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NASA NTRS1981

Histidyl-histidine catalysis of glycine condensation in fluctuating clay environments

Histidyl-histidine is a remarkably effective catalyst of peptide bond formation in the reaction of glycine in a fluctuating (hot-dry, cold-wet) clay environment. It has shown turnover numbers (molecules of glycine incorporated in oligoglycines per molecule of catalyst) as high as 18 in a single cycle and as high as 52 overall. A number of other dipeptides were tested, as well as monomeric histidine, N-acetyl histidine, and imidazole, none of which showed turnover numbers greater than one. Histidyl-histidine is a model for a prebiotic protoenzyme, and implications for the development of a simple translation mechanism are discussed.

White, D. H.↗
NASA NTRS2013

Terrestrial Analogs for Clay Minerals at Yellowknife Bay, Gale Crater, Mars

Sediments of the Sheepbed unit, Gale Crater, were analyzed by the CheMin X-ray diffraction instrument on the Curiosity Rover. The sediments consist of typical basalt minerals (Fe-forsterite, augite, pigeonite, plagioclase), as well as Fe oxide/hydroxides, Fesulfides, amorphous material, and a phyllosilicate. The phyllosilicate has a broad 001 peak at approx 1.0 nm, consistent with a poorly ordered smectite. However, in the absence of diagnostic tests possible on Earth, its identity is not clear. The position of the 06L diffraction band is generally used to distinguish dioctahedral from trioctahedral smectite, but it is beyond CheMin's range of 2 Theta. The measured position of the 02L diffraction band (approx 22.5deg 2 Theta by CheMin), implies that the smectite is trioctahedral. The exact position and shape of the 02L band is determined by the cations in the 'M' sites of the smectite; to constrain those cations, we sought analogs among terrestrial smectites, emphasizing those developed from basaltic precursors. A potential analog for the Sheepbed smectite is 'griffithite,' a variety of trioctahedral smectite in altered basalt of the Topanga formation, Griffith Park, Los Angeles. 'Griffithite' has an 02L diffraction band that is close in position and shape to that of the Sheepbed smectite, although 'griffithite' has a very sharp 001 peak, indicating a high degree of layer ordering not seen in the Sheepbed smectite. A typical chemical formula for 'griffithite,' determined by electron microprobe, is (Ca0.59 Na0.03) (Mg4.28 Fe1.83) (Si6.64 Al1.36) O20 (OH)4, normalized to Si+Al=8. This formula is consistent with a fully trioctahedral Fe-Mg smectite with Ca and Na as interlayer cations. In the Topanga basalt, four types of 'griffithite' are present: fine-grained, filling cracks and vesicles; coarse-grained, filling vesicles; coarse-grained, replacing olivine phenocrysts; and coarse-grained, replacing glassy mesostasis. The fine-grained 'griffithite' formed first, and the last three varieties may be contemporaneous. One sample shows agate (alpha- quartz) that was precipitated between the episodes of deposition of the fine-grained and coarse-grained 'griffithite.' 'Griffithite' is not unique as a possible terrestrial analog - some clay minerals from the Doushantou formation, China, have similar 02L diffraction bands, and many basalts contain smectites in vesicles and as replacements after olivine. Similar trioctahedral smectites occur also in the nakhlite martian meteorites - as veinlets and replacements of olivine. By understanding the formation of these terrestrial clays, we hope to constrain the nature and mechanism of formation of the Sheepbed clay mineral.

Treiman, Allan H↗
NASA NTRS1984

The colloidal chemistry of ceramic clays

The colloidal chemistry and mineralogy of two argil minerals were studied. Deposits of kaolin and of ceramic clays in the United States and England are discussed for the probable mechanism of formation. The structural modifications of the bed, original material associated with the clays and the proper use of flocculants are discussed.

