Impure reworked evaporitic sandstones, preserved on Meridiani Planum, Mars, are mixtures of roughly equal amounts of altered siliciclastic debris, of basaltic provenance (40
±
10% by mass), and ...chemical constituents, dominated by evaporitic minerals (jarosite, Mg-, Ca-sulfates
±
chlorides
±
Fe-, Na-sulfates), hematite and possibly secondary silica (60
±
10%). These chemical constituents and their relative abundances are not an equilibrium evaporite assemblage and to a substantial degree have been reworked by aeolian and subaqueous transport. Ultimately they formed by evaporation of acidic waters derived from interaction with olivine-bearing basalts and subsequent diagenetic alteration. The rocks experienced an extended diagenetic history, with at least two and up to four distinct episodes of cementation, including stratigraphically restricted zones of recrystallization and secondary porosity, non-randomly distributed, highly spherical millimeter-scale hematitic concretions, millimeter-scale crystal molds, interpreted to have resulted from dissolution of a highly soluble evaporite mineral, elongate to sheet-like vugs and evidence for minor synsedimentary deformation (convolute and contorted bedding, possible teepee structures or salt ridge features). Other features that may be diagenetic, but more likely are associated with relatively recent meteorite impact, are meter-scale fracture patterns, veins and polygonal fractures on rock surfaces that cut across bedding. Crystallization of minerals that originally filled the molds, early cement and sediment deformation occurred syndepositionally or during early diagenesis. All other diagenetic features are consistent with formation during later diagenesis in the phreatic (fluid saturated) zone or capillary fringe of a groundwater table under near isotropic hydrological conditions such as those expected during periodic groundwater recharge. Textural evidence suggests that rapidly formed hematitic concretions post-date the primary mineral now represented by crystal molds and early pore-filling cements but pre-date secondary moldic and vug porosity. The second generation of cements followed formation of secondary porosity. This paragenetic sequence is consistent with an extended history of syndepositional through post-depositional diagenesis in the presence of a slowly fluctuating, chemically evolving, but persistently high ionic strength groundwater system.
Complete sets of mineral abundances for relatively unaltered volcanic or volcaniclastic rocks in Gusev Crater have been determined by modeling Mössbauer subspectral areas as mineral weight ...percentages, and combining those percentages with the proportions of iron‐free minerals not detected by Mössbauer (normative plagioclase, apatite, and chromite, as calculated from Alpha Particle X‐Ray Spectrometer (APXS) chemical analyses). Comparisons of synthetic thermal emission spectra calculated for these mineral modes with measured Miniature Thermal Emission Spectrometer (Mini‐TES) spectra for the same rock classes show either good agreements or discrepancies that we attribute to sodic plagioclase compositions or unmodeled sulfate, glass, or pigeonite. The normative compositions of olivine, pyroxene, and feldspar calculated from APXS data are consistent with spectroscopic constraints on mineral compositions. Systematic variations between olivine abundances in APXS norms (which sample tens of micrometers depth) and olivine proportions measured by Mössbauer (which sample hundreds of micrometers depth) support the hypothesis that dissolution of olivine by acidic fluids has occurred on weathered rock surfaces.
Excavating into the shallow Martian subsurface has the potential to expose stratigraphic layers and mature regolith, which may hold a record of more ancient aqueous interactions than those expected ...under current Martian surface conditions. During the Spirit rover's exploration of Gusev crater, rover wheels were used to dig three trenches into the subsurface regolith down to 6–11 cm depth: Road Cut, the Big Hole, and The Boroughs. A high oxidation state of Fe and high concentrations of Mg, S, Cl, and Br were found in the subsurface regolith within the two trenches on the plains, between the Bonneville crater and the foot of Columbia Hills. Data analyses on the basis of geochemistry and mineralogy observations suggest the deposition of sulfate minerals within the subsurface regolith, mainly Mg‐sulfates accompanied by minor Ca‐sulfates and perhaps Fe‐sulfates. An increase of Fe2O3, an excess of SiO2, and a minor decrease in the olivine proportion relative to surface materials are also inferred. Three hypotheses are proposed to explain the geochemical trends observed in trenches: (1) multiple episodes of acidic fluid infiltration, accompanied by in situ interaction with igneous minerals and salt deposition; (2) an open hydrologic system characterized by ion transportation in the fluid, subsequent evaporation of the fluid, and salt deposition; and (3) emplacement and mixing of impact ejecta of variable composition. While all three may have plausibly contributed to the current state of the subsurface regolith, the geochemical data are most consistent with ion transportation by fluids and salt deposition as a result of open‐system hydrologic behavior. Although sulfates make up >20 wt.% of the regolith in the wall of The Boroughs trench, a higher hydrated sulfate than kieserite within The Boroughs or a greater abundance of sulfates elsewhere than is seen in The Boroughs wall regolith would be needed to hold the structural water indicated by the water‐equivalent hydrogen concentration observed by the Gamma‐Ray Spectrometer on Odyssey in the Gusev region.
