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At least 127 records · Page 7

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NASA NTRS1994

Formation of thin sulfide rinds on the CM parent body

Many of the textures that are observed in CM chondrites have been alternately assigned nebular, parent-body, or combined nebular-parent body origins. Since it is very difficult to substantiate the production of complex textures in the nebula, an alternate approach to this problem is to rigorously determine which of the observable textures could have been produced by reasonable aqueous alteration processes on the CM parent body. Potential parent body reactions involving S deserve special attention because S-bearing phase define many important CM textures, such as rims. We have examined the possibility that the thin (about 5 microns) rinds of sulfides observed around some partially dissolved olivines within the chondrules and matrixes of CM chondrites were formed by the preferential precipitation of sulfides at or near dissolving olivine boundaries during parent-body alteration. Our model defines two infinite and parallel planes of olivine that are separated by pure water. Average separation distances between olivine grains in CM chondrites at the time of accretion (about 100-200 microns) were estimated by assuming a closed system fluid/rock ratio of 45% and varying the bimodal grain-size distribution. We restrict our calculations to the case of an isochemical system with sufficient bisulfide in solution to account for precipitation of pyrrhotite at STP. Our model examines the possibility that dissolving olivines with compositions between Fo(sub 0.9) and Fo(sub 0.4) can produce a strong gradient of Fe(2+) at pHs from 7 to 12 such that the precipitation of pyrrhotite will be initiated at the olivine-fluid boundary. Since CM phase equilibria is consistent with highly reducing conditions, Fe released by olivines would largely remain in solution as Fe(2+) until the solubility product of a Fe(2+) bearing phase was exceeded. Our calculations indicate that all examined combinations of olivine composition and pH yield a strong Fe(2+) gradient at the time the pyrrhotite solubility is exceeded near the olivine-fluid boundary. This favors the initiation of sulfide precipitation around dissolving olivines. However, sulfide rinds are not observed around all partially dissolved olivine grains in CM chondrites, which suggests that the availability of aqueous sulfide species limits the production of the thin sulfide rinds.

Browning, L. B.↗

NASA NTRS1973

Sandstorms and eolian erosion on Mars.

Erosion rates are calculated for Mars from first principles and calibrated from wind tunnel experiments. The deduced abrasion rates are higher than eolian erosion rates on the earth because of the higher threshold velocities on Mars but lower than the total erosion rates on the earth because of the absence of aqueous erosion processes on contemporary Mars. The high erosion rates imply that, for scale lengths of less than a few hundred kilometers, Mars may be viewed only part way back to its ancient history. Because the meteorology of Mars is position-dependent, erosion rates may vary greatly from place to place. Martian sandstorms may be characterized by frequent grain-grain collisions, and the grain velocities and cloud height may approach values implied by the Maxwell-Boltzmann velocity distribution.

Sagan, C.↗

NASA NTRS1989

Functional Microspheres

Tiny beads develop from aqueous solution. Process forms beads of polyglutaraldehyde directly from solution. Beads of 0.5-to-1.0-micron diameter with fluorescent or magnetic properties made. Fluorescent or magnetic properties allow marked cells to be traced and identified. Useful in biology, clinical chemistry, and biochemistry.

Rembaum, Alan↗

NASA NTRS1988

Hellas Basin ejecta: A prime stratigraphic marker and sampling target

The Hellas Basin and associated ejecta deposits dominate a large portion of the southern highlands of Mars. These deposits have been particularly well-documented at the scale 1:5,000,000 in the Sinus Sabaeus (MC-20), Iapygia (MC-21) and Mare Tyrrhenum (MC-22) quadrangles (1,2,3) where they have been mapped as ancient hilly and cratered material. In MC-22 the ejecta deposit is interpreted to thin from west to east, away from Hellas. In the eastern part of MC-22, the outlines of some large older craters, such as Hershel, can be seen through the thin ejecta cover and some of these buried craters even have enough relief to act as depositional traps for later mostly eolian sediments. Superposed on the ejecta is a population of numerous intermediate-sized to smaller craters which indicates the relatively old age of the ejecta deposit and causes the unit to have rather rough surface topography. Numerous small channels on steeply sloping crater rims and regionally sloping surface indicate erosion, transportation and redeposition of substantial amounts of ejecta materials, probably by aqueous fluvial processes. Numerous more recent volcanic constructs and flows also are superposed on the ejecta.