Phelps, G. W.↗
NASA NTRS1986

Properties of filamentary sublimation residues from dispersions of clay in ice

Results are reported from experimental studies of the formation of ice mixed with mineral particles in an effort to simulate similar processes on natural surfaces such as at the Martian poles, on comet nuclei and on icy satellites. The study consisted of low-pressure, low-temperature sublimations of water ice from dilutions of water-clay (montmorillonite and Cabosil) dispersions of various component ratios. Liquid dispersions were sprayed into liquid nitrogen to form droplets at about -50 C. Both clay-water dispersions left a filamentary residue on the bottom of the Dewar after the water ice had sublimated off. The residue was studied with optical and SEM microscopy, the latter method revealing a high electrical conductivity in the residue. The results suggest that the sublimation of the water ice can leave a surface crust, which may be analogous to processes at the Martian poles and on comet nuclei. The process could proceed by the attachment of water molecules to salt crystals during the hottest part of the Martian year. The residue remaining was found to remain stable up to 370 C, be porous, and remain resilient, which could allow it to insulate ice bodies such as comets in space.

Saunders, R. S.↗
NASA NTRS1983

Fungi and bacteria involved in desert varnish formation

Desert varnish is a coating of ferromanganese oxides and clays that develops on rock surfaces in arid to semi-arid regions. Active respiration but not photosynthesis was detected on varnished rock surfaces from the Sonoran Desert. Light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations, and cultivation experiments indicate that both fungi, primarily dematiaceous hyphomycetes, and bacteria are found on and within desert varnish coatings from the arid regions studied. Some fungi grow as microcolonial fungi (MCF) on rocks, and microscopic observations suggest MCF become incorporated in the varnish coating. SEM-EDAX (energy dispersive X-ray systems) analyses indicate the MCF contain 3 of the characteristic elements of varnish: iron, aluminum, and silicon. In some locations, MCF are also enriched in manganese relative to the rock substratum. Furthermore, some of the dematiaceous hyphomycetes that have been cultivated are able to oxidize manganese under laboratory conditions. It is possible that manganese-oxidizing bacteria, which are found in varnish, also play an important role in varnish formation.

Taylor-George, S.↗
NASA NTRS2013

The Multi-Stage History of Mt. Sharp

The Curiosity rover is exploring Gale crater and Mt. Sharp, Gale's 5‐km high central mound. We are investigating the history of alteration and erosion of Mt. Sharp using orbital imagery, spectroscopy and rover observations. Our results suggest a significant time gap between emplacement of the upper and lower sections of the mound. Crater counts show that the lower mound was formed soon after Gale itself, and that it contains distinct units ranging in altitude from approximately ‐4,500 to ‐1,800 m. Spectral data suggest that many units contain phyllosilicates. We found that these clay‐bearing rocks occur in distinct layers concentrated below ‐2,900 m. Parts of the lower mound exhibit a transition from clays to sulfates with increasing altitude. The lower mound shows evidence of flowing water, including canyons and inverted channels. Wind erosion produced km‐scale yardangs and scalloped cliffs. Our mapping shows that many yardangs in the lower mound are clay‐bearing, with a predominant orientation of around N‐S. Curiosity's ground‐level images show myriad fine‐scale, mainly horizontal layers in the lower mound. The rover has found stream beds and conglomerates, indicating that water once flowed on the crater floor. Drilling near the deepest point in Gale produced abundant clay, providing additional evidence of aqueous alteration. Upper mound units range in altitude from ‐2,100 m to +500 m, and mantle the lower mound above an angular unconformity. Most upper mound units are composed of layers. The formation age of the upper mound is unknown, since few craters are preserved. Clay‐bearing layers are detectable in several locations, mainly at altitudes near ‐2,000 m. There is no evidence of water flow, but wind erosion has scalloped the surfaces and edges of layers, and fine‐scale yardangs are common. Correlations between yardangs and clay spectra are apparent only in the lowermost units of the upper mound. Yardang orientations vary, and include N‐S, NW‐SE, and NE‐SW. Upper mound units resemble the planet‐wide Medusae Fossae formation, dated as Hesperian and argued to be composed of ignimbrites. Medusae Fossae layers are easily eroded by wind, and our mapping demonstrates their resemblance to upper mound fine‐scale yardangs. The history of Mt. Sharp started with deposition and lithification of sediments shortly after crater formation. Some lower mound layers were partially altered to clays and sulfates, and water formed streams and canyons. Wind erosion of the lower mound produced large‐scale yardangs, particularly in clay‐rich layers, oriented generally N‐S. Upper mound units were emplaced following a considerable period of wind erosion. The absence of water flow on the upper mound suggests that these units were emplaced after atmospheric loss rendered water unstable at the surface. The shift in dominant wind direction, as indicated by yardang orientations, also argues for a time gap between erosion of the lower and upper mound. These observations are consistent with upper mound units being related to the Hesperian Medusae Fossae formation. During 2014 Curiosity is expected to reach the foot of Mt. Sharp and ascend through the clay‐rich layers, into the sulfate‐rich layers, and possibly past the interface with the upper mound. This will be a unique opportunity to field check geologic models on the surface of Mars.

