ABSTRACT: We present results from an ongoing two-year study at Mammoth Mountain, California. We t... more ABSTRACT: We present results from an ongoing two-year study at Mammoth Mountain, California. We track multiple layers, starting at a variety of initial conditions and subjected to different temperature gradients, from deposition to melt at two different sites. We examine samples with optical microscopy under cross-polarized light, with low-temperature scanning electron microscopy, and with an x-ray spectrometer. The neck ratio (bond diameter to grain radius) quickly approaches a value of 0.5-0.6. Density increases linearly throughout the ...
Isotopic variations measured within a single crystal of hydrated magnesium sulfate are greater th... more Isotopic variations measured within a single crystal of hydrated magnesium sulfate are greater than 30 permil for delta 2-H, almost 10 permil for delta18O in water of hydration; and greater than 3 permil in sulfate oxygen. These results are interpreted to indicate the relative humidity of the system during evaporation (15 to 20 percent in this test case) and constrain the volume of water involved. The theoretical basis of this system is the isotopic fractionation between the species in solution and those precipitated as evaporite salts. Precipitation preferentially accumulates more of the heavy isotopes of sulfur and oxygen in mineral sulfate, relative to sulfate in solution. During the course of mineral growth this leads to successive depletion of the respective heavier isotopes in the residual brine reflected in a parallel trend in successive precipitates or even in successive zones within a single crystal. The change in isotopic composition at any one time during the process, relative to the initial value, can be described by an isotopic version of the Rayleigh Fractionation equation, depending only on the extent of the completion of the process and the relevant fractionation factor. Evaporation preferentially removes isotopically lighter hydrogen and oxygen leading to successive extents of enrichment in the respective heavier isotopes in the residual water. However, the relative effects on hydrogen and oxygen isotopes differs as function of relative humidity [1]. ALL OF THESE CHANGES ARE PRESERVED IN THE MINERAL ISOTOPE COMPOSITIONS. We precipitated barium sulfate from epsomite or gypsum samples, which was reduced at 1450°C in the presence of graphite and glassy carbon in a Finnigan TC/EA to produce CO for O isotopic analysis in a Finnigan 253 mass spectrometer, while a separate subsample was oxidized to SO2 in a Costech Elemental Analyzer. However, to make progress with this approach we needed to make a large number of measurements of hydration water and so we developed a new analytical method [2]. We use a modification of the standard TC/EA continuous-flow protocol to measure both hydrogen and oxygen of water of hydration from the same small sample. We have proved the concept of this new approach by analyzing zones within crystals and individual grains, growing epsomite (magnesium sulfate heptahydrate) in the laboratory and by analysis of natural gypsum evaporites. We are now exploring the effects of varying the controlling parameters. Eventual application to Martian sulfates will reveal amount of water involved in sulfate formation, its isotopic composition(s) and details of the paleo-atmospheric humidity. [1] Gat JR and Gonfiantini R, (Eds) (1981) IAEA Technical Report Series. [2] Rohrssen MK, Brunner B Mielke RE and Coleman M (2008) Analyt. Chem. (in press).
TRIPLE OXYGEN ISOTOPES OF SULFATE AS A BIOSIGNATURE. K. Ziegler, M. L. Coleman, R. E. Mielke, E. ... more TRIPLE OXYGEN ISOTOPES OF SULFATE AS A BIOSIGNATURE. K. Ziegler, M. L. Coleman, R. E. Mielke, E. D. Young. Institute of Geophysics and Planetary Physics, University of California Los Angeles (UCLA), Los Angeles, CA 90095, USA, Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90095, USA (kziegler@ess.ucla.edu, eyoung@ess.ucla.edu), NASA Astrobiology Institute and Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA (randall.e.mielke@jpl.nasa.gov, max.coleman@jpl.nasa.gov).
ABSTRACT: We present results from an ongoing two-year study at Mammoth Mountain, California. We t... more ABSTRACT: We present results from an ongoing two-year study at Mammoth Mountain, California. We track multiple layers, starting at a variety of initial conditions and subjected to different temperature gradients, from deposition to melt at two different sites. We examine samples with optical microscopy under cross-polarized light, with low-temperature scanning electron microscopy, and with an x-ray spectrometer. The neck ratio (bond diameter to grain radius) quickly approaches a value of 0.5-0.6.
