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M. E. Zolensky

Publications and source records attributed to M. E. Zolensky.

15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Chemical and Physical Properties of Cometary Dust

Cometary dust particles are best preserved remnants of the matter present at the onset of the formation of the Solar System. In Space missions, telescopic observations and laboratory analyses advanced the knowledge on the properties of cometary dust. the only samples certified with a cometary origin were returned by the Stardust space mission from comet 81P/Wild2. The “chondritic porous” (here called “chondritic anhydrous”) interplanetary dust particles (CA-IDPs) and micrometeorites (CP-MMs), and the ultracarbonaceous Antarctic MMs (UCAMMs) also show strong evidence for a cometary origin. The elemental composition of cometary dust is generally consistent with the chondritic (CI) composition, with the notable exception of elevated contents in carbon and nitrogen compared with CI. The organic matter of cometary dust is mixed with minor amounts of crystalline (at least 25% of the minerals) and amorphous mineral phases. The most abundant crystalline minerals are ferromagnesian silicates (olivine and low-Ca pyroxenes), but High-Ca pyroxenes, refractory minerals and Low Ni Fe sulfides are also present. The crystalline olivine and low-Ca pyroxene compositions can vary from their Mg-rich end-member (forsterite and enstatite) to relatively Fe-rich compositions. Refractory minerals as well as secondary minerals likeLIME (low-iron, Mn-enriched) olivines, unusual Fe sulfides or mineral aggregates of specific compositions like Kosmochloric high-Ca pyroxene and FeO-rich olivine - KOOL grains) are also found. The presence of carbonates in cometary dust is still debated, but a phyllosilicate-like phase was observed in a UCAMM. The abundance of pyroxene to olivine (in numbers) is larger than in primitive meteorites (e.g. the Px/Ol ratio is usually larger than 1). GEMS phases (glass with embedded metals and sulfides) are abundant in cometary dust, although not systematically found. Some of the organic matter present in cometary dust particle resembles the insoluble organic matter (IOM) present in primitive meteorites, but amorphous carbon and exotic (e.g. N-rich) organic phases are also present. The hydrogen isotopic composition of cometary dust particles (in the organic matter) is usually rich in deuterium, tracing a formation at very low temperatures, either in the protosolar cloud or in the outer regions of the protoplanetary disk. The presolar dust concentration in cometary dust can reach about 1%, which is the most elevated value observed in extraterrestrial samples. The size distribution of cometary dust in comet trails is well represented by a power-law distribution (differential size distribution) with a mean power index N typically ranging from -3 to -4. Polarimetric and light scattering studies of cometary dust suggest mixtures of porous agglomerates of sub-micrometer minerals with organic matter, which is compatible with the in situ analyses of 67P/Churyumov-Gerasimenko by MIDAS (Rosetta) and with the studies of it Stardust samples, CA-IDPs, CP-MMs and UCAMMs. Cometary dust particles have low tensile strength, and low density.

C. Engrand↗
NASA NTRS2021

Mineralogy and Surface Modification of Small Grains Recovered from the Asteroid 162173 Ryugu

Surface material on airless bodies exposed to the interplanetary space experienced the bombardment by low-energy (~1 keV/nucleon) solar wind particles and micrometeoroid impacts. These processes, alongside the resultant surface modifications, and spectral darkening and reddening are called space weathering [1]. Space weathering of the Moon and the asteroid 25143 Itokawa belonging to S-type asteroids have been investigated intensively [e.g. 1-5]. The Hayabusa 2 spacecraft returned samples from the asteroid 162173 Ryugu C-type asteroid. The Ryugu samples give us the first opportunity to investigate space weathering of C-type asteroids. The Mineralogy-Petrology Fine (M-P F or Sand) sub-team mainly investigates small grains (typically ~100 μm across). The main purposes of the M-P F sub-team are to understand the variationof mineralogy of the allocated grains and the nature of space weathering of the asteroid Ryugu. The M-P F sub-team is comprised of 51 members belonging to 25 universities and laboratories

T. Noguchi↗
NASA NTRS2004

What are the P-type Asteroids Made Of?

