a small composite intrusive body emplaced in the shallow crust as four separate phases during the earliest stages of crustal extension. Phase 1 (oldest) consists of isotropic hornblende gabbro and a layered cumulate sequence. Phase 2 consists of quartz monzonite to quartz monzodiorite hosting mafic microgranitoid enclaves. Phase 3 is composed of quartz monzonite and is subdivided into mafic enclave-rich zones and enclave-free zones. Phase 4 consists of aphanitic dikes of mafic, intermediate and felsic compositions hosting mafic enclaves. Phases 2-4 enclaves record significant isotopic disequilibrium with surrounding granitoid host rocks, but collectively enclaves and host rocks form a cogenetic suite exhibiting systematic variations in Nd-Sr-Pb isotopes that correlate with major and trace elements. Phases 2-4 record multiple episodes of magma mingling among cogenetic hybrid magmas that formed via magma mixing and fractional crystallization at a deeper crustal. The mafic end-member was alkali basalt similar to nearby 6-4 Ma basalt with enriched OIB-like trace elements and Nd-Sr-Pb isotopes. The felsic end-member was a subalkaline crustal-derived magma. Phase 1 isotropic gabbro exhibits elemental and isotopic compositional variations at relatively constant SiO2, suggesting generation of isotropic gabbro by an open-system process involving two mafic end-members. One end-member is similar in composition to the OIB-like mafic end-member for phases 2-4; the second is similar to nearby 11-8 Ma tholeiite basalt exhibiting low epsilon (sub Nd), and depleted incompatible trace elements. Phase 1 cumulates record in situ fractional crystallization of an OIB-like mafic magma with isotopic evidence of crustal contamination by partial melts generated in adjacent Proterozoic gneiss. The Mt Perkins pluton records a complex history in a lithospheric scale magma system involving two distinct mantle-derived mafic magmas and felsic magma sourced in the crust. Mixing and fractional crystallization of these magmas at various levels in the crust generated a suite of intermediate composition magmas. U-Pb zircon SHRIMP ages of phase 1 (15.7 +/- 0.2 Ma), phase 3 (15.8 +/- 0.2 Ma) and phase 4 (15.4 +/- 0.3 Ma) document a 100-300k year timescale for petrogenetic processes recorded in the Mt Perkins magma system.

Danielson, Lisa R.↗

NASA NTRS1986

The reality of the secular change in solar wind nitrogen isotopes

Evidence concerning the isotopic composition of N in the early solar system currently seems to favor a picture of isotopic inhomogeneity rather than of a unique primordial composition modified by local processes. Certainly the range of N-15/N-14 ratios found in meteorites points to the existence of more than one nucleogenetic N component, though mass dependent modification of them explain the isotopic variation observed for N in the lunar regolith. The observational evidence is addressed which can be used to discriminate between such a model and one invoking a secular change in the composition of the solar wind. Three tests of this model were considered, starting with a search for light planetary N surviving in lunar rocks. Results so far are negative. The results of these tests may not eliminate the two component model for regolith N but they seriously weaken it. The alternate view, involving a secular change in solar wind N composition, has its problems but continues to survive by default.

Kerridge, J. F.↗

NASA NTRS1983

The composition of heavy ions in solar energetic particle events

Recent advances in determining the elemental, charge state, and isotopic composition of or approximate to 1 to or approximate to 20 MeV per nucleon ions in solar energetic particle (SEP) events and outline our current understanding of the nature of solar and interplanetary processes which may explain the observations. Average values of relative abundances measured in a large number of SEP events were found to be roughly energy independent in the approx. 1 to approx. 20 MeV per nucleon range, and showed a systematic deviation from photospheric abundances which seems to be organized in terms of the first ionization potential of the ion. Direct measurements of the charge states of SEPs revealed the surprisingly common presence of energetic He(+) along with heavy ion with typically coronal ionization states. High resolution measurements of isotopic abundance ratios in a small number of SEP events showed these to be consistent with the universal composition except for the puzzling overabundance of the SEP(22)Ne/(20)Ne relative to this isotopes ratio in the solar wind. The broad spectrum of observed elemental abundance variations, which in their extreme result in composition anomalies characteristic of (3)He rich, heavy ion rich and carbon poor SEP events, along with direct measurements of the ionization states of SEPs provided essential information on the physical characteristics of, and conditions in the source regions, as well as important constraints to possible models for SEP production.

