P21A-0209
Spectral Characterization of Mars Analogues From the Berlin Emissivity Database (BED)
Several well-recognized Martian soil analogues have been classified and studied in the past years. The JSC Mars-1, collected and distributed under control of the NASA Johnson Space Center, originates from Pu\'u Nene cinder cone in Hawaii, USA. It is a palagonitic tephra (glassy volcanic ash altered at low temperatures), whose spectral features resemble the bright regions on Mars. The Salten Skov, coming from a subsurface deposit in the Midjutland region of Denmark, is a Fe-oxide precipitate with a dark red color, composed mainly of goethite, hematite and maghemite, with mineralogical and magnetic close to those of the martian soil. Montmorillonite and palagonite are other natural materials commonly referred as Martian soil analogues. We present and discuss the emissivity spectra of these analogue minerals from the Berlin Emissivity Database spectral library. The Berlin Emissivity Database (BED) currently contains also emissivity spectra of plagioclase and potassium feldspars, low Ca and high Ca pyroxenes, olivine, elemental sulfur and a lunar highland soil sample measured in the wavelength range from 3 to 50 μm as a function of particle size. For each sample we measured the spectra of four particle size separates ranging from < 25 to 250 μm. The current main setup at the Planetary Emissivity Laboratory (PEL) at DLR consist of an emissivity device built at DLR coupled to a Fourier transform infrared spectrometer (Bruker VERTEX 80v) equipped with both a cooled MTC detector and a room temperature DTGS detector. All spectra were acquired with a spectral resolution of 4 cm- 1. The combination of detectors and spectrometer allows a unique wavelength coverage encompassing the whole thermal radiation range measured by spacecraft instruments. The emissivity device is currently purged with dry air, while the spectrometer is evacuated. In a future upgrade of the facility the emissivity device will be replaced by a planetary simulation chamber which can be evacuated and which allows to heat sample up to Mercury surface temperatures.
P21A-0210
Thermal Transformations of Lepidocrocite and Akaganeite to Hematite: Examination of Possible Precursors to Martian Crystalline Hematite
We examine the thermal transformations of lepidocrocite and akaganeite to hematite to determine if these minerals are viable precursors to Martian crystalline hematite. This is an extension of the work of Glotch et al. (2004) who demonstrated that precursor mineralogy and temperature of hematite formation have a strong influence on the infrared emissivity spectrum of coarsely crystalline hematite. Any indication that lepidocrocite or akaganeite were potential precursors to Martian crystalline hematite would yield information about the geochemical environment at Meridiani Planum at the time of their formation. In terrestrial settings, lepidocrocite is often thermodynamically unstable with respect to goethite and jarosite (if sulfate is present in the system). However, several factors can favor the formation of lepidocrocite. The presence of organics, a slow rate of Fe3+ hydrolysis, a low CO2 fugacity, or the presence of excess Fe2+ in solution all favor the precipitation of lepidocrocite rather than goethite. Precipitation of akaganeite, on the other hand, is favored in hydrothermal environments with a high Cl content and elevated temperatures near 60°C. The synthetic precursor minerals were heated in air to 150, 300, 500, and 700°C. The resulting products were imaged by transmission electron microscopy (TEM) and analyzed by X-ray diffraction, mid-IR emission spectroscopy, visible/near-IR reflectance spectroscopy, mid-IR attenuated total reflectance spectroscopy. Results of these analyses indicate that both lepidocrocite and akaganeite are unlikely to be precursors to Martian crystalline hematite. Laboratory studies suggest that a goethite to hematite pathway is the most likely scenario for the formation of Martian crystalline hematite.
P21A-0211
Reflectance microspectroscopy of natural rock samples in the visible and short-wave infrared
We have collected reflectance spectra of various rock samples in the 450-1650 nm wavelength range with a spatial resolution of 50 and 100 micrometers and we have compared three microscopic modalities, confocal, bright-field, and dark-field. High contrast spectra that are comparable to those obtained from macroscopic measurements have been obtained in dark field mode from rough, unprepared samples of jarosite, alunite, olivine, gibbsite, and other minerals and test targets. The scale of roughness of the samples is consistent with that obtained from a typical Mars rover rock abrasion tool. Spectral discrimination and spatial resolution are demonstrated at the sharp boundaries between two different minerals. The confocal and bright field modes are shown to suffer from previously known potential artifacts, but the usefulness of the confocal mode in establishing optimum focus automatically remains. These results support the conclusion that reflectance microspectroscopy in the visible to short-wave infrared can be a valuable tool for understanding mineral formation at the spatial scale of tens of micrometers and is suitable for unsupervised operation on the Martian surface.