Allen, C.↗
NASA NTRS1977

A critical evaluation of the application of amino acid racemization to geochronology and geothermometry

Attempts have been made to determine the age of biological samples by measuring the racemization of amino acids in protein samples. The pitfalls and inherent complications in diagenetic racemization studies are reviewed, and recent advances in improving techniques are outlined. Methodological topics include isolation of amino acids from geological samples, resolution of amino acid enantiomers, and the effects of acid hydrolysis. The theory and kinetics of amino acid racemization are discussed with attention to the derivation of the rate expression for amino acid racemization, isoleucine and the equilibrium constant, the mechanism of amino acid racemization, the racemization of 'bound' versus 'free' amino acids, and factors affecting the racemization rates of free amino acids in aqueous solution. Applications of amino acid racemization kinetics to geochronology is considered with reference to shells, marine sediments, and bones. Potential complications include heating and diagenesis, diagenetic formation of amino acids, the effect of clays, species effect, and contamination.

Williams, K. M.↗
NASA NTRSDate not supplied

Modeling Water-Rock Reactions Beneath the Greenheugh Pediment, Gale Crater, Mars

The Mars Science Laboratory Curiosity rover has been exploring the clay rich Glen Torridon unit in Gale crater since sol 2300 of the mission [1]. As identified in orbital data [2], this clay rich area [3] in the Murray formation is overlain with the Greenheugh Pediment unit to the south, which is part of the Stimson Formation [4]. Curiosity acquired the drill sample Hutton in the Upper Murray formation 2 – 3 meters below the Greenheugh Pediment [5,6]. This study uses thermochemical modelling to investigate the hypothesis for alteration in the Murray formation below the Greenheugh Pediment. Specifically, if the contact between the Greenheugh Pediment and Murray sediments was a conduit for diagenetic fluids (a low water/rock scenario) or if subaerial weathering altered the Murray sediments before cementation began (a high water/rock scenario) [6]. Here, we report on preliminary modeling where we have reacted the chemical composition for the Hutton drill sample with Gale Portage Water (GPW) at 25 °C, 50 °C and 200 °C, for 10% Fe3+/Fetot of the host rock.

SMR Turner↗
NASA NTRS2014

The Imprint of Atmospheric Evolution in the D/H of Hesperian Clay Minerals on Mars

The deuterium-to-hydrogen (D/H) ratio in strongly bound water or hydroxyl groups in ancient Martian clays retains the imprint of the water of formation of these minerals. Curiosity's Sample Analysis at Mars (SAM) experiment measured thermally evolved water and hydrogen gas released between 550 degrees Centigrade and 950 degrees Centigrade from samples of Hesperian-era Gale crater smectite to determine this isotope ratio. The D/H value is 3.0 (plus or minus 0.2) times the ratio in standard mean ocean water. The D/H ratio in this approximately 3-billion-year-old mudstone, which is half that of the present Martian atmosphere but substantially higher than that expected in very early Mars, indicates an extended history of hydrogen escape and desiccation of the planet.

Deuterium↗
NASA NTRS1987

Dunes in the north polar region of Mars - Their possible formation from low-density sedimentary aggregates

Low-density aggregates composed of submicron clay aerosols were formed experimentally as the sublimation residues of masses of dust-nucleated ice. These ice-dust mixtures are considered to be possible analogs of materials of Martian north polar deposits. Low-density (0.002 g/cu cm) spheroidal pellets formed from these materials in wind tunnel experiments are studied as possible candidates for the formation of dunes in the north polar region of Mars. It is shown that these particles move like sand grains under conditions of saltation and, taken in sufficient quantities, can form the dunes observed in the north circumpolar erg.

