The two most primitive solar system materials available are chondrite matrices (both interchondrule matrix and chondrule rims) and chondritic porous interplanetary dust particles (CP idps), and both…

This federal contract award to the Carnegie Institution of Washington, doing business as Carnegie Institution for Science, a renowned non-profit research organization, supports fundamental scientific research on early solar system materials. The $318,241.16 grant from NASA's Shared Services Center aims to investigate the formation and evolution of chondrite matrices and chondritic porous interplanetary dust particles, which contain clues about processes in the early solar system. The research will use electron microscopy techniques to analyze the abundances, compositions, and microstructures of different components within these primitive materials, in order to test competing models for their origins. This work does not involve any set-aside designation. The Carnegie Institution for Science has a long history of receiving federal research grants and contracts from agencies like NASA, NSF, NIH, and DOE to advance scientific understanding across disciplines.

The two most primitive solar system materials available are chondrite matrices (both interchondrule matrix and chondrule rims) and chondritic porous interplanetary dust particles (CP idps), and both contain presolar circumstellar grains, d-rich organic matter, fine grained crystalline silicates with similar ranges of compositions, and amorphous silicates. These common features suggest both are mixtures of materials inherited from the presolar molecular cloud and materials that were thermally processed in the nebula. Despite these common features, there is still no consensus about (1) whether matrix and CP idps are related, (2) how their components formed, or (3) what they tell US about processes in the early solar system. In the two-component model, matrix is dominated by CI-like material. Modest contributions from chondrules and inclusions, along with parent body modification, explain non-CI-like bulk matrix compositions. The higher abundances of presolar grains and organics in many CP idps indicate lower contributions from the thermally processed material, consistent with cometary origins. Nevertheless, for the thermally processed material to be so widespread probably requires that IT formed very early when radial disk transport was most vigorous. The alternative model is that matrix is the complement to chondrules, in which case the presolar grains, organic matter, etc. Were added to matrix late in a minor primitive component. Complementarity has far reaching consequences as IT suggests that chondrules and matrix formed in close proximity and were not later efficiently fractionated from one another despite their very different grain sizes. IT is an argument against the x-wind model and any other grain size sensitive processes such as forming and/or transporting chondrules in disk winds or planetesimal formation by pebble accretion or the streaming instability. These two models result in fundamentally different views of thermal processing and transport in the nebula, as well as accretion of planetesimals. IT is the aim of this proposal to TRY to test both models by combining focused ION beam (FIB) and electron microscopy techniques in ways that minimize the potential for operator or analytical bias, as well as provide checks for the accuracy and selfconsistency our protocols. (i) we will use point counting and quantitative elemental analysis in the electron microprobe to determine the abundances and bulk compositions of: (a) chondrules, (b) isolated metal, sulfide and silicate grains (>10 UM), (c) interchondrule matrix, (d) chondrule rims, and (d) refractory inclusions. To minimize the influence of parent body alteration, we will only analyze the most primitive chondrites available. A first order check of this approach will be to combine all the components in each meteorite and compare the estimated bulk compositions to the bulk compositions for their groups from the literature. (II) we will follow this up with high spatial resolution SEM studies of the most primitive matrix areas to determine the abundances and compositions of mineral grains>1 UM. These data will be used to estimate the contributions of chondrules and inclusions to matrix, as well as to search for grains that are unrelated to chondrules and inclusions. (III) we will use SEM-stem and TEM techniques to analyze FIB sections from these matrix areas to determine: (a) the bulk compositions of the FIB sections for comparison with the matrix compositions determined by empa, and (b) the compositions, microstructures and abundances of minerals and amorphous material>100 NM across (thickness of sections) for comparison with chondrules, inclusions and CP idps. We will use exactly the same techniques to analyze FIB sections of CP idps so that we can make direct comparisons. Armed with this data, we will compare the compositions and microstructures of matrix and its components to the expectations of the two-component and complementarity models.