King, Elbert A.↗

NASA NTRS1989

Major element composition of stratospheric micrometeorites

Results are presented on an element-composition study conducted on 200 interplanetary dust particles (IDPs) collected with NASA's U2 and RB 47 aircraft at altitudes near 20 km. These IDPs could be classified into two major morphological types, i.e., the 'porous' and the 'smooth' particle types, which showed significant compositional differences. Namely, elemental abundances found in porous particles are closely matching those of the CI chondrites, while the smooth particle group displayed systematic Ca and Mg depletions and contained stoichiometric 'excess' oxygen, consistent with the presence of hydrous phases. This fact, together with the occurrence of carbonates, magnetite framboids, and layer silicates, provides evidence that at least a significant number of the smooth-type IDPs were processed by aqueous activity. It is hypothesized that extensive aqueous activity only occurs in asteroids (as opposed to comets) and that the smooth class of IDPs is of an asteroidal origin.

Schramm, L. S.↗

NASA NTRS1991

Hot Oil Removes Wax

Mineral oil heated to temperature of 250 degrees F (121 degrees C) found effective in removing wax from workpieces after fabrication. Depending upon size and shape of part to be cleaned of wax, part immersed in tank of hot oil, and/or interior of part flushed with hot oil. Pump, fittings, and ancillary tooling built easily for this purpose. After cleaning, innocuous oil residue washed off part by alkaline aqueous degreasing process. Serves as relatively safe alternative to carcinogenic and environmentally hazardous solvent perchloroethylene.

Herzstock, James J.↗

NASA NTRS1993

Thermonucleator

Thermonucleator controls nucleation in selected region of crystallizing solution by varying local temperature and local supersaturation. Apparatus potentially offers better control of crystallization process in aqueous solution than use of stream of cold gas to induce nucleation by cooling part of bottom of crucible containing hot solution.

Demattei, Robert C.↗

NASA NTRS1995

The role of surface chemical analysis in a study to select replacement processes for TCA vapor degreasing

The role of surface-sensitive chemical analysis (ESCA, AES, and SIMS) in a study to select a process to replace 1, 1, 1-trichloroethane (TCA) vapor degreasing as a steel and aluminum bonding surface preparation method is described. The effort was primarily concerned with spray-in-air cleaning processes involving aqueous alkaline and semi-aqueous cleaners and a contamination sensitive epoxy-to-metal bondline. While all five cleaners tested produced bonding strength results equal to or better than those produced by vapor degreasing, the aqueous alkaline cleaners yielded results which were superior to those produced by the semi-aqueous cleaners. The main reason for the enhanced performance appears to be a silicate layer left behind by the aqueous alkaline cleaners. The silicate layer increases the polarity of the surface and enhances epoxy-to-metal bonding. On the other hand, one of the semi-aqueous cleaners left a nonpolar carbonaceous residue which appeared to have a negative effect on epoxy-to-metal bonding. Differences in cleaning efficiency between cleaners/processes were also identified. These differences in surface chemistry, which were sufficient to affect bonding, were not detected by conventional chemical analysis techniques.

Lesley, Michael W.↗

NASA NTRS1989

Interaction of a sodium ion with the water liquid-vapor interface

Molecular dynamics results are presented for the density profile of a sodium ion near the water liquid-vapor interface at 320 K. These results are compared with the predictions of a simple dielectric model for the interaction of a monovalent ion with this interface. The interfacial region described by the model profile is too narrow and the profile decreases too abruptly near the solution interface. Thus, the simple model does not provide a satisfactory description of the molecular dynamics results for ion positions within two molecular diameters from the solution interface where appreciable ion concentrations are observed. These results suggest that surfaces associated with dielectric models of ionic processes at aqueous solution interfaces should be located at least two molecular diameters inside the liquid phase. A free energy expense of about 2 kcal/mol is required to move the ion within two molecular layers of the free water liquid-vapor interface.

NASA Center ARC↗

NASA NTRS2005

Cobalt Oxide Hollow Nanoparticles Derived by Bio-Templating

We present here the first fabrication of hollow cobalt oxide nanoparticles produced by a protein-regulated site-specific reconstitution process in aqueous solution and describe the metal growth mechanism in the ferritin interior.

