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T Nakamura

Publications and source records attributed to T Nakamura.

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Oxygen-Bearing Organic Components in Ryugu Samples

The Hayabusa2 mission visited the near-Earth Cb-type asteroid (162173) Ryugu and has returned to Earth with the surface material of Ryugu. Ryugu is an airless rubble pile asteroid exposed to space weathering. Initial organic analyses indicate that Ryugu contains aliphatic rich, ketone and carboxyl functional groups, in associated with phyllosilicate and carbonate minerals. Here we investigate the alteration history of Ryugu by comparing the organic content of carbonate-bearing Ryugu samples to that of naturally and experimentally heated meteorites.

Q H S Chan↗
NASA NTRS2024

Ubiquitous Presence of Sodium-Bearing Magnesium Phosphate in CI Chondritic Materials

The discovery that the asteroid Ryugu samples returned by the JAXA Hayabusa2 spacecraft are chemically and mineralogically nearly identical to CI chondrites has made us re-recognize the importance of CI chondrites in the early solar system [e.g., 1]. These CI chondritic materials have undergone strong aqueous alteration in their parent bodies, resulting in the formation of abundant Mg-Fe phyllosilicates along with other altered minerals such as carbonates, magnetite, and pyrrhotite. Initial and subsequent AO analyses of the Ryugu samples have found that they are brecciated on the mm~μm scale and that a small amount of forsterite and other primary minerals survive in some of the brecciated clasts with evidence of less degrees of aqueous alteration (“less altered clast”) [e.g., 1]. In addition, these less altered clasts contain a rare Na-bearing Mg phosphate that is still poorly characterized. Despite the analytical attempt to identify its mineral species, their identity has not been clarified yet. These rare Mg phosphates could be one of the key phases to understanding the evolution of CI chondritic bodies since a similar Na-bearing Mg phosphate has been reported from the asteroid Bennu sample returned by the NASA OSIRIS REx mission, and the importance of these materials has been suddenly highlighted. Since the initial analysis of the Ryugu sample, we have been paying attention to these Mg phosphates in CI chondrites as well as Ryugu samples, and here we report the present results on their mineralogical analysis.

T Mikouchi↗
NASA NTRS2022

Oxygen Isotopes in AMMS and IDPS: Universality of Oxygen Isotope Systematics Of Crystalline Silicates in Comets

It has been suggested that the major source of crystalline silicates in comets is CR chondrule-like materials along with minor sources including O, R, CH-CB chondrite chondrule-like materials based on the comparisons of oxygen isotope systematics between cometary silicates and chondrules from various types of primitive chondrites [1-3]. However, cometary silicates used for these studies are from only two comets: Wild2 and a parent comet of U2-20GCA. It is uncertain that the oxygen isotope systematics represent that of crystalline silicates in all comets.

D Nakashima↗
NASA NTRS2022

Lithological variation of asteroid Ryugu samples returned by the Hayabusa 2 spacecraft: Assessment from the 18 particles distributed to the initial analysis “Stone” team

JAXA’s Hayabusa2 spacecraft successfully returned~5.4g of C-type asteroid Ryugu materials on Dec. 2020 [e.g., 1] and the recovered samples were extensively analyzed by initial analysis teams and Phase2 curation teams. The reported results show that Ryugu samples are similar to CI chondritesin chemistry and mineralogy, showing evidence for aqueous alteration in the parent body [e.g., 2,3]. As a “stone” team of the initial analysis, we received 18coarse particles (>1 mm) of Ryugu samples to characterize their mineralogy and petrology. We found that the samples were breccias of mm-to-sub mm size clasts. All of the clasts are mainly composed of Mg-Fe phyllosilicates, but the alteration degree appears slightly different from one clast to another. Here we report a lithological variation of Ryugu samples to propose their reasonable lithological classification based upon different mineral assemblages and to discuss the formation and evolution of the Ryugu parent body.