The P-type asteroids, together with the D asteroids, had been believed to be one of the most primitive asteroid classes having surface materials rich in carbon and/or organics. Upon a fall of a new type of meteorite, Tagish Lake in 2000, we came to have a possible sample of the D (and/or T) asteroids. In both spectrally and distance from the sun, the P asteroids are located in between the C/G/B/F asteroids and the D asteroids. Because it is believed that the former group are similar to (thermally metamorphosed) CI/CM chondrites and the latter the Tagish Lake meteorite, the surface material of the P asteroids may be understood in combination of those two meteorite groups. Taking that direction, this paper presents possibly the first quantitative characterization of the P asteroids in terms of carbonaceous chondrites and their experimental derivatives.

T. Hiroi↗
NASA NTRSDate not supplied

Constraints on the surface materials of Ryugu from spectral and water analysis of experimentally-heated CI carbonaceous chondrite

We performed heating experiments of the Orgueil CI chondrite in vacuum conditions at fO2 around I/W to evaluate systematic changes in mineralogy, water contents, and visible to infrared spectral features. Our goal is to interpret the spectra of Ryugu, the target C asteroid of the Hayabusa2 mission, because Ryugu shows spectral features similar to partially dehydrated carbonaceous chondrites. However heated carbonaceous chondrites can be easily contaminated by terrestrial water, which makes it almost impossible for laboratory data to be compared with spectra of asteroids directly. Therefore, our heated samples were analyzed without exposure to the air after experimental heating to minimize the effects of terrestrial water. The depth of the 2.7-µm absorption band and the water content of the heated Orgueil form a positive correlation trend which follows the results of experimental heating of CM and Tagish Lake meteorites using our experimental procedures. It is found that 500-°C heated Orgueil sample shows the best spectral match with Ryugu in terms of the low reflectance (~2%) at visible wavelengths and a weak absorption (~10%) at around 2.72 µm owing to survival of Mg-rich phyllosilicates. We suggest that Ryugu might have experienced heating and dehydration at a temperature around 500 °C, after aqueous alteration, and presently contains a small quantity of hydrated minerals equivalent to 1-2 wt.% of water at the surface.

K. Amano↗
NASA NTRSDate not supplied

Experimental reproduction of space weathering of C-type asteroids by He exposure: irradiation-energy and physical-property dependence

Visible and near-infrared observations of C-type asteroid 162173 Ryugu suggest that the surface color variation seems to have resulted from a surface-correlated process which changed the color from blue to red, but the mechanism for the change is not yet identified. Space weathering is one possible mechanism responsible for the color variation, but the spectral changes of C-type asteroids from space weathering are not yet fully understood. We have carried out He exposure experiments on hydrous carbonaceous chondrites in order to understand the irradiation-energy and the physical-property dependence of space weathering of C-type asteroids. He exposure to different porosities of the same meteorite samples results in different behavior of spectral changes. In addition, the meteorite samples with the same porosity and the same surface roughness show different spectral changes when the samples are exposed to He ions with different energies. Therefore, our experiments indicate that spectral changes by space weathering of C-type asteroids depend not only on the asteroid types but also on the physical properties of the regolith surface and the solar-wind He energy.

Michael E Zolensky↗
NASA NTRSDate not supplied

Reflectance spectra measurement plan of captured samples from Ryugu: current status

