Engineering topics

Rahman, Z.

Publications and source records attributed to Rahman, Z..

At least 37 records · Page 2

NASA NTRS2016

C Chondrite Clasts in H Chondrite Regolith Breccias: Something Different

Zag (H3-6) and Monahans (1998) (H5) are regolith breccias that contain 4.5 GY old halite crystals which in turn contain abundant inclusions of aqueous fluids, solids and organics [1-4]. We have previously proposed that these halites originated on a hydro-volcanically-active C-class asteroid, probably Ceres [3-7]. We have begun a detailed analysis of the included solids and organics and are re-examining the related carbonaceous (C)) chondrite clast we previously reported in Zag [5-7]. These new investigations will potentially reveal the mineralogy of asteroid Ceres. We report here on potentially identical C chondrite clasts in the H chondrite regolith breccias Tsukuba (H5-6) and Carancas (H4-5). The clast in Tsukuba was known before [8], but the Carancas clast is newly recognized.

Zolensky, M. E.↗

NASA NTRS2016

Noble Metal Arsenides and Gold Inclusions in Northwest Africa 8186

CK carbonaceous chondrites are a highly thermally altered group of carbonaceous chondrites, experiencing temperatures ranging between approx.576-867 C. Additionally, the mineralogy of the CK chondrites record the highest overall oxygen fugacity of all chondrites, above the fayalite-magnetite-quartz (FMQ) buffer. Metallic Fe-Ni is extremely rare in CK chondrites, but magnetite and Fe,Ni sulfides are commonly observed. Noble metal-rich inclusions have previously been found in some magnetite and sulfide grains. These arsenides, tellurides, and sulfides, which contain varying amounts of Pt, Ru, Os, Te, As, Ir, and S, are thought to form either by condensation from a solar gas, or by exsolution during metamorphism on the chondritic parent body. Northwest Africa (NWA) 8186 is a highly metamorphosed CK chondrite. This meteorite is predominately composed of NiO-rich forsteritic olivine (Fo65), with lesser amounts of plagioclase (An52), augite (Fs11Wo49), magnetite (with exsolved titanomagnetite, hercynite, and titanohematite), monosulfide solid solution (with exsolved pentlandite), and the phosphate minerals Cl-apatite and merrillite. This meteorite contains coarse-grained, homogeneous silicates, and has 120deg triple junctions between mineral phases, which indicates a high degree of thermal metamorphism. The presence of NiO-rich olivine, oxides phases all bearing Fe3+, and the absence of metal, are consistent with an oxygen fugacity above the FMQ buffer. We also observed noble metal-rich phases within sulfide grains in NWA 8186, which are the primary focus of the present study.

Srinivasan, P.↗

NASA NTRS2016

Organic Aggregates with (delta)D and delta(sup 15)N Anomalies in the Zag Clast Revealed by STXM and NanoSIMS

Xenolithic clasts are often found in a wide variety of meteorite groups. Some ordinary chondrite clasts are interesting since these clasts might have originated from Ceres which shares crossing orbits with a possible ordinary chondrite parent body, Hebe. The Zag meteorite contains a dark clast dominated by saponite, serpentine, carbonates, sulfides, magnetite, minor olivine and pyroxene, which is consistent with formation on a large, carbonaceous, aqueously active body, e.g., Ceres. Abundant large C-rich grains up to 20 microns were found in the Zag clast as well. Such large C-rich grains are unique among any other meteorites in our knowledge, and will provide important clues to decipher the origin of the clast and accretion history. C-rich grains were selected in the Zag dark clast using SEM and approximately 100 nm-thick sections were prepared using a focused ion beam (FIB) at NASA-JSC. The sections were analyzed using the scanning transmission X-ray microscope (STXM) on beamline 5.3.2.2 at Advanced Light Source, LBNL, and BL-13A at the Photon Factory, KEK. Subsequently, the FIB section was analyzed for H, C and N isotopic compositions using a CAMECA NanoSIMS 50L ion microprobe at Kochi Institute for Core Sample Research, JAMSTEC

