Search NASA⌕ Search

Engineering topics

T J McCoy

Publications and source records attributed to T J McCoy.

9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Nanoscale Mineralogy of Bennu Samples Returned by OSIRIS-REx

The OSIRIS-REx spacecraft returned regolith samples from asteroid Bennu and an initial sample was allocated for quick-look (QL) analyses. These QL particles were recovered from the avionics deck of the sample canister and were used to test the hypothesis that this dust is broadly representative of the bulk sample. The QL sample analyses showed that the materials are dominated by hydrated silicates, sulfides, magnetite, phosphates, and abundant organic matter, in addition to other minor/trace phases. Here we report our preliminary transmission electron microscope (TEM) observations for the nanoscale mineralogy of Bennu samples.

L P Keller↗
NASA NTRS2024

Identifying Solar Wind and Other Volatiles in Space-Weathered Samples From Asteroid Bennu

On September 24, 2023, NASA’s Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission returned >70 g of material from asteroid Bennu to Earth. The Sample Return Capsule was opened at NASA Johnson Space Center (JSC), and a spillover sample was collected from the avionics deck to perform quick-look (QL) analyses. In addition to providing a reconnaissance investigation of its mineralogy, the sample was also examined for evidence of surface exposure on asteroid Bennu by identifying signatures of space weathering. Space weathering changes the morphology, microstructure, and chemistry of regolith on the surfaces of airless bodies. Driven by micrometeoroid bombardment and solar wind irradiation, our understanding of how space weathering modifies particles on the surfaces of carbonaceous asteroids is still developing. To bolster the interpretation of remote sensing data and to further address driving Hypothesis 10, we must investigate the nanoscale structural and chemical changes in returned samples from Bennu to understand how space weathering affects carbonaceous surface materials. Here we explore evidence for solar wind irradiation in QL samples from asteroid Bennu.

M S Thompson↗
NASA NTRS2022

Global geologic map of asteroid (101955) Bennu indicates heterogeneous resurfacing in the past 500,000 years

Global geologic maps are useful tools for efficient interpretation of a planetary body, and they provide global context for the diversity and evolution of the surface. We used data acquired by the OSIRIS-REx spacecraft to create the first global geologic map of the near-Earth asteroid (101955) Bennu. As this is the first geologic map of a small, non-spherical, rubble-pile asteroid, we discuss the distinctive mapping challenges and best practices that may be useful for future exploration of similar asteroids, such as those to be visited with the Hera and Janus missions. By mapping on two centimeter-scale global image mosaics (2D projected space) and a centimeter-scale global shape model (3D space), we generated three input maps respectively describing Bennu’s shape features, geologic features, and surface texture. Based on these input maps, we defined two geologic units: the Smooth Unit and the Rugged Unit. The units are differentiated primarily on the basis of surface texture, concentrations of boulders, and the distributions of lineaments, mass movement features, and craters. They are bounded by several scarps. The Rugged Unit contains abundant boulders and signs of recent mass movement. It also has fewer small(<20 m), putatively fresh craters than the Smooth Unit, suggesting that such craters have been erased in the former. Based on these geologic indicators, we infer that the Rugged Unit has the younger surface of the two. Differential crater size-frequency distributions and the distribution of the freshest craters suggest that both unit surfaces formed ~10–65 million years ago, when Bennu was located in the Main Asteroid Belt, and the Smooth Unit has not been significantly resurfaced in the past 2 million years. Meanwhile, the Rugged Unit has experienced resurfacing within the past ~500,000years during Bennu’s lifetime as a near-Earth asteroid. The geologic units are consistent with global diversity in slope, surface roughness, normal albedo, and thermal emission spectral characteristics. The site on Bennu where the OSIRIS-REx mission collected a regolith sample is located in the Smooth Unit, in a small crater nested within a larger one. So although the Smooth Unit is an older surface than the Rugged Unit, the impact-crater settingindicates that the material sampled was recently exposed. Several similarities are apparent between Bennu and asteroid (162173) Ryugu from a global geologic perspective, including two geologic units distinguishable by variations in the number density of boulders, as well as in other datasets such as brightness.

E R Jawin↗
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 ~2–3 m, 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 1.6–2.2 Myr for craters less than a few meters to ~10–65 Myr for craters >100 m 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.