P21A-0212
Linear deconvolution of ATR-IR spectra of mineral mixtures for planetary surface studies
Attenuated total reflectance (ATR) is an infrared spectroscopic method useful for compositional analysis of powdered samples. ATR-IR is frequently used for chemical phase ID, but is seldom used in geological studies. Because it is effective with small grain sizes, ATR-IR could be a powerful tool for in situ mineral identification on future planetary lander missions, especially for the analysis of fine-grained regoliths, atmospheric dust, and outcrop grindings. Here we test the ability of the ATR-IR technique to quantitatively determine the modal mineralogy of powdered mineral mixtures. Mixtures were prepared from four mineral endmembers - olivine (Fo90), plagioclase (An60), calcite and gypsum - in known volumetric proportions and in a variety of grain sizes. ATR spectra of mineral mixtures and endmembers were collected in the range 400-4000 cm-1. Spectra of mixtures were modeled using the deconvolution method of Rogers et al. (2006), modified so that a measured grain-size distribution (GSD) could be included as a weighted factor in the fit. The signal-to-noise ratio increased for each mineral with decreasing grain size. This is expected because finer grain sizes have a better contact with the ATR crystal. For mixtures of a single grain size, the deconvolution-modeled proportions generally matched actual proportions within 10-20%. Occasionally, the deconvolution model produced poor matches to actual mineralogy and observed spectral shape. To assess the effect of clinging fines, fine-grained (<10 μm) calcite and gypsum were added in increments from 0 to 30% to a mixture of coarsely particulate (74- 147 μm) olivine and plagioclase. The fine-grained components of these mixtures were strongly overrepresented in the model - possibly the result of non-ideal mixing and surface area dominating over volume in linear spectral addition. Increasing the weight of the GSD in the deconvolution model mitigated the overestimation of fines, but increased the RMS error of the spectral fit. Given the present results, we conclude that deconvolution of ATR-IR spectra can quantitatively predict the mineralogy of fine-grained mixtures, but for mixed grain-size samples, it may be necessary to grind the mixture to a uniform particle size.
P21A-0213
Laboratory Thermal Infrared and Visible to Near-Infrared Spectral Analysis of Chert
Though basaltic materials dominate the composition of the Martian surface, a material with a relatively high silica component in an area of Eos Chasma was reported by [1] from thermal infrared (TIR) data. The spectrum of the silica phase resembles quartz or chert, but with the existing information it is difficult to tell which phase best fits the observations. Though quartz, chert, and amorphous silica are chemically identical (SiO2), their physical differences (e.g., microstructures) result in different TIR spectral characteristics. Previous studies have analyzed a limited number of chert samples using emission infrared spectroscopy [2] and transmission infrared spectroscopy [3]. We continue these preliminary studies with an investigation aiming to more completely understand and document the variation in spectral character of cherts. This knowledge may help to identify the silica phase in Eos Chasma and any future discoveries. Our study includes a more extensive sampling of geologic chert in hand sample (>15 samples) with various sources, methods of formation, surface textures, and crystallinities. We analyzed their visible to near-infrared (VNIR) reflectance spectra, as well as spectral features in TIR emission spectra. We measured multiple locations on each sample to determine spectral homogeneity across the sample and between various orientations. Where possible, natural, cut, and recently fractured surfaces were measured. We compared the collected TIR spectra for similarities and differences in shape and spectral contrast within each sample and between samples that may relate to variations in the samples' structure (e.g. crystallinity, and surface texture). VNIR measurements show features indicative of non-silica phases and water that may be present in the cherts. [1] Hamilton, V.E. (2005) Eos Trans. AGU, Fall Meeting Suppl., Abstract P24A-08. [2] Michalski, J.R. (2005) PhD Diss., ASU, Tempe. [3] Long, D. G. et al. (2001) Canadian Archaeological Assoc., 33rd Meeting.