Kebukawa, Y.↗

NASA NTRS2016

Noble Metal Arsenides and Gold Inclusions in Northwest Africa 8186

CK carbonaceous chondrites are a highly thermally altered group of carbonaceous chondrites, experiencing temperatures ranging between approximately 576-867 degrees Centigrade. Additionally, the mineralogy of the CK chondrites record the highest overall oxygen fugacity of all chondrites, above the fayalite-magnetite-quartz (FMQ) buffer. Me-tallic Fe-Ni is extremely rare in CK chondrites, but magnetite and Fe,Ni sulfides are commonly observed. Noble metal-rich inclusions have previously been found in some magnetite and sulfide grains. These arsenides, tellurides, and sulfides, which contain varying amounts of Pt, Ru, Os, Te, As, Ir, and S, are thought to form either by condensation from a solar gas, or by exsolution during metamorphism on the chondritic parent body. Northwest Africa (NWA) 8186 is a highly metamorphosed CK chondrite. This meteorite is predominately composed of NiO-rich forsteritic olivine (Fo65), with lesser amounts of plagioclase (An52), augite (Fs11Wo49), magnetite (with exsolved titanomagnetite, hercynite, and titanohematite), monosulfide solid solution (with exsolved pentlandite), and the phosphate minerals Cl-apatite and merrillite. This meteorite contains coarse-grained, homogeneous silicates, and has 120-degree triple junctions between mineral phases, which indicates a high degree of thermal metamorphism. The presence of NiO-rich olivine, oxides phases all bearing Fe3 plus, and the absence of metal, are consistent with an oxygen fugacity above the FMQ buffer. We also observed noble metal-rich phases within sulfide grains in NWA 8186, which are the primary focus of the present study.

Srinivasan, P.↗

NASA NTRS2016

Coordinated Isotopic and Mineral Characterization of Highly Fractionated 18O-Rich Silicates in the Queen Alexandra Range 99177 CR3 Chondrite

Carbonaceous chondrites contain a mixture of solar system condensates, pre-solar grains, and primitive organic matter. Each of these materials record conditions and processes in different regions of the solar nebula, on the meteorite parent body, and beyond the solar system. Oxygen isotopic studies of meteorite components can trace interactions of distinct oxygen isotopic reservoirs in the early solar system and secondary alteration processes. The O isotopic compositions of the earliest solar system condensates fall along a carbonaceous chondrite anhydrous mineral (CCAM) line of slope approximately 1 in a plot of delta 17O against delta 18O. This trend is attributed to mixing of material from 16O-poor and 16O-rich reservoirs. Secondary processing can induce mass-dependent fractionation of the O isotopes, shifting these compositions along a line of slope approximately 0.52. Substantial mass-dependent fractionation of O isotopes has been observed in secondary minerals in CAIs, calcite, and FUN inclusions. These fractionations were caused by significant thermal or aqueous alteration. We recently reported the identification of four silicate grains with extremely fractionated O isotopic ratios (delta 18O equals 37 - 55 per mille) in the minimally altered CR3 chondrite QUE 99177. TEM analysis of one grain indicates it is a nebular condensate that did not experience substantial alteration. The history of these grains is thus distinct from those of the aforementioned fractionated materials. To constrain the origin of the silicate grains, we conducted further Mg and Fe isotopic studies and TEM analyses of two grains.

Nguyen, A. N.↗

NASA NTRS2016

STXM-XANES Analysis of Organic Matter in Dark Clasts and Halite Crystals in Zag and Monahans Meteorites

Zag and Monahans meteorites (H5) contains xenolithic dark clasts and halite (NaCl) crystals [e.g., 1]. The proposed source of the H chondrites is asteroid 6 Hebe [2]. The modern orbits of 1 Ceres and 6 Hebe essentially cross, with aphelion/perihelion of Ceres and Hebe of 2.99/2.55 and 2.91/1.94 AU (Astronomical Units), respectively. Therefore, Ceres might be the source of the clasts and halite in Zag and Monahans meteorites. Recent results from NASA's Dawn mission shows that bright spots in Ceres's crater may be hydrated magnesium sulfate with some water ice, and an average global surface contains ammoniated phyllosilicates that is likely of outer Solar System origin. One dark clast and all halite crystals in Zag and Monahans meteorites contain carbon-rich particles. We report organic analyses of these carbon-rich particles using carbon, nitrogen, and oxygen X-ray absorption near edge structure (C-, N-, and O-XANES), in order to constrain the origin of the clast and halite crystals.

