Seiji Sugita

The JAXA Astromaterials Science Research Group developed a web-based database system for the Hayabusa2-returned sample from C-type asteroid Ryugu. The database (Ryugu Sample Database System; RS-DBS) is designed as an online catalog for users of wide scientific communities to choose their preferred samples and propose the sample loan through the JAXA Ryugu Sample Announcement of Opportunity. Ryugu samples can be sorted and given identification numbers as individual particles larger than 1 mm and aggregate samples consisting of less than 1 mm particle through the Phase1 curation (i.e., the initial description). The RS-DBS lists all samples with analytical data such as a microscopy image, size, weight, spectroscopic data, and shape model obtained by the initial description at the JAXA curation facility. The list also includes research results conducted by previous projects (i.e., the Hayabusa2 initial analysis team and Phase2 curation teams). The RS-DBS, built with open-source technolo...

The Hayabusa2 spacecraft collected samples from the surface of the carbonaceous near-Earth asteroid (162173) Ryugu and brought them to Earth. The samples were expected to contain organic molecules, which record processes that occurred in the early Solar System. We analyzed organic molecules extracted from the Ryugu surface samples. We identified a variety of molecules containing the atoms CHNOS, formed by methylation, hydration, hydroxylation, and sulfurization reactions. Amino acids, aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-heterocyclic compounds were detected, which had properties consistent with an abiotic origin. These compounds likely arose from an aqueous reaction on Ryugu’s parent body and are similar to the organics in Ivuna-type meteorites. These molecules can survive on the surfaces of asteroids and be transported throughout the Solar System.

Samples of the carbonaceous asteroid (162173) Ryugu were collected and brought to Earth by the Hayabusa2 spacecraft. We investigated the macromolecular organic matter in Ryugu samples and found that it contains aromatic and aliphatic carbon, ketone, and carboxyl functional groups. The spectroscopic features of the organic matter are consistent with those in chemically primitive carbonaceous chondrite meteorites that experienced parent-body aqueous alteration (reactions with liquid water). The morphology of the organic carbon includes nanoglobules and diffuse carbon associated with phyllosilicate and carbonate minerals. Deuterium and/or nitrogen-15 enrichments indicate that the organic matter formed in a cold molecular cloud or the presolar nebula. The diversity of the organic matter indicates variable levels of aqueous alteration on Ryugu’s parent body.

The Hayabusa2 spacecraft returned to Earth from the asteroid 162173 Ryugu on 6 December 2020. One day after the recovery, the gas species retained in the sample container were extracted and measured on-site and stored in gas collection bottles. The container gas consists of helium and neon with an extraterrestrial 3 He/ 4 He and 20 Ne/ 22 Ne ratios, along with some contaminant terrestrial atmospheric gases. A mixture of solar and Earth’s atmospheric gas is the best explanation for the container gas composition. Fragmentation of Ryugu grains within the sample container is discussed on the basis of the estimated amount of indigenous He and the size distribution of the recovered Ryugu grains. This is the first successful return of gas species from a near-Earth asteroid.

