Engineering topics

DeVincenzi, Donald L.

Publications and source records attributed to DeVincenzi, Donald L..

At least 19 records

NASA NTRS2002

Cometary Science After Hale-Bopp

Comets and the chondritic porous interplanetary dust particles (CP IDPs) that they shed in their comae are reservoirs of primitive solar nebula materials. The high porosity and fragility of cometary grains and CP IDPs, and anomalously high deuterium contents of pyroxene-rich CP IDPs imply these aggregate particles contain significant interstellar grain components. Spectrophotometry of comets at thermal IR wavelengths (3-40 microns) reveal the presence of a warm (near-IR) featureless emission modeled by amorphous carbon grains, and mid-IR and far-IR broad and narrow resonances modeled by chondritic (50% Fe and 50% Mg) amorphous and Mg-rich crystalline silicate minerals, respectively. Cometary amorphous silicate resonances are well matched by IR spectra of CP IDPs dominated by 0.1 micron spherules of Glass with Embedded Metal and Sulfides (GEMS) that are thought to be the interstellar Fe-bearing amorphous silicates produced in the cooling outflows of Asymptotic Giant Branch (AGB) stars. Acid-etched microtomed CP IDP samples, however, show that both the carbon phase (aliphatic) and the amorphous silicate phase (Mg-rich) are not optically absorbing while the embedded Fe nanoparticles make the IDPs dark. The CP IDPs suggest either significant processing has occurred in the ISM or that the AGB amorphous silicates have Mg-rich stoichiometry and possibly grew on Fe particle condensates. Cometary crystalline silicate resonances are well matched by IR spectra of laboratory submicron Mg-rich olivine crystals, [Mg(sub y),Fe(sub 1-y)]2SiO4 with y/ge0.85, and in the case of Hale-Bopp at r(sub h) less than or equal to approx. 1.5 AU, by Mg-rich pyroxene crystals, [Mg(sub x),Fe(sub 1-x)]SiO3 with x/ge0.85. While a fraction of AGB stardust (less than or equal to 15%) are Mg-rich crystals, this interstellar star dust component is insufficient to account for the deduced abundance of crystalline minerals in comet dust. An insufficient source of ISM Mg-rich crystals leads to the inference that Mg-rich crystals in comets may be hot, early solar nebula condensates that traveled large radial distances out to the comet-forming zone.

Wooden, Diane H.↗

NASA NTRS2002

Limits on the UV Photodecomposition of Carbonates on Mars

The effect of UV (ultraviolet) light on the stability of calcium carbonate in a simulated martian atmosphere was experimentally investigated. Sample cells containing C-13 labeled calcite were irradiated with a Xe arc lamp in 10 mbar of simulated martian atmosphere and a quadrupole mass spectrometer was used to monitor the headspace gases for the production of (13)CO2. We found no experimental evidence of the UV photodecomposition of calcium carbonate in a simulated martian atmosphere. Extrapolating the lower limit of detection of our experimental system to an upper limit of carbonate decomposition on Mars yields a quantum efficiency of 3.5 x 10(exp -8) molecules/photon over the wavelength interval of 190-390 nm and a maximum UV photodecomposition rate of 1.2 x 10(exp -13) kg m(exp -2) s(exp -1) from a calcite surface. The maximum loss of bulk calcite due to this process would be 2.5 nm yr(exp -1). However, calcite is expected to be thermodynamically stable on the surface of Mars and potential UV photodecomposition reaction mechanisms indicate that while calcium carbonate may decompose under vacuum, it would be stable in a CO2 atmosphere. Given the expected stability of carbonate on Mars and our inability to detect carbonate decomposition, we conclude that it is unlikely that the apparent absence of carbonate on the martian surface is due to UV photo decomposition of calcite in the current environment.