P21A-0214
Experimental Constraints on Trace Element Behavior in Martian Evaporite Minerals
The Mars Exploration Rovers, Spirit and Opportunity, have detected a distinctive suite of evaporite minerals at the Martian surface precipitated from fluids derived from basaltic weathering under low pH conditions. Orbital spectroscopic methods have confirmed global distributions of these materials. The formation and stability of these mineral assemblages have been well modeled at Meridiani Planum for major element chemistry. However, in addition to providing major element chemistry of Martian surface materials, the APXS (Alpha-Proton X-Ray Spectrometer) instruments onboard the Mars Exploration Rovers have returned a selection of trace element abundances in soils and rocks including Ni, Zn, and Cr. These measurements have shown considerable trace element abundance variability that is not well-understood. Accordingly, it is of some interest to constrain the trace element partitioning behavior for the distinctive evaporite minerals that likely exist at Meridiani Planum, including gypsum, Mg- and Fe-sulfates. Determining trace element partitioning during the formation of these materials is difficult through experimental means due to various kinetic effects and complicating factors. Also, analysis of trace element abundances in the final precipitated mineral can be further complicated by the presence of ubiquitous fluid inclusions. Here we describe an experimental approach and preliminary results of trace element incorporation into gypsum (CaSO4\dot2H2O) – which precipitates early in an evolving evaporation system and for which the precipitation process is well-understood. We record the behavior of Ni, Zn and Cr individually during the carefully controlled precipitation of gypsum at constant pH and temperature (25°C). Future experiments will examine the behavior of these elements for increasingly more complex evaporite formation systems more fully analogous to Meridiani Planum mineralogy.
P21A-0215
Experimental Constraints on Trace Element Mobility in Martian Basalt
It is widely believed that aqueous alteration on Mars has been strongly influenced by low pH conditions. Experimental work has shown that these low pH environments result in the mobility of elements, such as Fe (III) and Al, that are relatively insoluble under most near surface conditions on Earth. Although these studies have increased our understanding of major element behavior, little is known about the mobility of trace elements under Martian conditions. The Mars Exploration Rovers have provided and continue to provide analyses of Ni, Zn, and Cr at both the Spirit and Opportunity landing sites. In-situ rock and soil analyses show that these trace elements are highly variable, which generates many questions about the processes that control their distribution. Among the issues that need to be considered are the roles of meteoritic contributions, aqueous alteration, residual enrichments, evaporative concentrations, and so forth. A central question to addressing these issues is the nature of the mobility of Ni, Zn, and Cr during aqueous alteration under Martian conditions. Accordingly, we have begun a series of batch aqueous alteration experiments on synthesized Martian basalt in an attempt to better understand the mobility of Ni, Zn, and Cr on the Martian surface. Basalt analog compositions are the same as those used in previous studies from our lab and are based on average S- and Cl-free Pathfinder soil, with Ni, Zn, and Cr added in the form of oxides. Mixtures of sulfuric and hydrochloric acids, with varying concentrations (ranging from 1M H2SO4/0.25M HCl to 100 μM H2SO4/25 μM HCl and a S:Cl mole ratio of 4, comparable to typical soils), are added to synthesized basalt in order to achieve a water-to-rock ratio of 10. Fluid-rock mixtures are allowed to react in Teflon beakers at 25 ° C for a period of 14 days, during which time small amounts of fluid are extracted and analyzed for major and trace elements to constrain the nature of alteration mechanisms. At the end of the experiments, residual material is fully characterized for mineralogy, chemistry, and texture and final fluids are evaporated and evaporite minerals similarly characterized. In this poster, we will fully describe our experimental approaches and present initial results.
P21A-0216
Recent Results from the Mars Exploration Rover Rock Abrasion Tool
The Rock Abrasion Tool (RAT) serves as the sample preparation device on the Mars Exploration Rovers (MER) science payload. The RAT grinds a circular area 45 millimeter in diameter and to a depth of 0-15 mm into Martian rock. This is intended to remove the altered outer layers of rock as well as overlying surface fines in preparation for imaging and spectral observations. In addition to acting as a facilitator for other instruments, RAT telemetry acquired during grinding may be used to assess the physical properties of the rocks that it grinds. The most direct rock measurement extractable from the RAT grinding process is the energy expended per unit of rock volume removed. This has been termed the RAT Specific Grind Energy (SGE) and in terms of rock bulk physical properties, correlates roughly with unconfined compressive strength. Recent results from the Mars Exploration Rovers will be presented as will comparisons between Earth rocks and Martian rocks in terms of their SGEs and other physical properties. Although SGE is an uncommon metric for rock physical properties, the SGE calculated from the RAT engineering data, and linked with data from other instruments in the payload, represent the most comprehensive database yet created of the physical properties of Martian rocks. RAT SGE continues to be helpful in understanding the geologic history of Mars and will be of great value in instrument design for future Mars missions.
