Iron Isotope Cosmochemistry

Iron is the most abundant element in the Earth and the 4th most abundant in the crust and mantle; Fe is involved in every stage of planetary formation and differentiation. Iron isotope ratios are robust process tracers used to understand the origin of the Solar System, planetary formation, and differentiation processes such as the moon-forming giant impact, core-mantle segregation, and crust formation. In this dissertation, I report the most complete dataset of high-precision iron isotope compositions of a wide range of extraterrestrial samples including carbonaceous, ordinary, and enstatite chondrites, aubrites, brachinites, HED meteorites: howardites, eucrites and diogenites), martian meteorites, angrites, lunar meteorites, lunar regolith and ungrouped meteorites. I discuss iron isotope fractionations among these extraterrestrial materials in term of solar nebular processing, asteroidal parent-body processing, planetary differentiation: core-mantle differentiation and crust formation), magmatism, and planetary surface processing. In Chapter 1, I introduce some basic knowledge about the meteorites and lunar samples, which comprise the research objectives in following chapters. In addition, the general concepts of the nucleosynthesis of Fe isotopes and mass-dependent Fe isotope fractionation mechanisms are also discussed. At last, I review the technique of high precision isotopic analyses of iron using anion-exchange chromatography and MC-ICP-MS. In Chapter 2, I focus on the non-mass-dependent fractionation of Fe isotopes and examine the possible isotopic anomalies in some of the oldest meteorites in the Solar System, which could help in understanding the stellar building blocks of our Solar System. The solar nebula was made of materials from the nucleosynthesis of older generation stars. The solar nebula was initially thought to have been chemically and isotopically well mixed. However, since late 1960s, isotopic anomalies have been observed in both bulk meteorite and mineral scales. These isotopic anomalies are relic signals of the original building blocks of our Solar System, surviving from the mixing of early solar nebula. With the instrumental advances such as the application of MC-ICP-MS, smaller and smaller scale isotopic anomalies can be identified in meteorite samples. By looking at these anomalies, we could acquire information about the original building blocks of our Solar System. I reexamined the 54Cr anomalies: discovered in the 1980s and for which the origin is still debated) by investigating the collateral effects on 58Fe nuclide. These neutron-rich nuclides are expected to be produced together in Type II supernovae or Type Ia supernovae. Even though these 54Cr anomalies have been long observed, the carrier phases and the stellar origin had not been identified until our research. By measuring 58Fe, I put constraints on the nucleosynthetic origins: most probably Type II supernovae). From Chapter 3 to 7, I emphasize mass-dependent fractionations of Fe isotopes. First, in Chapter 3, I present the most complete Fe isotope dataset of CI chondrites using large sample masses: ~1 g). CI chondrites have been recognized as the meteorite group whose composition resembles the: non-volatile elemental) bulk composition of the solar nebula. The Fe isotope compositions of five different stones of Orgueil, one of Ivuna and one of Alais are highly homogeneous. I propose that this average represents the best estimate of bulk Fe isotope composition of our Solar System, and that the homogeneity of CI chondrites reflects the initial Fe isotopic homogeneity of the well-mixed solar nebula. In contrast, larger Fe isotopic variations have been found between separate ~1g pieces of the same ordinary chondrite samples. As shown in the mass-balance calculation in the paper, the Fe isotopic heterogeneities in ordinary chondrites are controlled by the abundances of chondritic components, specifically chondrules, whose Fe isotope compositions have been fractionated by evaporation and re-condensation during multiple heating events. Due to this Fe isotopic heterogeneity exhibited in ordinary chondrites, caution should be taken when interpreting the Fe isotope data from small masses of samples. In Chapter 4, I report the most comprehensive Fe isotope database for the enstatite meteorite group: EH, EL, aubrite-main group and Shallowater). In addition to bulk samples, I also analyzed mineral phases separated from enstatite meteorites to assess the Fe isotope budget of the metal/silicate/sulfide components of enstatite meteorite parent bodies and, more generally, to estimate the Fe isotopic fractionation between metal and sulphide that can be applied to any type of material. I find that all enstatite chondrites: with the exception of EL6) have the same Fe isotopic composition, which is identical with that of the carbonaceous and ordinary chondrites. Relatively larger Fe isotopic fractionation in EL6 chondrites and aubrite achondrites are discussed in terms of the origins of these meteorites with metal/sulfide/silicate differentiation. Finally, I provide a new estimate of the Fe isotopic fractionation factor between metal and sulfide at the equilibrium temperature range of aubrites, which agrees well with the theoretical equilibrium fractionation between Fe-metal and troilite reported previously. In Chapter 5, I investigate the Fe isotope compositions of the crustal materials from several planets or asteroidal bodies, including the Moon, Mars, 4 Vesta, and the angrite parent-body. The Earth-Moon system is widely accepted to have formed in the aftermath of the Giant Impact event, and the elevated Fe isotope composition of lunar rocks when compared to chondrites was once proposed as the first isotopic evidence of the Giant Impact. However, my studies on these planetary crusts have shown that the Moon and the Earth are not the only planetary system having heavier Fe isotope compositions compared to chondrites. These isotopic fractionations shown in planetary crusts are more likely to be formed during magmatic processes, such as fractional crystallization or partial melting controlled by oxygen fugacities, instead of previously proposed evaporative fractionation during the Giant Impact. In Chapter 6, I study the Fe isotope compositions of Graves Nunataks: GRA) 06128 and 06129, the oldest felsic crustal material known in the Solar System, and brachinites, a group of ultramafic meteorites genetically linked with GRA. The formation of felsic continental crust on the Earth is closely associated with plate tectonics and is unique among all known Solar System materials. However, the recent identification of meteorites GRA 06128/9 as evolved felsic crustal materials has challenged the canonical view that the earliest planetary crusts were dominantly basaltic in composition. Here, I show that GRA meteorites are isotopically different from the terrestrial continental crust. I then propose that GRA meteorites were formed as Fe -S-rich felsic melts by preferential melting of sulfides during partial melting of precursor chondritic source materials. The proposed origin for GRA therefore contrasts strongly with the continental crust formation on Earth and represents a paradigm shift in our understanding of felsic crust formation in the absence of plate tectonics and even before core formation in the early Solar System history. In Chapter 7, I examine the Fe isotope fractionation during evaporation and the formation mechanism of the nanophase metallic iron widely observed in lunar regolith. All planetary bodies are under continuous bombardment by cosmic ray radiation, solar wind sputtering, and meteorite impacts. For those planetary bodies that lack protective atmospheres, these bombardments could alter the optical features of their surface in a process called space weathering. Two leading theories have been proposed to explain the nanophase metallic iron formed by space weathering:: 1) the solar wind reduction model, and: 2) the vapor recondensation model. I implemented stepwise leaching experiments on Apollo regolith and have successfully isolated the isotopic signature of nanophase metallic iron on the surface of minerals. My results provide strong isotopic support for the vapor recondensation model and further reveal the isotopic effect of the space weathering mechanism

