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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Spectroscopy of Mars form 2.04 to 2.44 micron during the 1993 opposition: Absolute calibration and atmospheric vs mineralogic origin of narrow absorption features

We present moderate-resolution (lambda/delta lambda = 300 to 370) reflectance spectral of Mars from 2.04 to 2.44 microns that were obtained at United Kingdom Infrared Telescope (UKIRT) during the 1993 opposition. Seven narrow absorption features were detected and found to have a Mars origin. By comparison with solar and Mars atmospheric spectra, five of these features were attributed all or in part to Mars atmospheric CO2 or CO (2.052 +/- 0.003, 2.114 +/- 0.002, 2.150 +/- 0.003, 2.331 +/- 0.001, and 2.357 +/- 0.002 microns). Two of the bands (2.331 +/- 0.001 and 2.357 +/- 0.002 micron) appear to have widths and depths that are consistent with additional, nonatmospheric absorptions, although a solar contribution cannot be entirely ruled out. Two other weak bands centered at 2.278 +/- 0.002 and 2.296 +/- 0.002 microns may be at least partially mineralogic in origin. The data provide no conclusive identification of the mineralogy responsible for these absorption features. However, examination of terrestrial spectral libraries and previous mineralogy responsible for these absorption features. However, examination of terrestrial spectral libraires and previous moderate spectral resolution mineral studies indicates that the most likely origin of these features is either (bi)carbonate or (bi)sulfate anions in framework silicates of (Fe, Mg)-OH bonds in sheet silicates. If the bands are caused by phyllosilicate minerals, then an explanation must be found for the extremely narrow widths of the cation-OH features in the Mars spectra as compared to terrestrial minerals.

Bell, James F., III↗
NASA NTRS1993

Spatial Variations in the Spectral Properties of Bright Regions on Mars

Much of the surface of Mars is covered by material that is bright and reddish at visible wavelengths and which is interpreted as chemically altered soil. High spatial resolution data from the ISM near-infrared imaging spectrometer on the Phobos 2 spacecraft have provided new information about the composition and compositional heterogeneity of this soil. Most bright soil exhibits a weak, narrow absorption feature near 2.2 micron, suggesting the presence of poorly crystalline phyllosilicate. The strength of the 3.0-micron H2O absorption exhibits spatially coherent variations, with stronger absorptions occurring in specific geologic units. These variations may result from differences in the content of molecular water in soils developed on different deposits. Additionally, the position and shape of the 0.9-micron Fe(3+) absorption indicate hematite to be present in bright soils covering many areas, including Tharsis. However, other large areas covered by bright soil, including much of Arabia, exhibit a deeper absorption at a longer wavelength, suggesting occurrence of ferric minerals other than hematite. These spectral heterogeneities indicate that bright martian soil is compositionally diverse and not completely homogenized by eolian activity. The compositional differences may result from different histories of chemical alteration of parent materials and their resulting soils, possibly including local effects of liquid water.

Murchie, Scott↗
NASA NTRS1997

Workshop on Parent-Body and Nebular Modification of Chondritic Materials

Topics considered include: thermal Metamorphosed Antarctic CM and CI Carbonaceous Chondrites in Japanese Collections, and Transformation Processes of Phyllosilicates; use of Oxygen Isotopes to Constrain the Nebular and Asteroidal Modification of Chondritic Materials; effect of Revised Nebular Water Distribution on Enstatite Chondrite Formation; interstellar Hydroxyls in Meteoritic Chondrules: Implications for the Origin of Water in the Inner Solar System; theoretical Models and Experimental Studies of Gas-Grain Chemistry in the Solar Nebula; chemical Alteration of Chondrules on Parent Bodies; thermal Quenching of Silicate Grains in Protostellar Sources; an Experimental Study of Magnetite Formation in the Solar Nebula; the Kaidun Meteorite: Evidence for Pre- and Postaccretionary Aqueous Alteration; a Transmission Electron Microscope Study of the Matrix Mineralogy of the Leoville CV3 (Reduced-Group) Carbonaceous Chondrite: Nebular and Parent-Body Features; rubidium-Strontium Isotopic Systematic of Chondrules from the Antarctic CV Chondrites Yamato 86751 and Yamato 86009: Additional Evidence for Late Parent-Body Modification; oxygen-Fugacity Indicators in Carbonaceous Chondrites: Parent-Body Alteration or High-Temperature Nebular Oxidation; thermodynamic Modeling of Aqueous Alteration in CV Chondrites; asteroidal Modification of C and O Chondrites: Myths and Models; oxygen Fugacity in the Solar Nebular; and the History of Metal and Sulfides in Chondrites.