Hayabusa2 spacecraft is equipped with Optical Navigation Camera (ONC) andNear-infrared Spectrometer (NIRS3), and has obtained reflectance spectra of the C-type near-Earth asteroid Ryugu over a wavelength range of 0.40–0.95 μm and 1.8–3.2 μm, respectively. It was revealed that Ryugu exhibits globally very low albedo (less than 0.02 at 0.55 and 2.0 μm), a slightly positive spectral slope, and an ubiquitous weak but sharp OH absorption band centered at 2.72 μm,showing a little regional heterogeneities. Thus, the surface material of Ryugu can be estimated as relatively similar to moderately heated carbonaceous chondrites, e.g., moderately dehydrated CI and CM, and enriched in carbon (Kitazato et al., 2019; Sugita et al., 2019; Tatsumi et al., 2020).Hayabusa2 successfully has performed twice touch down operations, and the captured sample will be brought back to the Earth in late 2020 (Morota et al., 2020; Tachibana et al., in preparation). To clarify Ryugu’s mineralogical and physicochemical properties and their varieties, effective for spectral characteristics obtained by ONC and NIRS3, several grains are planned to be distributed to several primary analysis groups. In this study, we report the current status of our spectral analysis plan in Hayabusa2 MINeralogy and PETrology of coarse grains (MIN-PET CG) team led by T. Nakamura, and the latest rehearsal analysis result using carbonaceous chondrite samples. MIN-PET CG rehearsal measurements have been performed to obtain detailed spectral properties of Ryugu grains with diverse spatial resolutions ranging from μm to mm scale or larger; using a few mm size polished CM sample with several microscopic imaging spectrometers covering various spatial range; with 200 μmor finer spatial resolution at Institut d’Astrophysique Spatiale, ~50 and 150 μm spatial resolution invisible and IR ranges at Brown University, and with 40 μm or larger spatial resolution at Tohoku University, and using mm-size CM and CI grains with a diffuse reflectance spectrometer with a few mm resolution at Tohoku University. Diffuse reflectance spectroscopy measurements undergo to use several mm-size CM or CI chondrite grains with Bruker VERTEX 70v, which covers ~0.38–15 μm in wavelength. To keep returned samples out of atmosphere avoiding any terrestrial contamination, wehave prepared an air shutoff cell to put samples and standard materials together kept in a N2 purged condition (Amano et al., 2020). Samples are Murchison CM chondrite showing typically ~5%reflectance with a strong OH absorption band at ~2.8 μm, and laboratory heated CI chondrite showing~3% reflectance, and a weak OH absorption band at ~2.7 μm. We will perform (1) fixed angle condition as laboratory standard setting at incident, emission, and phase angles of 30°, 0°, 30°, or 0°,30°, 30°, and (2) various angle conditions for photometric corrections. Future lab analyses of samples returned from Ryugu will provide direct and detailed information on the mineralogical and physicochemical properties of Ryugu, and relationship of spectral characteristics obtained by remote sensing and laboratory instruments.

M. Matsuoka↗
NASA NTRSDate not supplied

Early History of Ryugu’s Parent Asteroid: Evidence from Return Sample

Near-Earth Cb-type asteroid (162173) Ryugu is a rubble pile asteroid made of fragments of the original parent asteroid [1-5]. It is possible that the fragments from various depths of the original asteroid are on the surface of the present-day Ryugu. Therefore, samples collected from Ryugu are expected to retain formation and evolution history of the interior of Ryugu’s parent asteroid. In this study, we will focus on understanding the early history of Ryugu’s parent asteroid. For this purpose, we need to understand: 1) when and where in the solar nebula Ryugu’s parent asteroid formed, 2) the original mineralogy and the abundance and composition of water-rich ice in the accreted materials, 3) how these materials chemically and mineralogically evolved, and 4) how the parent body was destroyed by a catastrophic collision.

T. Nakamura↗
NASA NTRSDate not supplied

Mineralogical Variation of the C1 Lithologies in the Kaidun Meteorite

The Kaidun meteorite is a polymict microbreccia, characterized by the presence of numerous clasts of various chondritic and achondritic materials. Chondritic clasts are C1, C2, CM1, CM2, CV3, EH3-5, EL3, and ordinary chondrite-related materials [1,2]. There is significant evidence that aqueous alteration in the carbonaceous chondrite clasts in Kaidun occurred primarily in their parent bodies prior to accumulation to the Kaidun body. Thus, the observation of highly aqueously altered materials (C1 clasts) can provide quantitative constraints on the geologic history of the asteroidal parent bodies. Additionally, the lack of petrological features complicates the classification of C1 materials, but recent studies of new meteorite falls and Ryugu samples continue to emphasize the diversity of C1 materials [e.g., 3,4]. Considering the unprecedentedly diverse origin of clasts in Kaidun, it is expected to contain unknown C1 materials, including ungrouped C1, which will further increase the diversity of those materials. Therefore, this study aims to systematically understand C1 materials by comparing Kaidun C1 with known C1s such as CI1, CM1 and CR1. Since textural observations and chemical composition analyses of carbonates, sulfides, and phyllosilicates in C1 materials in Kaidun have not yet been adequately performed, this study focuses mainly on such analyses.

