Making Mercury's Core with Light Elements

Recent results obtained from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft showed the surface of Mercury has low FeO abundances (less than 2 wt%) and high S abundances (approximately 4 wt%), suggesting the oxygen fugacity of Mercury's surface materials is somewhere between 3 to 7 log10 units below the IW buffer. The highly reducing nature of Mercury has resulted in a relatively thin mantle and a large core that has the potential to exhibit an exotic composition in comparison to the other terrestrial planets. This exotic composition may extend to include light elements (e.g., Si, C, S). Furthermore, has argued for a possible primary floatation crust on Mercury composed of graphite, which may require a core that is C-saturated. In order to investigate mercurian core compositions, we conducted piston cylinder experiments at 1 GPa, from 1300 C to 1700 C, using a range of starting compositions consisting of various Si-Fe metal mixtures (Si5Fe95, Si10Fe90, Si22Fe78, and Si35Fe65). All metals were loaded into graphite capsules used to ensure C-saturation during the duration of each experimental run. Our experiments show that Fe-Si metallic alloys exclude carbon relative to more Fe-rich metal. This exclusion of carbon commences within the range of 5 to 10 wt% Si. These results indicate that if Mercury has a Si-rich core (having more than approximately 5 wt% silicon), it would have saturated in carbon at low C abundances allowing for the possible formation of a graphite floatation crust as suggested by. These results have important implications for the thermal and magmatic evolution of Mercury

Carbon on Mercury's Surface - Origin, Distribution, and Concentration

Distinctive low-reflectance material (LRM) was first observed on Mercury in Mariner 10 flyby images. Visible to near-infrared reflectance spectra of LRM are flatter than the average reflectance spectrum of Mercury, which is strongly red sloped (increasing in reflectance with wavelength). From Mariner 10 and early MErcury, Surface, Space, ENvironment, GEochemistry, and Ranging (MESSENGER) flyby observations, it was suggested that a higher content of ilmenite, ulvospinel, carbon, or iron metal could cause both the characteristic dark, flat spectrum of LRM and the globally low reflectance of Mercury. Once MESSENGER entered orbit, low Fe and Ti abundances measured by the X-Ray and Gamma-Ray Spectrometers ruled out ilmenite, and ulvospinel as important surface constituents and implied that LRM was darkened by a different phase, such as carbon or small amounts of micro- or nanophase iron or iron sulfide dispersed in a silicate matrix. Low-altitude thermal neutron measurements of three LRM-rich regions confirmed an enhancement of 1-3 weight-percent carbon over the global abundance, supporting the hypothesis that LRM is darkened by carbon

Experimental petrology and origin of Fra Mauro rocks and soil

Melting experiments over the pressure range 0 to 20 kilobars were conducted on Apollo 14 igneous rocks 14310 and 14072 and on comprehensive fines 14259. The mineralogy and textures of rocks 14310 and 14072 are presumed to be the result of near-surface crystallization. The chemical compositions of the samples show special relationships to multiply-saturated liquids in the system: anorthite-forsterite-fayalite-silica at low pressure. Partial melting of a lunar crust consisting largely of plagioclase, low calcium pyroxene, and olivine, followed by crystal fractionation at the lunar surface is proposed as a mechanism for the production of the igneous rocks and soil glasses sampled by Apollo 14

Experimental Investigation into the Thermal and Magmatic Evolution of Mercury

During the time that the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft was in orbit around the innermost planet, new and exciting results regarding the planets structure, chemical makeup, and diverse surface were revealed, confirming that Mercury is a geochemical endmember among the terrestrial planets. Data from this mission, more specifically data from the X-Ray Spectrometer and Gamma-Ray Spectrometer onboard MESSENGER, has been used to provide insight into the thermal and magmatic evolution of Mercury. This dissertation consists of five chapters that, as a whole, have substantially increased our knowledge about Mercury through a high pressure and high temperature experimental investigation. First, we identified nine distinct geochemical regions that have characteristic major element compositions. We computed silicate and sulfide mineralogy of these regions and petrologically classified them according to IUGS specifications. The diversity of the rocks and minerals on Mercury was then compared to other planetary bodies revealing the wide range in diversity of the mercurian surface. Second, we conducted sink-float experiments on a melt composition similar to the composition of the largest volcanic field on the planet to provide insight into crust formation on Mercury. These results suggested a primary floatation crust composed of graphite is possible given a magma ocean event on Mercury. Third, we experimentally determined the phase assemblages associated with the largest volcanic field on the planet. From this data we were able to provide insight into eruption scenarios that produced the northern volcanic plains on Mercury. Fourth, we determined the sulfide concentration at sulfide saturation in mercurian-like melts by conducting sulfide solubility experiments on a synthetic rock composition matching the northern volcanic plains. These results indicated that the high amounts of sulfur on the surface of Mercury measured by MESSENGER are a direct consequence of the low oxygen fugacity of the planet, which allowed transport of S towards the surface in reducing melts which have a higher carrying capacity for S than oxidized melts. Finally, we investigated the carbon concentration at graphite saturation in Fe-rich metals with various amounts of Si to determine the amount of C that would be soluble in the mercurian core as a function of core composition and temperature. The results of this dissertation provide important information regarding the evolution of Mercury from its primary magma ocean event to the current state of the planet