Saunders, R. S.↗
NASA NTRS1987

Chemical interactions between the present-day Martian atmosphere and surface minerals

Thermochemical and photochemical reactions between surface minerals and present-day atmospheric constituents are predicted to produce microscopic effects on the surfaces of mineral grains. Relevant reactions hypothesized in the literature include conversions of silicates and volcanic glasses to clay minerals, conversion of ferrous to ferric compounds, and formation of carbonates, nitrates, and sulfates. These types of surface-atmosphere interactions are important for addressing issues such as chemical weathering of minerals, biological potential of the surface environment, and atmospheric stability in both present and past Martian epochs. It is emphasized that the product of these reactions will be observable and interpretable on the microscopic surface layers of Martian surface rocks using modern techniques with obvious implications for sample return from Mars. Macroscopic products of chemical weathering reactions in past Martian epochs are also expected in Martian surface material. These products are expected not only as a result of reactions similar to those proceeding today but also due to aqueous reactions in past epochs in which liquid water was putatively present. It may prove very difficult or impossible however to determine definitively from the relic macroscopic product alone either the exact weathering process which led to its formation or the identity of its weathered parent mineral. The enormous advantages of studying Martian chemical weathering by investigating the microscopic products of present-day chemical reactions on sample surfaces are very apparent.

Prinn, Ronald↗
NASA NTRS1988

Chemical interactions between the present-day Martian atmosphere and surface minerals: Implications for sample return

Thermochemical and photochemical reactions between surface minerals and present-day atmospheric constituents are predicted to produce microscopic effects on the surface of mineral grains. Relevant reactions hypothesized in the literature include conversions of silicates and volcanic glasses to clay minerals, conversion of ferrous to ferric compounds, and formation of carbonates, nitrates, and sulfates. These types of surface-atmosphere weathering of minerals, biological potential of the surface environment, and atmospheric stability in both present and past Martian epochs. It is emphasized that the product of these reactions will be observable and interpretable on the microscopic surface layers of Martian surface rocks using modern techniques with obvious implications for sample return from Mars. Macroscopic products of chemical weathering reactions in past Martian epochs are also expected in Martian surface materials. These products are expected not only as a result of reactions similar to those proceeding today but also due to aqueous reactions in past epochs in which liquid water was putatively present. It may prove very difficult or impossible, however, to determine definitively from the relic macroscopic product alone either the exact weathering process which led to its formation of the identity of its weathering parent mineral. The enormous advantages of studying the Martian chemical weathering by investigating the microscopic products of present-day chemical reactions on sample surfaces are very apparent.

Prinn, Ronald↗
NASA NTRSDate not supplied

Phyllosilicate Formation on Early Mars Via Open-System Acid Alteration of Basaltic Glass

Smectites are widespread on Mars, but neutral/alkaline conditions favorable for smectite formation have surprisingly not led to abundant carbonates. Smectite formation on Mars could also occur in acidic environments unfavorable for carbonate formation. Acidic smectite formation has been demonstrated in batch (closed hydrologic) systems, however, the mechanisms and octahedral composition of smectite forming in acidic flow-through (open hydrologic) systems are not fully understood. Stapafell basaltic glass was hydrothermally altered (190◦C) at two flow rates corresponding to low and high water to rock ratio (W/R) and initial pH (pH_0) values of 2, 3, 4 and 6, and a batch low W/R experiment was conducted at pH_0 2. Kaolinite, montmorillonite and chlorite formed at pH_0 2 at low W/R; no phyllosilicates formed at pH_0 2 at high W/R; and lizardite formed at pH_0 ≥3 at both W/R ratios. Lizardite, kaolinite, and montmorillonite in these experiments formed by precipitation from solution and chlorite likely formed through alteration of montmorillonite and/or basalt. Saponite formed at pH_0 2 in batch conditions by alteration of basaltic glass. Comparison of experimental data with martian phyllosilicate assemblages indicated that smectite formation on Mars likely occurred under water-limited conditions. Al-rich smectite could form in open-system low W/R subsurface environments under a narrow range of pH (pH <3) while saponite could form in closed low W/R systems under acidic to alkaline conditions. Combined open and closed hydrological regimes could be responsible for development of clay mineral stratigraphies observed on Mars. The acidic conditions required for formation of Al-rich smectite were unfavorable for carbonate precipitation, but carbonate precipitation could occur together with Fe/Mg-smectite in closed systems at pH >4. The lack of carbonates occurring together with Fe/Mg-smectite could be cause by low pCO2 in subsurface closed environments and/or by overall lack of carbonate precipitation despite significant oversaturation.