Few simple labeling methods exist for simultaneous fluorescence and electron microscopy of bacter... more Few simple labeling methods exist for simultaneous fluorescence and electron microscopy of bacteria and biofilms. Here we describe the synthesis, characterization, and application of fluorescent nanoparticle quantum dot (QD) conjugates to target microbial species, including difficult to label Gram-negative strains. These QD conjugates impart contrast for both environmental scanning electron microscopy (ESEM) and fluorescence microscopy, permitting observation of living and fixed bacteria and biofilms. We apply these probes for studying biofilms extracted from perennial cold springs in the Canadian High Arctic, which is a particularly challenging system. In these biofilms, sulfur-metabolizing bacteria live in close association with unusual sulfur mineral formations. Following simple labeling protocols with the QD conjugates, we are able to image these organisms in fully-hydrated samples and visualize their relationship to the sulfur minerals using both ESEM and fluorescence microscop...
Quantum dots (fluorescent semiconductor nanocrystals, QDs) have optical and physical properties t... more Quantum dots (fluorescent semiconductor nanocrystals, QDs) have optical and physical properties that make them superior to fluorescent dyes for detection of microorganisms in environmental samples, especially in the field or in flight instruments where optical instrumentation is limited. They are extremely bright, providing a significant fluorescent signal even upon excitation with low-power LEDs. Their absorbance is broad, but their emission spectra are narrow, allowing for many colours to be excited with a single light source and the resulting emission to be readily deconvolved without output filters. They are both fluorescent and electron-dense, permitting them to be used for both fluorescence and electron microscopy. They are resistant to electron radiation and the oxidants most likely to be found on Mars. The challenge for their use in a potential wet-chemistry instrument is two-fold: first, to coat them with specific organic ligands for targeting bacteria in a non-Earth-centric fashion. Second, to ensure their stability during transport and determine potential false-positive results that may arise due to environmental conditions. We present some results on labelling of biofilm samples from the Canadian High Arctic, and some future plans for improvement of labelling techniques and targets that will address the goals of near-term Mars missions.
We will report measurements of the attenuation properties of polycrystalline water ice and CO2 cl... more We will report measurements of the attenuation properties of polycrystalline water ice and CO2 clathrate hydrates samples obtained in the frequency range 3x10-6 to 10-2 Hz, which encompasses the tidal frequencies of Europa and Enceladus. Previous attenuation measurements obtained on a variety of planetary materials have demonstrated that the mechanisms driving attenuation in the frequency range 10-4 to 1 Hz are controlled by the same parameters controlling the creep properties of these materials: temperature, stress, microstructure (including grain size), and the presence of second-phase impurities. Thus, accurate control and characterization of the microstructure and composition of tested samples are key steps toward the development of empirical relationships describing the mechanical response of these materials. This is the reason why we have invested significant effort in the development of synthesis procedures for the production of our samples. Both water ice and clathrate hydrate samples are grown from H2O ice seeds, which are produced by grinding ice crystals pre-grown at -30°C from pure de-ionized liquid water. A high pressure - low temperature vessel, which achieves pressures up to 200 bars and temperatures within the range -50 - +50 °C, is used for the growth of clathrate hydrates. These are synthesized by reaction of ice seeds with CO2 at temperatures close to the melting point of ice in order to improve reaction kinetics. Characterization of the samples composition and microstructure is carried out via crossed-polarized cryo-microscopic observations, and via imaging with a Scanning Electron Microprobe equipped with a liquid - nitrogen cooled stage (CryoSEM). The Energy Dispersive Spectrometer capability of the SEM provides elemental composition for verification of the purity of the samples. For clathrate hydrates, Raman microspectroscopy is also used to ensure the homogeneity of sample composition. We will show that the grain size of the ice seeds is not affected by the transformation into clathrate hydrates. However, the sub-grain structure obviously undergoes significant changes, which might be reflected in the mechanical behavior. In order to remove microporosity, a compaction system has been implemented, which consists to the application of high pressures under vacuum and at very low temperatures. We will show the result of compaction experiments in terms of residual porosity and microstructure evolution. We will also present initial measurements on the attenuation properties of polycrystalline water ice and CO2 clathrate hydrates at the stress conditions and tidal frequencies approaching those of icy satellites such as Europa and Enceladus. Acknowledgements: We gratefully acknowledge C. McCarthy and H. Engelhardt for technical advise and support. MC is supported by a NASA Postdoctoral Fellowship, administered by Oak Ridge Associated Universities. This work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2009, California Institute of Technology. Government sponsorship acknowledged.