<p><strong>Introduction.</strong> Images obtained by the optical navigation camera (ONC) onboard Hayabusa2 have revealed nearly one hundred craters on the surface of asteroid Ryugu and have been estimated to of impact origin [1,2,3]. In this study, we review our recent findings about craters on asteroid Ryugu and discuss about implications for DART and Hera missions.</p> <p><strong>Gravity-regime cratering scaling.</strong> Although we expected to find craters on Ryugu because of the past finding of crater candidates on similarly small asteroid Itokawa [4], we did not expect craters possessing classic morphologies, such as circular shape, raised rim, and wall slumping, which are consistent with gravity-controlled formation [1]. This gravity-controlled crater formation on Ryugu was confirmed unambiguously by the artificial impact experiment by small carryon impact (SCI) including uninterrupted imaging of excavation and deposition processes of impact ejecta [5], allowing us to estimate crater-projectile size relation using gravity-regime crater scaling for coarse-grain targets [6]. This led to crater retention age estimation on different geologic units on Ryugu, which helps us understand the evolution of Ryugu. Morota et al. [2] inferred that asteroid Ryugu may have experienced sunward orbital excursion after leaving the asteroid main belt and before arrival at the current orbit based on the distinct bimodal color distribution and crater size frequency distribution (CSFD) of craters on Ryugu.</p> <p><strong>Depth-age relation and cross examination with sample analyses. </strong>Further analysis of CSFD on Ryugu yielded a relation between crater retention age as a function of surface layer depth [7], which indicate that crater retention age increases rapidly from ~0.4 Myr at 1 m of depth to 3 Myr at 2 m when the recent impactor population in near-Earth asteroids (NEAs) by [8] is used. Preliminary 21Ne measurement results from Ryugu samples indicate that comic-ray exposure (CRE) ages are ~5 Myr [9]. Although the shielding depth for cosmic rays for these samples may be relatively large (1 to 2 m) owing to the low density (1.19 g/cc) of Ryugu, the sample CRE ages are older than the crater counting estimates for these depths. Because of the great uncertainty in model parameters for crater retention age for asteroid Ryugu, the fact that CRE age and crater retention age agree within a factor of ~10 is significant. However, a more important point may be that this rough agreement occur only when NEA population is used for impactors. If crater retention age is estimated with main-belt asteroids (MBAs) populations, crater retention age would be much younger (~1 kyr), greatly deviating from the observed CRE ages. This suggests that Ryugu may have stayed in an orbit collisionally decoupled from MBA after leaving the main belt. A decisive conclusion would need more data from both sample analysis and image analysis, but this discussion clearly demonstrates that comparison between CRE ages and crater chronology is extremely important.</p> <p><strong>Comparison with asteroid Bennu and outlook for Dimorphos and Didymos craters. </strong>One thing we should look at before applying observation results on Ryugu craters to DART and Hera observations is comparison with craters on asteroid Bennu. Although Ryugu and Bennu are very similar in general morphologic properties of craters, there are significant differences. One is depth/diameter (d/D) ratio dependence on crater diameter D. The d/D ratio increases with crater diameter D on Ryugu but decrease on Bennu [10,11]. This contrasting difference may reflect different subsurface mechanical structures on these two asteroids. In fact, Ryugu has evidence for regional to global mass motion (i.e., equator to mid latitude mass wasting) [1,2] and Bennu exhibits evidence for more local mass wasting [12,13]. Such different styles of mass motion may be related to difference in d/D ratios on Ryugu and Bennu.</p> <p>Another difference is the gap between crater retention times between craters on regolith and boulder surfaces on the two asteroids. Although crater number density on regolith are similar to each other within the factor of three [7], those of “mini-craters” on boulder surfaces are very different. Bennu has about 30 time more intra-boulder mini-craters than Ryugu [14,15].</p> <p>The fact that these similar C-complex asteroids exhibit such substantial differences on craters suggests that Dimorphos, whose materialistic and dynamical properties are very different from Ryugu and Bennu, will show us very interesting new aspects of cratering on small bodies via DART and Hera missions [16,17].</p> <p><strong>References: </strong></p> <p>[1] Sugita et al. (2019) Science, 364,…

N. Sakatani1, S. Tanaka1, T. Okada1, T. Kouyama2, A. Miura1, Naru Hirata3, H. Senshu4, T. Arai5, Y. Shimaki1, H. Demura3, K. Suko3, T. Sekiguchi6, J. Takita7, T. Fuhuhara8, M. Taguchi8, T. Müller9, A. Hagermann10, J. Biele11, M. Grott11, M. Hamm11,20, M. Delbo12, M. Ito1, Naoyuki Hirata13, M. Arakawa13, K. Ogawa14,13, K. Wada4, T. Kadono15, R. Honda16, K. Shirai13, T. Saiki1, H. Imamura1, Y. Takagi17, H. Yano1, M. Hayakawa1, C. Okamoto13, H. Sawada1, S. Nakazawa1, Y. Iijima1, S. Sugita18, T. Morota18, M. Yamada4, S. Kameda8, E. Tatsumi19, Y. Yokota1, H. Suzuki20, C. Honda3, K. Yoshioka17, M. Matsuoka1, and Y. Cho18. 1Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (3-1-1 Yoshino-dai, Chuo-ku, Sagamihara, Kanagawa, Japan, sakatani@plaenta.sci.isas.jaxa.jp). 2National Institute of Advanced Industrial Science and Technology, Japan. 3University of Aizu, Japan. 4Chiba Institute of Technology, Japan. 5Ashikaga University, Japan. 6Hokkaido University of Edu...