Zolensky, M. E.↗
NASA NTRS1994

Petrology of Impact-Melt Rocks at the Chicxulub Multiring Basin, Yucatan, Mexico

Compositions and textures of melt rocks from the upper part of the Chicxulub structure are typical of melt rocks at other large terrestrial impact structures. Apart from variably elevated iridium concentrations (less than 1.5 to 13.5 +/- 0.9 ppb) indicating nonuniform dissemination of a meteoritic component, bulk rock and phenocryst compositions imply that these melt rocks were derived exclusively from continental crust and platform-sediment target lithologies. Modest differences in bulk chemistry among samples from wells located approximately 40 km apart suggest minor variations in relative contributions of these target lithologies to the melts. Subtle variations in the compositions of early-formed pyroxene and plagioclase also support minor primary differences in chemistry between the melts. Evidence for pervasive hydrothermal alteration of the porous mesostasis includes albite, K-feldspar, quartz, epidote, chlorite, and other phyllosilicates, as well as siderophile element-enriched sulfides, suggesting the possibility that Chicxulub, like Sudbury, may host important ore deposits.

Schuraytz, Benjamin C.↗
NASA NTRS1995

The Weathering of Antarctic Meteorites: Climatic Controls on Weathering Rates and Implications for Meteorite Accumulation

Weathering of meteorites includes a variety of chemical and mineralogical changes, including conversion of metal to iron oxides, or rust. Other changes include the devitrification of glass, especially in fusion crust. On a longer time scale, major minerals such as olivine, pyroxene, and feldspar are partially or wholly converted to various phyllosilicates. The degree of weathering of meteorite finds is often noted using a qualitative system based on visual inspection of hand specimens. Several quantitative weathering classification systems have been proposed or are currently under development. Wlotzka has proposed a classification system based on mineralogical changes observed in polished sections and Mossbauer properties of meteorite powders have also been used. In the current paper, we discuss induced thermoluminescence (TL) as an indicator of degree of weathering of individual meteorites. The quantitative measures of weathering, including induced TL, suffer from one major flaw, namely that their results only apply to small portions of the meteorite.

Benoit, P. H.↗
NASA NTRS1999

Differential Scanning Calorimetry and Evolved Gas Analysis of Hydromagnesite

Volatile-bearing minerals (e.g., Fe-oxyhydroxides, phyllosilicates, carbonates and sulfates) may be important phases on the surface of Mars. In order to characterize these phases the Thermal and Evolved Gas Analyzer (TEGA) flying on the Mars'98 lander will perform analyses on surface samples from Mars. Hydromagnesite [Mg5(CO3)4(OH)2.4H2O] is considered a good standard mineral to examine as a Mars soil analog component because it evolves both H2O and CO2 at temperatures between 0 and 600 C. Our aim here is to interpret the DSC signature of hydromagnesite under ambient pressure and 20 sccm N2 flow in the range 25 to 600 C. The DSC curve for hydromagnesite under the above conditions consists of three endothermic peaks at temperatures 296, 426, and 548 and one sharp exotherm at 511 C. X-ray analysis of the sample at different stop temperatures suggested that the exotherm corresponded with the formation of crystalline magnesite. The first endotherm was due to dehydration of hydromagnesite, and then the second one was due to the decomposition of carbonate, immediately followed by the formation of magnesite (exotherm) and its decomposition to periclase (last endotherm). Evolution of water and CO2 were consistent with the observed enthalpy changes. A library of such DSC-evolved gas curves for putative Martian minerals are currently being acquired in order to facilitate the interpretation of results obtained by a robotic lander.