Laboratory experiments have been conducted to aid understanding of the global carbon cycle on Tit... more Laboratory experiments have been conducted to aid understanding of the global carbon cycle on Titan. In particular, we aim to understand how liquid hydrocarbons flow on and under its surface. A chamber has been built in order to simulate the conditions on Titan’s surface. There temperatures vary between 90 K at the winter pole to 94 K at the equator. At these temperatures both methane and ethane are in the liquid phase at pressures above the triple point. Although no rain has been observed by either the Cassini spacecraft or the Huygens probe, the presence of hydrocarbon clouds at the pole, along with river channels and lakes, suggest that liquids condense, fall and run on the surface. Our experiments reproduce these conditions. A pot of liquid hydrocarbons is maintained at a temperature of 92 K and drops form at the tip of a capillary. These drops fall onto an ice target placed on a stage whose temperature is controlled by the flow of liquid nitrogen. Different ice targets have been used: polycrystalline ice with different porosities, as well as single ice crystals. We will present the results of these experiments, which show that water ice can rapidly absorb a large amount of hydrocarbons. These experiments also suggest that the ice must be saturated in hydrocarbons before lakes start forming. During these experiments, no formation of methane or ethane clathrates has been observed, although the experiments are conducted within their stability field. The kinetics of clathrate formation is poorly known, but other experiments performed at higher pressure suggest that they would form rapidly on geological timescales. Titan’s upper crust could therefore be composed of ice saturated with liquid hydrocarbons lying on top of a layer of clathrates. The presence of this layer would influence Titan’s interior temperature profile since the conductivity of clathrates can be up to one order of magnitude smaller than that of water ice. This layer could be destabilized during volcanic or tectonic events that have affected Titan’s surface in a geologically recent past, providing a source for Titan’s atmospheric methane. This work has been carried out at the Jet Propulsion Laboratory-California Institute of Technology, under contract with NASA.
We present new techniques for the synthesis and the characterization of clathrate hydrates, as we... more We present new techniques for the synthesis and the characterization of clathrate hydrates, as well as preliminary mechanical measurements. We also compare the microstructure and the mechanical behavior of clathrate hydrate with that of water ice at the same conditions.
Meridiani Planum sediments formed in an acid environment and include jarosite and other evaporiti... more Meridiani Planum sediments formed in an acid environment and include jarosite and other evaporitic sulfate minerals. Nodular spheroidal concretions appear to have grown in situ and are predominantly hematite. The source of the Rio Tinto, S. Spain, drains an area of extensive sulfide mineralization and is dominated by acid mine drainage processes. The system is not a Mars analog but potentially similar processes of sulfide oxidation produce sulfate rich waters which feed into the river and precipitate a large range of evaporitic sulfates including jarosite. Iron oxide minerals associated with the evaporites are either dispersed or bedded but not nodular. The water compositions appear to be mixtures of a few discreet end-members: the two most significant occur in undiluted form as inputs to the river and are relevant to many such systems. They both have all sulfur totally oxidized as sulfate. The first is a bright red water, pH ~1.5, Fe/S 0.5 and 23 g/L iron which is greater than 95% Fe3+. Its sulfate oxygen isotope composition is +2‰SMOW and about +7‰, relative to the water O isotope composition. These data indicate pyrite oxidation by Fe3+ with O in sulfate coming mainly from water. The second end-member is a pale green water, pH ~0.7, Fe/S 0.7, 50 g/L iron present mainly as Fe2+ and O isotope composition of sulfate about +6‰SMOW , about +12.5‰ relative to the water O value. Oxygen in sulfate comes mainly from atmospheric oxygen resulting from pyrite oxidation by molecular oxygen dissolved in water. Although the Rio Tinto system reactions probably are microbiologically mediated (relevant genera have been identified there) similar processes could occur abiotically but more slowly. Meridiani Planum sediments and nodules can be described by a plausible set of similar end-member processes. The primary source of sulfate is oxidation of sulfides present in basalt (pyrite, FeS2 or pyrrhotite, FeS) and weathering would have produced oxidized sulfate rich solutions at low pH. Ground water migration could produce evaporitic ponds where various bedded sulfate mineral sediments could form. The intergranular pore-spaces would be water filled. Most terrestrial spheroidal nodular concretions form by radial diffusion in pore-water of a chemical component of a very different oxidation state from that of the surrounding water. A nodular concretion is most usually formed by the reaction of the diffusive component with others in the pore-water. There are two main possible reaction sets for formation of the Blueberries that are consistent with all current data. 1. Local concentrations of organic matter (pre-biotic or biotic) formed reduction spots in which a small amount of Fe3+ either in solution or from evaporite mineral salts, was reduced to Fe2+ and then diffused radially to form an iron oxide nodule by reaction with inwardly diffusing dissolved oxygen. 2. Similar local concentrations of organic matter could also have engendered sulfate reduction and consequent outward diffusion of dissolved sulfide reacted with iron in solution to produce an iron sulfide nodule, subsequently oxidized in situ to hematite (maybe via goethite). Our current work is successfully identifying chemical and stable isotopic characteristics for both microbial and abiotic modes of all relevant reactions.