Quinn, Richard↗

NASA NTRS2002

Spectroscopic Detection of a Stellar-like Photosphere in an Accreting Protostar

We present high-resolution (R is approximately equal to 18,000), high signal-to-noise 2 micron spectra of two luminous, X-ray flaring Class I protostars in the rho Ophiuchi cloud acquired with the NIRSPEC (near infrared spectrograph) of the Keck II telescope. We present the first spectrum of a highly veiled, strongly accreting protostar which shows photospheric absorption features and demonstrates the stellar nature of its central core. We find the spectrum of the luminous (L (sub bol) = 10 solar luminosity) protostellar source, YLW 15, to be stellar-like with numerous atomic and molecular absorption features, indicative of a K5 IV/V spectral type and a continuum veiling r(sub k) = 3.0. Its derived stellar luminosity (3 stellar luminosity) and stellar radius (3.1 solar radius) are consistent with those of a 0.5 solar mass pre-main-sequence star. However, 70% of its bolometric luminosity is due to mass accretion, whose rate we estimate to be 1.7 x 10(exp -6) solar masses yr(exp -1). We determine that excess infrared emission produced by the circumstellar accretion disk, the inner infalling envelope, and accretion shocks at the surface of the stellar core of YLW 15 all contribute significantly to its near-IR (infrared) continuum veiling. Its rotational velocity v sin i = 50 km s(exp -1) is comparable to those of flat-spectrum protostars but considerably higher than those of classical T Tauri stars in the rho Oph cloud. The protostar may be magnetically coupled to its circumstellar disk at a radius of 2 - 3 R(sub *). It is also plausible that this protostar can shed over half its angular momentum and evolve into a more slowly rotating classical T Tauri star by remaining coupled to its circumstellar disk (at increasing radius) as its accretion rate drops by an order of magnitude during the rapid transition between the Class I and Class II phases of evolution. The spectrum of WL 6 does not show any photospheric absorption features, and we estimate that its continuum veiling is r(sub k) is greater than or equal to 4.6. Its low luminosity (2 solar masses) and high veiling dictate that its central protostar is very low mass, M is approx. 0.1 solar masses. We also evaluate multi-epoch X ray data along with these spectra and conclude that the X ray variabilities of these sources are not directly related to their protostellar rotation velocities.

Greene, Thomas P.↗

NASA NTRS2001

Artificial Cells: Prospects for Biotechnology

A variety of techniques can now be used to alter the genome of a cell. Although these techniques are very powerful, they also have limitations related to cost and efficiency of scale. Artificial cells designed for specific applications combine properties of biological systems such as nano-scale efficiency, self-organization and adaptability at relatively low cost. Individual components needed for such structures have already been developed, and now the main challenge is to integrate them in functional microscopic compartments. It will then become possible to design and construct communities of artificial cells that can perform different tasks related to therapeutic and diagnostic applications.

Pohorille, Andrew↗

NASA NTRS2001

Mars Sample Handling Protocol Workshop Series: Workshop 2a (Sterilization)

The Space Studies Board of the National Research Council provided a series of recommendations to NASA on planetary protection requirements for future Mars sample return missions. One of the Board's key findings suggested, although current evidence of the martian surface suggests that life as we know it would not tolerate the planet's harsh environment, there remain 'plausible scenarios for extant microbial life on Mars.' Based on this conclusion, all samples returned from Mars should be considered potentially hazardous until it has been demonstrated that they are not. In response to the National Research Council's findings and recommendations, NASA has undertaken a series of workshops to address issues regarding NASA's proposed sample return missions. Work was previously undertaken at the Mars Sample Handling and Protocol Workshop 1 (March 2000) to formulate recommendations on effective methods for life detection and/or biohazard testing on returned samples. The NASA Planetary Protection Officer convened the Mars Sample Sterilization Workshop, the third in the Mars Sample Handling Protocol Workshop Series, on November 28-30, 2000 at the Holiday Inn Rosslyn Westpark, Arlington, Virginia. Because of the short timeframe between this Workshop and the second Workshop in the Series, which was convened in October 2000 in Bethesda, Maryland, they were developed in parallel, so the Sterilization Workshop and its report have therefore been designated as '2a'). The focus of Workshop 2a was to make recommendations for effective sterilization procedures for all phases of Mars sample return missions, and to answer the question of whether we can sterilize samples in such a way that the geological characteristics of the samples are not significantly altered.