Lauer, H. V., Jr.↗
NASA NTRS2000

Thermal and Evolved Gas Analyses at Reduced Pressures: A Mineral Database for the Thermal Evolved Gas Analyzer (TEGA)

Volatile-bearing minerals (e.g., Fe-oxyhydroxides, phyllosilicates, carbonates, and sulfates) may be important phases on the surface of Mars. The Thermal Evolved Gas Analyzer (TEGA), which was part of the Mars Polar Lander payload, was to detect and identify volatile-bearing phases in the Martian regolith. The TEGA instrument is composed of a differential scanning calorimetry (DSC) interfaced with an evolved gas analyzer (EGA). The EGA consists of a Herriott cell of a tunable-diode laser (TDL) spectrometer that determines CO, and H2O abundances. The sample chamber in TEGA operates at about 100 mbar (-76 torr) with a N2 carrier gas flow of 0.4 sccm. Essentially no information exists on the effects of reduced pressure on the thermal properties of volatile-bearing minerals. Here we present a database for the thermal behavior of volatile-bearing phases under reduced pressure conditions.

Lauer, H. V., Jr.↗
NASA NTRS1999

J6 Himalia: New Compositional Evidence and Interpretations for the Origin of Jupiter's Small Satellites

New narrowband spectrophotometric data of J6 Himalia, some of which are spatially resolved, support its C-type classification. The new spectra confirm the presence of a weak absorption feature centered near 0.7 micron attributed to oxidized iron in phyllosilicates, products of aqueous alteration, which varies in depth on opposite sides of the satellite. Evaluation of older UBV photometry of J6 and J7 Elara compared to UBV photometry of C-class (and subclass) asteroids showing spectral evidence of the 0.7-microns absorption feature suggests that J6 Himalia is an F-class asteroid. We propose that the parent body of the prograde Jovian satellites originated as part of the Nysa asteroid family. Evolutionary models of the Jovian system are used to address the capture and dispersal of the irregular satellites.

Vilas, Faith↗
NASA NTRS2000

Thermal and Evolved Gas Analysis of Hydromagnesite and Nesquehonite: Implications for Remote Thermal Analysis on Mars

Volatile-bearing minerals (e.g., Fe-oxyhydroxides, phyllosilicates, carbonates, and sulfates) may be important phases on the surface of Mars. In order to characterize these potential phases the Thermal Evolved-Gas Analyzer (TEGA), which was onboard the Mars Polar Lander, was to have performed differential scanning calorimetry (DSC) and evolved-gas analysis of soil samples collected from the surface. The sample chamber in TEGA operates at about 100 mbar (approximately 76 torr) with a N2, carrier gas flow of 0.4 seem. Essentially, no information exists on the effects of reduced pressure on the thermal properties of volatile-bearing minerals. In support of TEGA, we have constructed a laboratory analog for TEGA from commercial instrumentation. We connected together a commercial differential scanning calorimeter, a quadruple mass spectrometer, a vacuum pump, digital pressure gauge, electronic mass flow meter, gas "K" bottles, gas dryers, and high and low pressure regulators using a collection of shut off and needle valves. Our arrangement allows us to vary and control the pressure and carrier gas flow rate inside the calorimeter oven chamber.

Lauer, H. V., Jr.↗
NASA NTRS2000

The Search for Water and Other Volatiles in Martian Surface Materials: The Thermal Evolved Gas Analyzer (TEGA)

Volatile-bearing minerals and phases (e.g., Fe-oxyhydroxides, phyllosilicates, carbonates, sulfates, palagonites, glasses) may be important components of the Martian regolith. However, essentially no information exists on the mineralogical composition of volatile-bearing phases in the regolith. The Thermal Evolved Gas Analyzer (TEGA), which was part of the Mars Polar Lander payload, was to determine the abundances of two of the most important volatile compounds (i.e., water and carbon dioxide) in the martian soil and to identify the minerals or phases that harbor these volatiles. The TEGA instrument was composed of a differential scanning calorimeter (DSC) interfaced with evolved gas analysis (EGA). The EGA consisted of a Herriott cell of a tunable-diode laser (TDL) spectrometer that determines CO2 and H2O abundances. The sample chamber was to operate at about 100 mbar (-76 torr) with a N2 carrier gas flow of 0.4 sccm. Specifications of TEGA are described in detail elsewhere in this volume.