P21A-0217
Hydrated Iron Sulfate Minerals by FT-IR, ESEM and XRD: Effects of Hydration, Metal Ions, and Oxidative State
Data from the Mars Exploration Rovers (MER) and orbital remote sensing have determined that iron-bearing sulfates and iron-sulfates account for much of the mineralogical variation on Martian chemical sediments. We have begun a comprehensive study to evaluate a suite of hydrated iron sulfate minerals at different levels of oxidation or mineral phases using micro-FT-IR, ESEM and XRD. Selected minerals include jarosite, copiapite, coquimbite, halotrichite, kornelite, melanterite, rhomboclase, roemerite, rozenite, and szomolnokite. The structure and wavelength of the water bands are controlled by the immediate proximity of the water molecules to the Fe3+ and Fe2+ cores. Iron and aluminum change the fundamental vibration amplitudes and shift the energy requirement for a specific bond vibration. The original mineral spectral signature can be present even after oxidative products form on the iron sulfate surfaces and basic spectral lines can be analyzed. When mineral samples were sectioned and analysis performed on the interior mineral surfaces, the spectra showed the predominant spectral lines under both conditions with most variations occurring in peak definition. ESEM-EDAX and XRD analysis confirmed the presence of oxidative products on the mineral surfaces even when the mineral samples were stored in anoxic conditions (under mineral oil) and refrigerated in airtight containers after sampling. Spectral variability between 30 micron spots within 200x200 micron areas showed minimal compositional / spectral variability. The micro-spectroscopic approach permits the study of complex iron sulfate mineral structures (e.g. evaporite sequences, crystal formations) to determine the hydration, metal ion, and oxidative state in terrestrial analog systems and on future Mars missions, without destruction of the sample.
P21A-0218
Evaluating laboratory and satellite data of small terrestrial impact and volcanic craters as Mars analogs
This research is designed to explore formational and subsequent erosional processes for small terrestrial craters using spaceborne, airborne, and field-based data combined with later laboratory spectral analyses. Quantifying and differentiating formation and erosional processes for these different crater types have implications for climate history and the surface evolution of Mars. We focused our studies on El Elegante maar crater in the Pinacate Volcanic Field (PVF) of north-central Mexico and Meteor Crater, an impact crater in central Arizona, due to their similarity in size, morphology, age, and weathering history. Topographic mapping and detailed surface classifications were conducted at each crater using differential GPS, topographic laser profiles, and a Forward Looking Infrared (FLIR) camera along half-kilometer radial transects (from crater rims into near field ejecta). Samples of surficial fines and small blocks were collected for laboratory-based thermal infrared (TIR) spectral analyses and comparison to remote sensing image data. The minor vegetation component present at each field site was quantified and used for later removal of its spectral component in the image data. The terrestrial instruments selected for their spectral range, resolution, and similarities to current Mars datasets were: 1) IKONOS, 2) Hyperion, 3) Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), and 4) Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). The different composition of the pre-formation host rocks (i.e., basalt at El Elegante and sandstone/limestone at Meteor Crater) provides an opportunity to investigate the effects of composition and sediment mixing. The TIR emission spectra collected at the University of Pittsburgh were used as an accuracy assessment for the surface compositional maps of both craters using techniques such as linear deconvolution, image classification, and spectral matching. Such detailed mapping was found to be essential for understanding of the effects of sediment transport and weathering in small crater environments. The laboratory generated hyperspectral data were required for accurate end-member selection to properly utilize the techniques employed for compositional map generation. Both the composition and ejecta size/distribution were found to influence sediment transport at each crater. Factors such as these are important for insight into the evolution and modification of the Martian surface, but may not be available without field-based (i.e., rover) data. This work has direct implications for determining the presence and role of volatiles in Martian cratering processes with the development of techniques for distinguishing maar-like volcanoes formed by the interaction of lava with water/ice from small impact craters.
P21A-0219
Detecting Water/Ice in Simulated Martian Regoliths using Impedance Spectroscopy
The overall goal of this project is to design a simple (low power and mass), in-situ instrument to detect the presence, abundance and state (liquid, solid, bound in minerals, and location) of water in soils. Understanding the state, distribution and cycling of water is central to answering several science and engineering questions such as the role of water in (1) the evolution of a planetary surface, (2) the mechanics of chemical weathering and erosion, (3) the potential of the habitat to harbor life and (4) the availability of sufficient extractable water resources on a planetary surface for in-situ development of propellant, life support systems and for habitat creation. We will describe the operating principles of the instrument and sensitivity limits obtained from laboratory tests on a variety of soil/water mixtures with varying water content, ionic concentration, soil type and temperatures (+25C to -65C).