Mössbauer spectroscopy is a powerful tool for quantitative mineralogical analysis of Fe‐bearing materials. The miniature Mössbauer spectrometer MIMOS II is a component of the Athena science payload ...launched to Mars in 2003 on both Mars Exploration Rover missions. The instrument has two major components: (1) a rover‐based electronics board that contains power supplies, a dedicated central processing unit, memory, and associated support electronics and (2) a sensor head that is mounted at the end of the instrument deployment device (IDD) for placement of the instrument in physical contact with soil and rock. The velocity transducer operates at a nominal frequency of ∼25 Hz and is equipped with two 57Co/Rh Mössbauer sources. The reference source (∼5 mCi landed intensity), reference target (α‐Fe2O3 plus α‐Fe0), and PIN‐diode detector are configured in transmission geometry and are internal to the instrument and used for its calibration. The analysis Mössbauer source (∼150 mCi landed intensity) irradiates Martian surface materials with a beam diameter of ∼1.4 cm. The backscatter radiation is measured by four PIN‐diode detectors. Physical contact with surface materials is sensed with a switch‐activated contact plate. The contact plate and reference target are instrumented with temperature sensors. Assuming ∼18% Fe for Martian surface materials, experiment time is 6–12 hours during the night for quality spectra (i.e., good counting statistics); 1–2 hours is sufficient to identify and quantify the most abundant Fe‐bearing phases. Data stored internal to the instrument for selectable return to Earth include Mössbauer and pulse‐height analysis spectra (512 and 256 channels, respectively) for each of the five detectors in up to 13 temperature intervals (65 Mössbauer spectra), engineering data for the velocity transducer, and temperature measurements. The total data volume is ∼150 kB. The mass and power consumption are ∼500 g (∼400 g for the sensor head) and ∼2 W, respectively. The scientific measurement objectives of the Mössbauer investigation are to obtain for rock, soil, and dust (1) the mineralogical identification of iron‐bearing phases (e.g., oxides, silicates, sulfides, sulfates, and carbonates), (2) the quantitative measurement of the distribution of iron among these iron‐bearing phases (e.g., the relative proportions of iron in olivine, pyroxenes, ilmenite, and magnetite in a basalt), (3) the quantitative measurement of the distribution of iron among its oxidation states (e.g., Fe2+, Fe3+, and Fe6+), and (4) the characterization of the size distribution of magnetic particles. Special geologic targets of the Mössbauer investigation are dust collected by the Athena magnets and interior rock and soil surfaces exposed by the Athena Rock Abrasion Tool and by trenching with rover wheels.
Nanoparticles assembled from poly(d,l-lactic acid)−poly(ethylene glycol) (PLA−PEG) block copolymers may have a therapeutic application in site-specific drug delivery. A series of AB block copolymers ...based on a fixed PEG block (5 kDa) and a varying PLA segment (2−110 kDa) have been synthesized by the ring-opening polymerization of d,l-lactide using stannous octoate as a catalyst. These copolymers assembled to form spherical nanoparticles in aqueous media following precipitation from a water-miscible organic solvent. 1H NMR studies of the PLA−PEG nanoparticles in D2O confirmed their core−shell structure, with negligible penetration of the hydrated PEG chains into the PLA core. The influence of the PLA block molecular weight on the hydrodynamic size and micellar aggregation number of the assemblies was determined by dynamic and static light scattering techniques. The hydrodynamic radius of the PLA−PEG 2:5−30:5 nanoparticles was solely dependent on the copolymer architecture and scaled linearly as N PLA 1/3, where N PLA is the number of monomeric units in the PLA block. The PEG chains of the small PLA−PEG 2:5 and 3:5 assemblies appeared to be fairly splayed as a consequence of their relatively low aggregation number and high surface coverage. However, as N PLA was increased to 6 kDa the area available per PEG chain at the periphery of the shell decreased significantly and then remained fairly constant with further increases in the molecular weight of the PLA block. The aggregation number and hence particle size of nanoparticles produced from copolymers with a PLA block of 45 kDa or more was found to also depend on the concentration of copolymer dissolved in the organic phase during preparation. This suggested that that the PEG chains had little influence on the assembly of the higher molecular weight copolymers.