A Titan chamber has been set up in order to investigate the physical and chemical behavior of dro... more A Titan chamber has been set up in order to investigate the physical and chemical behavior of drops of liquid methane and ethane with substrates of water ice. They imply that Titan’s subsurface must be saturated with liquid hydrocarbons.
We describe the results of fabrication and analysis of iron sulfide precipitated chimney-like str... more We describe the results of fabrication and analysis of iron sulfide precipitated chimney-like structures under anoxic hydrothermal conditions as a step toward understanding the structure and surface chemistry bringing about the emergence of life on any wet, rocky planet.
We will present measurements of the attenuation properties of CO2 clathrate hydrates and polycrys... more We will present measurements of the attenuation properties of CO2 clathrate hydrates and polycrystalline water ice. These laboratory data are necessary to support models of tidal heating within the icy shells of Europa and Enceladus. Particularly, the attenuation properties of clathrates, likely involved in Enceladus’ outgassing, remain unconstrained. Samples are synthesized from ice seeds with a grain size of 150 - 425 microns. Seeds of carbon dioxide clathrate hydrates are synthesized within a high pressure - low temperature vessel, by reaction of CO2 at 30-40 bars with the ice seeds at -10 to -1 °C. Solid samples are produced from the compaction of the seeds at -80 °C, under vacuum and at a 100-MPa pressure applied over several hours. The microstructure of the samples before and after testing is characterized by optical cryo-microscopy and by Cryo - Scanning Electron Microprobe (CryoSEM). The CryoSEM is equipped with an Energy Dispersive Spectrometer, which provides elemental composition of the samples. Microstructural evolution and potential changes in composition resulting from clathrate dissociation can be assessed with these techniques. Cyclic loading measurements are being conducted with the Planetary Tides Simulation Facility at JPL, a cryogenic uniaxial compression system, within the frequency range 3x10-6 - 10-3 Hz, which encompasses the orbital frequencies of Enceladus and Europa. We will compare and contrast the attenuation observed for clathrate hydrates and polycrystalline ice in order to characterize the microstructural mechanisms driving dissipation in these samples. We will address the implications of these new observations in the context of icy satellites. Acknowledgements: MC is supported by a NASA Postdoctoral Program Fellowship, administered by Oak Ridge Associated Universities. This work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2009, California Institute of Technology. Government sponsorship acknowledged.
Microbial pyrite oxidation experiments in spiked water and the triple oxygen isotopes of resultin... more Microbial pyrite oxidation experiments in spiked water and the triple oxygen isotopes of resulting sulfate suggest that Delta17OSO4 signatures can trace microbial vs. inorganic sulfate formation, and, therefore, have the potential as biosignature.
The triple isotopes of oxygen (Delta17O' = delta17O'-0.528 × delta18O' using logarith... more The triple isotopes of oxygen (Delta17O' = delta17O'-0.528 × delta18O' using logarithmic deltas) can trace the oxygen sources of sulfate produced during sulfide oxidation, an important biogeochemical process on Earth's surface and possibly also on Mars [1]. delta18OSO4 compositions are determined by the isotopic selectivity of the mechanism(s) responsible for their changes, and the delta18O value of the reactants (O2 vs. H2O). The relative proportional importance and contribution of each of those sources and mechanisms, as well as their associated isotopic fractionations, are not well understood. We are investigating the use of Delta 17O as a quantitative and qualitative tracer for the different processes and oxygen sources involved in sulfate production. Delta17O signatures are distinct fingerprints of these reservoirs, independent of fractionation factors that can be ambiguous. We conducted controlled abiotic and biotic (Acidithiobacillus ferrooxidans, A.f.) labora...