Fan, C. Y.↗

NASA NTRS1984

The composition of heavy ions in solar energetic particle events

Fan, C. Y.↗

NASA NTRS2015

Petrology of Anomalous Eucrites

Most mafic achondrites can be broadly categorized as being "eucritic", that is, they are composed of a ferroan low-Ca clinopyroxene, high-Ca plagioclase and a silica phase. They are petrologically distinct from angritic basalts, which are composed of high-Ca, Al-Ti-rich clinopyroxene, Carich olivine, nearly pure anorthite and kirschsteinite, or from what might be called brachinitic basalts, which are composed of ferroan orthopyroxene and high-Ca clinopyroxene, intermediate-Ca plagioclase and ferroan olivine. Because of their similar mineralogy and composition, eucrite-like mafic achondrites formed on compositionally similar asteroids under similar conditions of temperature, pressure and oxygen fugacity. Some of them have distinctive isotopic compositions and petrologic characteristics that demonstrate formation on asteroids different from the parent of the HED clan (e.g., Ibitira, Northwest Africa (NWA) 011). Others show smaller oxygen isotopic distinctions but are otherwise petrologically and compositionally indistinguishable from basaltic eucrites (e.g., Pasamonte, Pecora Escarpment (PCA) 91007). The degree of uniformity in delta O-17 of eucrites and diogenites is one piece of evidence considered to favor of a magma-ocean scenario for their petrogenesis. Given that the O isotopic differences separating Pasamonte and PCA 91007 from other eucrites are small, and that there is an absence of other distinguishing characteristics, a legitimate question is: Did the HED parent asteroid fail to homogenize via a magma-ocean stage, thus explaining outliers like Pasamonte? We are initiating a program of study of anomalous eucrite-like achondrites as one part of our effort to seek a resolution of this issue. Here we present preliminary petrologic information on Asuka (A-) 881394, Elephant Moraine (EET) 87520 and EET 87542. We will have studied several more by conference time.

Mittlefehldt, D. W.↗

NASA NTRS2009

Impact Histories of Vesta and Vestoids inferred from Howardites, Eucrites, and Diogenites

The parent body of the howardites, eucrites and diogenites (HEDs) is thought to be asteroid (4) Vesta [1]. However, several eucrites have now been recognized, like NWA 011 and Ibitira, with major element compositions and mineralogy like normal eucrites but with different oxygen isotope compositions and minor element concentrations suggesting they are not from the same body [2, 3]. The discoveries of abnormal eucrites and V-type asteroids that are probably not from Vesta [see 4] raise the question whether the HEDs with normal oxygen isotopes are coming from Vesta [3]. To address this issue and understand more about the evolution of Vesta in preparation for the arrival of the Dawn spacecraft, we integrate fresh insights from Ar-Ar dating and oxygen isotope analyses of HEDs, radiometric dating of differentiated meteorites, as well as dynamical and astronomical studies of Vesta, the Vesta asteroid family (i.e., the Vestoids), and other V-type asteroids.