Analyses of outcrops created by the impact craters Endurance, Fram and Eagle reveal the broad lateral continuity of chemical sediments at the Meridiani Planum exploration site on Mars. Approximately ...ten mineralogical components are implied in these salt-rich silicic sediments, from measurements by instruments on the Opportunity rover. Compositional trends in an apparently intact vertical stratigraphic sequence at the Karatepe West ingress point at Endurance crater are consistent with non-uniform deposition or with subsequent migration of mobile salt components, dominated by sulfates of magnesium. Striking variations in Cl and enrichments of Br, combined with diversity in sulfate species, provide further evidence of episodes during which temperatures, pH, and water to rock ratios underwent significant change. To first order, the sedimentary sequence examined to date is consistent with a uniform reference composition, modified by movement of major sulfates upward and of minor chlorides downward. This reference composition has similarities to martian soils, supplemented by sulfate anion and the alteration products of mafic igneous minerals. Lesser cementation in lower stratigraphic units is reflected in decreased energies for grinding with the Rock Abrasion Tool. Survival of soluble salts in exposed outcrop is most easily explained by absence of episodes of liquid H
2O in this region since the time of crater formation.
The Mössbauer (MB) spectrometer on Opportunity measured the Fe oxidation state, identified Fe‐bearing phases, and measured relative abundances of Fe among those phases at Meridiani Planum, Mars. ...Eight Fe‐bearing phases were identified: jarosite (K,Na,H3O)(Fe,Al)(OH)6(SO4)2, hematite, olivine, pyroxene, magnetite, nanophase ferric oxides (npOx), an unassigned ferric phase, and metallic Fe (kamacite). Burns Formation outcrop rocks consist of hematite‐rich spherules dispersed throughout S‐rich rock that has nearly constant proportions of Fe3+ from jarosite, hematite, and npOx (29%, 36%, and 20% of total Fe). The high oxidation state of the S‐rich rock (Fe3+/FeT ∼ 0.9) implies that S is present as the sulfate anion. Jarosite is mineralogical evidence for aqueous processes under acid‐sulfate conditions because it has structural hydroxide and sulfate and it forms at low pH. Hematite‐rich spherules, eroded from the outcrop, and their fragments are concentrated as hematite‐rich soils (lag deposits) on ripple crests (up to 68% of total Fe from hematite). Olivine, pyroxene, and magnetite are primarily associated with basaltic soils and are present as thin and locally discontinuous cover over outcrop rocks, commonly forming aeolian bedforms. Basaltic soils are more reduced (Fe3+/FeT ∼ 0.2–0.4), with the fine‐grained and bright aeolian deposits being the most oxidized. Average proportions of total Fe from olivine, pyroxene, npOx, magnetite, and hematite are ∼33%, 38%, 18%, 6%, and 4%, respectively. The MB parameters of outcrop npOx and basaltic‐soil npOx are different, but it is not possible to infer mineralogical information beyond octahedrally coordinated Fe3+. Basaltic soils at Meridiani Planum and Gusev crater have similar Fe‐mineralogical compositions.
We demonstrate the viability of using an ink-jet printer to produce a formulation capable of controlling the release of a drug. This is shown for the drug felodipine, an antihypertensive, with ...polyvinyl pirrolidone (PVP) as an excipient. As felodipine is a poorly water soluble drug, its molecular dispersion in a soluble polymer (ie. PVP) is a commonly used approach to improve bioavailability. Various ratios of felodipine and PVP in an ethanol-DMSO mixture (95/5) were dispensed in picoliter quantities using a piezoelectric ‘ink-jet’ head onto a hydrophobic substrate. The resultant formulation spots were characterized using atomic force microscopy, localized nano-thermal analysis, ATR-IR and imaging confocal Raman spectroscopy. Intimate mixing of the felodipine and PVP within the micro-dots was observed. ATR-IR confirmed the known molecular level interaction of felodipine and PVP through hydrogen bonding. Nanothermal analysis indicated a single glass transition point, indicative of an intimate polymer drug mixture, which is lowered as the drug concentration increases. Confocal Raman microscopy mapping on single micro-scale droplets allowed the visualization of the drug distribution in the spots as well as facilitating characterization of the release of the drug. The drug release can be altered through control of the drug loading. As inkjet printing is an inherently scalable technology, this proof of principal work with single deposited micro-spot formulations demonstrates the potential of this approach to print practical dosage forms (e.g. as an array of many thousands of spots with different release profiles). This, for example, raises the possibility in the future of producing dosage forms at points of care with one or more drugs which have been formulated for the needs of individual patients.