ABSTRACT: We present results from an ongoing two-year study at Mammoth Mountain, California. We t... more ABSTRACT: We present results from an ongoing two-year study at Mammoth Mountain, California. We track multiple layers, starting at a variety of initial conditions and subjected to different temperature gradients, from deposition to melt at two different sites. We examine samples with optical microscopy under cross-polarized light, with low-temperature scanning electron microscopy, and with an x-ray spectrometer. The neck ratio (bond diameter to grain radius) quickly approaches a value of 0.5-0.6. Density increases linearly throughout the ...
Isotopic variations measured within a single crystal of hydrated magnesium sulfate are greater th... more Isotopic variations measured within a single crystal of hydrated magnesium sulfate are greater than 30 permil for delta 2-H, almost 10 permil for delta18O in water of hydration; and greater than 3 permil in sulfate oxygen. These results are interpreted to indicate the relative humidity of the system during evaporation (15 to 20 percent in this test case) and constrain the volume of water involved. The theoretical basis of this system is the isotopic fractionation between the species in solution and those precipitated as evaporite salts. Precipitation preferentially accumulates more of the heavy isotopes of sulfur and oxygen in mineral sulfate, relative to sulfate in solution. During the course of mineral growth this leads to successive depletion of the respective heavier isotopes in the residual brine reflected in a parallel trend in successive precipitates or even in successive zones within a single crystal. The change in isotopic composition at any one time during the process, relative to the initial value, can be described by an isotopic version of the Rayleigh Fractionation equation, depending only on the extent of the completion of the process and the relevant fractionation factor. Evaporation preferentially removes isotopically lighter hydrogen and oxygen leading to successive extents of enrichment in the respective heavier isotopes in the residual water. However, the relative effects on hydrogen and oxygen isotopes differs as function of relative humidity [1]. ALL OF THESE CHANGES ARE PRESERVED IN THE MINERAL ISOTOPE COMPOSITIONS. We precipitated barium sulfate from epsomite or gypsum samples, which was reduced at 1450°C in the presence of graphite and glassy carbon in a Finnigan TC/EA to produce CO for O isotopic analysis in a Finnigan 253 mass spectrometer, while a separate subsample was oxidized to SO2 in a Costech Elemental Analyzer. However, to make progress with this approach we needed to make a large number of measurements of hydration water and so we developed a new analytical method [2]. We use a modification of the standard TC/EA continuous-flow protocol to measure both hydrogen and oxygen of water of hydration from the same small sample. We have proved the concept of this new approach by analyzing zones within crystals and individual grains, growing epsomite (magnesium sulfate heptahydrate) in the laboratory and by analysis of natural gypsum evaporites. We are now exploring the effects of varying the controlling parameters. Eventual application to Martian sulfates will reveal amount of water involved in sulfate formation, its isotopic composition(s) and details of the paleo-atmospheric humidity. [1] Gat JR and Gonfiantini R, (Eds) (1981) IAEA Technical Report Series. [2] Rohrssen MK, Brunner B Mielke RE and Coleman M (2008) Analyt. Chem. (in press).
TRIPLE OXYGEN ISOTOPES OF SULFATE AS A BIOSIGNATURE. K. Ziegler, M. L. Coleman, R. E. Mielke, E. ... more TRIPLE OXYGEN ISOTOPES OF SULFATE AS A BIOSIGNATURE. K. Ziegler, M. L. Coleman, R. E. Mielke, E. D. Young. Institute of Geophysics and Planetary Physics, University of California Los Angeles (UCLA), Los Angeles, CA 90095, USA, Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90095, USA (kziegler@ess.ucla.edu, eyoung@ess.ucla.edu), NASA Astrobiology Institute and Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA (randall.e.mielke@jpl.nasa.gov, max.coleman@jpl.nasa.gov).
ABSTRACT: We present results from an ongoing two-year study at Mammoth Mountain, California. We t... more ABSTRACT: We present results from an ongoing two-year study at Mammoth Mountain, California. We track multiple layers, starting at a variety of initial conditions and subjected to different temperature gradients, from deposition to melt at two different sites. We examine samples with optical microscopy under cross-polarized light, with low-temperature scanning electron microscopy, and with an x-ray spectrometer. The neck ratio (bond diameter to grain radius) quickly approaches a value of 0.5-0.6.