Solar System Remote Sensing : September 20-21, 2002, Pittsburgh, Pennsylvania

This international meeting presents the current state of research over a wide range of topics including:; Photometric theory; Spectroscopic modeling; Laboratory exploration of scattering phenomena; Space weathering processes throughout the inner solar system; Photometric and spectroscopic studies of the Moon, Mars, Mercury, and asteroids; Photometric and spectroscopic studies of cold, icy places such as comets and outer planet satellites.This international meeting presents the current state of research over a wide range of topics including:; Photometric theory; Spectroscopic modeling; Laboratory exploration of scattering phenomena; Space weathering processes throughout the inner solar system; Photometric and spectroscopic studies of the Moon, Mars, Mercury, and asteroids; Photometric and spectroscopic studies of cold, icy places such as comets and outer planet satellites.sponsors, University of Pittsburgh ... [and others]conveners, William Cassidy, Deborah Domingue, Robert M. Nelson ; scientific organizing committee William Cassidy ... [and others].PARTIAL CONTENTS: Interpreting Photometry of Planetary Regoliths: Progress and Problems as Seen from Kharkov / Yu.G. Shkuratov--Toward an Improved Single-Particle Model for Large, Irregular Grains / W.M. Grundy, B. Schmitt, S. Doute--A New Method for Estimating the Single Scattering Phase Functions of Regolith Grains / P. Helfenstein--The Opposition Effect: A Very Unusual Case / R.M. Nelson--Coherent Backscattering by Random Particulate Media in the Solar System / K. Muinonen--The Diverse Surface Compositions of the Galilean Satellites / R.W. Carlso