Scott, E. R. D.↗

NASA NTRS1994

Evidence for a Meteoritic Component in Impact Melt Rock from the Chicxulub Structure

The Chicxulub structure in Yucatan, Mexico, has recently been recognized as a greater then 200-km-diameter multi-ring impact crater of K-T boundary age. Crystalline impact melt rocks and breccias from within the crater, which have compositions similar to those of normal continental crustal rocks and which show shock metamorphic effects, have been studied for trace element and Re-Os isotope compositions. Re-Os isotope systematics allow the sensitive and selective determination of an extraterrestrial component in impact-derived rocks. A melt rock sample shows elevated iridium concentrations, an osmium concentration of 25 ppb, and a low Os-187/Os-188 ratio of 0.113, which are incompatible with derivation from the continental crust. Even though the Os-187/Os-188 ratio is slightly lower than the range so far measured in meteorites, a mantle origin seems unlikely for mass balance reasons and because the cratering event is unlikely to have excavated mantle material. The data support the hypothesis of a heterogeneously distributed meteoritic component in the Chicxulub melt rock. A sample of impact glass from the Haitian K-T boundary at Beloc yielded about 0.1 ppb osmium and an Os-187/0s-188 ratio of 0.251, indicating the presence of a small meteoritic component in the impact ejecta as well.

Koeberl, Christian↗

NASA NTRS2014

CO Self-Shielding as a Mechanism to Make O-16 Enriched Solids in the Solar Nebula

Photochemical self-shielding of CO has been proposed as a mechanism to produce solids observed in the modern, O-16 depleted solar system. This is distinct from the relatively O-16 enriched composition of the solar nebula, as demonstrated by the oxygen isotopic composition of the contemporary sun. While supporting the idea that self-shielding can produce local enhancements in O-16 depleted solids, we argue that complementary enhancements of O-16 enriched solids can also be produced via CO-16 based, Fischer-Tropsch type (FTT) catalytic processes that could produce much of the carbonaceous feedstock incorporated into accreting planetesimals. Local enhancements could explain observed O-16 enrichment in calcium-aluminum-rich inclusions (CAIs), such as those from the meteorite, Isheyevo (CH/CHb), as well as in chondrules from the meteorite, Acfer 214 (CH3). CO selfshielding results in an overall increase in the O-17 and O-18 content of nebular solids only to the extent that there is a net loss of CO-16 from the solar nebula. In contrast, if CO-16 reacts in the nebula to produce organics and water then the net effect of the self-shielding process will be negligible for the average oxygen isotopic content of nebular solids and other mechanisms must be sought to produce the observed dichotomy between oxygen in the Sun and that in meteorites and the terrestrial planets. This illustrates that the formation and metamorphism of rocks and organics need to be considered in tandem rather than as isolated reaction networks.

Solar Nebula↗

NASA NTRS1985

Absolute isotopic abundances of Ti in meteorites

A general formalism is presented for determining possible isotope compositions of exotic Ti, and illustrated with results from Ti isotope abundances measured in Ca-Al-rich inclusions of the Allende and Leoville meteorites and samples of other meteorites. Previously identified correlations between Ti-50 and Ca-48 in FUN (isotope fractionation effects and unknown nucleosynthetic effects) inclusions is shown to hold true, thereby supporting contributions from a neutron-rich equilibrium or nucleosynthetic equilibrium during formation of the meteorites. Extension of the study to carbonaceous meteorites indicated that condensation, volatilization and recondensation occurred during formation, although the isotope fractionation observed cannot yet be explained.

Niederer, F. R.↗

NASA NTRS1993

The fractionation of noble gases in diamonds of CV3 Efremovka chondrite

It was shown that in diamonds of Efremovka CV3 the noble gases with normal isotopic compositions are fractionated in different degree while the correlation of isotopic anomalous components is nearly constant. Some data for noble gases in DE-4 sample of Efremovka chondrite are considered. In contrast to DE-2 sample the DE-4 was treated except conc. HClO4, 220 C in addition with mixture of conc. H2SO4+H3PO4 (1:1), 220 C, twice. Noble gases analysis were performed in Germany at Max Plank Institute fur Chemie. Noble gases were released by oxidation of samples at stepped heating from 420 C to 810 C and by pyrolysis at 580, 590, and 680 C.

