MR13A-1692
Liquid water in small solar system bodies, and the possibilities for evolution of life
Much attention has been focused on the few large satellites of Jupiter and Saturn that have evidence of interior layers of liquid water, and the possibility that they may be suitable habitats for life. For life to evolve in these regions, they would have to, at a minimum, produce the necessary chemical constituents to provide energy for building organic matter, be protected from temperature extremes and radiation, and last long enough for evolution to progress. The type of organisms that could form in such habitats could be similar to those that evolved in the pre-photosynthetic, anoxic early Earth. The probability of extra-terrestrial life evolving in our solar system would increase greatly if such suitable habitats had been more common. We examine the possibilities for suitable habitats in the more numerous set of moderate-sized (< 1000 km in diameter) ice-rich planetesimals that may populate the Asteroid Belt and Kuiper Belt. We modeled the thermal evolution of 200-1000 km planetesimals, assuming cold accretion of undifferentiated bodies comprised of a mixture of chondritic rock and water ice. The heat sources for these planetesimals are short- and long-lived radioactive isotopes, and the latent heat from hydration reactions. We vary the planetesimals initial size, surface temperature, ice/rock ratio and the 26Al content (which is very sensitive to the timing of accretion). Each modeled planetesimal undergoes a pulse of radioactive heating, followed by slow cooling. Some water from the melting ice phase migrates upward to form an "internal ocean" layer beneath a still frozen crust, while some water reacts with the remaining rock to form a hydrated silicate (serpentinized) core. In warmer planetesimals, these hydrated silicates can break-down, and a second phase of water production and migration occurs. If the frozen rock/ice crust becomes too thin, we assume that crustal overturn will result in loss of any underlying liquid. Many models produce liquid water layers lasting hundreds of millions of years. These water layers overlay a large core of serpentinzing silicate, which would be producing hydrogen, methane, sulfate and possibly complex organics to the water layer. We will explore the possible biogeochemical cycling that could develop in these systems.
MR13A-1693
Experimental Synthesis of Organic Compounds From Inorganic Materials by the Simulated Impact on the Early Earth
How to prepare prebiotic organic molecules on the early Earth has been debated vigorously. One of points of debates is how to overcome the difficulty to produce prebiotic organic molecules under moderately oxidizing CO2 and N2-rich early atmosphere. Previous investigators suggested the existence of early oceans well before 4.0 Ga, late heavy bombardments at around 4.0 Ga, and the earliest life at 3.8 Ga. In order to connect these geological evidences, we hypothesized that meteorite impacts, which brought many reductants, on the early oceans followed by interaction with the atmosphere were responsible for production of prebiotic organic molecules. In order to simulate the impact reaction, we performed shock-recovery experiments with single-stage propellant gun. The shocked materials are composed of mixture of iron, nickel, carbon, water and gaseous nitrogen or dissolved ammonia. The carbon in the starting materials is enriched in 99% of 13C so that the C-bearing products can be distinguished from contaminants. These mixtures were encapsulated in metal containers and then shocked with impact velocities of 1 km/s. Analyses of the experimental products were performed using the state-of-the-art LC/MS and GC/MS. Various organic molecules including bio molecules composed only of 13C are detected, verifying syntheses of those organic molecules during the shock experiments. This result further suggests that the late heavy bombardment on the early oceans, dynamic high-pressure conditions, triggered to form a large mass and variety of prebiotic organic molecules on the early Earth.