Kim, Jae-Woo↗

NASA NTRS2007

Mobile Element Studies in Rocks (RAT) from Columbia Hills/West Spur at Gusev

Using elemental abundances determined by SPIRIT APX spectrometer on rocks and soils at Gusev Plains and Columbia Hills/ West Spur regions, the Athena Team discussed the aqueous geochemical implications at these sites on Mars. They suggested that these rocks were exposed to variable degrees of aqueous alteration (low to high) at Gusev crater. Earlier, we developed analytical procedures for studying aqueous geochemical behavior of fluids on rocks at Meridiani. In the present study, we apply these methods to rocks at Columbia Hills/West Spur in order to understand the significance of the Gusev rock results in reference to aqueous geochemical processes on Mars . The data analysis procedure is based on treating SO3 ("a") and Cl ("b") as two variables and tracking the relationship between "a" and "b" when the fluids undergo evaporation. This process of evaporation leads to concentration changes in these two elements finally producing salt assemblages on Martian rocks. In some cases on plotting "a"/ "b" versus "b" in salt assemblages, they yield a hyperbolic distribution. The relationship is transformed into a straight line when "a"/"b" is again plotted against 1/"b" in the system. Earlier, we used this procedure in the case of Merdiani rock abrasion tool (RAT) rocks and in this study, we discuss the application of this procedure to Gusev rocks. This study shows that the Gusev Plains rocks were exposed to low SO3/Cl solutions (sulfate-poor) for short period of time (weak interaction), whereas solutions with high SO3/Cl ratios (sulfate-rich) seem to have pervasively interacted with Columbia Hills/ West Spur rocks (strong interaction) at Gusev crater. Our conclusions seem to be consistent with the Mossbauer results given for these rocks

Rao, M. N.↗

NASA NTRS2004

Precipitation of Secondary Phases from the Dissolution of Silicate Glasses

Basaltic and anorthositic glasses were subjected to aqueous weathering conditions in the laboratory where the variables were pH, temperature, glass composition, solution composition, and time. Leached layers formed at the surfaces of glasses followed by the precipitation of X-ray amorphous iron and titanium oxides in acidic and neutral solutions at 25 C over time. Glass under oxidative hydrothermal treatments at 150 C yielded a three-layered surface; which included an outer smectite layer, a Fe-Ti oxide layer and an innermost thin leached layer. The introduction of Mg into solutions facilitated the formation of phyllosilicates. Aqueous hydrothermal treatment of anorthositic glasses (high Ca, low Ti) at 200 C readily formed smectite, whereas, the basaltic glasses (high Ti) were more resistant to alteration and smectite was not observed. Alkaline hydrothermal treatment at 2000e produced zeolites and smectites; only smectites formed at 200 C in neutral solutions. These mineralogical changes, although observed under controlled conditions, have direct applications in interpreting planetary (e.g., meteorite parent bodies) and terrestrial aqueous alteration processes.

Ming, Douglas W.↗

NASA NTRS2013

A Moderate D/H Ratio for a Surficial Water Reservoir on Mars

Martian surface morphology implies that Mars was once warm enough to maintain persistent liquid water on its surface and that water played a significant role in the formation of weathered/altered terrains [e.g., 1, 2, 3]. Volatiles exhaled by volcanic activity would have been the dominant greenhouse gases and would have significantly affected the Martian climate. The enrichment of some volatile elements in the atmosphere, which would have dissolved in surface water, could also have influenced water chemistry (e.g., acidity) and played a significant role in weathering and aqueous alteration processes. While much of this picture is qualitative, Martian meteorites contain records of major Martian volatile reservoirs. This study characterizes Martian surficial volatile reservoirs based on in situ ion microprobe analyses of volatile abundances and H-isotopes of glassy phases (groundmass glass [GG] and impact melt [IM]) in Martian basalts (shergottites). Although these meteorites are of igneous origin, some glassy phases underwent impact-induced modification that trapped surficial and atmospheric volatile components [4, 5]; e.g., inert gases contained in IMs from EETA79001 (EETA79) match the relative abundances of modern Martian atmosphere [6]. Analyses of these glassy phases demonstrate that surficial volatile reservoirs have distinct D/H ratios from their magmatic volatiles.