Display omitted
The Glen Torridon stratigraphic sequence marks the transition from the low energy lacustrine‐dominated Murray formation (Mf) (Jura member: Jm) to the more diverse Carolyn Shoemaker formation (CSf) ...(Knockfarril Hill member: Knockfarril Hill; Glasgow member: Glasgow). This transition defines a change in depositional setting. Alpha Particle X‐ray Spectrometer (APXS) results and statistical analysis reveal that the bulk primary geochemistry of Mf targets are broadly in family with CSf targets, but with subtle compositional and diagenetic trends with increasing elevation. APXS results reveal significant compositional differences between Jura_GT and the stratigraphically equivalent Jura on Vera Rubin ridge (Jura_VRR). The data define two geochemical facies (high‐K or high‐Mg), with a strong bimodal grain distribution in Jura_GT and Knockfarril Hill. The contact between Knockfarril Hill and Glasgow is marked by abrupt sedimentological changes but a similar composition for both. Away from the contact, the Knockfarril Hill and Glasgow plot discretely, suggesting a zone of common alteration at the transition and/or a gradual transition in provenance with increasing elevation in the Glasgow member. APXS results point to a complex history of diagenesis within Glen Torridon, with increasing diagenesis close to the Basal Siccar Point unconformity on the Greenheugh pediment, and with proximity to the beginning of the clay sulfate transition. Elemental mobility is evident in localized enrichments or depletions in Ca, S, Mn, P, Zn, Ni. The highly altered Hutton interval, in contact with the unconformity on Tower butte, is also identified on Western Butte, indicating that the “interval” was once laterally extensive.
Plain Language Summary
The Mars Science Laboratory Curiosity rover has traversed the Glen Torridon locale in Gale crater, Mars. The rover has provided evidence in the rocks of a change from a lake setting to a river setting, with increasing elevation through the rock record. Geochemical results from the Alpha Particle X‐ray Spectrometer (APXS) confirm a slow change in composition over time as the sediments that formed the rock were laid down. Fluids percolated through the sediments, altering the composition, with localized enrichments of calcium, sulfur, manganese, phosphorus, sodium, zinc, nickel, which are now present as veins, and small (typically <0.3 cm; more rarely, 0.5–2 cm) rectangular nodules and concentrations.
Key Points
Alpha Particle X‐ray Spectrometer data for Glen Torridon, Gale crater documents subtle compositional changes
Multiple episodes of alteration and diagenesis identified
Compositional similarities between Glen Torridon members confirms the highly localized nature of the Vera Rubin ridge alteration
The subsurface chlorine depth distribution at Gale crater has been studied using measurements from the Alpha Particle X‐ray Spectrometer (APXS) and Dynamic Albedo of Neutrons (DAN) instruments ...onboard NASA's Curiosity Mars rover. These measurements have been acquired at or near ∼30 drill holes made by Curiosity along its 30 km drive. APXS measured a ∼15 micron surface layer of bedrock and shallow depth of ∼5 cm of drill tailings. DAN is sensitive to the bulk (∼50 cm depth) chlorine abundance and that of other neutron absorbing elements. Joint analysis of APXS and DAN data shows that the chlorine distribution at Gale crater consists of two components: surficial chlorine with concentrations >1 wt.%, possibly controlled by aeolian deposition of Cl‐rich dust and surface alteration, and subsurface chlorine with concentrations <1 wt.%, likely a result of groundwater activity in the past.
Plain Language Summary
The Curiosity rover has been exploring layered sediments enriched with hydrated mineral phases which were formed in past epochs due to the interaction with fluids in Gale crater, Mars. Curiosity carries 10 science instruments to conduct remote and contact measurements and has already made ∼30 drill holes along its 30 km drive, testing samples of Martian soils and rocks. One of Curiosity's science tasks is to measure the elemental composition of the Martian surface and chlorine is considered here as an important chemical component that could tell us what has occurred on Mars in the past. Several instruments aboard Curiosity are capable of estimating the concentration of chlorine and we selected two of them (Dynamic Albedo of Neutrons and Alpha Particle X‐ray Spectrometer) to evaluate how chlorine is distributed with depth using data acquired at drill locations. We found that the chlorine distribution at Gale crater consists of two components: surficial chlorine with concentration >1%, possibly controlled by wind‐driven deposition of Cl‐rich dust and surface alteration, and subsurface chlorine with concentration <1%, likely a result of groundwater activity in the past.
Key Points
A correlation between Alpha Particle X‐ray Spectrometer drill tailings and Dynamic Albedo of Neutrons measurements of subsurface chlorine was found
Chlorine depth distribution consists of surficial chlorine (>1 wt.%) and bulk chlorine (<1 wt.%) components
The surficial Cl is controlled by Aeolian deposition and surface alteration, and bulk Cl is a result of groundwater activity
PDF
