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Scott A. Sandford

Publications and source records attributed to Scott A. Sandford.

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2023

The Nature of Insoluble Organic Matter in Sutter’s Mill and Murchison Carbonaceous Chondrites: Testing the Effect of X-ray Computed Tomography (XCT) and Exploring Parent Body Organic Molecular Evolution

This study analyzed samples of the Murchison and Sutter’s Mill carbonaceous chondrite meteorites in support of the future analysis of samples returned from the asteroid (10155) Bennu by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission. Focusing specifically on the insoluble organic matter (IOM), this study establishes that a total of 1.3 g of bulk sample from a single chondritic meteorite is sufficient to obtain a wide range of cosmochemical information, including light element analysis (H, C, and N), isotopic analysis (D/H, 13 C/ 12 C, and 15 N/ 14 N), and X-ray fluorescence spectroscopy for major elemental abundances. IOM isolated from the bulk meteorite samples was analyzed by light element and isotopic analysis as described above, 1 H and 13 C solid-state nuclear magnetic resonance spectroscopy, Raman spectroscopy, and complete noble gas analyses (abundances and isotopes). The samples studied included a pair from Murchison (CM2), one of which had been irradiated with high-energy X-rays in the course of computed tomographic imaging. No differences between the irradiated and non-irradiated Murchison samples were observed in the many different chemical and spectroscopic analyses, indicating that any X-ray–derived sample damage is below levels of detection. Elemental, isotopic, and molecular spectroscopic data derived from IOM isolated from the Sutter’s Mill sample reveals evidence that this meteorite falls into the class of heated CM chondrites.

planetary science↗
NASA NTRS2021

The Stardust Sample Return Mission

Stardust was a Discovery class NASA mission that successfully collected dust from the coma of a Jupiter family comet, 81P/Wild 2, and returned it to Earth in 2006 for study in terrestrial laboratories. Study of the returned samples revolutionized our understanding of the nature of the materials involved in comet formation. They demonstrated that comets contain a diverse set of materials that originated from numerous locations in the protosolar disk, were mixed together and assembled into a cometary parent body, and subsequently stored in a manner that resulted in very little parent body alteration. They represent a snapshot of the diversity of processes, environments, and materials present during the early stages of the formation of our planetary system.

organics↗
NASA NTRS2020

Widespread carbon-bearing materials on near-Earth asteroid (101955) Bennu

(101955) Bennu is a dark, Earth orbit-crossing, asteroid thought to be assembled from the fragments of an ancient collision. Spatially-resolved visible and near-infrared spectra of Bennu provide details about its surface properties and composition. In addition to a hydrated phyllosilicate band, we detect a ubiquitous 3.4-micron absorption feature, which we attribute to a mix of organic and carbonate materials. The shape and depth of this absorption feature vary across Bennu’s surface, spanning the range seen among similar main-belt asteroids. Its distribution does not correlate with the temperature, reflectance, spectral slope, or hydrated minerals although those characteristics correlate with each other in some cases. The deepest 3.4-micron absorptions occur on individual boulders. The variations may be due to differences in abundance, recent exposure, or space weathering.

Amy A. Simon↗
NASA NTRS2020

Visible–near infrared spectral indices for mapping mineralogy and chemistry with OSIRIS-REx

The primary objective of the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission is to return to Earth a pristine sample of carbonaceous material from the primitive asteroid (101955) Bennu. To support compositional mapping of Bennu as part of sample site selection and characterization, we tested 95 spectral indices on visible to near infrared laboratory reflectance data from minerals and carbonaceous meteorites. Our aim was to determine which indices reliably identify spectral features of interest. Most spectral indices had high positive detection rates when applied to spectra of pure, single-component materials. The meteorite spectra have fewer and weaker absorption features and, as a result, fewer detections with the spectral indices. Indices targeting absorptions at 0.7 and 2.7–3 µm, which are attributable to hydrated minerals, were most successful for the meteorites. Based on these results, we identified a set of 17 indices that are most likely to be useful at Bennu. These indices detect olivines, pyroxenes, carbonates, water/OH-bearing minerals, serpentines, ferric minerals, and organics. Particle size and albedo are known to affect band depth but had a negligible impact on interpretive success with spectral indices. Preliminary analysis of the disk-integrated Bennu spectrum with these indices is consistent with expectations given the observed absorption near 3 lm. Our study prioritizes spectral indices to be used for OSIRIS-REx spectral analysis and mapping and informs the reliability of all index-derived data products, including a science value map for sample site selection.

Hannah H. Kaplan↗