S J Ralston↗
NASA NTRSDate not supplied

Mapping Organic-Mineral Associations in Jezero crater

The search for potential signs of life on Mars, a primary aim of the Mars 2020 mission, is greatly informed by the detection of organic matter1. The presence of organic matter also provides key information about the habitability and biological potential of the planet throughout its history. The Perseverance rover was designed for in situ science with the ability to collect a suite of promising samples for eventual return to Earth. One of its instruments, Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC), is a deep ultraviolet (DUV) Raman and fluorescence spectrometer designed to map the distribution of organic molecules and minerals on rock surfaces at a resolution of 100 μm2. With its unique spectral mapping capabilities, SHERLOC enables a novel understanding of organic-mineral relationships on Mars to better determine their formation, deposition, and preservation mechanisms. The rover’s landing site within Jezero crater combines a high potential for past habitability as the site of an ancient lake basin with a diverse set of minerals, including carbonates and clays, that may preserve organic materials and potential biosignatures. The Jezero crater floor includes three formations (fm); two of these, Máaz and Séítah, were explored as part of the mission’s first campaign. Here, we report the detection of multiple species of aromatic organic molecules using Raman and fluorescence spectroscopy across ten targets in the two formations. This is the first evidence of organic molecules in Martian materials obtained using Raman spectroscopy, and among the first using fluorescence spectroscopy, beyond Earth3. We report specific spatial patterns and classes of organic molecules in these compositionally distinct formations, potentially indicating different fates of carbon in these environments. Our findings indicate that there is a diversity of aromatic molecules prevalent on the Martian surface and these materials persist despite exposure to surface conditions. These organic molecules are largely found within minerals linked to aqueous processes, suggesting that these processes may have had a key role in organic synthesis, transport from their point of origin, or preservation.

Sunanda Sharma↗
NASA NTRS2010

Thermal Infrared Emission Spectroscopy of Synthetic Allophane and its Potential Formation on Mars

Allophane is a poorly-crystalline, hydrous aluminosilicate with variable Si/Al ratios approx.0.5-1 and a metastable precursor of clay minerals. On Earth, it forms rapidly by aqueous alteration of volcanic glass under neutral to slightly acidic conditions [1]. Based on in situ chemical measurements and the identification of alteration phases [2-4], the Martian surface is interpreted to have been chemically weathered on local to regional scales. Chemical models of altered surfaces detected by the Mars Exploration Rover Spirit in Gusev crater suggest the presence of an allophane-like alteration product [3]. Thermal infrared (TIR) spectroscopy and spectral deconvolution models are primary tools for determining the mineralogy of the Martian surface [5]. Spectral models of data from the Thermal Emission Spectrometer (TES) indicate a global compositional dichotomy, where high latitudes tend to be enriched in a high-silica material [6,7], interpreted as high-silica, K-rich volcanic glass [6,8]. However, later interpretations proposed that the high-silica material may be an alteration product (such as amorphous silica, clay minerals, or allophane) and that high latitude surfaces are chemically weathered [9-11]. A TIR spectral library of pure minerals is available for the public [12], but it does not contain allophane spectra. The identification of allophane on the Martian surface would indicate high water activity at the time of its formation and would help constrain the aqueous alteration environment [13,14]. The addition of allophane to the spectral library is necessary to address the global compositional dichotomy. In this study, we characterize a synthetic allophane by IR spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM) to create an IR emission spectrum of pure allophane for the Mars science community to use in Martian spectral models.

