Engineering topics

D. Nakashima

Publications and source records attributed to D. Nakashima.

5 records

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

Olivine Compositional Variation of Asteroid Ryugu Samples: Possible Precursors of Ryugu’s Parent Asteroid

JAXA’s Hayabusa2 spacecraft successfully recovered samples from Cb-type asteroid Ryugu and returned samples are now under detailed scrutiny by the international community. The ongoing initial analysis has so far revealed that the Ryugu samples are pristine primitive asteroidal materials mostly composed of secondary minerals such asphyllosilicates, carbonates, Fe sulfides and magnetite associated with organic matter [e.g., 1]. However, some samples contain small amounts of anhydrous silicates and oxides such as olivine that are thought to be the precursors of the Ryugu parent asteroid. Their sizes are mostly <5 mm, and detailed mineralogical analysis is possible using an electron microprobe with field emission gun (FE-EPMA). Here we report results of our extensive FE-EPMA analysis of an hydrous minerals focusing on olivine to compare with literature chondritic data. We also performed synchrotron XRD of olivine crystals to evaluate the shock degree of Ryugu samples. These analyses allow us to discuss the formation of Ryugu in light of the solar system early evolution.

T Mikouchi↗

NASA NTRSDate not supplied

Analysis of "Stone" Samples from C-Type Asteroid Ryugu

As a part of activities of initial analysis, we analyzed eighteen Ryugu “stone” samples of 1 ~ 8mm in size: seven stones from the 1st touch down site and eleven from the 2nd touch down site. Ryugu stones were analyzed first using X-rays, UV, visible, near-infrared, mid-infrared, and muon probes for surface reflectance spectra, internal 3D structure and element distribution, crystal structures, and bulk composition of light elements such as C, N, and O. Measurements for magnetic, thermal, and physical properties using some stones were also performed. TOF-SIMS analysis of fluid inclusions as being continued. Small particles separated from some stones were analyzed by IR-CT. Based on 3D-CT images of individual stones, objects of interests were identified, separated by pFIB cutting, and exposed by polishing on the surface of epoxy disks. FE-EPMA/FE-SEM analysis was made on ~40 polished epoxy disks for chemical composition and textural observation. FIB sections and small (~15 μm in size) fragments were separated from polished surface and analyzed by TEM, STXM,XRF, and nano-CT.

T. Nakamura↗

NASA NTRSDate not supplied

Olivine Mineralogy of Asteroid Ryugu Samples and CI Chondrites: Further Evidence for their Common Origin

Initial analysis of asteroid Ryugu samples has revealed that they were mm-mm scale brecciamostly composed of aqueously altered phases (e.g., Mg-Fe phyllosilicates, carbonates) and showed remarkablesimilarities to CI chondrites in mineralogy and chemistry [e.g., 1,2]. Our detailed analysis of Ryugu samples hasdetected small amounts (<<1 vol.%) of unaltered silicates that would escape severe aqueous alteration [3]. Olivine isthe most abundant (>90 vol%) phase among such unaltered silicates. Although most Ryugu olivine grains aresmaller than 5 mm, they bear important information about the precursors of the parent Ryugu asteroid. In thisabstract we report additional results of olivine mineralogical study of Ryugu samples, and especially compare witholivine grains in CI chondrites (Ivuna and Orgueil) to further discuss their relationship and possible common origin.

T. Mikouchi↗

NASA NTRSDate not supplied

Shock-Induced Deformation Recorded in the Regolith Particles from C-Type Asteroid Ryugu

The Hayabusa 2 mission successfully returned with samples of C-type near-Earth asteroid (162173) Ryugu on December of 2020. Ryugu samples contain large quantities of volatiles such as water and noble gases. Studying Ryugu samples is a great opportunity to understand the shock metamorphism on water-bearing rubble-pile asteroids. In this study, we have examined shock metamorphism on sixteen coarse mm-sized particles recovered by the Hayabusa 2 mission.

M. Kikuiri↗