Few simple labeling methods exist for simultaneous fluorescence and electron microscopy of bacter... more Few simple labeling methods exist for simultaneous fluorescence and electron microscopy of bacteria and biofilms. Here we describe the synthesis, characterization, and application of fluorescent nanoparticle quantum dot (QD) conjugates to target microbial species, including difficult to label Gram-negative strains. These QD conjugates impart contrast for both environmental scanning electron microscopy (ESEM) and fluorescence microscopy, permitting observation of living and fixed bacteria and biofilms. We apply these probes for studying biofilms extracted from perennial cold springs in the Canadian High Arctic, which is a particularly challenging system. In these biofilms, sulfur-metabolizing bacteria live in close association with unusual sulfur mineral formations. Following simple labeling protocols with the QD conjugates, we are able to image these organisms in fully-hydrated samples and visualize their relationship to the sulfur minerals using both ESEM and fluorescence microscop...
Quantum dots (fluorescent semiconductor nanocrystals, QDs) have optical and physical properties t... more Quantum dots (fluorescent semiconductor nanocrystals, QDs) have optical and physical properties that make them superior to fluorescent dyes for detection of microorganisms in environmental samples, especially in the field or in flight instruments where optical instrumentation is limited. They are extremely bright, providing a significant fluorescent signal even upon excitation with low-power LEDs. Their absorbance is broad, but their emission spectra are narrow, allowing for many colours to be excited with a single light source and the resulting emission to be readily deconvolved without output filters. They are both fluorescent and electron-dense, permitting them to be used for both fluorescence and electron microscopy. They are resistant to electron radiation and the oxidants most likely to be found on Mars. The challenge for their use in a potential wet-chemistry instrument is two-fold: first, to coat them with specific organic ligands for targeting bacteria in a non-Earth-centric fashion. Second, to ensure their stability during transport and determine potential false-positive results that may arise due to environmental conditions. We present some results on labelling of biofilm samples from the Canadian High Arctic, and some future plans for improvement of labelling techniques and targets that will address the goals of near-term Mars missions.
We will report measurements of the attenuation properties of polycrystalline water ice and CO2 cl... more We will report measurements of the attenuation properties of polycrystalline water ice and CO2 clathrate hydrates samples obtained in the frequency range 3x10-6 to 10-2 Hz, which encompasses the tidal frequencies of Europa and Enceladus. Previous attenuation measurements obtained on a variety of planetary materials have demonstrated that the mechanisms driving attenuation in the frequency range 10-4 to 1 Hz are controlled by the same parameters controlling the creep properties of these materials: temperature, stress, microstructure (including grain size), and the presence of second-phase impurities. Thus, accurate control and characterization of the microstructure and composition of tested samples are key steps toward the development of empirical relationships describing the mechanical response of these materials. This is the reason why we have invested significant effort in the development of synthesis procedures for the production of our samples. Both water ice and clathrate hydrate samples are grown from H2O ice seeds, which are produced by grinding ice crystals pre-grown at -30°C from pure de-ionized liquid water. A high pressure - low temperature vessel, which achieves pressures up to 200 bars and temperatures within the range -50 - +50 °C, is used for the growth of clathrate hydrates. These are synthesized by reaction of ice seeds with CO2 at temperatures close to the melting point of ice in order to improve reaction kinetics. Characterization of the samples composition and microstructure is carried out via crossed-polarized cryo-microscopic observations, and via imaging with a Scanning Electron Microprobe equipped with a liquid - nitrogen cooled stage (CryoSEM). The Energy Dispersive Spectrometer capability of the SEM provides elemental composition for verification of the purity of the samples. For clathrate hydrates, Raman microspectroscopy is also used to ensure the homogeneity of sample composition. We will show that the grain size of the ice seeds is not affected by the transformation into clathrate hydrates. However, the sub-grain structure obviously undergoes significant changes, which might be reflected in the mechanical behavior. In order to remove microporosity, a compaction system has been implemented, which consists to the application of high pressures under vacuum and at very low temperatures. We will show the result of compaction experiments in terms of residual porosity and microstructure evolution. We will also present initial measurements on the attenuation properties of polycrystalline water ice and CO2 clathrate hydrates at the stress conditions and tidal frequencies approaching those of icy satellites such as Europa and Enceladus. Acknowledgements: We gratefully acknowledge C. McCarthy and H. Engelhardt for technical advise and support. MC is supported by a NASA Postdoctoral Fellowship, administered by Oak Ridge Associated Universities. This work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2009, California Institute of Technology. Government sponsorship acknowledged.