Rummel, John D.↗

NASA NTRS2001

Plasma CVD of Carbon Nanotubes

Carbon nanotubes(CNT) exhibit remarkable mechanical and unique electronic properties and thus have created excitement in the research community about their potential in electronics, computing, sensor and structural applications. Realization of these applications critically depends on the ability to control the properties(such as diameter, chirality) as well purity. We have investigated CNT growth using an inductively coupled plasma(ICP) process using hydrocarbon feedstock. The catalyst required for nanotube growth consists of thin sputtered layers of aluminum and iron(10 nm each) and aligned carbon nanotubes have been obtained. Optical emission diagnostics as well as a plasma modeling effort have been undertaken to understand growth mechanisms. This presentation will discuss growth characteristics under various pressure, power and feedgas compositions and our understanding from modeling and diagnostics.

Delzeit, Lance↗

NASA NTRS2001

Calculating Free Energies Using Average Force

A new, general formula that connects the derivatives of the free energy along the selected, generalized coordinates of the system with the instantaneous force acting on these coordinates is derived. The instantaneous force is defined as the force acting on the coordinate of interest so that when it is subtracted from the equations of motion the acceleration along this coordinate is zero. The formula applies to simulations in which the selected coordinates are either unconstrained or constrained to fixed values. It is shown that in the latter case the formula reduces to the expression previously derived by den Otter and Briels. If simulations are carried out without constraining the coordinates of interest, the formula leads to a new method for calculating the free energy changes along these coordinates. This method is tested in two examples - rotation around the C-C bond of 1,2-dichloroethane immersed in water and transfer of fluoromethane across the water-hexane interface. The calculated free energies are compared with those obtained by two commonly used methods. One of them relies on determining the probability density function of finding the system at different values of the selected coordinate and the other requires calculating the average force at discrete locations along this coordinate in a series of constrained simulations. The free energies calculated by these three methods are in excellent agreement. The relative advantages of each method are discussed.

Darve, Eric↗

NASA NTRS2001

Mars Sample Handling Protocol Workshop Series: Workshop 2

Numerous NASA reports and studies have identified Planetary Protection (PP) as an important part of any Mars sample return mission. The mission architecture, hardware, on-board experiments, and related activities must be designed in ways that prevent both forward- and back-contamination and also ensure maximal return of scientific information. A key element of any PP effort for sample return missions is the development of guidelines for containment and analysis of returned sample(s). As part of that effort, NASA and the Space Studies Board (SSB) of the National Research Council (NRC) have each assembled experts from a wide range of scientific fields to identify and discuss issues pertinent to sample return. In 1997, the SSB released its report on recommendations for handling and testing of returned Mars samples. In particular, the NRC recommended that: a) samples returned from Mars by spacecraft should be contained and treated as potentially hazardous until proven otherwise, and b) rigorous physical, chemical, and biological analyses [should] confirm that there is no indication of the presence of any exogenous biological entity. Also in 1997, a Mars Sample Quarantine Protocol workshop was convened at NASA Ames Research Center to deal with three specific aspects of the initial handling of a returned Mars sample: 1) biocontainment, to prevent 'uncontrolled release' of sample material into the terrestrial environment; 2) life detection, to examine the sample for evidence of organisms; and 3) biohazard testing, to determine if the sample poses any threat to terrestrial life forms and the Earth's biosphere. In 1999, a study by NASA's Mars Sample Handling and Requirements Panel (MSHARP) addressed three other specific areas in anticipation of returning samples from Mars: 1) sample collection and transport back to Earth; 2) certification of the samples as non-hazardous; and 3) sample receiving, curation, and distribution. To further refine the requirements for sample hazard testing and the criteria for subsequent release of sample materials from quarantine, the NASA Planetary Protection Officer convened an additional series of workshops beginning in March 2000. The overall objective of these workshops was to develop comprehensive protocols to assess whether the returned materials contain any biological hazards, and to safeguard the purity of the samples from possible terrestrial contamination. This document is the report of the second Workshop in the Series. The information herein will ultimately be integrated into a final document reporting the proceedings of the entire Workshop Series along with additional information and recommendations.

