Surface Processes on Metal Worlds: Space Weathering and Regolith Formation on Metal-Rich Asteroids

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Description
ABSTRACTWith the National Aeronautics and Space Administration (NASA) Psyche Mission, humans will soon have the first opportunity to explore a new kind of planetary body: one composed mostly of metal as opposed to stony minerals or ices. Identifying the composition

ABSTRACTWith the National Aeronautics and Space Administration (NASA) Psyche Mission, humans will soon have the first opportunity to explore a new kind of planetary body: one composed mostly of metal as opposed to stony minerals or ices. Identifying the composition of asteroids from Earth-based observations has been an ongoing challenge. Although optical reflectance spectra, radar, and orbital dynamics can constrain an asteroid’s mineralogy and bulk density, in many cases there is not a clear or precise match with analogous materials such as meteorites. Additionally, the surfaces of asteroids and other small, airless planetary bodies can be heavily modified over geologic time by exposure to the space environment. To accurately interpret remote sensing observations of metal-rich asteroids, it is therefore necessary to understand how the processes active on asteroid surfaces affect metallic materials. This dissertation represents a first step toward that understanding. In collaboration with many colleagues, I have performed laboratory experiments on iron meteorites to simulate solar wind ion irradiation, surface heating, micrometeoroid bombardment, and high-velocity impacts. Characterizing the meteorite surface’s physical and chemical properties before and after each experiment can constrain the effects of each process on a metal-rich surface in space. While additional work will be needed for a complete understanding, it is nevertheless possible to make some early predictions of what (16) Psyche’s surface regolith might look like when humans observe it up close. Moreover, the results of these experiments will inform future exploration beyond asteroid Psyche as humans attempt to understand how Earth’s celestial neighborhood came to be.
Date Created
2023
Agent

Strange New Worlds: Development of Active Nuclear Technologies and Techniques for Planetary Science Applications

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Description
Information about the elemental composition of a planetary surface can be determined using nuclear instrumentation such as gamma-ray and neutron spectrometers (GRNS). High-energy Galactic Cosmic Rays (GCRs) resulting from cosmic super novae isotropically bombard the surfaces of planetary bodies in

Information about the elemental composition of a planetary surface can be determined using nuclear instrumentation such as gamma-ray and neutron spectrometers (GRNS). High-energy Galactic Cosmic Rays (GCRs) resulting from cosmic super novae isotropically bombard the surfaces of planetary bodies in space. When GCRs interact with a body’s surface, they can liberate neutrons in a process called spallation, resulting in neutrons and gamma rays being emitted from the planet’s surface; how GCRs and source particles (i.e. active neutron generators) interact with nearby nuclei defines the nuclear environment. In this work I describe the development of nuclear detection systems and techniques for future orbital and landed missions, as well as the implications of nuclear environments on a non-silicate (icy) planetary body. This work aids in the development of future NASA and international missions by presenting many of the capabilities and limitations of nuclear detection systems for a variety of planetary bodies (Earth, the Moon, metallic asteroids, icy moons). From bench top experiments to theoretical simulations, from geochemical hypotheses to instrument calibrations—nuclear planetary science is a challenging and rapidly expanding multidisciplinary field. In this work (1) I describe ground-truth verification of the neutron die-away method using a new type of elpasolite (Cs2YLiCl6:Ce) scintillator, (2) I explore the potential use of temporal neutron measurements on the surface of Titan through Monte-Carlo simulation models, and (3) I report on the experimental spatial efficiency and calibration details of the miniature neutron spectrometer (Mini-NS) on board the NASA LunaH-Map mission. This work presents a subset of planetary nuclear science and its many challenges in humanity's ongoing effort to explore strange new worlds.
Date Created
2022
Agent

Exploration of Spectrally Featureless Asteroids: Reflectance Measurements of Meteorites and Characterization of a Commercial Camera System for the Psyche Mission

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Description
Characterizing the surface mineralogy of asteroids is critical to constraining their formation history and provides insight into the processes of planetary formation. One method of determining the surface mineralogy of asteroids is comparison of their visible to near-infrared reflectance (VNIR)

