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T. J. McCoy

Publications and source records attributed to T. J. McCoy.

8 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Coordinated Analysis of Phosphates in Samples From Asteroid (101955) Bennu

Asteroid (101955) Bennu is a B-type asteroid and a prime candidate for investigating the remnants of planet formation and enhancing our understanding of potential sources of crucial bio-essential elements for the early Earth. Remote observations of the surface of Bennu unveiled a terrain of boulders primarily composed of hydrated phyllosilicates, organic molecules, and carbonates. The hydrated nature of Bennu, the abundance of carbonates, and the presence of cm-scale carbonate veins provide clues to the nature of the building blocks of Bennu’s parent body and to its complex geological history. Here we present the first mineralogical, chemical, and isotopic results of analysis of phosphates in samples returned from Bennu by NASA’s OSIRIS-REx mission. We seek to test the hypothesis that heating of Bennu’s parent asteroid resulted in hydrothermal alteration in which melted ice reacted with the initial constituents.

J. J. Barnes↗
NASA NTRS2024

Search for Presolar Materials and Isotopically Anomalous Diffuse Insoluble Organic Matter in Samples From Asteroid 101955 Bennu

Carbonaceous asteroids allow us to study the original materials that formed the planets in the protoplanetary disk. They contain organic matter and (sub-)micrometer-size dust grains, called presolar grains, that condensed in the circumstellar envelopes of evolved stars and the ejecta of stellar explosions, such as novae and supernovae, before the formation of our Solar System. The isotopically anomalous organics are thought to have formed in the interstellar medium and the early Solar System. Whereas presolar grains provide insight into the building blocks of our Solar System, studying organics can help us understand the origin of life on Earth. These organics might have contributed to ingredients that helped life emerge. The return of samples from asteroid 101955 Bennu by NASA’s Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission gives us a new opportunity to elucidate the formation mechanism(s) and evolution of organics, as well as the abundance and distribution presolar grains in carbonaceous asteroids. Here, we report on our ongoing work to characterize the isotopic and chemical compositions, microstructure, distribution, and abundance of insoluble organic matter (IOM) and presolar grains in Bennu samples. This work supports hypotheses 2 and 3 of the OSIRIS-REx Sample Analysis Plan.

P. Haenecour↗
NASA NTRS2023

Preliminary Examination of Returned Samples From Bennu Using Quantitative Particle Analysis in the Scanning Electron Microscope

The sample of regolith collected from asteroid Bennu by NASA’s OSIRIS-REx spacecraft will land in Utah on September 24, 2023. A 100-mg aliquot of fine Bennu dust adhering to the internal surfaces of the sample return capsule and associated hardware will be collected by curation staff during disassembly and analyzed immediately by members of the sample analysis team in a “Quick-Look” (Q-L) procedure. The Q-L objectives are (1) to provide images for release to the public to inform on the nature of the returned sample, and (2) to perform a reconnaissance investigation of the mineralogic characteristics of the returned material for science purposes. We will determine the minerals that occur in the dust, assess their diversity, and determine relative abundances at the >5% level using a combination of optical microscopy, Fourier-transform infrared spectroscopy, X-ray powder diffraction, and field-emission scanning electron microscopy (SEM). Here we describe the procedures and techniques developed for the Q-L analyses using analog samples analyzed by SEM equipped with energy dispersive X-ray spectroscopy (EDX). To test these techniques, we have applied them to several samples, including powders of the Murchison (Fig. 1) and Orgueil meteorites, as well as simulant samples prepared by the mission.