P21A-0220
Laboratory Measurements of Oxygen Gas Release from Basaltic Minerals Exposed to UV- Radiation: Implications for the Viking Gas Exchange Experiments
The biology experiments onboard the Viking Landers determined that the Martian soils at Chryse and Utopia Planitia contain an unknown chemical compound of a highly oxidizing nature. The Gas Exchange Experiments (GEx) demonstrated that the humidification of a 1-cc Martian soil sample resulted in the production of as much as 790 nanomoles of oxygen gas. Yen et al. (2000) have provided experimental evidence that superoxide radicals can be generated on plagioclase feldspar (labradorite) grain surfaces by exposure to ultraviolet (UV) light in the presence of oxygen gas. Adsorbed superoxide radicals are thought to react readily with water vapor, and produce oxygen gas in quantities sufficient to explain the Viking GEx results. Direct evidence for the formation of oxygen gas, however, was not provided in the experiments of Yen et al (2000). Accordingly, the motivation of this study is to determine whether superoxide radicals adsorbed on labradorite surfaces are capable of producing oxygen gas upon exposure to water vapor. We have constructed an experimental apparatus that is capable of monitoring oxygen gas release from basaltic mineral powders that have been exposed to UV-radiation under Martian atmospheric pressure conditions. The apparatus consists of a stainless-steel vacuum chamber with a UV- transparent window where sample radiation exposures are performed. The vacuum chamber has multiple valved ports for injection of gases and water vapor. The vacuum chamber is connected via a precision leak valve to a quadrupole mass spectrometer, which measures changes in the composition of the headspace gases over our mineral samples. We will report on the results of our experiments, which are aimed at detecting and quantifying oxygen gas release from UV-exposed basaltic mineral samples using this new experimental facility. These results will further constrain whether superoxide ions adsorbed on mineral surfaces provide a viable explanation for the Viking GEx results, which have been of considerable controversy in the roughly three decades since the measurements were first made.
P21A-0221
A Thermal Infrared Emission Spectra Library for Unpowdered Meteorites
Mid-infrared thermal emission spectra have been obtained for whole-rock (unpowdered) samples of the following 25 meteorites: Abee, Admire, Allende, Bondoc, Brahin, Bruderheim, Canyon Diablo, Carichic, Clover Springs, Dhofar 007, Estherville, Holbrook, Juancheng, Kapoeta, Long Island, Marion, Modoc, ALH77225, ALH77233, ALH84082, LEW85322, ALH85025, ALH79029, ALH77004, and LEW86015. Meteorites were provided through the Center for Meteorite Studies at ASU, Johnson Space Center and the NASA Antarctic Meteorite Working Group, and from private collections. The database was prepared to aid in the on-going detection and interpretation of meteorites on Mars using the Miniature Thermal Emission Spectrometer (Mini-TES) instruments on both Mars Exploration Rovers. It therefore includes several specimens of low, moderate, and high weathering intensities, reflecting different levels of water exposure in desert and non-desert environments. Unweathered falls are also considered. Samples represent all three chondrite classes, stony irons (mesosiderites and pallasites), and select achondrites. Special consideration is given to dust-covered iron-nickel meteorites as part of a separate study designed to evaluate the Mini-TES spectra of iron-nickel meteorites on Mars. All samples were analyzed at or near a temperature of 80° C using a modified Nicolet Nexus 670 FT-IR spectrometer at the Mars Space Flight Facility at Arizona State University. Data were collected within the 2000 to 200 wavenumber (5 to 50 microns) mid-infrared range. The results show that many meteorite types display moderate to wide variability in the depth and position of prominent absorption features, making them easily distinguishable from each other. Most previous meteorite spectroscopy studies have either focused on near-infrared reflectance spectra [e.g. 1], and/or involved powdered samples to represent asteroid regoliths in the mid-infrared [e.g. 2 & 3]. Particle size- related issues are often at the heart of interpretation of asteroid spectroscopic studies in the mid-infrared [4]. However, the high-resolution Itokawa imaging results of the Hayabusa mission have shown that not all asteroid surfaces are dominated by powdered materials [e.g. 5]. It is therefore anticipated that whole-rock, mid-infrared emission spectra may serve a further purpose in studies conducted with Spitzer Space Telescope and other space-born observatories equipped with mid-infrared detectors. The library will therefore continue to be augmented with additional spectra, to include unweathered carbonaceous chondrites and achondrites at a minimum. All spectra are available through the Arizona State University Thermal Emission Spectral Library. References: [1] Sato K. and Miyamoto M. (1998) Antarctic Meteorite Research 11, 155-162. [2] Salisbury J.W. et al. (1991) NASA Technical Memorandum #4300, 262-204. [3] Dameron S.N. and Burbine T.H. (2006) LPSC XXXVII, abstract #1828. [4] Emery J.P. et al. (2006) Icarus 182, 496-512. [5] Miyamoto et al. (2007) Science 316, 1011- 1014. http://speclib.asu.edu