MR13A-1694
Polymerization of amino acids under high-pressure conditions: Implication to chemical evolution on the early Earth
Prebiotic polymerization of amino acids is the most fundamental reaction to promote the chemical evolution for origin of life. Polymerization of amino acids is the dehydration reaction. This questions as to if submarine hydrothermal conditions, thus hydrated enironments, were appropreate for peptide formations. Our previous experiments implied that non-aqueous and high-pressure environments (more than 20 MPa) would be suitable for polymerization of amino acids (Ohara et al., 2006). This leads to the hypothesis that the first peptides may have formed in the Hadean oceanic crustal environments, where dehydration proceeded with availability of appropriate temperatures and pressures. In the present study, experiments simulating the crustal conditions were performed with various pressures (1-175 MPa) and temperatures (100- 200 C degree) using autoclaves. Purified powders (100 mg) of alanine, glycine, valine and aspartic acid were used in the experiments without mixing water in order to examine the solid-solid reactions. The products were analyzed using HPLC and LC-MS. Results indicate that: (1) longer time is required to form peptide compared to those of previous aqueous experiments; (2) pressure has a role to limit the production of melanoidine and cyclic amino acids, which are inhibitors for elongation of peptides; (3) glycine was polymerized up to 11-mer, which was not formed in any previous experiments without catalyses; (4) valine was polymerized up to 3-mer; and (5) aspartic acid was polymerized to 4-mer, accompanied with production of other amino acids. It is noteworthy that high-pressure environments favor all examined polymerization reactions. Such situations would have happened inside of deep oceanic crusts of the early Earth.
MR13A-1695
Metabolic Activity of Bacteria at High Pressure
Over the last 20 years, there has been increasing evidence for the presence of a large number of microbes in the oceanic subsurface. Such a habitat has a very low energy input because it is deprived of light. A few meters below the sediment surface, conditions are already anoxic in most cases, sulfate reduction and/or methanogenesis becoming thus the primary respiratory reactions of organic matter. Neither the fate of methanogenesis, nor the fate of Dissimilatory Metal-Reduction (DMR) has been investigated so far as a function of pressure. For this reason, we measured experimentally the pressure limits of microbial anaerobic energetic metabolism. In practice, we measured in situ the kinetics of selenite respiration by the bacterial model Shewanella oneidensis MR-1 under high hydrostatic pressure (HHP) between 0 and 150 MPa at 30°C. MR-1 stationary-phase cells were used in Luria-Bertani (LB) medium amended with lactate as an additional electron donor and sodium selenite as an electron acceptor. In situ measurements were performed by X- ray Absorption Near-Edge Structure (XANES) spectroscopy in both a diamond-anvil cell and an autoclave. A red precipitate of amorphous Se(0) was virtually observed at any pressure to 150 MPa. A progressive reduction of selenite Se(IV) into selenium Se(0) was also observed in the evolution of XANES spectra with time. All kinetics between 0.1 and 150 MPa can be adjusted to a first order kinetic law. MR-1 respires all available selenite up to 60 MPa. Above 60 MPa, the respiration yield decreases linearly as a function of pressure and reaches 0 at 155 ±5 MPa. This indicates that selenite respiration by Shewanella oneidensis MR-1 stops at about 155 MPa, whereas its growth is arrested at 50 MPa. Hence, the present results show that the respiration of selenium by the strain MR-1 occurs efficiently up to 60 MPa and 30°C, i.e. from the surface of a continental sediment to an equivalent depth of about 2 km, or beneath a 5-km water column and a depth of marine sediment of 500 m, or even beneath a water column of 6 km in surface sediments. This suggests that the metabolic activity of surface microorganisms that receive nutrients through sea water percolation into the deeper parts of the sediment, or that sink with the sediment, may represent a significant fraction of the total activity observed in subsurface environments. The present results indicate also that cells in stationary phase at HHP, which preclude growth, can still have a short-term metabolic activity independent of the growth-related activity. Consequently, surface microorganisms have the ability to impact significantly and rapidly on biogeochemical cycles in deep environments.
MR13A-1696
Isothermal compression of ice at 870 K
A recent 300 K compression study on H2O ice demonstrated that the ice changes its compressibility at 40 and 60 GPa, possibly due to the phase transitions of ice VII to dynamically disordered ice VII, and subsequently to dynamically disordered ice X (Sugimura et al., 2008, Phys. Rev. B). An intermediate phase, dynamically disordered ice VII, is highly compressible, while dynamically disordered ice X has much smaller compressibility. Here, we conducted high temperature compression experiments of H2O ice from 29 to 63 GPa at a constant temperature of 863 - 874 K at the beamline BL10XU, SPring-8. High pressure and temperature conditions were generated in an externally heated diamond anvil cell. The isothermal volume compression was examined relatively to the room temperature volume of ice VII determined from the equation of state introduced by the previous compression study. The volumes above 45 GPa at 870 K cannot be explained by the equation of state of ice VII evaluated from the volumes at relatively low P-T. In addition, ice is highly compressible from 45 to 55 GPa, and becomes less compressible above 55 GPa, compared to ice VII. The anomalous volume reduction beginning at 45 GPa is most likely associated with the phase transition of ice VII to dynamically disordered ice VII. The volumes of ice above 55 GPa at 870 K is over 5% larger than those of dynamically disordered ice X at 300 K. Such a large volume increase cannot be explained with a thermal expansion. It is plausible that the less compressible ice at 870 K is not dynamically disordered ice X, possibly suggesting a new phase.