Design of a compliant wheel for a miniature rover to be used on Mars

The Jet Propulsion Laboratory has identified the need for a compliant wheel for a miniature martian rover vehicle. This wheel must meet requirements of minimum mass, linear radial deflection, and reliability in cryogenic conditions over a five year lifespan. Additionally, axial and tangential deflections must be no more than 10 percent of the radial value. The team designed a wheel by use of finite element and dimensionless parameter analysis. Due to the complex geometry of the wheel, a finite element model describing its behavior was constructed to investigate different wheel configurations. Axial and tangential deflections were greatly reduced but did not meet design criteria. A composite material was selected for its high strength, toughness, fatigue resistance, and damping characteristics. The team chose a Kevlar fiber filled thermoplastic composite. This report is divided into four primary sections. First, the introduction section gives background information, defines the task, and discusses the scope and limitations of the project. Second, the alternative designs section introduces alternative design solutions, addresses advantages and disadvantages of each, and identifies the parameters used to determine the best design. Third, the design solution section introduces the methods used to evaluate the alternates, and gives a description of the design process used. Finally, the conclusion and recommendations section evaluates the wheel design, and offers recommendations pertaining to improvement of the design solution

Graphite as Material for Production of Crucibles Using Clay Slip Casting Method (A Case study of Sama Borkno Graphite in Warji Local Government Area of Bauchi state)

Purpose: This research work investigated the use of graphite as material for production of crucibles by using clay slip casting method. Methodology: The graphite used was sourced from a graphite deposit located at Sama Borkno in Warji Local Government Area of Bauchi state. Clay, kaolin, fireclay silica, lime were used to bind the materials together and to make the slip more plastics and to strengthen the crucible. The investigation covered the assessment of chemical compositions of the graphite sample obtained, processing of the graphite obtained into crucible, determination of physical properties of crucible such as shrinkage, porosity, refractoriness, shock resistance and heat conductivity by ASTM standard methods. Findings: The result of the chemical analysis for the graphite sample showed that the beneficiated graphite has enough percentage of carbon content suitable for crucible production.   The shrinkage tests conducted on the samples showed percentage shrinkage of the sample ranges from 2-17 %. The results of the thermal shock tests showed that all the samples can withstand sudden change in temperature when exposed to different temperatures. The refractoriness test for the sample showed that all the samples can withstand temperatures above 12000C. Conductivity test showed good heat conductance of the samples. After the tests, it was found that sample "B" possess all the requirements required for graphite crucible production. The Crucible was produced by slip casting forming method of ceramic bodies. The crucible produced was tested by melting a brass. Unique Contribution to Theory, Practice and Policy: The study recommends that government should encourage the full time mining of indigenous graphite by providing a conducive atmosphere and assistance to miners. Some additives such as grog should also be added to the samples mixtures so as to improve the properties

The Chemical and Physical Impacts of Magma Ocean Solidification: Insights into Lunar Magma Ocean Solidification, Mantle Formation, and Mantle Evolution.