Michael E Zolensky↗
NASA NTRS2021

Thermally Altered Subsurface Material of Asteroid 162173 Ryugu

Studies of meteorite analysis and theoretical modeling have indicated the possibility that some carbonaceous near-Earth asteroids are thermally altered due to radiative heating during close approaches to the Sun in addition to parent body processes (Nakamura, 2005; Marchi et al., 2009; Chaumard et al., 2012). In April 2019, the Hayabusa2 mission successfully completed an artificial impact experiment on the carbonaceous near-Earth asteroid 162173 Ryugu (Arakawa et al., 2020), which provided an opportunity to investigate the effects of radiative heating through the exposed subsurface material. Here we report observations of the Ryugu’s subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Spectra of the subsurface material exhibit a slightly stronger and peak-shifted hydroxyl absorption feature compared to that observed for the surface, indicating that space weathering and/or radiative heating caused a subtle change in the spectrum of Ryugu surface. However, the shape of the absorption feature still suggests that the subsurface material experienced heating above 300 ˚C similar to the surface. In contrast, our thermal modeling shows that radiative heating does not increase the subsurface temperature at 1 m depth above 200 ˚C even if the semimajor axis is reduced down to 0.344 au. This supports that the Ryugu material would have been preferentially altered due to radiogenic and/or impact heating on the parent body rather than radiative heating.

Asteroids↗
NASA NTRS2020

Characterization of the Ryugu Surface By Means Of the Variability of the Near-Infrared Spectral Slope in NIRS3 Data

The Near-Earth Asteroid 162173 Ryugu (1999 JU3) was investigated by the JAXA Hayabusa2 mission from June 2018 to November 2019. The data acquired by NIRS3 spectrometer revealed a dark surface with a positive near-infrared spectral slope. In this work we investigated the spectral slope variations across the Ryugu surface, providing information about physical/chemical properties of the surface. We analysed the calibrated, thermally and photometrically corrected NIRS3 data and we estimated the mean value of spectral slope between 1.9 μm and 2.5 μm, corresponding to 0.163. Starting from the mean value of slope and moving in step of 1 standard deviation (0.022), we defined 9 “families of slope”, the Low-Red-Slope families (LR1, LR2 and LR3) and the High-Red-Sloped families (HR1, HR2, HR3, HR4, HR5, HR6). The mean values of some spectral parameters were estimated for each family, such as the reflectance factor at 1.9 μm, the spectral slope, the depth of bands at 2.7 μm and at 2.8 μm. A progressive spectral reddening, darkening and weakening/narrowing of OH bands is observed moving from the LR families to the HR families. We concluded that the spectral variability observed among families is the resulting contribution of the thermal metamorphism experienced by Ryugu after the catastrophic disruption of its parent body and space weathering processes that occurred on airless bodies as Ryugu, such as impact cratering and solar wind irradiation. As a consequence, the HR1, LR1, LR2 and LR3 families, corresponding to equatorial ridge and crater rims, are the less altered regions on Ryugu surface, which experienced the minor alteration and OH devolatilization; the HR2, HR3, HR4, HR5 families, coincident with floors and walls of impact craters, are the most altered areas, result of the three processes occurred on Ryugu. The strong reddening of the HR6 family (coincident with Ejima Saxum) is likely due to the fine-sized material covering the large boulder.

Ryugu↗
NASA NTRSDate not supplied

The Comet Astrobiology Exploration Sample Return (CAESAR) Mission

The Comet Astrobiology Exploration Sample Return (CAESAR) mission will acquire and return to Earth for laboratory analysis a minimum of 80 grams of surface material from the nucleus of comet 67P/Chur-yumov-Gerasimenko (67P). CAESAR will characterize the surface region sampled, preserve the collected sample in a pristine state, and return evolved volatiles by capturing them in a separate gas reservoir. NASA Goddard Space Flight Center provides project management, systems engineering, safety and mission assurance, contamination control, mission operations, and many other important functions. Northrop Grumman Space Systems will build the spacecraft, based on Dawn mission heritage, which like CAESAR, uses solar electric propulsion. CAESAR was selected by for Phase A study in the New Frontiers 4 Competition and will be proposed to New Frontiers 5.Collection of a sample from the surface of comet 67P is facilitated by a set of cameras that together provide images to support sample site selection, perform optical navigation, and document the sample before, during, and after col-lection. The sample is collected at the end of an arm during a 5-second touch-and-go (TAG) maneuver with the Sample Acquisition System (SAS)designed by Honeybee Robotics for the surface properties of comet 67P observed by the Rosetta mission. After sample collection, and while the sample is still cold (< -80°C), the TAG Arm inserts the sample container into the Sample Containment System (SCS) mounted inside the Sample Return Capsule (SRC). The SCS is sealed, preventing the sample from escaping into space. The sample is slowly warmed inside the SCS to enable sublimation of volatiles, which are collected in the Gas Containment System (GCS), a passively cooled gas reservoir. Separating the volatiles from the solid sample protects the solid sample from alteration. Once all sublimated H2O is transferred to the GCS, the GCS is sealed to capture the volatile sit contains, and the SCS is vented to space to maintain the solid sample under vacuum. The SCS vent is closed before Earth entry to prevent atmospheric contamination. Detailed laboratory analyses of the sample from 67P will trace the history of volatile reservoirs, delineate the chemical pathways that led from simple interstellar species to complex molecules, constrain the evolution of the comet, and evaluate the role of comets in delivering water and prebiotic organics to the early Earth. CAESAR will achieve these goals by carrying out coordinated sample analyses that will link macroscopic properties of the comet with microscale mineralogy, chemistry, and isotopic studies of volatiles and solids. Most of the sample (≥75%) will be set aside for analyses by generations of scientists using continually advancing tools and methods, yielding an enduring scientific treasure that only sample return can provide. This presentation will review development conducted during NF4 Phase A and discuss the NF5 mission concept.