Crater morphology and surface age of asteroid (162173) Ryugu are characterized using the high‐resolution images obtained by the Hayabusa2 spacecraft. Our observations reveal that the abundant boulders on and under the surface of the rubble‐pile asteroid affect crater morphology. Most of the craters on Ryugu exhibit well‐defined circular depressions, unlike those observed on asteroid Itokawa. The craters are typically outlined by boulders remaining on the rim. Large craters (diameter > 100 m) host abundant and sometimes unproportionally large boulders on their floors. Small craters (<20 m) are characterized by smooth circular floors distinguishable from the boulder‐rich exterior. Such small craters tend to have dark centers of unclear origin. The correlation between crater size and boulder number density suggests that some processes sort the size of boulders in the shallow (<30 m) subsurface. Furthermore, the crater size‐frequency distributions (CSFDs) of different regions on Ryugu record multiple geologic events, revealing the diverse geologic history on this 1‐km asteroid. Our crater‐counting analyses indicate that the equatorial ridge is the oldest structure of Ryugu and was formed 23–30 Myr ago. Then, Ryugu was partially resurfaced, possibly by the impact that formed the Urashima crater 5–12 Myr ago. Subsequently, a large‐scale resurfacing event formed the western bulge and the fossae 2–9 Myr ago. Following this process, the spin of Ryugu slowed down plausibly due to the YORP effect. The transition of isochrons in a CSFD suggests that Ryugu was decoupled from the main belt and transferred to a near‐Earth orbit 0.2–7 Myr ago.

Hayabusa2 at the asteroid Ryugu Asteroids fall to Earth in the form of meteorites, but these provide little information about their origins. The Japanese mission Hayabusa2 is designed to collect samples directly from the surface of an asteroid and return them to Earth for laboratory analysis. Three papers in this issue describe the Hayabusa2 team's study of the near-Earth carbonaceous asteroid 162173 Ryugu, at which the spacecraft arrived in June 2018 (see the Perspective by Wurm). Watanabe et al. measured the asteroid's mass, shape, and density, showing that it is a “rubble pile” of loose rocks, formed into a spinning-top shape during a prior period of rapid spin. They also identified suitable landing sites for sample collection. Kitazato et al. used near-infrared spectroscopy to find ubiquitous hydrated minerals on the surface and compared Ryugu with known types of carbonaceous meteorite. Sugita et al. describe Ryugu's geological features and surface colors and combine...

... Received Date: 7 February 2011 Revised Date: 2 May 2011 Accepted Date: 5 May 2011 Please cite this article as: Hong, PK, Sugita, S., Okamura ... The first data suggesting the existence of ice were obtained by radar observations by the Clementine mission (Nozette et al., 1996). ...

C-type asteroids are considered to be primitive small Solar-System bodies enriched in water and organics, providing clues for understanding the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing and on-asteroid measurements with Hayabusa2, but further studies are expected by direct analyses of returned samples. Here we describe the bulk sample mainly consisting of rugged and smooth particles of millimeter to submillimeter size, preserving physical and chemical properties as they were on the asteroid. The particle size distribution is found steeper than that of surface boulders11. Estimated grain densities of the samples have a peak around 1350 kg m-3, which is lower than that of meteorites suggests a high micro-porosity down to millimeter-scale, as estimated at centimeter-scale by thermal measurements. The extremely dark optical to near-infrared reflectance and the spectral profile with weak...

Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measured the mineralogy and bulk chemical and isotopic compositions of Ryugu samples. The samples are mainly composed of materials similar to those of carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37° ± 10°C, about 5.2 − 0.7 + 0.8 million (statistical) or 5.2 − 2.1 + 1.6 million (systematic) years after the formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles that of the Sun’s photosphere than other natural samples do.

Introduction: Hayabusa obtained many high-resolution images and revealed that this asteroid has many unique morphological features which are not seen on other small planetary bodies. One of the most symbolic configurations are quasi-circular depressions (QCD) on boulder-rich surfaces, which are inferred as impact craters (Hirata et al,. 2009). If the QCDs are impact craters, then the surface crater retention age of Itokawa can be estimated based on crater chronology approach. However, age estimates has great uncertainty: 75Myr-1Gyr (Michel et al., 2009). The uncertainty in age results mostly from the uncertainty in crater scaling formed on the boulder-rich surface observed on rubble-pile bodies. The impact energy required for forming a crater on a small body is much smaller than that on a large body because of the limitation of catastrophic disruption energy (Benz and Asphaug, 1999). Impact cratering with such small energy on rubble-pile bodies are expected to follow a scaling low b...