Space Weathering of Airless Bodies

In preparation for missions to primitive asteroids and to better interpret recent remote sensing datasets from Mercury, the Moon, and other objects, we need a better understanding of how the space environment alters the surfaces of airless bodies from a remote sensing perspective, how analysis of returned samples provides ground truth for interpreting the spectral data, and how laboratory experiments provide quantitative constraints on the processes involved.Organizer Universities Space Research Association ; Conveners Lindsay Keller, NASA Johnson Space Center, Ed Cloutis, University of Winnipeg, Paul Lucey, University of Hawaii, Tim Glotch, Stony Brook University ; Scientific Organizing Committee Lindsay Keller, NASA Johnson Space Center [and 9 others]PARTIAL CONTENTS: The Many Forms of Space Weathering -- Latitudinal Variation in Spectral Properties of the Lunar Maria and Implications for Space Weathering -- Latitude-Dependence of Median Grain Size in the Lunar Regolith -- Space Weathering Effects in the Thermal Infrared: Lessons from LRO Diviner -- Effects of Space Weathering on Thermal Infrared Emissivity Spectra of Bulk Lunar Soils Measured Under Simulated Lunar Conditions -- The Maturely, Immature Orientale Impact Basin -- Estimating the Degree of Space Weathering at the Chang'E-3 Landing Site: Radiative-Transfer Modeling of Nanophase Iron Abundance -- The Microstructure of a Micrometeorite Impact into Lunar Olivine--Simulation of Micrometeorite Impacts Through In Situ Dynamic Heating of Lunar Soil--Problems at the Leading Edge of Space Weathering as Revealed by TEM Combined with Surface Science Techniques--Rates of Space Weathering in Lunar Soils--Space Weathering: From Itokawa to Mercury via the Moon--Space Weathering on Itokawa Surface Deduced from Shape and Surface Features of Hayabusa Regolith Particles--Surface Exposure Ages of Space-Weathered Grains from Asteroid 25143 Itokawa

Exploration and Utilisation of Lunar Resources affected by Space Weathering

This thesis aims to develop a study with regards to the exploration of the lunar surface through the resources produced by space weathering. Space weathering events shall be discussed, in terms of how the physical and chemical characteristics of the lunar regolith is affected. Through hydrogen reduction, the products formed from space weathering interactions shall be produced within the lunar simulants JSC-1 and FJS-3. This is followed up with characterising the processed samples via a Scanned Electron Microscope (SEM) to confirm the formation of npFe0 and SMFe – a product of space weathering. Thereafter, a preliminary quantification of the presence of npFe0 and SMFe within one of the samples is obtained through a Mossbauer analysis, this is to provide the basis for ¨ future more accurate quantification of npFe0 and SMFe to be created. In addition to these experiments, an analysis on the samples reflectance within the ultraviolet (UV) region of the electromagnetic spectrum is conducted – finding a preliminary correlation between decreasing reddening gradient and increasing reduction temperatures (the temperature in which the sample was reduced at). Finally, an equation was fitted to this correlation in order to mathematically describe the relationship between the sample’s reflectance spectra and reduction temperature (the duration of this reduction was first conducted for 2 hours and then 4 hours). This preliminary mathematical model allows for interpolation of the reddening gradient – a characteristic dependent on the products of space weathering, for both the lunar simulants JSC-1 and FJS-3, when a specific reduction temperature is provided. Ultimately providing the basis for a mathematical model to determine the quantities of npFe0 and SMFe within the lunar regolith by viewing its corresponding UV reflectance spectra

Space weathering simulations through controlled growth of iron nanoparticles on olivine

Airless planetary bodies are directly exposed to space weathering. The main spectral effects of space weathering are darkening, reduction in intensity of silicate mineral absorption bands, and an increase in the spectral slope towards longer wavelengths (reddening). Production of nanophase metallic iron (npFe0) during space weathering plays major role in these spectral changes. A laboratory procedure for the controlled production of npFe0 in silicate mineral powders has been developed. The method is based on a two-step thermal treatment of low-iron olivine, first in ambient air and then in hydrogen atmosphere. Through this process, a series of olivine powder samples was prepared with varying amounts of npFe0 in the 7-20 nm size range. A logarithmic trend is observed between amount of npFe0 and darkening, reduction of 1 µm olivine absorption band, reddening, and 1 µm band width. Olivine with a population of physically larger npFe0 particles follows spectral trends similar to other samples, except for the reddening trend. This is interpreted as the larger, ~40-50 nm sized, npFe0 particles do not contribute to the spectral slope change as efficiently as the smaller npFe0 fraction. A linear trend is observed between the amount of npFe0 and 1 µm band center position, most likely caused by Fe2+ disassociation from olivine structure into npFe0 particles.Peer reviewe

Understanding the Composition and Evolution of the Lunar Surface Through Laboratory Space Weathering Simulations and Remote Sensing

Ph.D

Mineralogical analysis and iron abundance estimation of the Moon using the SIR-2, HySI and M3 spectrometers on-board the munar orbiter chandrayaan-1

The work presented in this thesis is focused on mineralogical studies of the Moon aiming to create maps of iron abundances. We used the data from visible to near-infrared (VISNIR) spectrometers on-board Chandrayaan-1 spacecraft, with our major concentration on the Spectrometer InfraRed-2 (SIR-2) data. The SIR-2 on-ground and in-flight calibrations are discussed. The location of the SIR-2 tracks on the imaging spectrometers, Moon Mineralogy Mapper (M3), and Hyper-Spectral Imager (HySI) is determined by comparing the radiance profiles of the three instruments measured at the same Coordinated Universal Time (UTC) and the same photometric conditions...thesi