Rampe, E. B.↗
NASA NTRSDate not supplied

The Role of Olivine in Fe-Carbonate Formation in Gale Crater, Mars

Carbonates have been identified in remote sensing datasets, martian meteorites, and in-situ with rovers at Gale and Jezero craters. In Gale crater, traces of carbonate have been found by the SAM instrument throughout the Mars Science Laboratory mission, e.g., at Rocknest and Pahrump Hills, with models for carbonate formation at Pahrump Hills explored by [9]. Further up-section, CheMin data of clay-rich Glen Torridon (GT) samples show that five out of seven drill samples from GT contain Fe-carbonate alongside phyllosilicates. The GT sediments were deposited in a lacustrine environment and subsequently underwent multiple episodes of diagenesis. In this work, we explore the role of olivine in the formation of carbonates by modelling the interaction of different martian olivines with a previously modeled Gale groundwater. We then explore the incongruent dissolution of host rocks within the GT sediments by mixing olivine with quantities of the Kilmarie drill sample chemical composition as the reactant rock.

S M R Turner↗
NASA NTRSDate not supplied

Mineralogical Characterization of a Potential Mars-Analog Field Site: Gypsum- and Carbonate-Bearing Formations in the Quebradas Back Country, New Mexico, USA

The Quebradas Back Country field site is located approximately six miles east of Socorro, NM, USA and provides access to Pennsylvanian and Permian age sedimentary formations that record environments ranging from lacustrine to hypersaline supratidal mudflats in deposits of carbonate, sulfate, and clay minerals. These deposits demonstrate a critical climate transition from cold and wet to largely arid conditions, which may parallel the drying of ancient Mars. The Quebradas sulfate and carbonate deposits can provide insight into the formation and weathering of Mars-relevant sulfates and elucidate potential causes for the prevalence of calcium sulfate and paucity of calcium carbonate on Mars. Deciphering the environmental cues held within evaporites is particularly timely now with mounting evidence for sulfate-rich fluids in Jezero crater and the Curiosity rover analyzing the sulfate-bearing unit in Gale crater.

S J Ralston↗
NASA NTRSDate not supplied

Testing Destruction of Clay Minerals By Silica-Poor Brines in Gale Crater, Mars Using Laboratory and Field Experiments

The Mars Science Laboratory (MSL) Curiosity rover landed in Gale crater to investigate the cause for mineralogical changes seen from orbit, including the clay-sulfate mineral transition observed on its central mound, Aeolis Mons. The lower strata show spectral signatures of clay minerals, hematite, and hydrated Mg sulfates, and the upper strata are dominated by hydrated Mg sulfate signatures. This significant transition has been observed in other locations on Mars, and therefore processes related to the clay mineral-sulfate transition are likely important broadly across Mars. The bulk mineralogy of ~3.7 Ga sedimentary rocks in Gale crater is a product of variations in sediment sources and depositional processes, with overprinting by episodes of early and late diagenetic alteration. Sedimentary analyses of the smectite clay minerals observed in the Glen Torridon (GT) region of Mount Sharp suggest formation in a lacustrine aqueous environment. Examination of the Vera Rubin ridge (VRR) strata indicate that it was formed at the same time as GT and later altered by extensive diagenesis. Recent work suggests that the observed mineral transition from smectites and talc-serpentinites in GT to iron oxides and oxyhydroxides and VRR may have resulted from extensive diagenetic alteration by density driven, silica-poor brines sourced from the overlying sulfur-bearing unit on Mount Sharp. This process of alteration by silica-poor brines is observed in limited locations on Earth. We are therefore working to demonstrate the impacts of silica poor brines on clay mineral alteration in laboratory column and terrestrial analog burial experiments. Column experiments allow the investigation of dissolution and precipitation under conditions that represent a closer analog to natural environments, while burial experiments allow examination of weathering reactions of a known starting material after a specific period of time in a natural field environment. Both methods are valuable for interpreting the water-rock interactions between clay minerals and brines. In preparation for these longer-term column and burial experiments, we are performing preliminary batch dissolution experiments on materials relevant to Glen Torridon: nontronite and serpentinite. We are using magnesium sulfate brine solutions relevant to those proposed on Mars. The results of this study can provide constraints on the characteristics of the diagenetic fluids that formed the altered minerals in Gale crater. They can also provide insights into the role of brine density-driven diagenesis in past aqueous environments on Mars, which have been proposed to be widespread.

J E Valdueza↗