OSIRIS-REx↗
NASA NTRS2022

Crater population on asteroid (101955) Bennu indicates impact armouring and a young surface

The impactor-to-crater size scaling relationships that enable estimates of planetary surface ages rely on an accurate formulation of impactor–target physics. An armouring regime, specific to rubble-pile surfaces, has been proposed to occur when an impactor is comparable in diameter to a target surface particle (for example, a boulder). Armouring is proposed to reduce crater diameter, or prevent crater formation in the asteroid surface, at small crater diameters. Here, using measurements of 1,560 craters on the rubble-pile asteroid (101955) Bennu, we show that the boulder population controls a transition from crater formation to armouring at crater diameters ~2–3m, below which crater formation in the bulk surface is increasingly rare. By combining estimates of impactor flux with the armouring scaling relationship, we find that Bennu’s crater retention age (surface age derived from crater abundance) spans from 1.6–2.2Myr for craters less than a few meters to ~10–65Myr for craters >100m in diameter, reducing the maximum surface age by a factor of >15 relative to previous estimates. The range of crater retention ages, together with latitudinal variations in large-crater spatial density, indicate that ongoing resurfacing processes render the surface many times younger than the bulk asteroid.

E. B. Bierhaus↗
NASA NTRS2019

Craters, Boulders and Regolith of (101955) Bennu Indicative of an Old and Dynamic Surface

Small, kilometre-sized near-Earth asteroids are expected to have young and frequently refreshed surfaces for two reasons: collisional disruptions are frequent in the main asteroid belt where they originate, and thermal or tidal processes act on them once they become near-Earth asteroids. Here we present early measurements of numerous large candidate impact craters on near-Earth asteroid (101955) Bennu by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) mission, which indicate a surface that is between 100 million and 1 billion years old, predating BennuaCTMs expected duration as a near-Earth asteroid. We also observe many fractured boulders, the morphology of which suggests an influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface. However, the surface also shows signs of more recent mass movement: clusters of boulders at topographic lows, a deficiency of small craters and infill of large craters. The oldest features likely record events from Bennua time in the main asteroid belt.

K. J. Walsh↗
NASA NTRSDate not supplied

IIAB IRON METEORITES: FORMATION AND RELATION TO OTHER METEORITE GROUPS.

The IIAB iron meteorites are one of the largest iron meteorite groups that formed by fractional crystallization [1]. Iron meteorites formed over a range of oxygen fugacities (fO2)[2], most formed relatively reduced at~ IW–4to –2.5 (IABs), where IW= iron-wüstite buffer, to relatively oxidized at IW–1(IVBs) [2,3]. While the IIABs contain reduced mineral phases (daubré elite [1]),the fO2for IIABs is poorly constrained. The fO2of iron meteorites may have become more reducing during cooling, with oxidized phases (i.e., chromite) forming at higher temperatures and daubré elite forming at lower temperatures [4]. The O-and Cr-isotope compositions of silicates and chromite in meteorites, including iron meteorites, can determine potential genetic links to other meteorite sand con-strain if a meteorite is from the non-carbonaceous (NC) or carbonaceous (CC) group [e.g., 5–8]. Iron meteorite groups have been identified as being in the NCor CC group using Mo[9]and Ni [10] isotope compositions of their metallic component. Numerous iron meteorites contain minor amounts of silicates and oxides [e.g., 11], but most have not been analyzed for their Cr or Ti isotope compositions, with some exceptions (e.g., IIIABs [6,7],a IIG, and a IIAB[7]). We analyzed the compositions of silicates and chromite in six IIAB iron meteorites to investigate the relationship between IIABs and known meteorite groups, the fO2of IIABs, and the origin of chromite in the IIABs. *full abstract in document

Meteorite↗
NASA NTRSDate not supplied

Space Weathering in OSIRIS-REx Samples From Bennu: Impact Melt Deposits

Early analyses of regolith samples from asteroid Bennu delivered by the OSIRIS-REx spacecraft showed a mineralogy dominated by hydrated silicates, sulfides, magnetite, phosphates, and abundant organic matter, in addition to other minor/trace phases. A major objective of the sample analysis campaign is to understand the nature and extent of space weathering processes recorded by returned samples from Bennu. Here we report our preliminary transmission electron microscope (TEM) observations of impact melt deposits on surfaces of Bennu sample particles.

L. P. Keller↗