P21A-0222
Comparisons of Thermal Emission Spectroscopy and Laser-Ablation Inductively Coupled Plasma Mass Spectrometry Derived Bulk Chemistries for Natural Surfaces of Volcanic Rocks
The GRS and TES datasets provide unique and complementary insights into the bulk compositions of martian surface materials. GRS measures the composition of the upper few tens of centimeters of the surface while TES measures the composition of the upper hundred microns. Recent GRS studies have reported global distributions of bulk chemical abundances for Si, K, Fe, Th, and K/Th (Karunatillake et al., 2007; Taylor et al., 2007). A major result from these studies is the near uniform distribution of relative Si concentrations across martian low-albedo regions. This is significant because a primary difference between the TES Surface Type 1 and Surface Type 2 global spectral end-members is the modeled abundance of high-silica mineral-phases (e.g. Bandfield et al., 2000; Wyatt et al., 2002; McSween et al., 2003). A way of reconciling this apparent discrepancy between the two datasets is to account for the different penetration depths of the two techniques and attribute compositional variations to near-surface coatings of high-silica phases. This, however, leads to another question involving the accuracy of linear deconvolution results for materials with surface coatings. Laboratory studies by Rampe et al. (2007) reveal that secondary alteration products on a surface can cause non- linear mixing between spectral end-members and thus affect the modeled abundances of primary minerals in a mixture. This is significant because small amounts of weathering products on the martian surface may thus result in modeled primary mineral abundances that differ from the actual composition, resulting in a possible misclassification of volcanic compositions. In this study, we further the work by Rampe et al. (2007) and examine the accuracy of bulk chemical oxide abundances derived from thermal infrared laboratory measurements of chemically weathered natural surfaces and fresh cut surfaces of basalt. TES has mainly been utilized as a mineralogical tool, but thermal emission spectroscopy also provides a means for deriving chemical oxide abundances. Chemical compositions can be calculated from deconvolved modal mineralogies (vol. %) by combining the compositions of the spectral endmembers (wt. % oxides) in proportion to their relative modeled abundances. Wyatt et al. (2001) quantified the uncertainties in derived chemical compositions for fresh cut surfaces of volcanic rocks and demonstrated their use in correctly classifying compositions based on total silica contents. This study will specifically examine natural surfaces of volcanic rocks and whether non-linear mixing of mineral-phase spectral endmembers, which can adversely affect modeled mineral abundances, also affects derived chemical oxide abundances or if substitution of chemically similar phases results in consistent values. We analyze the bulk chemistries of basaltic natural surfaces using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and electro microprobe (EMP) and compare bulk chemistries to values derived from thermal emission data.
P21A-0223
Br/Cl Partitioning in Halite and Hydrohalite on Mars
Within Meridiani Planum outcrops, Br may be present in the hundreds of ppm range. Relative to Cl, this suggests that Br is probably 1-10% of Cl; relative to Earth seawater (Br = 0.35% of Cl), these are "high" Br concentrations. Because of low Br concentrations on Earth, Br largely precipitates as a minor constituent in halite(NaCl) crystals rather than as a separate phase. This is also likely to be the case for Mars. However, on Mars much higher ratios of Br/Cl are expected in solid solutions of chloride minerals, and there may exist a greater number of accessory bromide minerals (which are exceedingly rare on Earth) in late-stage crystallization products of brines undergoing extreme drying or freezing. Bromide chemistries were incorporated into the FREZCHEM model that has been frequently used for simulating Martian environments. The Siemann-Schramm model was used to partition Br into halite (or hydrohalite) crystals. We examined evaporation and freezing as the dominant mechanisms for Br incorporation into halite(or hydrohalite). For example, a saturated halite solution with 1% Br(mole basis) begins precipitating a solid solution of 0.046% NaBr in the halite crystal, which increases to 6.1% by the time that the water phase has evaporated to 1% of the initial solution. The evaporation process preferentially increases the solution phase Br concentration relative to Cl, which leads to the increasing Br% incorporation into halite. In addition we also examined the consequences of alternating wetting/drying and thawing/freezing cycles on Br/Cl migration and subsequent reprecipitation and fractionation in Martian environments. Partial dissolution of halite will preferentially remove high Br from upper sediment layers that will lead to reduction in upper sediment halite-Br and a subsequent increase in halite-Br in lower sediments, in agreement with Mars Rover findings. Bromide- rich tracer horizons may be indicative of major transitions in climate (drying or freezing episodes) or late stages of freezing or drying of flood deposits.