Asteroid Regolith Weathering: A Large-Scale Observational Investigation

As bodies lacking an atmosphere or significant protection from solar wind particles, asteroids are subject to processes that modify the physical state and spectral properties of their regoliths. By investigating the relevant factors that contribute towards asteroid regolith modification, this work will provide crucial insight into the nature of these processes. I propose and test two major hypotheses: 1) that physical (mechanical) breakdown is caused by both meteoroid bombardment and thermal fatigue cycling, and thus regolith grain size depends on asteroid size and rotation period, and 2) changes in spectral properties (space weathering) are due to solar wind bombardment and depend on an object\u27s mineralogy, sun-distance, and surface age.I develop and validate a thermophysical modeling (TPM) approach that analyzes multiepoch (pre- and post-opposition) thermal infrared observations for asteroids without prior shape or spin information, in order to determine various thermophysical properties -- chiefly the thermal inertia. This TPM approach is applied to over 250 asteroids to determine their thermal inertia. Combining other thermal inertia datasets with mine, for a total of over 300 objects, a characteristic grain size is estimated for each object. Next, a multiple linear model is used to quantify the grain size dependence on asteroid diameter and rotation period, which are both shown to be statistically-significant model predictors. I also identify grain size differences between spectral groups { namely the M-types, which exhibit 4 times larger regolith grains, on average.Spectral data from meteorite and irradiated samples, spanning the visible and near-infrared regions, are used to develop an index to quantify the degree of space weathering. This space weathering index is applied to asteroid spectral observations and used in a multi-linear model to determine the predictor variables that increase the perceived amount of asteroid space weathering. Perihelion distance, diameter, and the average sun distance are found as statistically-significant factors in the multiple linear model. I also present evidence that regolith grains smaller than 0.5 mm enhance the extent of space weathering

Spacesuit Integrated Carbon Nanotube Dust Mitigation System For Lunar Exploration

Lunar dust proved to be troublesome during the Apollo missions. The lunar dust comprises of fine particles, with electric charges imparted by solar winds and ultraviolet radiation. As such, it adheres readily, and easily penetrates through smallest crevices into mechanisms. During Apollo missions, the powdery dust substantially degraded the performance of spacesuits by abrading suit fabric and clogging seals. Dust also degraded other critical equipment such as rovers, thermal control and optical surfaces, solar arrays, and was thus shown to be a major issue for surface operations. Even inside the lunar module, Apollo astronauts were exposed to this dust when they removed their dust coated spacesuits. This historical evidence from the Apollo missions has compelled NASA to identify dust mitigation as a critical path. This important environmental challenge must be overcome prior to sending humans back to the lunar surface and potentially to other surfaces such as Mars and asteroids with dusty environments. Several concepts were successfully investigated by the international research community for preventing deposition of lunar dust on rigid surfaces (ex: solar cells, thermal radiators). However, applying these technologies for flexible surfaces and specifically to spacesuits has remained an open challenge, due to the complexity of the suit design, geometry, and dynamics. The research presented in this dissertation brings original contribution through the development and demonstration of the SPacesuit Integrated Carbon nanotube Dust Ejection/Removal (SPIcDER) system to protect spacesuits and other flexible surfaces from lunar dust. SPIcDER leverages the Electrodynamic Dust Shield (EDS) concept developed at NASA for use on solar cells. For the SPIcDER research, the EDS concept is customized for application on spacesuits and flexible surfaces utilizing novel materials and specialized design techniques. Furthermore, the performance of the active SPIcDER system is enhanced by integrating a passive technique based on Work Function Matching coating. SPIcDER aims for a self-cleaning spacesuit that can repel lunar dust. The SPIcDER research encompassed numerous demonstrations on coupons made of spacesuit outerlayer fabric, to validate the feasibility of the concept, and provide evidence that the SPIcDER system is capable of repelling over 85% of lunar dust simulant comprising of particles in the range of 10 m-75m, in ambient and vacuum conditions. Furthermore, the research presented in this dissertation proves the scalability of the SPIcDER technology on a full scale functional prototype of a spacesuit knee joint-section, and demonstrates its scaled functionality and performance using lunar dust simulant. It also comprises detailed numerical simulation and parametric analysis in ANSYS Maxwell and MATLAB for optimizing the integration of the SPIcDER system into the spacesuit outerlayer. The research concludes with analysis and experimental results on design, manufacturability, operational performance, practicality of application and astronaut safety. The research aims primarily towards spacesuit dust contamination. The SPIcDER technology developed in this research is however versatile, that can be optimized to a wide range of flexible surfaces for space and terrain applications-such as exploration missions to asteroids, Mars and dust-prone applications on Earth