Solidification of a lunar magma ocean (LMO) after a giant planetary collision event formed the Moon’s gravitationally unstable juvenile mantle. Hybridization of the lunar mantle during the overturn of late-crystallized Ti- rich ilmenite-bearing cumulates (IBC) in the lunar interior is called upon to explain the variable Ti and REE abundances of melts. We experimentally investigated hybridization reactions in experiments that juxtapose an IBC glass against presynthesized dunite in a reaction couple at temperatures of 1100-1300 ºC and pressures of 0.5-2.02 GPa for 0.33-31.66 hours. We then model chemical fractionation during LMO solidification, mantle hybridization, and partial melting of hybridized and unhybridized cumulates to evaluate the formation of lunar basalts, picritic glasses, and crustal cumulates. Subsolidus experiments produce garnet in the IBC at 2 GPa. Supersolidus experiments exhibit dissolution of olivine material into the IBC melt and the formation of clinopyroxene at the IBC melt-dunite interface. Simple numerical simulations suggest that mechanical mixing may be required in addition to dissolution-precipitation reactions to produce volumetrically significant hybridized mantle sources capable of producing lunar melts over geologically relevant timescales. Geochemical models indicate that plagioclase floatation efficiency during LMO solidification and crustal formation must be \u3e90% to explain the negative Eu anomaly demonstrated by lunar melts. Melting models demonstrate that unhybridized cumulates could produce low-Ti melts, and hybridized garnet-free sources can generate many intermediate to high-Ti melts. The Heavy Rare Earth Element depleted compositions of some high-Ti lunar melts require a ~0.25-5% garnet component in the downwelling IBC or hybridized sources. The need for garnet combined with isotope ratios of high-Ti lunar basalts indicates the cumulate overturn is likely required. Geochemical models of LMO solidification also demonstrate that the Moon likely contains90% of the lunar HPE budget should initially be concentrated in the lunar crust and upper mantle cumulates following LMO solidification

Preliminary Investigation of the Geologic Controls of Graphite Mineralization and Exploration Potential of the Wa-Lawra Belt: Implications for Kambale Graphite Deposit

The Kambale graphite deposit is located within the Wa‐Lawra greenstone belt in NW Ghana. Historical records, recent exploration, unpublished material and accessible surface and subsurface exposures provide a valuable preliminary case study of the deposit. Examination of three transversal trenches and re-logging of eleven Rotary Air Blast (RAB) drill holes in the western part of the deposit reveal moderately to intensely sheared metasedimentary rocks of the lower Birimian formation such as mica schist, graphitic schist, quartzite, and a few pegmatite intrusions. Optical microscopic studies show that the deposit occasionally occurs in a complex mineral paragenesis of quartz ± calcite ± hornblende ± magnetite ± pyrrhotite ± rutile ± chalcocite ± graphite and other gangue minerals, often found around the boundaries of large magnesian ferrohornblende minerals, which tend to form quartz crystals. The Kambale deposit is characterized by numerous faults and shears, associated with brittle-ductile deformation at the NE part of the main shear with fewer faults and shears at the southern and western zones, generally trending E-W between 150˚ and 320˚, dipping in NE-SW direction at an average of 060˚. The rocks have undergone medium-high grade metamorphism under high T/medium P facies typically estimated as (∼600-750◦C, 5.0–8.0 kbar), in amphibolite-granulite facies. The genesis of the flake graphite in Kambale is believed to be as a result of the high grade metamorphism, where deep-seated CO2-rich fluid phase of crustal origin invaded the metamorphosed rocks. The intensity of the pore fluid pressures aided in the genesis of the graphite by hydraulic fracturing of the underlying rocks under regional syntectonic deformation. Keywords: geologic controls, graphite, trench mapping, rotary air blast, graphitic schist, Wa-Lawra greenstone belt, Kambale, NW Ghan

Experimental Constraints on the Origin of Lunar High-Ti Ultramafic Glasses

Phase equilibria and dissolution rate experiments are used to develop a petrogenetic model for the high-Ti lunar ultramafic glasses. Near-liquidus phase relations of the Apollo 14 black glass, the most Ti-rich lunar ultramafic glass, are determined to 2.2-GPa. The liquidus is saturated with Cr-spinel at 1-atm, olivine between approximately 0.5- and 1.5-GPa, and low-Ca pyroxene + Cr-spinel above 1.5-GPa. Ilmenite does not crystallize near the liquidus and implies that high-Ti ultramafic glasses are not produced by melting of an ilmenite-saturated source. We infer that high-Ti ultramafic magmas are derived from low-Ti ultramafic parent magmas by assimilation of ilmenite +/- clinopyroxene +/- urKREEP +/- pigeonite in the shallow lunar interior. Heat is provided by adiabatic ascent of the low-Ti ultramafic primary magmas from the deeper lunar interior and crystallization of olivine during assimilation. The assimilation reaction is modeled by mass balance and requires that ilmenite and high-Ca pyroxene are assimilated in a approximately 3:1 ratio, a much higher ratio than the proportion in which these minerals are thought to exist in the lunar interior. In an effort to understand the kinetic controls on this reaction, the dissolution of ilmenite is examined experimentally in both low- and high-Ti lunar magmas. We find that ilmenite dissolves incongruently to Cr-spinel and a high-Ti melt. The dissolution reaction proceeds by a diffusion-controlled mechanism. An assimilation model for the origin of high-Ti melts is developed that leaves the magma ocean cumulates in their initial stratigraphic positions and obviates source hybridization models that require lunar overturn