P21A-0224
Mineral Precipitation in Porous Media: Laboratory Diffusion Experiments as Analogues for Concretion Formation in Utah and on Mars
We present results of laboratory gel diffusion experiments designed to simulate the precipitation of iron minerals in natural systems. Liesegang bands and crystals of various iron minerals were formed in aqueous gels, "mini- concretions" of mineral precipitate were formed in both sand and a sand/agarose mixture, and the formation of hollow mineral spheres was observed in gel precipitation experiments where organics were introduced. These mineral structures are analogous to concretion forms observed in the Navajo Sandstone region of Utah, which have been suggested as terrestrial analogs for the "blueberry" hematite concretions on Mars. Iron mineral precipitates (perhaps with a gel precursor) occur in many forms in the Navajo Sandstone, including "mini- concretions" (solid concretions 1-2 mm in diameter), "rind-like" concretions (hollow spheres of hematite several cm in diameter, surrounding a region of sandstone), and Liesegang banding (banded patterns that form at reaction fronts through diffusion of ions from one reservoir to another). On Mars only small (4-5mm) and mini-concretions (~ 1mm) have been observed; Liesegang bands or large rind-like concretions have not yet been discovered. The varying conditions that give rise to each of these mineral structures in the laboratory indicate that the small, spheroidal types of iron precipitates found in the Utah and Martian environments may be diagnostic of the diffusion medium, presence of organics, and characteristics of fluid in that region.
P21A-0225
Development of a Hollow-Fiber Gas Correlation Radiometer for Column Measurements of Formaldehyde, Methane, and Water Vapor on Mars
Development of a passive hollow-core fiber gas correlation radiometer instrument is presented for column absorption measurements of methane, formaldehyde and water vapor in the Martian atmosphere. This nadir viewing instrument consists of three sub-instruments for detecting CH4, H2CO, and H2O at 3.44 microns, 3.63 microns, and 3.12 microns respectively. At the core of each sub-instrument is a hollow-core optical fiber filled with a sample of the gas of interest which acts as a spectral filter. Gas correlation radiometers are a robust, reliable, highly developed technology. Adapting the newly available hollow-core optical fibers into this technology offers a substantial reduction in instrument mass and volume. This lightweight and compact instrument is highly suitable for deployment on a Mars orbiting mission. Performance of a Mars orbiting version of the hollow-core fiber instrument has been simulated assuming a 2 meter long, 500 micron inner diameter hollow-core fiber gas correlation cell, a 92.8 degree sun-synchronous orbit from 400 km with a horizontal sampling scale of 10 x 10 km2. Initial results indicate that for one second of averaging, a detection limit of 1 ppbv is possible for formaldehyde, with slightly better than 1 ppbv for methane. Because of its comprehensive measurement of both methane, formaldehyde, and water vapor at relevant detection limits and spatial scales, this instrument has the potential for localizing sources of these disequilibrium species on the Martian surface to aid in determining whether their origin is biogenic or geologic.
P21A-0226
Sulphur Dioxide: High Resolution Ultra-Violet Photoabsorption Cross Section Measurements at 200K.