K. Ogiya↗
NASA NTRSDate not supplied

Understanding the Heating Kinetics of Asteroid Ryugu By Comparison to Naturally and Experimentally Heated Meteorites

The Hayabusa2 mission visited the near-Earth Cb-type asteroid (162173) Ryugu and has returned to Earth surface material of Ryugu. Ryugu is an airless rubble pile asteroid exposed to space weathering [1]. Visible and near infrared remote observations recorded an absorption feature at 2.72 μm indicating the presence of OH– bearing hydrous components. The weak 2.72 μm feature suggested that Ryugu was once organic- and water-rich and subsequently dehydrated by a brief period of surficial heating with resemblance to “thermally metamorphosed carbonaceous chondrites”, “CI-/CM-like”, or “CY” chondrites [2, 3]. However, initial examination of the returned samples did not identify any significant heating of >150 °C [4, 5], and contrastingly, amino acid analysis of Ryugu samples suggested similarities to thermally-altered meteorites on the grounds of the predominant straight-chain n-ω-amino acid abundances [6]. In this study, we aim at addressing the nonconformal interpretations to the thermal history of Ryugu by comparing the organic composition of fresh Ryugu samples to that of chondritic meteorites that have been naturally (long-term radiogenic thermal metamorphism and short-term heating) and experimentally heated.

Q. H. S. Chan↗
NASA NTRSDate not supplied

Comet Wild 2 Sample Track 3D Images and S-XRF Stereo Maps

The NASA Stardust mission to comet Wild 2 returned to Earth in 2006 with cometary material trapped in aerogel. The cometary particles were captured at a relative velocity of 6.1 km/s, creating three-dimensional (3D) tracks containing void space, compressed aerogel, melted aerogel, and fragmented cometary material. Each track represents a unique hypervelocity impact event. The nature of each track forming event, including the original state of the impactor, is recorded in 3D track morphology and material distribution. Tracks were cut from sampling tiles in thin aerogel “keystones” translucent to optical light.

D. S. Ebel↗
NASA NTRSDate not supplied

Olivine Compositional Systematics of CI Chondrites and Asteroid Ryugu

Recent findings of rare anhydrous silicates (especially, olivine) in asteroid Ryugu samples suggest that small amounts of precursor materials escaped subsequent aqueous alteration in the Ryugu parent body [e.g., 1]. The origins of these anhydrous grains are considered to be either AOA-like or chondrule-like materials [2,3]. We have studied CI chondrites Ivuna and Orgueil on the same manner to analyze Ryugu samples and found the similar occurrence of anhydrous silicates in these brecciated meteorites [4]. In this abstract we report the mineralogy of olivine grains in another CI chondrite Alais to compare with Orgueil and Ivuna as well as Ryugu samples to better understand their origins through compositional systematics obtained by detailed FE-EPMA analysis.

T. Mikouchi↗
NASA NTRSDate not supplied

Comparison of the Bright Boulders on the Surface of the C-Type Asteroid Bennu with White Clasts in the Murchison CM Chondrite Breccia

Spectroscopic observations of asteroid Bennu suggest that the materials on the surface of the asteroid are most similar to aqueously-altered CM- or possibly CI-type carbonaceous chondrites [1], although a relationship with heated CM [2] or CR chondrites [1] is also possible. Recently, [3] detected unusually bright boulders (Fig. 1A) on the surface of Bennu. The band ratio indicates the presence of an absorption feature beyond 0.85μm and is consistent with the presence of mafic minerals such as pyroxene or olivine. The hyperspectral data suggest that the exogenic boulders have the same distinctive pyroxene composition as the howardite-eucrite-diogenite (HED) meteorites. However, similar mineralogical features were also observed in indigenous, thermally metamorphosed white clasts reported in samples of the Murchison CM2 (Fig. 2B; [4-5]) and is an alternative interpretation for the bright boulders observed on Bennu. In addition to detailed petrographic characteristics, we report here further chemistry, O, Cr, and Ti isotopes of the clasts in order to confirm their classification, and discuss their possible relationship to Bennu.

I. Kerraouch↗