Ming, D. W.↗
NASA NTRS2001

Constraints on the Composition of Trojan Asteroid 624 Hektor

We present a composite spectrum of Trojan asteroid 624 Hektor, 0.3-3.6 microns, which shows that there is no discernible 3-micron absorption band. Such a band would indicate the presence of OH or H2O- bearing silicate minerals, or macromolecular carbon-rich organic material of the kind seen on the low-albedo hemisphere of Saturn's satellite Iapetus (Owen et al. 2000). The absence of spectral structure is itself indicative of the absence of the nitrogen-rich tholins (which show a distinctive absorption band attributed to N-H). The successful models in this study all incorporate the mineral pyroxene (Mg, Fe SiO3, the composition of hypersthene), which matches the red color of Hektor. Pyroxene is a mafic mineral common in terrestrial and lunar lavas, and is also seen in Main Belt asteroid spectra. An upper limit to the amount of crystalline H20 ice (30-micron grains) in the surface layer of Hektor is 3 weight percent. The upper limit for serpentine, as a representative of hydrous silicates, is much less stringent, at 40 percent, based on the shape of the spectral region around 3 gm. Thus, the spectrum at 3 gm does not preclude the presence of a few weight percent of volatile material in the surface layer of Hektor. All of the models we calculated require elemental carbon to achieve the low geometric albedo that matches Hektor. This carbon could be of organic or inorganic origin. By analogy, other D-type asteroids could achieve their red color, low albedo, and apparent absence of phyllosilicates, from compositions similar to the models presented here.

Cruikshank, Dale P.↗
NASA NTRS2002

Heterogeneous Distribution of Carbonaceous Material in Murchison Matrix: In Situ Observations Using Energy Filtered Transmission Electron Microscopy

Energy filtered TEM (Transmission Electron Microscopy) has been used to study the location of carbonaceous material in situ in Murchison matrix. Carbon occurs frequently as narrow rims around sulfide grains, but is rare in regions of matrix that are dominated by phyllosilicates. Additional information is contained in the original extended abstract.

Brearley, Adrian J.↗
NASA NTRS2002

Hydrated Minerals on Asteroids: The Astronomical Record

Knowledge of the hydrated mineral inventory on the asteroids is important for deducing the origin of Earth's water, interpreting the meteorite record, and unraveling the processes occurring during the earliest times in solar system history. Reflectance spectroscopy shows absorption features in both the 0.6-0.8 and 2.5-3.5 micrometers regions, which are diagnostic of or associated with hydrated minerals. Observations in those regions show that hydrated minerals are common in the mid-asteroid belt, and can be found in unexpected spectral groupings, as well. Asteroid groups formerly associated with mineralogies assumed to have high temperature formation, such as M- and E-class asteroids, have been observed to have hydration features in their reflectance spectra. Some asteroids have apparently been heated to several hundred degrees Celsius, enough to destroy some fraction of their phyllosilicates. Others have rotational variation suggesting that heating was uneven. We summarize this work, and present the astronomical evidence for water- and hydroxyl-bearing minerals on asteroids.

Rivkin, A. S.↗
NASA NTRS2003

Hydrated Minerals on Asteroids: The Astronomical Record

Knowledge of the hydrated mineral inventory on the asteroids is important for deducing the origin of Earth's water, interpreting the meteorite record, and unraveling the processes occurring during the earliest times in solar system history. Reflectance spectroscopy shows absorption features in both the 0.6-0.8 and 2.5-3.5-micron regions, which are diagnostic of or associated with hydrated minerals. Observations in those regions show that hydrated minerals are common in the mid-asteroid belt, and can be found in unexpected spectral groupings as well. Asteroid groups formerly associated with mineralogies assumed to have high-temperature formation, such as M- and E-class steroids, have been observed to have hydration features in their reflectance spectra. Some asteroids have apparently been heated to several hundred degrees Celsius, enough to destroy some fraction of their phyllosilicates. Others have rotational variation suggesting that heating was uneven. We summarize this work, and present the astronomical evidence for water- and Hydroxl-bearing minerals on asteroids.