A G Hayes↗
NASA NTRSDate not supplied

Aqueous Alteration on the Ryugu Parent Body Constrained by Chemical Equilibrium Models

The composition of solid samples returned from the asteroid 162173 Ryugu byHayabusa2 indicates aqueous alteration of rocks that formed a parent body of Ryugu [1, 2]. As on parent bodies of carbonaceous chondrites [3-5], Ryugu materials could have went through (1) accretion of anhydrous and reduced rocky grains together with water-rich ices, (2) melting of ices in the body’s interior through release of radiogenic heat [6], and (3)aqueous alteration of rocky and organic materials that produced secondary minerals, salt- and organic-bearing water solutions, gases, and altered organic matter. Although the bulk chemical composition and major mineralogy (phyllosilicates, magnetite, pyrrhotite, carbonates, phosphates, etc.) of Ryugu [1,2]are similar to those of CI carbonaceous chondrites [3-5, 7], the lack of sulfates and a deficiency of oxygen in the returned samples suggest a distinct alteration pathway. Chondritic materials [3-5] do not indicate complete chemical equilibration though low-temperature parent body processes. However, calculations of chemical equilibria in modeling rock-water-gas type systems[e.g., 8, 9], could assess deviations of chondritic materials from equilibrium conditions and constrain partitioning of chemical elements between solid, aqueous, and gas phase for different stages of alteration. Here we constrained speciation of solid, aqueous, and gaseous phases during aqueous alteration on the Ryugu parent body through chemical equilibrium calculations.

M Yu Zolotov↗
NASA NTRSDate not supplied

Ryugu-Like Phyllosilicate Clast from A Giant Cluster IDP of Probable Cometary Origin: Evidence for Material Exchange Between Asteroidal and Cometary Regions

The presence of hydrous minerals in comets is currently an open question. They were commonly produced inside primitive meteorite parent bodies but apparently not inside the active comets that never contained liquid water. Despite examination of hundreds of particles returned from the Jupiter Family comet Wild 2 by the Stardust(SD) spacecraft, no phyllosilicates have yet been found. Near IR spectra obtained by the Rosetta spacecraft of short-period comet 67P Churyumov-Gerasimenko (67P CG) similarly did not reveal the presence of phyllosilicate minerals. IR spectral features in ejecta from comet Temple 1were interpreted as hydrated minerals but this match is controversial. Studies of a giant cluster interplanetary dust particle (IDP) have demonstrated that the IDP has a large number of chemical and physical properties consistent with its derivation from a comet including 1) its porous aggregate morphology similar to fragile aggregate particles imaged from comet 67P CG, 2) an unequilibrated mineral assemblage, 3) mineral isotopic compositions similar to like minerals in comet Wild 2, 4) uncorrelated Fe-Mn ratios of olivines that mimic those from Wild 2, 5) high presolar silicate abundance [8] and 6) Kool grains which are observed in comet Wild 2 but not in chondrites. Our examination of 70+>5 μm fragments from the IDP have shown that it is overwhelmingly composed of anhydrous silicates. We have observed, however, a 5 x 15 μm porous aggregate fragment (LT10), which contains a rare phyllosilicate clast encased in anhydrous mineral and rock fragments. We conducted detailed TEM and O isotopic analyses of this particle to constrain its origin.

D J Joswiak↗