Usui, Tomohiro↗

NASA NTRS2014

Surviving High-temperature Components in CI Chondrites

The CI1 chondrites, while having the most solar-like compo-sition of any astromaterial available for laboratory analysis, have also been considerably altered by asteroidal processes including aqueous alteration. It is of fundamental importance to determine their pre-alteration mineralogy, so that the state of matter in the early Solar System can be better determined. In the course of a re-examination of the compositional range of olivine and low-Ca pyroxene in CI chondrites Orgueil, Ivuna and Alais [1] we found the first reported complete CAI, as already reported [2], with at-tached rock consisting mainly of olivine and low-Ca pyroxene. The range of residual olivine major element compositions we have determined in the CIs (Fig. 1) may now be directly com-pared with those of other astromaterials, including Wild 2 grains. The abundance of olivine and low-Ca pyroxene in CIs is higher than is generally appreciated, and in fact much higher than for some CMs [1]. We also noted numerous rounded objects varying in shape from spheres to oblate spheroids, and ranging up to 100μm in size (Fig. 2), which have been previously noted [3] but have not been well documented or appreciated. We characterized the mineralogy by transmission electron microscopy and found that they consist mainly of rather fine-grained, flaky single phase to intergrown serpentine and saponite. These two materials in fact dominate the bulk of the host CI1 chondrites. With the exception of sparse spinels, the rounded phyllosilicate objects are remarka-bly free of other minerals, suggesting that the precursor from which the phyllosilicates were derived was a homogeneous mate-rial. We suggest that these round phyllosilicates aggregates in CI1 chondrites were cryptocrystalline to glassy microchondrules. If so then CI chondrites cannot be considered chondrule-free. Small though they are, the abundance of these putative microchondrules is the same as that of chondrules in the Tagish Lake meteorite.

Zolensky, M.↗

NASA NTRS2017

Surveying Clay Mineral Diversity in the Murray Formation, Gale Crater, Mars

The CheMin XRD instrument aboard Mars Science Laboratory (MSL) has documented clay minerals in various drill samples during its traverse of Gale Crater's floor and ascent of Mt. Sharp. The most recent samples, named Marimba, Quela and Sebina were acquired from the Murray Formation in the Murray Buttes region of lower Mt. Sharp. Marimba and Quela come from a approx. 30 m package of finely laminated lacustrine mudstones. Sebina comes from an overlying package of heterolithic mudstone-sandstones. Clay minerals make up approx.15-25 wt.% of the bulk rock with similar contributions to XRD patterns in all three samples. Broad basal reflections at approx. 10deg 2(theta) CoK(alpha) indicate the presence of 2:1 group clay minerals. The 02(lambda) clay mineral band lies at approx. 22.9deg 2(theta), a region typically occupied by Fe-bearing dioctahedral 2:1 clay minerals like nontronite or Fe-illite. The low humidity within the CheMin instrument, which is open to the martian atmosphere, promotes loss of interlayer H2O and collapse of smectite interlayers making them difficult to distinguish from illites. However, based on the low K content of the bulk samples, it appears that smectitic clay minerals are dominant. Peak dehydroxylation of the Marimba sample measured by the SAM instrument on MSL occurred at 610C and 780C. Fe-bearing smectites are not consistent with these dehydroxylation temperatures. Thus, we suggest that a mixture of dioctahedral and trioctahedral smectite phases are present giving the appearance of intermediate octahedral occupancy in XRD. Dioctahedral smectites have not previously been reported in Gale Crater by MSL. Earlier in the mission, relatively clay mineral rich samples (approx. 20 wt.%) from lacustrine mudstones in Yellowknife Bay (YKB) were found to contain ferrian saponites. It is proposed that YKB saponites formed via isochemical aqueous alteration of detrital olivine close to the time of sediment deposition, under anoxic to poorly oxidizing conditions. In terrestrial settings where alteration sequences of basaltic rocks or sediments are observed, first-stage alteration clay minerals are typically trioctahedral smectite species, as reported from YKB. In later alteration stages trioctahedral clay minerals are replaced by dioctahedral clays as a result of removal and/or oxidation of Fe2+ and Mg. Observed changes in clay mineralogy between YKB and Murray Buttes samples correspond with differences in bulk mineralogy, including: 1) a transition from magnetite to hematite as the main Fe-oxide, 2) increasing abundances of Ca-sulfates and 3) a reduction in the quantity of reactive mafic minerals. This mineralogical change indicates an increasing degree of aqueous alteration and oxidation of mafic detritus in the upper part of the Murray Formation. These results broaden the spectrum of mineralogical facies documented by MSL. Together sedimentology and mineralogy indicate a long-lasting, dynamic fluvial-lacustrine system encompassing a range aqueous geochemical processes under varying redox conditions. Future work is needed to unravel the influence of global and local controls on the range of ancient conditions observed at Gale Crater.