Rivkin, A. S.↗
NASA NTRS2003

Palagonitic (Not Andesitic) Mars: Evidence from Thermal Emission and VNIR Spectra of Palgonitic Alteration Rinds on Basaltic Rock

Visible and near-IR (VNIR) spectra of both Martian bright and dark regions are characterized by a ferric absorption edge extending from approx. 400 to 750 nm, with bright regions having about twice the reflectivity at 750 nm as dark regions. Between 750 nm to beyond 2000 nm, bright and dark regions have nearly constant and slightly negative spectral slopes, respectively. Depending on location, bright regions have shallow reflectivity minima in the range 850-910 nm that are attributed to ferric oxides. Similarly, dark regions have shallow reflectivity minima near approx. 950 and 1700-2000 nm that are attributed to ferrous silicate minerals (pyroxene). Among terrestrial geologic materials, the best spectral analogues for Martian bright regions are certain palagonitic tephras from Mauna Kea Volcano (Hawaii). By definition, palagonite is a "yellow or orange isotropic mineraloid formed by hydration and devitrification of basaltic glass". The ferric pigment in palagonite is nanometer-sized ferric oxide particles (np-Ox) dispersed throughout the hydrated basaltic glass matrix. The hydration state of the np-Ox particles is not known, but the best Martian spectral analogues contain allophane-like materials and not crystalline phyllosilicates.

R V Morris↗
NASA NTRS2003

Thermal Emission Spectra of Altered Tephras and Constraints on the Composition of Martian Dust

We have begun to create a comprehensive set of thermal infrared (TIR, approx. 1650-200/cm, approx. 6-50 microns) spectra of palagonitic and hydrothermally altered soils that exhibit a range of mineralogical and chemical compositions for use in analyzing MGS TES data. Palagonite, a phyllosilicate-poor hydrolytically altered tephra, has been suggested as a possible component of the martian soil/dust based on visible and near infrared (VNIR) spectral similarities with martian dusty regions. The chemistry and crystallinity of altered tephras are highly variable depending on the parent material and local environmental conditions, and are important indicators of alteration processes.

Hamilton, Victoria E.↗
NASA NTRS2003

Palagonitic Mars from Rock Rinds to Dust: Evidence from Visible, Near-IR, and Thermal Emission Spectra of Poorly Crystalline Materials

Visible and near-IR (VNIR) spectral data for Martian bright regions are characterized by a general shape consisting of a ferric absorption edge extending from about 400 to 750 nm and relatively constant reflectivity extending from about 750 nm to beyond 2000 nm . Among terrestrial geologic materials, the best spectral analogues are certain palagonic tephras from Mauna Kea Volcano (Hawaii). By definition, palagonite is a yellow or orange isotropic mineraloid formed by hydration and devitrification of basaltic glass. The ferric pigment in palagonite is nanometer-sized ferric oxide particles (np-Ox) dispersed throughout the hydrated basaltic glass matrix. The hydration state of the np-Ox particles is not known, and the best Martian spectral analogues contain allophane-like materials and not crystalline phyllosilicates. We show here that laboratory VNIR and TES spectra of palagonitic alteration rinds developed on basaltic rocks are spectral endmembers that provide a consistent explanation for both VNIR and TES data of Martian dark regions.

Morris, R. V.↗
NASA NTRS2003

Hydrothermal Alteration on Basaltic Mauna Kea Volcano as a Template for Identification of Hydrothermal Alteration on Basaltic Mars

Certain samples of palagonitic tephra from Mauna Kea Volcano (Hawaii) are spectral analogues for bright martian surface materials at visible and near-IR wavelengths because both are characterized by a ferric absorption edge extending from about 400 to 750 nm and relatively constant reflectivity extending from about 750 nm to beyond 2000 nm. Palagonite is a yellow or orange isotropic mineraloid formed by hydration and devitrification of basaltic glass. For Mars-analogue palagonite, the pigment is nanometersized ferric oxide particles (np-Ox) dispersed throughout an allophane-like hydrated basaltic glass matrix. Crystalline phyllosilicates are not generally detected, and the hydration state of the is not known. The poorly crystalline nature of glass alteration products implies relatively low temperature formation pathways. We report here x-ray diffraction, major element, Mossbauer, and VNIR data for 9 basaltic tephras. Thermal emission spectra are reported in a separate abstract. Our multidisciplinary approach both tightly constrains mineralogical interpretations and maximizes overlap with datasets available for the martian surface available now and in the future.

Morris, R. V.↗