Asteroids↗
NASA NTRS2020

Exogenic Basalt on Asteroid (101955) Bennu

When rubble-pile asteroid 2008 TC3 impacted Earth on October 7, 2008, the recovered rock fragments indicated that such asteroids can contain exogenic material. However, spacecraft missions to date have only observed exogenous contamination on large, monolithic asteroids that are impervious to collisional disruption. Here we report the presence of meter-scale exogenic boulders on the surface of near-Earth asteroid (101955) Bennu - the 0.5-km, rubble-pile target of the OSIRIS-REx mission which has been spectroscopically linked to the CM carbonaceous chondrite meteorites. Hyperspectral data indicate that the exogenic boulders have the same distinctive pyroxene composition as the howardite-eucrite-diogenite (HED) meteorites that come from (4) Vesta, a 525-km diameter asteroid that has undergone differentiation and extensive igneous processing. Delivery scenarios include the infall of Vesta fragments directly onto Bennu or indirectly onto Bennu’s parent body, where the latter’s disruption created Bennu from a mixture of endogenous and exogenic debris. Our findings demonstrate that rubble-pile asteroids can preserve evidence of inter-asteroid mixing that took place at macroscopic scales well after planetesimal formation ended. Accordingly, the presence of HED-like material on the surface of Bennu provides previously unrecognized constraints on the collisional and dynamical evolution of the inner main belt.

Asteroids↗
NASA NTRSDate not supplied

Antarctic Meteorites: A Statistical Look at a Uniquely Valuable Resource

As of the 2019-20 field season, the U.S. Antarctic meteorite program has collected >23,000 meteorites. The U.S. collection is valuable in that it is classified in its entirety. The systematic collection methods employed have pro-vided meteorites of >40 types, many of which are the first of their type ever recognized. One of the early drivers for characterization of the entire U.S. Antarctic collection was to allow statistical comparisons. Early statistical assessments examined mass distributions and the relative frequency of meteorite types as well as comparisons to a defined set of modern falls. Using these statistics some have argued that the flux of H chondrites changed over time. Harvey used model size distributions to deconstruct the contribution of wind movement, meteorite supply and search losses to the Antarctic collection. Mass-based statistics and size distribution comparisons were examined, including comparison with modern falls/Saharan finds. Focus has been on geospatial statistics, with a comprehensive overview of the statistics of the Antarctic collections provided from the first 35 seasons of U.S. collection by ANSMET, as well as more recent assessments.

Antarctic meteorite↗
NASA NTRSDate not supplied

Initial Characterization of Intermediate Bennu Particles to Evaluate Lithologic Diversity and Mineralogic and Redox Equilibria

The OSIRIS-REx spacecraft returned regolith from asteroid Bennu to Earth September 24, 2023 [1]. As part of initial science allocations and sample analysis plan [2], JSC science team members received aggregate material from within the TAGSAM head (OREX-803017-0) to characterize. Here we report the results of analyses that have been carried out to determine mineralogic composition, surface features, and overall lithologic diversity in Bennu particles. These initial observations will inform additional analyses that will address the nature of pre-biotic and pre-solar material, formation location of Bennu, geologic history of the asteroid, and its impact/collisional/re-accretion history [3].

Bennu↗
NASA NTRSDate not supplied

Coordinated Analysis of Isotopically Anomalous Nanoglobules and Insoluble Organic Matter in Quick-Look Samples From Asteroid Bennu

Spectral characterization of B-type asteroid Bennu by the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft indicated abundant organic matter with similarities to insoluble organic matter (IOM) in meteorites. IOM in chondritic samples occurs in multiple forms, including a fluffy morphology and submicron-sized rounded nanoglobules. Isotopic anomalies in H, C, and N have been observed in both morphologies and are postulated to result from low-temperature chemical reactions in the molecular cloud or outer protoplanetary disk [e.g., 2,3]. We tested the hypothesis that Bennu also contains such isotopically anomalous organic matter by conducting coordinated in situ analysis of “quick-look” samples collected from the avionics deck of the OSIRIS-REx sample canister. This study expands our understanding of the fundamental nature of Bennu and its pre-accretionary environment by investigating the morphologies and isotopic distribution of presolar organic matter in Bennu.

A N Nguyen↗