Laboratory experiments have been conducted to aid understanding of the global carbon cycle on Tit... more Laboratory experiments have been conducted to aid understanding of the global carbon cycle on Titan. In particular, we aim to understand how liquid hydrocarbons flow on and under its surface. A chamber has been built in order to simulate the conditions on Titan’s surface. There temperatures vary between 90 K at the winter pole to 94 K at the equator. At these temperatures both methane and ethane are in the liquid phase at pressures above the triple point. Although no rain has been observed by either the Cassini spacecraft or the Huygens probe, the presence of hydrocarbon clouds at the pole, along with river channels and lakes, suggest that liquids condense, fall and run on the surface. Our experiments reproduce these conditions. A pot of liquid hydrocarbons is maintained at a temperature of 92 K and drops form at the tip of a capillary. These drops fall onto an ice target placed on a stage whose temperature is controlled by the flow of liquid nitrogen. Different ice targets have been used: polycrystalline ice with different porosities, as well as single ice crystals. We will present the results of these experiments, which show that water ice can rapidly absorb a large amount of hydrocarbons. These experiments also suggest that the ice must be saturated in hydrocarbons before lakes start forming. During these experiments, no formation of methane or ethane clathrates has been observed, although the experiments are conducted within their stability field. The kinetics of clathrate formation is poorly known, but other experiments performed at higher pressure suggest that they would form rapidly on geological timescales. Titan’s upper crust could therefore be composed of ice saturated with liquid hydrocarbons lying on top of a layer of clathrates. The presence of this layer would influence Titan’s interior temperature profile since the conductivity of clathrates can be up to one order of magnitude smaller than that of water ice. This layer could be destabilized during volcanic or tectonic events that have affected Titan’s surface in a geologically recent past, providing a source for Titan’s atmospheric methane. This work has been carried out at the Jet Propulsion Laboratory-California Institute of Technology, under contract with NASA.
We present new techniques for the synthesis and the characterization of clathrate hydrates, as we... more We present new techniques for the synthesis and the characterization of clathrate hydrates, as well as preliminary mechanical measurements. We also compare the microstructure and the mechanical behavior of clathrate hydrate with that of water ice at the same conditions.
Meridiani Planum sediments formed in an acid environment and include jarosite and other evaporiti... more Meridiani Planum sediments formed in an acid environment and include jarosite and other evaporitic sulfate minerals. Nodular spheroidal concretions appear to have grown in situ and are predominantly hematite. The source of the Rio Tinto, S. Spain, drains an area of extensive sulfide mineralization and is dominated by acid mine drainage processes. The system is not a Mars analog but potentially similar processes of sulfide oxidation produce sulfate rich waters which feed into the river and precipitate a large range of evaporitic sulfates including jarosite. Iron oxide minerals associated with the evaporites are either dispersed or bedded but not nodular. The water compositions appear to be mixtures of a few discreet end-members: the two most significant occur in undiluted form as inputs to the river and are relevant to many such systems. They both have all sulfur totally oxidized as sulfate. The first is a bright red water, pH ~1.5, Fe/S 0.5 and 23 g/L iron which is greater than 95% Fe3+. Its sulfate oxygen isotope composition is +2‰SMOW and about +7‰, relative to the water O isotope composition. These data indicate pyrite oxidation by Fe3+ with O in sulfate coming mainly from water. The second end-member is a pale green water, pH ~0.7, Fe/S 0.7, 50 g/L iron present mainly as Fe2+ and O isotope composition of sulfate about +6‰SMOW , about +12.5‰ relative to the water O value. Oxygen in sulfate comes mainly from atmospheric oxygen resulting from pyrite oxidation by molecular oxygen dissolved in water. Although the Rio Tinto system reactions probably are microbiologically mediated (relevant genera have been identified there) similar processes could occur abiotically but more slowly. Meridiani Planum sediments and nodules can be described by a plausible set of similar end-member processes. The primary source of sulfate is oxidation of sulfides present in basalt (pyrite, FeS2 or pyrrhotite, FeS) and weathering would have produced oxidized sulfate rich solutions at low pH. Ground water migration could produce evaporitic ponds where various bedded sulfate mineral sediments could form. The intergranular pore-spaces would be water filled. Most terrestrial spheroidal nodular concretions form by radial diffusion in pore-water of a chemical component of a very different oxidation state from that of the surrounding water. A nodular concretion is most usually formed by the reaction of the diffusive component with others in the pore-water. There are two main possible reaction sets for formation of the Blueberries that are consistent with all current data. 1. Local concentrations of organic matter (pre-biotic or biotic) formed reduction spots in which a small amount of Fe3+ either in solution or from evaporite mineral salts, was reduced to Fe2+ and then diffused radially to form an iron oxide nodule by reaction with inwardly diffusing dissolved oxygen. 2. Similar local concentrations of organic matter could also have engendered sulfate reduction and consequent outward diffusion of dissolved sulfide reacted with iron in solution to produce an iron sulfide nodule, subsequently oxidized in situ to hematite (maybe via goethite). Our current work is successfully identifying chemical and stable isotopic characteristics for both microbial and abiotic modes of all relevant reactions.
