Surface Morphologies and Space Weathering Features of Ryugu Samples
Surface morphologies and space weathering features of Ryugu samples
T. Matsumoto↗
Engineering topics
M. Matsumoto
Publications and source records attributed to M. Matsumoto.
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↗
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↗
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↗
Mineralogy and Space Weathering of Fine Fraction Recovered from Asteroid (162173) Ryugu
JAXA Hayabusa2 spacecraft brought back 5.4 g of samples from the near-Earth C-type asteroid (162173) Ryugu to Earth on December6th, 2020 [1]. The returned samples give us a unique opportunity to investigate material from the surface of a C-type asteroid that is expected to record space weathering. Here, we report the mineralogy of fine fraction of the Ryugu grains and a variation of their surface features related to space weathering.
T. Noguchi↗
Direct Measurement of the Composition of Aqueous Fluids from the Parent Body of Asteroid 162173 Ryugu
Imaging using X-ray absorption contrast by synchrotron nano-computed tomography (47.4 nm/voxel, 7keV) of a Ryugu pyrrhotite crystal (C0002-FC012-from the second touch-down site) revealed probable fluid inclusions (Fig. 1A,B) [1]. The inclusions were completely encapsuled in pyrrhotite, suggesting the fluids were trapped in the early stages of crystal growth, and filled with low-Z material. We performed Time-of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS) depth profiling and high-resolution map-ping at -120°C to exposure and measure the composition of the trapped fluids in a frozen state.
M Zolensky↗
Aqueous alteration of Cb-type asteroid Ryugu
The samples from the asteroid Ryugu, which returned to Earth in the winter of 2020 [1], were stored under pure Nitrogen conditions at the Extraterrestrial Materials Curation Center of ISAS. After basic description [2-3], they were distributed to six initial analysis teams in Japan in June 2021. The initial analysis "Stone" team, which was responsible for the analysis of coarse particles (>1 mm in size), consisted of about 150 scientists from Japan and abroad, and conducted a series of analyses We analyzed sixteen coarse Ryugu particles 1 ~ 8 mm in size: six from the 1st touch-down site and ten from the 2nd touch-down site. Individual coarse samples were cut by Xe-FIB or wire-saw to expose particular objects or textures to be exposed on the surface based on 3D structure and element distribution obtained by synchrotron X-ray CT analysis and XRF analysis, respectively. FE-SEM/EDS and FE-EPMA/WDS analysis were made on all polished sections. TEM observation of many FIB sections was made to see microstructures and to compare with carbonaceous chondrites. Many other analyses were carried out to characterize mineralogical and compositional properties and summary of the analysis procedures is described in [4]. X-ray CT analysis showed that all sixteen Ryugu particles are composed of fine-grained material, with no chondrules and CAIs larger than 100 μm in size. FE-EPMA observation showed that Ryugu samples are breccias, consisting of many small rock fragments of different compositions, lithologies, and histories. The most common lithology includes Mg-rich saponite and serpentine, dolomite, magnesite, hydroxyapatite, pyrrhotite, and magnetite as main constituents. The mineralogy of this major lithology supports the classification of Ryugu samples as CI chondrites, which experienced extensive aqueous alteration in Ryugu’s parent asteroid. Based on the obtained mineralogical properties, we performed chemical modeling of aqueous alteration of Ryugu’s parent asteroid [5]. Numerical simulations [6-8] to reproduce thermal history and impact-induced destruction of the Ryugu’s parent asteroid were also carried out using mineralogical and physical properties of the Ryugu samples. In the talk, I would like to explain the conditions of aqueous alteration occurred in the parent asteroid of Ryugu in order to show how the water in the asteroid changed the mineralogy and chemistry of the nebular dust.
T. Nakamura↗
Update on Measurement of the Composition of Ryugu Fluid Inclusions
Imaging using X-ray absorption contrast by synchrotron nano-computed tomography of a Ryugu pyrrhotite crystal (C0002-FC012 - from the second Hayabusa2 spacecraft touch-down site) revealed probable fluid inclusions in the center of a crystal of pyrrhotite, suggesting the parent fluids were trapped in the early stages of crystal growth on Ryugu’s parent asteroid. We previously described the performance of Time-of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS) depth profiling and high-resolution mapping at -120°C to expose and measure the composition of the trapped fluids in a frozen state in two Ryugu inclusions [1,2]. Here we report results from follow-on measurements of additional inclusions in the same pyrrhotite crystal, and the initial results of measurement of standards. The ultimate goal is to reveal the quantitative composition of the fluids that caused aqueous alteration, in particular the H2O:CO2 ratio, which will also facilitate cosmochemical modeling of the alteration process.
M Zolensky↗
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↗