Rummel, John D.↗

NASA NTRS2001

The Biogeochemistry of Sulfur in Hydrothermal Systems

The incorporation of sulfur into many biomolecules likely dates back to the development of the earliest metabolic strategies. Sulfur is common in enzymes and co-enzymes and is an indispensable structural component in many peptides and proteins. Early metabolism may have been heavily influenced by the abundance of sulfide minerals in hydrothermal systems. The incorporation of sulfur into many biomolecules likely dates back to the development of the earliest metabolic strategies. Sulfur is common in enzymes and co-enzymes and is an indispensable structural component in many peptides and proteins. Early metabolism may have been heavily influenced by the abundance of sulfide minerals in hydrothermal systems. Understanding how sulfur became prevalent in biochemical processes and many biomolecules requires knowledge of the reaction properties of sulfur-bearing compounds. We have previously estimated thermodynamic data for thiols, the simplest organic sulfur compounds, at elevated temperatures and pressures. If life began in hydrothermal environments, it is especially important to understand reactions at elevated temperatures among sulfur-bearing compounds and other organic molecules essential for the origin and persistence of life. Here we examine reactions that may have formed amino acids with thiols as reaction intermediates in hypothetical early Earth hydrothermal environments. (There are two amino acids, cysteine and methionine, that contain sulfur.) Our calculations suggest that significant amounts of some amino acids were produced in early Earth hydrothermal fluids, given reasonable concentrations H2, NH3, H2S and CO. For example, preliminary results indicate that glycine activities as high as 1 mmol can be reached in these systems at 100 C. Alanine formation from propanethiol is also a favorable reaction. On the other hand, the calculated equilibrium log activities of cysteine and serine from propanethiol are -21 and -19, respectively, at 100 C. These results indicate that while amino acid formation with thiols as intermediates is favored in some cases, other mechanisms may have been necessary to produce significant amounts of other amino acids. Coupled with our previous results for thiols, these studies imply that sulfur may have been easily incorporated into the organic geochemistry of early Earth hydrothermal systems, leading to its widespread use in biomolecules. Formation of more complex biomolecules in hydrothermal systems may have required sulfur-bearing organic compounds as reaction intermediates.

Schulte, Mitchell↗

NASA NTRS2001

Effects of warming and drying of soils on the ectomycorrhizal community of a mixed Pinus contorta/Picea engelmannii stand in Yellowstone Park

Restriction Fragment Length Polymorphisms (RFLPs) analyses were used to determine patterns of change in ectomycorrhizal community structure response to seasonal warming and drying of soils. Soil cores (42 total, 21 from cold and wet soil in early June, and 21 from dry, warm soil in late August) were collected from replicate blocks in a mixed-conifer forest stand in Yellowstone. Results indicated no significant differences in species richness (2.62 species/core, SE 0.2 in June; 3.25, SE 0.2 in August), however there was a significant effect on ectomycorrhizal infection (P<0.05), mean number of EM tips/core was significantly lower in June (185.8, SE 34) than in August (337 SE 78). Data indicated no difference in overall EM fungal species composition, however among system dominants, two species (Cortinarius 9 and Cortinarius 10) were more abundant in August than in June (P<0.02). The remaining dominant fungal species exhibited no differences in relative abundance. Results are discussed in relation to soil fertility and composition.