Fisenko, A. V.↗

NASA NTRS2005

Nitrogen Isotopic Anomalies in a Hydrous Interplanetary Dust Particle

Interplanetary dust particles (IDPs) collected in the stratosphere are the fine-grained end member (5 - 50 microns in size) of the meteoritic material available for investigation in the laboratory. IDPs are derived from either cometary or asteroidal sources. Some IDPs contain cosmically primitive materials with isotopic signatures reflecting presolar origins. Recent detailed studies using the NanoSIMS have shown there is a wide variation of isotopic signatures within individual IDPs; grains with a presolar signature have been observed surrounded by material with a solar isotopic composition. The majority of IDPs studied have been anhydrous. We report here results from integrated NanoSIMS/FIB/TEM/Synchrotron IR studies of a hydrous IDP, focused on understanding the correlations between the isotopic, mineralogical and chemical compositions of IDPs.

Smith, J. B.↗

NASA NTRS1972

Elemental and isotopic abundances in the solar wind

The use of collecting foils and lunar material to assay the isotopic composition of the solar wind is reviewed. Arguments are given to show that lunar surface correlated gases are likely to be most useful in studying the history of the solar wind, though the isotopic abundances are thought to give a good approximation to the solar wind composition. The results of the analysis of Surveyor material are also given. The conditions leading to a significant component of the interstellar gas entering the inner solar system are reviewed and suggestions made for experimental searches for this fraction. A critical discussion is given of the different ways in which the basic solar composition could be modified by fractionation taking place between the sun's surface and points of observation such as on the Moon or in interplanetary space. An extended review is made of the relation of isotopic and elemental composition of the interplanetary gas to the dynamic behavior of the solar corona, especially processes leading to fractionation. Lastly, connection is made between the subject of composition, nucleosynthesis and the convective zone of the sun, and processes leading to modification of initial accretion of certain gases on the Earth and Moon.

Geiss, J.↗

NASA NTRS2012

Compound-Specific Carbon, Nitrogen, and Hydrogen Isotopic Ratios for Amino Acids in CM and CR Chondrites and their use in Evaluating Potential Formation Pathways

Stable hydrogen, carbon, and nitrogen isotopic ratios (oD, 013C, and olSN) of organic compounds can revcal information about their origin and formation pathways. Several formation mechanisms and environments have been postulated for the amino acids detected in carbonaceous chondrites. As each proposed mechanism utilizes different precursor molecules, the isotopic signatures of the resulting amino acids may indicate the most likely of these pathways. We have applied gas chromatography with mass spectrometry and combustion isotope ratio mass spectrometry to measure the compound-specific C, N, and H stable isotopic ratios of amino acids from seven CM and CR carbonaceous chondrites: CM1I2 Allan Hills (ALH) 83100, CM2 Murchison, CM2 Lewis Cliff (LEW) 90500, CM2 Lonewolf Nunataks (LON) 94101, CRZ Graves Nunataks (GRA) 95229, CRZ Elephant Moraine (EET) 92042, and CR3 Queen Alexandra Range (QUE) 99177. We compare the isotopic compositions of amino acids in these meteorites with predictions of expected isotopic enrichments from potential formation pathways. We observe trends of decreasing ODC and increasing oD with increasing carbon number in the aH, (l-NH2 amino acids that correspond to predictions made for formation via Streckercyanohydrin synthesis. We also observe light ODC signatures for ~-alanine, which may indicate either formation via Michael addition or via a pathway that forms primarily small, straight-chain, amine-terminal amino acids (n-ro-amino acids). Higher deuterium enrichments are observed in amethyl amino acids, indicating formation of these amino acids or their precursors in cold interstellar or nebular environments. Finally, individual amino acids are more enriched in deuterium in CR chondrites than CM chondrites, reflecting different parent-body chemistry.

Elsila, Jamie E.↗