MR13A-1697
Phase Relations and Properties of Salty ices VI and VII: Implications for Solar System Ices
Ice VI and ice VII may be important in the interiors of Europa, Ganymede, Callisto and Titan. Oceans and interior pore waters in these bodies likely contain dissolved salts. To address the role of salt on ice VI and ice VII, we investigated phase equilibria in the system H2O -NaCl at 1 molal (5.5 wt%) NaCl in an externally heated diamond-anvil cell. Phase identifications were made by optical microscopy combined with Raman spectroscopy. Experiments were conducted at 22-150°C and up to 5 GPa by allowing the cell to thermally equilibrate at a given temperature and then varying pressure isothermally while observing phase changes. The liquidus curves of ice VI and ice VII in a 5.5 wt% NaCl solution were determined. Melting was observed from 22 to 80°C (ice VI) and from 35 to 150°C (ice VII). Both melting curves are steeper than the respective NaCl-free curves, indicating that the freezing-point depression at this bulk composition increases with pressure. The intersection of the two liquidus curves indicates that VI-VII-liquid triple point is shifted toward lower T and higher P relative to pure H2O. The 5.5 wt% NaCl bulk composition crystallizes into a single solid phase of NaCl-bearing ice VI or ice VII solid solution over the investigated T range (the subscript 'ss' indicates solid solution). Large single crystals of ice VIss or ice VIIss can also be grown by slow compression of the cell from near-liquidus conditions to the solidus. Raman spectra of these crystals clearly show zoning in these crystals. The zoning persists for days at 22°C, indicating relatively slow Na+ and Cl- diffusivity. The large depression of the freezing point in a 1 molal NaCl solution has important implications for the oceans and interiors of the icy satellites of Jupiter and Saturn. Salty fluids may remain stable to much greater depth than expected. This would promote extensive hydrothermal metamorphism of the silicate interiors. If not limited to ice VI and VII, this behavior may suppress formation of ices at the bottoms of deep oceans in Titan and the Galilean satellites. The observation that ices VI and VII form solid solutions with NaCl from 22 to 150°C is also important. The qualitative inference of low Na+ and Cl- diffusivity suggests that compositional gradients could persist over at least modest time scales in these ices. Moreover, the presence of NaCl in ice VI and VII will likely reduce their viscosity and increase electrical conductivity.
MR13A-1698
The ice VII-ice X phase transition with implications for planetary interiors
A significant amount of research on the high pressure polymorphs of H2O have detailed the lattice structure and density of these phases, namely ice VI, ice VII, and ice X. These high pressure ices are noteworthy as they may comprise a considerable part of the interior of large icy planets and satellites. However, there is a dearth of data on how the incorporation of an impurity, charged or non-charged, affects the ice VII-ice X transition. This study examined the ice VII-ice X transition that occurs at approximately 62 GPa with a pure system and two select impure systems. Solutions of pure H2O, 1.6 mole percent NaCl in H2O, and 1.60 mole percent CH3OH in H2O were compressed in a diamond anvil cell (DAC). The experiments were performed at the GSECARS 13-BM-D beam line at the Advanced Photon Source at Argonne National Laboratory. Powder diffraction data of the ice samples were collected using monochromatic X-ray radiation, 0.2755 Å, and a MAR 345 online imaging system at intervals of approximately 2 GPa up to ~71.5, ~74.5, and ~68 GPa, respectively. Analyses of the data provided volume-pressure relations (at 298 K) which were used to detail the ice VII-ice X phase transition. The pressure of the phase transition, based upon an interpretation of the X-ray diffraction data, was found to vary as a function of the impurity type. Thus, the depth of the ice VII-ice X phase transition within an ice-rich planetary body can be influenced by trace-level impurities.