Cullings, Kenneth↗

NASA NTRS2001

The AIRES Optical Design

AIRES (Airborne InfraRed Echelle Spectrometer) is the facility spectrometer for SOFIA (Stratospheric Observatory For Infrared Astronomy). AIRES is a long-slit (approximately 160 in) spectrometer designed to cover the 17 to 210-micron range with good sensitivity using three spectroscopic arrays. Initially, only the 30-130 micron, mid-wavelength array will be available. The instrument has a cryogenic K-mirror to perform field rotation and a slit-viewing camera (lambda < 28 microns, FOV = 160 in diameter) to image source morphology and verify telescope pointing. AIRES employs a large echelle grating to achieve a spectral resolving power (lambda/delta lambda) of approximately 1.0 x 10(exp 6)/lambda (sub mu), where lambda (sub mu) is the wavelength in microns. Hyperfine, Inc. has ruled and tested the AIRES' echelle; its wave-front error is 0.028 waves RMS (root mean square) at 10.6 microns. The instrument is housed in a liquid-helium cryostat which is constrained in diameter (approximately 1 m) and length (approximately 2 m) by the observatory. Hence, the length of the echelle (approximately 1.1 m) and the focal length of its collimator (approximately 5.2 m) severely drive the optical design and packaging. The final design uses diamond-turned aluminum optics and has up to 19 reflections inside the cryostat, depending on the optical path. This design was generated, optimized, and toleranced using Code V. The predicted performance is nearly diffraction-limited at 17 microns; the error budget is dominated by design residuals. Light loss due to slit rotation and slit curvature has been minimized. A thorough diffraction analysis with GLAD (G-Level Analysis Drawer) was used to size the mirrors and baffles; the internal light loss is shown to be a strong function of slit width.

Haas, Michael R.↗

NASA NTRS2001

Molecular Dynamics Studies of Structure and Functions of Water-Membrane Interfaces

A large number of essential cellular processes occur at the interfaces between water and membranes. The selectivity and dynamics of these processes are largely determined by the structural and electrical properties of the water-membrane interface. We investigate these properties by the molecular dynamics method. Over the time scales of the simulations, the membrane undergoes fluctuations described by the capillary wave model. These fluctuations produce occasional thinning defects in the membrane which provide effective pathways for passive transport of ions and small molecules across the membrane. Ions moving through the membrane markedly disrupt its structure and allow for significant water penetration into the membrane interior. Selectivity of transport, with respect to ionic charge, is determined by the interfacial electrostatic potential. Many small molecules. of potential significance in catalysis, bioenergetics and pharmacology, are shown to bind to the interface. The energetics and dynamics of this process will be discussed.

Pohorille, Andrew↗

NASA NTRS2001

Better, Cheaper, Faster Molecular Dynamics

Recent, revolutionary progress in genomics and structural, molecular and cellular biology has created new opportunities for molecular-level computer simulations of biological systems by providing vast amounts of data that require interpretation. These opportunities are further enhanced by the increasing availability of massively parallel computers. For many problems, the method of choice is classical molecular dynamics (iterative solving of Newton's equations of motion). It focuses on two main objectives. One is to calculate the relative stability of different states of the system. A typical problem that has' such an objective is computer-aided drug design. Another common objective is to describe evolution of the system towards a low energy (possibly the global minimum energy), "native" state. Perhaps the best example of such a problem is protein folding. Both types of problems share the same difficulty. Often, different states of the system are separated by high energy barriers, which implies that transitions between these states are rare events. This, in turn, can greatly impede exploration of phase space. In some instances this can lead to "quasi non-ergodicity", whereby a part of phase space is inaccessible on time scales of the simulation. To overcome this difficulty and to extend molecular dynamics to "biological" time scales (millisecond or longer) new physical formulations and new algorithmic developments are required. To be efficient they should account for natural limitations of multi-processor computer architecture. I will present work along these lines done in my group. In particular, I will focus on a new approach to calculating the free energies (stability) of different states and to overcoming "the curse of rare events". I will also discuss algorithmic improvements to multiple time step methods and to the treatment of slowly decaying, log-ranged, electrostatic effects.