Characterizing the surface mineralogy of asteroids is critical to constraining their formation history and provides insight into the processes of planetary formation. One method of determining the surface mineralogy of asteroids is comparison of their visible to near-infrared reflectance (VNIR) spectra with laboratory spectra from meteorites and minerals. Subsequent in-situ investigation of these asteroids by spacecraft can supplement or supersede interpretations derived from Earth-based observations.I investigated a suite of aubrites, sulfide minerals, and metal-rich chondrites in a variety of forms (hand samples, powders, and slabs) to identify similarities with ‘spectrally featureless’ asteroids. I collected VNIR spectra and powder X-ray diffraction patterns of these samples and compared their overall reflectance and spectral slope with X-complex and T-, L-, and D-type asteroid spectra. The Psyche Mission will orbit asteroid (16) Psyche beginning in 2026. I provide a pre-flight assessment of the surface composition of Psyche by comparing spectra of Psyche to a large spectral library of possible surface analog materials (e.g., iron meteorites, mesosiderites, pallasites, sulfides, enstatite, ordinary, and metal-rich chondrites, endmember silicates, and mixtures of silicates, metal, and sulfides). Spectra of Psyche are generally consistent with iron meteorite powder, mixtures of iron meteorite powder and low-Fe, low-Ca pyroxene, sulfide minerals, and the CH/CBb chondrite Isheyevo. Next, I demonstrate some anticipated capabilities of the Psyche Multispectral Imager by comparing spectral parameters derived from Imager-convolved data to those from high resolution laboratory spectra. I offer preliminary strategies for classifying surface composition based on Imager filter ratios and overall reflectance. Last, I present an assessment of a benchtop, commercial-off-the-shelf (COTS) version of the Psyche Imager. The COTS Imager uses the same model CCD and a similar f-number commercial camera lens. I measured the gain, full well, linearity, read noise, quantum efficiency, and modulation transfer function to compare with eventual calibration data from the flight Imager. I validate the results of a radiometric model developed for the flight Imager with signal measurements from the COTS Imager. This work demonstrates that the COTS Imager is an effective testbed for validating Imager requirements and developing software and procedures for eventual calibration of the flight instrument.
Date Created
2021
Agent

Effects of Magma Ocean Crystallization and Overturn on the Development of Nd-142 and W-182 Isotopic Heterogeneities in the Primordial Mantle

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Description

One possible mechanism to explain the observed variability of the short- lived 146Sm → 142Nd and 182Hf → 182W systems recorded in some early Earth rocks is crystal-liquid fractionation and overturn in an early magma ocean. This process could also

One possible mechanism to explain the observed variability of the short- lived 146Sm → 142Nd and 182Hf → 182W systems recorded in some early Earth rocks is crystal-liquid fractionation and overturn in an early magma ocean. This process could also potentially explain the deviation between the 142Nd isotopic composition of the accessible Earth and the chondritic average. To examine these effects, the magma ocean solidification code of Elkins-Tanton (2008) and a modified Monte Carlo algorithm, designed to randomly choose physically reasonable trace element partition coefficients in crystallizing mantle phases, are used to model the isotopic evolution of early Earth reservoirs. This model, also constrained by the 143Nd composition of the accessible Earth, explores the effects of changing the amount of interstitial liquid trapped in cumulates, the half-life of 146Sm, the magnitude of late accretion, and the simplified model of post-overturn reservoir mixing. Regardless of the parameters used, our results indicate the generation of early mantle reservoirs with isotopic characteristics consistent with observed anomalies is a likely outcome of magma ocean crystallization and overturn of shallow, enriched, and dense (i.e., gravitationally unstable) cumulates. The high-iron composition and density of a hypothesized, early-formed enriched mantle reservoir is compatible with seismic observations indicating large, low-shear velocity provinces (LLSVPs) (e.g., Trampert et al., 2004) present in the mantle today. Later melts of an enriched reservoir are likely to have remained isolated deep within the mantle (e.g., Thomas et al., 2012), consistent with the possibility that the presently observed LLSVPs could be partially or fully composed of remnants of an early enriched reservoir.

Date Created
2014-12-15
Agent