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Cosmic Origins

Modal mineralogy of carbonaceous chondrites (bulk & separates) by Position Sensitive Detector X-ray Diffraction: low temperature mineral evolution and implications for spectroscopy

Active Technology Project

Project Introduction

Modal mineralogy of carbonaceous chondrites (bulk & separates) by Position Sensitive Detector X-ray Diffraction: low temperature mineral evolution and implications for spectroscopy
This is a proposal to study the evolution of low temperature mineral assemblages, dominated by serpentines, in primitive carbonaceous chondrites (CCs). The team would utilize optical light microscopy (OLM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), state-of-the-art X-ray diffraction (XRD), mid-infrared (MIR) spectroscopy, plus experiments in synthesis of serpentines. The proposal would involve 3 main tasks targeted at exploring 3 key hypotheses: 1. Determine the modal mineralogy of the most primitive CCs. Including quantifying the abundance of amorphous silicate (and the extent of its hydration) and tochilinite. • Here the underlying hypothesis being tested is that amorphous silicate is a dominant matrix component in primitive CCs. 2. Decipher the mineralogical evolution of hydrated asteroids. • Here the underlying hypothesis being tested is that a systematic relationship exists between composition and crystal form in CC serpentines. 3. Produce a mineral abundance database to both help link meteorites to asteroids and space missions to define their target • Here the underlying hypothesis being tested is that amorphous Fe-silicate yields spectral features to discriminate primitive CCs. What motivates the project? Accretion of hydrous asteroids may have profoundly influenced development of Earth's key systems and the origin and evolution of its life. Understanding the processes that led to hydration of asteroids is therefore a key part of explaining the origin of Earth like planets. As a result of their scientific values hydrous asteroids are targets for sample return missions like OSIRIS-REx. This proposal would employ a cutting-edge X-ray diffraction system, the Position Sensitive Detector XRD (PSD-XRD) to study bulk CC samples and separates, in combination with TEM, SEM and hydrothermal experiments to reveal the nature and dynamic evolution of hydration processes in asteroids. Our ability to understand the mineralogical evolution of meteorites and recognize their asteroid parent bodies remotely would be improved by constrained mineral abundances for meteorite powders used in spectral comparisons. PSD-XRD provides a means of determining modal abundances in powdered samples that are ideal for spectral measurements. By integrating accurate mineral abundance data and MIR spectra for the same powders, mineralogical controls on spectral features can be constrained and so can the surface mineralogy of asteroids. We consider meteorites in our collections to represent the puzzle pieces from which the solar system's evolution and the formation of planets can be reconstructed. What is needed to put the pieces together is to place these samples in context within the solar system. This is a key driver of the modern age of sample return missions exemplified by Hayabusa and the upcoming OSIRIS-REx and H2. Here is a chance to bridge the gap between our understanding of meteorite sample mineralogy and asteroid mineralogy. By extension the provenance of meteorite samples would be constrained to provide much needed context and facilitate targeting of asteroids for future missions. A Planetary Major Equipment (PME) Request (Investigator Instrument) accompanies this proposal where the PI seeks to purchase a dedicated PSD-XRD array. More »

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