Pohorille, Andrew↗

NASA NTRS2001

Composition of Hydrothermal Vent Microbial Communities as Revealed by Analyses of Signature Lipids, Stable Carbon Isotopes and Aquificales Cultures

Extremely thermophilic microbial communities associated with the siliceous vent walls and outflow channel of Octopus Spring, Yellowstone National Park, have been examined for lipid biomarkers and carbon isotopic signatures. These data were compared with that obtained from representatives of three Aquificales genera. Thermocrinis ruber. "Thermocrinis sp. HI", Hydrogenobacter thermophilus TK-6, Aquifex pyrophilus and Aquifex aeolicus all contained phospholipids composed not only of the usual ester-linked fatty acids, but also ether-linked alkyls. The fatty acids of all cultured organisms were dominated by a very distinct pattern of n-C-20:1 and cy-C-21 compounds. The alkyl glycerol ethers were present primarily as CIS() monoethers with the expection of the Aquifex spp. in which dialkyl glycerol ethers with a boarder carbon-number distribution were also present. These Aquificales biomarker lipids were the major constituents in the lipid extracts of the Octopus Spring microbial samples. Two natural samples, a microbial biofilm growing in association with deposition of amorphous silica on the vent walls at 92 C, and the well-known 'pink-streamers community' (PSC), siliceous filaments of a microbial consortia growing in the upper outflow channel at 87 C were analyzed. Both the biofilm and PSC samples contained mono and dialkyl glycerol ethers with a prevalence of C-18 and C-20 alkyls. Phospholipid fatty acids were comprised of both the characteristic Aquificales n-C-20:1 and cy-C-21, and in addition, a series of iso-branched fatty acids from i-C-15:0 to i-C-21:0, With i-C-17:0 dominant in the PSC and i-C-19:0 in the biofilm, suggesting the presence of two major bacterial groups. Bacteriohopanepolyols were absent and the minute quantities of archaeol detected showed that Archaea were only minor constituents. Carbon isotopic compositions of the PSC yielded information about community structure and likely physiology. Biomass was C-13-depleted (10.9%) relative to available CO2 from the source water inorganic carbon pool with lipids further depleted by 6.3% relative to biomass The C-20-21 Aquificales fatty acids of the PSC were somewhat heavier than the iso-branched fatty acids. The carbon isotopic signatures of lipid biomarkers were also explored using a pure culture, T ruber, previously isolated from the PSC. Cells grown on C02 with O2 and both H2 and thiosulfate as electron donors were only slightly depleted (3.3%) relative to the C-source while cells grown on formate with O2 showed a major discrimination (19.7%), possibly the result of a metabolic branch point involving the assimilation of C-formate to biomass and the dissimilation to CO2 associated with energy production. T. ruber lipids were slightly heavier than biomass (+1.3%) whether cells were grown using CO2 or formate. Fatty acids from CO2 grown T. ruber cells were a so slightly heavier (average +2.1%) than biomass. The relatively depleted PSC C-20-21 fatty acids suggest that any associated Thermocrinis biomass would also be similarly depleted and much too light to be explained by growth on CO2. The C-fractionations determined with the pure culture suggest that growth of Thermocrinis in the PSC is more likely to occur on formate, presumably generated by geothermal activity. This study points to the value of the analysis of the structural and isotopic composition of lipid blomarkers both in pure culture studies, and in establishing community structure and physiology, as a complement to genomic profiles of microbial diversity. This is especially so when the members of the microbial community are novel and difficult to cultivate in the laboratory.