MR13A-1699
Thermal conductivity of ice VII using the time-domain thermo-reflectance method in the diamond anvil cell: Implications for the icy planetary bodies
As a planetary body ages, the heat trapped and generated in its interior escapes to the surface. Thermal conductivity is a fundamental parameter that governs the thermal evolution and internal dynamics of the planetary body. Due to exceedingly small sample size under high pressure, measuring the thermal conductivity of compressed solids is challenging. Here we report new experimental data on the thermal conductivity of liquid H2O and ice VII up to 11 GPa and at 300 K, using the time-domain thermo- reflectance technique (TDTR) and the diamond anvil cell. The measurements were carried out at the Material Research Laboratory, University of Illinois. We load ruby balls as the pressure marker and a mica sheet as a thermal insulating layer. A thin film of aluminum (Al) is coated on the mica sheet and served as a transducer (Antonelli et al., 2006). A short optical pump pulse with duration ~ 100 fs and energy ~ 1 nJ is focused to a ~10 micron-diameter spot on the Al film, raising its temperature by several degrees Kelvin, which in turn causes a slight change in reflectivity. Over the next few nanoseconds following the absorption of the pulse, the Al film cools via heat conduction through the film itself, across the interface, and into the sample. From time-dependent measurement of reflectivity, we can extract the value of the thermal conductivity of the sample by modeling one-dimensional heat flow. With increasing pressure, liquid H2O crystallized into multiple grains of tetragonal ice VI. Upon further compression to ~ 3.3 GPa, the grain boundaries disappeared due to the formation of the cubic ice VII. We have determined the effect of pressure on the thermal conductivity of ice VII between 3 and 11 GPa. We will discuss the implications of our data for the thermal evolution of icy planetary bodies where ice VII may be a significant component.
MR13A-1700
New Optical Constants of Amorphous and Crystalline H2O-ice, 3-20 micrometers
We will present new optical constants for the amorphous and crystalline H2O-ice in the spectral range 3-20 μm. Our new measurements provide high temperature resolution for crystalline H2O-ice, 10 K intervals from 20-150 K, including temperatures relevant to Solar System ices. We have found that the shape of the 3 μm feature in amorphous H2O-ice is strongly dependant on deposition temperature and the high and low density phases of amorphous H2O-ice are not easily distinguishable. We will present methods of measuring the change in band shape with phase and temperature. We acknowledge financial support from the NASA Origins of the Solar System Program and the NASA Planetary Geology and Geophysics Program.
MR13A-1701
Elasto-Viscoplastic Micromechanical Modelling of the Transient Creep of Ice
There are significant issues in Geophysics related to the elasto-viscoplastic behavior of polycrystalline materials such as ice and minerals. One can evoke for example the post-seismic deformations in fault regions due to the viscoelastic behavior of the lower crust and/or the upper mantle, the uplift of continents associated to post-glacial rebound, the attenuation of seismic waves associated to viscous dissipation along the travel path of the wave, and more generally all situations in which the mechanical response of the material involves both elasticity and viscoplasticity. For ice, transient effects associated to the elasto- viscoplastic behavior are encountered when ice flow changes direction rapidly, such as for glaciers flowing above irregular bedrocks or for sea-ice coming up against an off-shore rig. Besides those geophysical issues, applying recent micromechanical approaches to the transient creep response of ice, as in this first study, is highly valuable for understanding the elementary deformation mechanisms, such as glide and climb of dislocations. A salient feature of the rheology of polycrystalline ice is the decrease of the strain-rate by more than two orders of magnitude during transient creep, to reach a secondary creep regime at a strain which is systematically of ~ 1%. We use a recent mean-field micromechanical model, which aims at bridging scales between the rheology of single grain and the one of polycrystals by evaluating the intergranular interactions as deformation proceeds. The model takes into account the long-term memory effects which manifests itself by the fact that local stress and strain-rate in grains depend on the whole mechanical history of the polycrystal. It is shown that the strong hardening amplitude during the transient creep is entirely explained by the stress redistribution within in the different grains of the specimen, whereas the experimentally observed hardening kinetic is much too slow to be explained by the same process. This latter is attributed to the hardening of hard glide slip systems (prismatic slip) in the transient regime. Moreover, the model very well reproduces the permanent creep-rate of several highly anisotropic specimens of the GRIP ice core (Greenland) exhibiting pronounced crystallographic textures, when accounting for a single grain rheology that well matches the experimental one. Our results are also consistent with recent findings on dislocation dynamics in ice.