Sulphur Dioxide plays an important role not only within the Earth's atmosphere but also within the complex chemistry of both the upper atmosphere of Venus and the volcanically active Jovian moon Io. The lack of high resolution laboratory studies has prevented the full, accurate determination of absorption cross sections which are the basis for reliable photochemical models. High resolution laboratory measurements of SO2 are essential to resolve the complex SO2 spectrum and yield accurate photoabsorption cross sections. Using the Imperial College UV Fourier Transform Spectrometer new high resolution (λ/δλ ~ 450,000) measurements have been recorded over a range of temperatures and pressures. As part of an on-going series of measurements, current laboratory work focused on photoabsorption cross sections of SO2 at 200K across the wavelength range 220 → 325 nm. These measurements not only compliment previous room temperature measurements obtained at Imperial College in the 190 → 220 nm and 220 → 328 nm ranges (Stark et al., JGR Planets 104, 16, 585 (1999) and Rufus et al.,( JGR Planets 108, 2, 5 (2003)), but also coincide with the wavelength regions being recorded by the Venus Express mission through the UV-IR spectrometer SPICAV (ESA-SCI(2001)6). Our new measurements will allow accurate analysis of the chemical processes in the upper atmosphere of Venus. These absorption cross section measurements are the first to be acquired at this resolution, temperature and pressure. Results will be presented. This work was supported in part by NASA Grant NNG05GA03G, PPARC (UK), and the Leverhulme Trust.
P21A-0227
Micro-Scanning Electron Microscope and X-ray Spectrometer for Planetary Exploration
Scanning Electron Microscopy combined with electron-induced X-ray Fluorescence Spectroscopy (SEM-EDX) is one of the most powerful techniques for characterizing surface morphology and composition with spatial resolution of a micrometer or better. SEM-EDX can elucidate natural processes such as low-temperature diagenesis, thermal or pressure induced metamorphism, volcanism/magmatism, atmosphere/crust interaction and the like. This information is useful for the investigation of the natural history of solar system objects. We are developing a prototype micromachined scanning electron microscope with X-ray spectrometer (MSEMS) for solar system exploration. The MSEMS is comprised of a carbon nanotube field emission (CNTFE) electron source integrated with a micro-electro-mechanical-system (MEMS) based electron gun and electron optics structure. The MSEMS system will utilize a piezoelectric sample stage, having scan ranges from a few angstroms to several hundreds of microns. Compared with conventional electron sources, the CNTFE source offers advantages of low power usage, ultra-small source size and simplicity of electrostatic focusing. The MSEMS instrument, including CNTFE source, MEMS electron optic column and piezoelectric sample stage, is envisioned to be 1-2 cm in height and will operate in the range of 500 eV to 15 KeV. The imaging resolution of MEMS is predicted to be ~10 nm at 5 KeV and the spatial resolution of the X-ray spectrometer will be ~1 μm at 15 KeV. We will present field emission data from our CNTFE source as well as the MEMS electron gun and piezostage designs.
P21A-0228
Effects of Chemical Weathering on TIR-Derived Bulk Compositions From Deconvolution Models of Mineral Mixtures
The Martian surface may be chemically altered on regional scales. Thermal infrared (TIR) spectroscopy and spectral deconvolution are commonly used to determine mineral abundances of the surface. Chemically weathered surfaces tend to be intimate mixtures of igneous minerals and fine-grained alteration products. To understand how alteration products affect deconvolution models of TIR spectra and model-derived bulk compositions, we measured TIR spectra of physical mineral mixtures, composed of an igneous component (augite, andesine, or 50-50 weight percent augite-andesine) and an alteration phase (montmorillonite clay or synthetic amorphous silica). Weathering products can cause significant differences between the actual and the modeled primary igneous mineral abundances and cause the false identification of significant amounts of volcanic glass in deconvolution models (Rampe et al., 2007). We calculated the bulk oxide compositions (Hamilton et al., 2000) from spectral model results of our physical mixtures and compared them to the actual bulk compositions of the mixtures. Previous studies have shown that bulk chemical compositions can be derived from TIR spectral model results (Hamilton et al., 2001; Wyatt et al., 2001), and bulk oxide data of the Martian surface are commonly derived from spectral models of data from the Thermal Emission Spectrometer (TES) (Hamilton et al., 2001; Hurowitz et al., 2007). In alkali-vs.-SiO2 plots, model-derived compositions for clay- bearing mixtures were similar to the actual compositions of the mixtures; however, model-derived compositions for silica-bearing mixtures varied significantly from the actual values of the mixtures. In Al2O3-vs.- (CaO+Na2O+K2O)-vs.-(FeO+MgO) ternary plots, the model-derived compositions of clay-bearing mixtures followed trends typical of terrestrial basalt weathering, whereas the model-derived compositions for silica-bearing mixtures followed trends seen in compositional data derived from TES spectra from Mars (Hurowitz et al., 2007). Our data show that chemical weathering and precipitation of amorphous silica may account for some of the chemical variations of rocks on Mars as derived from TES spectral data.