Jahnke, Linda L.↗

NASA NTRS2001

A Novel Catalyst Deposition Technique for the Growth of Carbon Nanotubes

This viewgraph presentation provides information on the development of a technique at NASA's Ames Research Center by which carbon nanotubes (NT) can be grown. The project had several goals which included: 1) scaleability, 2) ability to control single wall nanotube (SWNT) and multiwall nanotube (MWNT) formation, 3) ability to control the density of nanotubes as they grow, 4) ability to apply standard masking techniques for NT patterning. Information regarding the growth technique includes its use of a catalyst deposition process. SWNTs of varying thicknesses can be grown by changing the catalyst composition. Demonstrations are given of various methods of masking including the use of transmission electron microscopic (TEM) grids.

Delzeit, Lance↗

NASA NTRS2001

Deuterium Fractionation in Analogs of Interstellar Ices: Laboratory Measurements

A question of key interest in the field of Astrobiology is the extent to which organic compounds made in space may play a role in the origin of life in planetary systems. In general, the best proof that at least some interstellar materials survive incorporation into forming stellar/planetary systems is their identification in extraterrestrial samples through detection of the isotopic anomalies they may carry. In the case of organic compounds, the chief isotopic anomalies that might be expected are the enrichment of D and 15N. and such enrichments are seen in primitive extraterrestrial materials, for example, in the organics in carbonaceous chondrites and interplanetary dust particles. In my talk I will review the various astrochemical processes by which deuterium can become enriched in organic compounds and will discuss some recent laboratory experiments that examine one of these processes in particular. name]y the UV photolysis of interstellar ices. Finally, I will review the current state of our knowledge of D enrichments in primitive solar system materials and discuss the constraints these data place on the relative importance of the various possible interstellar D enrichment processes.

Sandford, Scott A.↗

NASA NTRS2001

Iceland as a Model for Chemical Alteration on Mars

Subglacial volcanic activity on Iceland has led to the formation of a variety of silicate and iron oxide-rich alteration products that may serve as a model for chemical alteration on Mars. Multiple palagonitic tuffs, altered pillow lavas, hydrothermal springs and alteration at glacial run-off streams were observed during a recent field trip in Iceland. Formation of alteration products and ferrihydrite in similar environments on Mars may have contributed to the ferric oxide-rich surface material there. The spectral and chemical properties of Icelandic alteration products and ferrihydrites are presented here.

Bishop, Janice L.↗

NASA NTRS2001

Spectroscopic and Geochemical Analyses of Ferrihydrite from Hydrothermal Springs in Iceland and Applications to Mars

Ferrihydrite samples were collected from a thermal spring and a cold stream in the Landmannalaugar region of Iceland. Chemical and spectroscopic analyses have been performed on the air-dried and fine-grained fractions of these samples. The ferrihydrite from the cold stream is a pure sample, containing small amounts of Ca, P and Si, which do not form minerals detectable with X-ray diffraction (XRD) or reflectance and transmittance spectroscopy. The ferrihydrite from the thermal pool is a less pure sample, containing larger amounts of amorphous Si and P. The XRD and spectral features for this sample are also consistent with a less crystalline structure. Some of the Si is incorporated in the structure of the ferrihydrite. The Ca, P and possibly some of the Si may be biogenic. The spectral character of these Icelandic ferrihydrites is compared with those of synthetic ferrihydrites and other iron oxide/oxyhydroxide minerals. Ferrihydrite is characterized by a broad Fe3+ excitation band near 0.92 microns (approx. 10900/cm) and a strong Fe-O absorption feature near 475/cm (approx. 21 microns) in transmittance spectra. Multiple bands due to H2O and OH are also present for ferrihydrite. Natural ferrihydrites frequently exhibit a band near 950-1050/cm (approx. 10 microns) that is typically not observed for synthetic ferrihydrites and may be due to some Si in the structure. An additional pair of spectral bands near 1400 and 1500/cm (approx. 7 microns) are characteristic of pure ferrihydrites from natural and synthetic sources. Hydrothermal springs may have been present at one time on Mars in association with volcanic activity. Ferrihydrite formation in such an environment may have contributed to the ferric oxide-rich surface material on Mars.

Bishop, Janice↗