MSL↗

NASA NTRS2019

New Perspectives of Ancient Mars: Mineral Diversity and Crystal Chemistry at Gale Crater, Mars from the CheMin X-Ray Diffractometer

The Mars Science Laboratory Curiosity rover arrived at Mars in August 2012 with a primary goal of characterizing the habitability of ancient and modern environments. Curiosity landed in Gale crater to study a sequence of ~3.5 Ga old sedimentary rocks that, based on orbital visible/near-infrared reflectance spectra, contain secondary minerals that suggest deposition and/or alteration in liquid water. The sedimentary sequence that comprises the lower slopes of Mount Sharp within Gale crater may preserve a dramatic shift on early Mars from a relatively warm and wet climate to a cold and dry climate based on a transition from smectite-bearing strata to sulfate-bearing strata. The rover is equipped with cameras and geochemical and mineralogical instruments to examine the sedimentology and identify compositional changes within the stratigraphy. These observations provide information about variations in depositional and diagenetic environments over time. The Chemistry and Mineralogy (CheMin) instrument is one of two internal laboratories on Curiosity and includes a transmission X-ray diffractometer (XRD) and X-ray fluorescence (XRF) spectrometer with a Co-K source. CheMin measures loose sediment samples scooped from the surface and drilled rock powders. The XRD provides quantitative mineralogy of scooped and drilled samples to a detection limit of ~1 wt.%. Curiosity has traversed >20 km since landing and has primarily been exploring the site of a predominantly ancient lake environment fed by groundwater and streams emanating from the crater rim. Results from CheMin demonstrate an incredible diversity in the mineralogy of fluvio-lacustrine rocks that signify variations in source rock composition, sediment transport mechanisms, and depositional and diagenetic fluid chemistry. Abundant trioctahedral smectite and magnetite at the base of the section may have formed from low-salinity pore waters with a circumneutral pH within lake sediments. A transition to dioctahedral smectite, hematite, and Ca-sulfate going up section suggests a change to more saline and oxidative aqueous conditions within the lake waters themselves and/or within diagenetic fluids. The primary minerals detected in fluvio-lacustrine samples by CheMin also suggest diversity in the igneous source regions for the sediments, where abundant pyroxene and plagioclase in most samples suggest a basaltic protolith, but sanidine and pyroxene in one sample may have been sourced from a potassic trachyte, and tridymite and sanidine in another sample may have been transported from a rhyolitic source. Crystal chemistry of major phases in each sample have been calculated from refined unit-cell parameters, providing further constraints on aqueous alteration processes and igneous protoliths for the sediments. Perhaps one of the biggest mysteries revealed by the CheMin instrument is the high abundance of X-ray amorphous materials (15 to 73 wt.%) in all samples measured to date. X-ray amorphous materials were detected by CheMin based on the observation of broad humps in XRD patterns. How these materials formed, their composition, and why they persist near the martian surface remain a topic of debate. The sedimentology and composition of the rocks analyzed by Curiosity demonstrate that habitable environments persisted intermittently on the surface or in the subsurface of Gale crater for perhaps more than a billion years.

Rampe, E. B.↗

NASA NTRS2020

Evidence for Multiple Diagenetic Episodes in Ancient Fluvial‐Lacustrine Sedimentary Rocks in Gale Crater, Mars

The Curiosity rover's exploration of rocks and soils in Gale crater has provided diverse geochemical and mineralogical data sets, underscoring the complex geological history of the region. We report the crystalline, clay mineral, and amorphous phase distributions of four Gale crater rocks from an 80‐m stratigraphic interval. The mineralogy of the four samples is strongly influenced by aqueous alteration processes, including variations in water chemistries, redox, pH, and temperature. Localized hydrothermal events are evidenced by gray hematite and maturation of amorphous SiO 2 to opal‐CT. Low‐temperature diagenetic events are associated with fluctuating lake levels, evaporative events, and ground water infiltration. Among all mudstones analyzed in Gale crater, the diversity in diagenetic processes is primarily captured by the mineralogy and X‐ray amorphous chemistry of the drilled rocks. Variations indicate a transition from magnetite to hematite and an increase in matrix‐associated sulfates suggesting intensifying influence from oxic, diagenetic fluids up section. Furthermore, diagenetic fluid pathways are shown to be strongly affected by unconformities and sedimentary transitions, as evidenced by the intensity of alteration inferred from the mineralogy of sediments sampled adjacent to stratigraphic contacts.

C N Achilles↗

NASA NTRSDate not supplied

The Metal-Rich Lithology within the Aguas Zarcas Breccia: Characterization, Origin, and Evolution

Carbonaceous chondrites are important since they provide critical insights into the early history of the Solar System. They have experienced a wide range of processes, including aqueous alteration and thermal metamorphism or a combination of both that provide important information about the environment of their evolution. We investigated the petrography, mineralogy, chemistry, and isotopic composition of an unusual “metal-rich lithology” (hereafter Met-1) from Aguas Zarcas using numerous analytical techniques, in order to properly understand its characteristics, affinities, origin and formation history.

I Kerraouch↗