Kebukawa, Y.↗

NASA NTRS2016

Indigenous Carbonaceous Matter in the Nakhla Mars Meteorite

Detailed microanalysis of the Martian meteorite Nakhla has shown there are morphologically distinct carbonaceous features spatially associated with low-T aqueous alteration phases including salts and id-dingsite. A comprehensive suite of analytical instrumentation including optical microscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, focused ion beam (FIB) microscopy, transmission electron microscopy (TEM), two-step laser mass spectrometry (mu-L(sup 2)MS), laser mu-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and nanoscale secondary ion mass spectrometry (NanoSIMS) are being used to characterize the carbonaceous matter and host mineralogy. The search for carbonaceous matter on Mars has proved challenging. Viking Landers failed to unambiguously detect simple organics at either of the two landing sites although the Martian surface is estimated to have acquired at least 10(exp15) kg of C as a consequence of meteoritic accretion over the last several Ga. The dearth of organics at the Martian surface has been attributed to various oxidative processes including UV photolysis and peroxide activity. Consequently, investigations of Martian organics need to be focused on the sub-surface regolith where such surface processes are either severely attenuated or absent. Fortuitously since Martian meteorites are derived from buried regolith materials they provide a unique opportunity to study Martian organic geochemistry.

Clemett, S. J.↗

NASA NTRS2016

The Microstructure of Lunar Micrometeorite Impact Craters

The peak of the mass flux of impactors striking the lunar surface is made up of objects approximately 200 micrometers in diameter that erode rocks, comminute regolith grains, and produce agglutinates. The effects of these micro-scale impacts are still not fully understood. Much effort has focused on evaluating the physical and optical effects of micrometeorite impacts on lunar and meteoritic material using pulsed lasers to simulate the energy deposited into a substrate in a typical hypervelocity impact. Here we characterize the physical and chemical changes that accompany natural micrometeorite impacts into lunar rocks with long surface exposure to the space environment (12075 and 76015). Transmission electron microscope (TEM) observations were obtained from cross-sections of approximately 10-20 micrometers diameter craters that revealed important micro-structural details of micrometeorite impact processes, including the creation of npFe (sup 0) in the melt, and extensive deformation around the impact site.

Noble, S. K.↗

NASA NTRS2015

Evolution of the Oxidation State of the Earth's Mantle: Challenges of High Pressure Quenching

The oxidation state of the Earth's mantle during formation remains an unresolved question, whether it was constant throughout planetary accretion, transitioned from reduced to oxidized, or from oxidized to reduced. We investigate the stability of Fe3+ at depth, in order to constrain processes (water, late accretion, dissociation of FeO) which may reduce or oxidize the Earth's mantle. Experiments of more mafic compositions and at higher pressures commonly form a polyphase quench intergrowth composed primarily of pyroxenes, with interstitial glass which hosts nearly all of the more volatile minor elements. In our previous experiments on shergottite compositions, variable fO2, T, and P is less than 4 GPa, Fe3+/TotFe decreased slightly with increasing P, similar to terrestrial basalt. For oxidizing experiments less than 7GPa, Fe3+/TotFe decreased as well, but it's unclear from previous modelling whether the deeper mantle could retain significant Fe3+. Our current experiments expand our pressure range deeper into the Earth's mantle and focus on compositions and conditions relevant to the early Earth. Experiments with Knippa basalt as the starting composition were conducted at 1-8 GPa and 1800 C, using a molybdenum capsule to set the fO2 near IW, by buffering with Mo-MoO3. TEM and EELS analyses revealed the run products from 7-8 GPa quenched to polycrystalline phases, with the major phase pyroxene containing approximately equal Fe3+/2+. A number of different approaches have been employed to produce glassy samples that can be measured by EELS and XANES. A more intermediate andesite was used in one experiment, and decompression during quenching was attempted after, but both resulted in a finer grained polyphase texture. Experiments are currently underway to test different capsule materials may affect quench texture. A preliminary experiment using liquid nitrogen to greatly enhance the rate of cooling of the assembly has also been attempted and this technique will be refined in further experiments.