A Titan chamber has been set up in order to investigate the physical and chemical behavior of dro... more A Titan chamber has been set up in order to investigate the physical and chemical behavior of drops of liquid methane and ethane with substrates of water ice. They imply that Titan’s subsurface must be saturated with liquid hydrocarbons.
We describe the results of fabrication and analysis of iron sulfide precipitated chimney-like str... more We describe the results of fabrication and analysis of iron sulfide precipitated chimney-like structures under anoxic hydrothermal conditions as a step toward understanding the structure and surface chemistry bringing about the emergence of life on any wet, rocky planet.
We will present measurements of the attenuation properties of CO2 clathrate hydrates and polycrys... more We will present measurements of the attenuation properties of CO2 clathrate hydrates and polycrystalline water ice. These laboratory data are necessary to support models of tidal heating within the icy shells of Europa and Enceladus. Particularly, the attenuation properties of clathrates, likely involved in Enceladus’ outgassing, remain unconstrained. Samples are synthesized from ice seeds with a grain size of 150 - 425 microns. Seeds of carbon dioxide clathrate hydrates are synthesized within a high pressure - low temperature vessel, by reaction of CO2 at 30-40 bars with the ice seeds at -10 to -1 °C. Solid samples are produced from the compaction of the seeds at -80 °C, under vacuum and at a 100-MPa pressure applied over several hours. The microstructure of the samples before and after testing is characterized by optical cryo-microscopy and by Cryo - Scanning Electron Microprobe (CryoSEM). The CryoSEM is equipped with an Energy Dispersive Spectrometer, which provides elemental composition of the samples. Microstructural evolution and potential changes in composition resulting from clathrate dissociation can be assessed with these techniques. Cyclic loading measurements are being conducted with the Planetary Tides Simulation Facility at JPL, a cryogenic uniaxial compression system, within the frequency range 3x10-6 - 10-3 Hz, which encompasses the orbital frequencies of Enceladus and Europa. We will compare and contrast the attenuation observed for clathrate hydrates and polycrystalline ice in order to characterize the microstructural mechanisms driving dissipation in these samples. We will address the implications of these new observations in the context of icy satellites. Acknowledgements: MC is supported by a NASA Postdoctoral Program Fellowship, administered by Oak Ridge Associated Universities. This work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2009, California Institute of Technology. Government sponsorship acknowledged.
Microbial pyrite oxidation experiments in spiked water and the triple oxygen isotopes of resultin... more Microbial pyrite oxidation experiments in spiked water and the triple oxygen isotopes of resulting sulfate suggest that Delta17OSO4 signatures can trace microbial vs. inorganic sulfate formation, and, therefore, have the potential as biosignature.
The triple isotopes of oxygen (Delta17O' = delta17O'-0.528 × delta18O' using logarith... more The triple isotopes of oxygen (Delta17O' = delta17O'-0.528 × delta18O' using logarithmic deltas) can trace the oxygen sources of sulfate produced during sulfide oxidation, an important biogeochemical process on Earth's surface and possibly also on Mars [1]. delta18OSO4 compositions are determined by the isotopic selectivity of the mechanism(s) responsible for their changes, and the delta18O value of the reactants (O2 vs. H2O). The relative proportional importance and contribution of each of those sources and mechanisms, as well as their associated isotopic fractionations, are not well understood. We are investigating the use of Delta 17O as a quantitative and qualitative tracer for the different processes and oxygen sources involved in sulfate production. Delta17O signatures are distinct fingerprints of these reservoirs, independent of fractionation factors that can be ambiguous. We conducted controlled abiotic and biotic (Acidithiobacillus ferrooxidans, A.f.) labora...
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Papers by Randall Mielke