MR13A-1702
Preliminary Measurements on the Mechanical Properties of Clathrate Hydrates with Implications for the Internal Dynamics of Icy Satellites
Surface features potentially associated with cryovolcanism have been identified on Titan, and the processes taking place beneath the surface are likely associated with the dissociation of clathrate hydrates and the release of methane. On Enceladus, the South Pole plume discovered by the Cassini-Huygens mission contains a large proportion of volatiles, in amounts consistent with models of clathrate hydrates dissociation at depth (Kieffer et al., Science 314, 1764-1766, 2006). The stability of clathrate hydrates is relatively well constrained in pure and mixed gas systems (e.g., Sloan, Clathrate hydrates of natural gases, Marcel Dekker, New York, 1998). Recent measurements of clathrate destabilization in presence of ammonia, a likely component of Titan's interior, led to the development of a new model of cryovolcanism (Choukroun et al., Lunar Planet. Sci. Conf., #1837, Houston, 2008). Internal dynamics relies on ice convection at depth on Titan and Enceladus (e.g., Tobie et al., Icarus 175, 496-502, 2005), and on relatively large tidal stresses on Enceladus. Clathrates are expected to destabilize when subject to stress (Durham et al., J. Geophys. Res. 108 (B4), 2182, 2003). Therefore, addressing the mechanical properties of clathrate hydrates in these environments is a necessary step toward better understanding cryovolcanic processes. We have developed a new apparatus for growing clathrate hydrates samples with controlled geometry, composition, and grain size. This system consists of a high-pressure autoclave and a cooling system and supports gas pressures up to 500 bars, and temperatures within the range -50 – 150 °C. We have started the production of clathrate hydrates of CH4, CO2, and N2 with this system, with the purpose to test their mechanical properties using an Instron compression system (Castillo-Rogez et al., submitted to J. Geophys. Res.; Castillo-Rogez et al., this meeting). We will present initial measurements on the creep response and on the viscoelastic response of clathrate hydrates as a function of frequency. These measurements will provide new information on the behavior of clathrate hydrates during dynamic motions within icy satellites.
MR13A-1703
Clathrates from Carbonates: New In-Situ Observations of Carbonate-Derived Methane at Mantle Pressures
It has previously been shown that carbonate minerals, such as calcite, can be reduced at mantle pressures and temperatures in the presence of FeO and H2O to produce methane (Scott et al., 2004). We have performed new experiments in the Fe-calcite-H2O system at pressures from 2 to 10 GPa and temperatures from 500 to 2000 °C. We used both laser and resistively heated diamond anvil cells for all experiments and a combination of Raman spectroscopy and synchrotron X-ray diffraction for analysis. Our motivation was to explore a more reducing system than previous experiments in order to favor the methane-forming reaction. We were particularly interested to see if, by improving the methane yield, we can detect the formation of heavier hydrocarbons. As expected, by using Fe rather than FeO as the reducing agent, we observe increased methane production as indicated by Raman spectroscopy. Powder X-ray diffraction data confirm previous results that the oxidation of iron at these conditions produces magnetite. We also detect Ca(OH)2 and a few diffraction lines from an as yet unidentified phase. Furthermore, we have conducted experiments with Au-lined gaskets to conclusively demonstrate that steel gaskets are not necessary for these reactions to proceed. Finally, spectroscopic evidence suggests the formation of a methane-hydrate structure upon temperature quench from 5 GPa and 650 °C (by room temperature the pressure had decreased to 2 GPa; we cannot further constrain the P-T conditions of this clathrate formation from our current dataset). Notably, however, we have not detected the presence of hydrocarbons heavier than methane.