Danielson, L. R.↗

NASA NTRS2015

Problems at the Leading Edge of Space Weathering as Revealed by TEM Combined with Surface Science Techniques

Both transmission electron micros-copy (TEM) and surface analysis techniques such as X-ray photoelectron spectroscopy (XPS) were instrumen-tal in making the first characterizations of material generated by space weathering in lunar samples [1,2]. Without them, the nature of nanophase metallic Fe (npFe0) correlated with the surface of lunar regolith grains would have taken much longer to become rec-ognized and understood. Our groups at JSC and UVa have been using both techniques in a cross-correlated way to investigate how the solar wind contributes to space weathering [e.g., 3]. These efforts have identified a number of ongoing problems and knowledge gaps. Key insights made by UVa group leader Raul Barag-iola during this work are gratefully remembered.

Christoffersen, R.↗

NASA NTRS2015

Evolution of the Oxidation State of the Earth's Mantle

Danielson, L. R.↗

NASA NTRS2015

Fe and O EELS Studies of Ion Irradiated Murchison CM2 Carbonaceous Chondrite Matrix

Introduction: The physical and chemical response of hydrated carbonaceous chondrite materials to space weathering processes is poorly understood. Improving this understanding is a key part of establishing how regoliths on primitive carbonaceous asteroids respond to space weathering processes, knowledge that supports future sample return missions (Hayabusa 2 and OSIRISREx) that are targeting objects of this type. We previously reported on He+ irradiation of Murchison matrix and showed that the irradiation resulted in amorphization of the matrix phyllosilicates, loss of OH, and surface vesiculation. Here, we report electron energy-loss spectroscopy (EELS) measurements of the irradiated material with emphasis on the Fe and O speciation. Sample and Methods: A polished thin section of the Murchison CM2 carbonaceous chondrite was irradiated with 4 kilovolts He(+) (normal incidence) to a total dose of 1 x 10(exp 18) He(+) per square centimeter. We extracted thin sections from both irradiated and unirradiated regions in matrix using focused ion beam (FIB) techniques with electron beam deposition for the protective carbon strap to minimize surface damage artifacts from the FIB milling. The FIB sections were analyzed using a JEOL 2500SE scanning and transmission electron microscope (STEM) equipped with a Gatan Tridiem imaging filter. EELS spectra were collected from 50 nanometer diameter regions with an energy resolution of 0.7 electronvolts FWHM at the zero loss. EELS spectra were collected at low electron doses to minimize possible artifacts from electron-beam irradiation damage. Results and Discussion: Fe L (sub 2,3) EELS spectra from matrix phyllosilicates in CM chondrites show mixed Fe(2+)/Fe(3+) oxidation states with Fe(3+)/Sigma Fe approximately 0.5. Fe L(sub 2,3) spectra from the irradiated/ amorphized matrix phyllosilicates show higher Fe(2+)/Fe(3+) ratios compared to spectra obtained from pristine material at depths beyond the implantation/amorphization layer. We also obtained O Ka spectra from phyllosilicates in both regions of the sample. The O Ka spectra show a pre-edge feature at approximately 530.5 electronvolts that is related to O 2p states hybridized with Fe 3d states. The intensity ratio of the O Ka pre-edge peak relative to the main part of the O Ka edge (that results from transitions of O 1s to 2p states) is lower in the irradiated layer compared to the pristine material and may reflect the loss of O (as OH) as was observed by IR spectroscopy. Conclusions: In addition to amorphization and OH loss, EELS spectra of He(+) irradiated matrix phyllosilicates in Murchison show that some of the Fe(3+) is reduced to Fe(2+). Spectral deconvolution is underway to extract quantitative ratios from the EELS spectra.

Keller, L. P.↗

NASA NTRS2015

Identification of Highly Fractionated (18)O-Rich Silicate Grains in the Queen Alexandra Range 99177 CR3 Chondrite

Carbonaceous chondrites contain a mixture of solar system condensates, presolar grains, and primitive organic matter. The CR3 chondrite QUE 99177 has undergone minimal al-teration [1], exemplified by abundant presolar silicates [2, 3] and anomalous organic matter [4]. Oxygen isotopic imaging studies of this meteorite have focused on finding submicrometer anomalous grains in fine-grained regions of thin sections. Here we present re-sults of an O isotopic survey of larger matrix grains.

Nguyen, A. N.↗

NASA NTRS2015

Guidance Navigation and Control for the Europa Clipper Mission Concept

No abstract available

Brugarolos, P.↗

NASA NTRS2015

Ion Irradiation Experiments on the Murchison CM2 Carbonaceous Chondrite: Simulating Space Weathering of Primitive Asteroids

Remote sensing observations show that space weathering processes affect all airless bodies in the Solar System to some degree. Sample analyses and lab experiments provide insights into the chemical, spectroscopic and mineralogic effects of space weathering and aid in the interpretation of remote- sensing data. For example, analyses of particles returned from the S-type asteroid Itokawa by the Hayabusa mission revealed that space-weathering on that body was dominated by interactions with the solar wind acting on LL ordinary chondrite-like materials [1, 2]. Understanding and predicting how the surface regoliths of primitive carbonaceous asteroids respond to space weathering processes is important for future sample return missions (Hayabusa 2 and OSIRIS-REx) that are targeting objects of this type. Here, we report the results of our preliminary ion irradiation experiments on a hydrated carbonaceous chondrite with emphasis on microstructural and infrared spectral changes.

Keller, L. P.↗

NASA NTRS2015

Agglutinates in Howardite NWA 1769: Space Weathering on Vesta

No abstract available

Liu, Y.↗

NASA NTRS2014

Diversity in C-Xanes Spectra Obtained from Carbonaceous Solid Inclusions from Monahans Halite

Monahans meteorite (H5) contains fluid inclusion- bearing halite (NaCl) crystals [1]. Microthermometry and Raman spectroscopy showed that the fluid in the inclusions is an aqueous brine and they were trapped near 25degC [1]. Their continued presence in the halite grains requires that their incorporation into the H chondrite asteroid was post metamorphism [2]. Abundant solid inclusions are also present in the halites. The solid inclusions include abundant and widely variable organics [2]. Analyses by Raman microprobe, SEM/EDX, synchrotron X-ray diffraction and TEM reveal that these grains include macromolecular carbon similar in structure to CV3 chondrite matrix carbon, aliphatic carbon compounds, olivine (Fo99−59), high- and low-Ca pyroxene, feldspars, magnetite, sulfides, lepidocrocite, carbonates, diamond, apatite and possibly the zeolite phillipsite [3]. Here we report organic analyses of these carbonaceous residues in Monahans halite using C-, N-, and O- X-ray absorption near edge structure (XANES). Samples and Methods: Approximately 100 nm-thick sections were extracted with a focused ion beam (FIB) at JSC from solid inclusions from Monahans halite. The sections were analyzed using the scanning transmission X-ray microscope (STXM) on beamline 5.3.2.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory for XANES spectroscopy. Results and Discussion: C-XANES spectra of the solid inclusions show micrometer-scale heterogeneity, indicating that the macromolecular carbon in the inclusions have complex chemical variations. C-XANES features include 284.7 eV assigned to aromatic C=C, 288.4-288.8 eV assigned to carboxyl, and 290.6 eV assigned to carbonate. The carbonyl features obtained by CXANES might have been caused by the FIB used in sample preparation. No specific N-XANES features are observed. The CXANES spectra obtained from several areas in the FIB sections include type 1&2 chondritic IOM like, type 3 chondritic IOM like, and none of the above. The natures of the macromolecular carbon in the solid inclusions observed by C-XANES are consistent with the previous studies showing that the carbonaceous solid inclusions have not originated from Monahans parent body [1-3], and have various origins, including various chondritic meteorite parent bodies as well as other unknown source(s).

Kebukawa, Y.↗

NASA NTRS2014

Metal-Silicate Partitioning of Tungsten from 10 to 50 GPa

Geochemical models of core formation are commonly based on core and mantle abundances of siderophile elements that partitioned between silicate and metal in a magma ocean in the early Earth. Tungsten is a moderately siderophile element that may provide constraints on the pressure, temperature, composition, and oxygen fugacity conditions, and on the timing of core formation in the Earth. Previous experimental studies suggest that pressure exerts little to no influence over W metal-silicate partitioning up to 24 GPa, and indicate that the stronger influences are temperature, composition, and oxygen fugacity. However, core formation models based in part on W, predict metal-silicate equilibration pressures outside the available experimental pressure range, requiring extrapolation of parameterized models. Therefore, higher pressure experimental data on W were needed to constrain this important parameter.

Shofner, G. A.↗