WEATHERING, BRECCIA STRUCTURE, AND MERIDIONAL CRACKS. S. Sasaki, S. Sugita, E. Tatsumi, H. Miyamoto, C. Honda, T. Morota, O. S. Barnouin, M. Hirabayashi, S. Kanda, M. Kanamaru, N. Hirata, T. Hiroi, T. Nakamura, T. Noguchi,R. Honda, T. Michikami, S. Watanabe, N. Namiki, P. Michel, S. Kameda, T. Kouyama, H. Suzuki, M. Yamada, H. Kikuchi, D. L. Domingue, Y. Cho, K. Yoshioka, M. Hayakawa, M. Matsuoka, R. Noguchi, N. Sakatani, H. Sawada, Y. Yokota , and M. Yoshikawa, Osaka Univ. (Dept. Earth & Space Sci., Toyonaka 560-0043, Japan, sasakisho@ess.sci.osaka-u.ac.jp), Univ. Tokyo, Univ. Aizu, Nagoya Univ., Johns Hopkins Univ., Applied Physics Lab, Auburn Univ., Brown Univ., Tohoku Univ., Kyushu Univ., Kochi Univ., Kinki Univ., NAOJ, Observatoire de la Cote d'Azur, Rikkyo Univ., AIST, Meiji Univ., Chiba Inst. Tech., PERC, Planetary Sci. Inst., ISAS/JAXA

DEFORMATION. M. Hirabayashi1, E. Tatsumi2, H. Miyamoto3, G. Komatsu4, S. Sugita2, S. Watanabe5, D. J. Scheeres6, O. S. Barnouin7, P. Michel8, C. Honda9, T. Michikami10, Y. Cho2, T. Morota5, Naru Hirata9, Naouki Hirata11, N. Sakatani12, S. R. Schwartz13, R. Honda14, Y. Yokota15, S. Kameda16, H. Suzuki12, T. Kouyama17, M. Hayakawa15, M. Matsuoka15, K. Yoshioka2, K. Ogawa11, H. Sawada15, M. Yoshikawa15, and Y. Tsuda15, 1Auburn University, Auburn, AL 36849, USA, (thirabayashi@auburn.edu). 2University of Tokyo, Bunkyo-ku, Tokyo 1130033, Japan, 3University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan, 4Universit delgi Studi “G. d’Annunzio,” Pescara 65127, Italy, 5Nagoya University, Nagoya, Aichi 464-8601, 6CU Boulder, Boulder, CO 8039, USA, 7APL/JHU, Laurel, MD 20723, USA, 8Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice 06304, France, 9University of Aizu, Ikki-machi, Fukushima 965-8580, Japan, 10Kindai University, Higashi-Hiroshima, Hiroshima 739-21...

Hayabusa2 is scheduled to arrive at the C-type asteroid 162173 Ryugu on July 2018. During its 18-month stay, Hayabusa2 will sample surface materials at three different locations on the asteroid (Yoshikawa et al., 2014). To maximize the scientific gains of Hayabusa2 mission, it is important to select the landing sites from scientific aspects that are derived from integration of remote sensing data obtained by on-board instruments, ONC, NIRS3, TIR, LIDAR, and MASCOT, and laboratory experiment data obtained by using meteorites and simulant of asteroidal materials. Therefore, the Interdisciplinary Science Team which draws the general picture of a scientific scenario of Hayabusa2 (Kobayashi et al., 2014) newly organized four working groups in 2014. The main purpose of these WGs is to select the best landing site by integrating remote sensing data and meteoritical knowledge, and is to expand planetary science into new research fields via the WG process. Meteorite WG: The primary purpose o...

THE NIRS3 SPECTROMETER ON HAYABUSA2. R.E. Milliken, K. Kitazato, L. Riu, T. Iwata, M. Abe, M. Ohtake, S. Matsuura, T. Arai, Y. Nakauchi, T. Nakamura, M. Mastuoka, H. Senshu, N. Hirata, T. Hiroi, C. Pilorget, R. Brunetto, F. Poulet, J.-P. Bibring, D. Takir, D.L. Domingue, F. Vilas, M.A. Barucci, D. Perna, E. Palomba, A. Galiano, K. Tsumura, T. Osawa, M. Komatsu, A. Nakato, T. Arai, N. Takato, T. Matsunaga, Y. Takagi, K. Matsumoto, T. Kouyama, Y. Yokota, E. Tatsumi, N. Sakatani, Y. Yamamoto, T. Okada, S. Sugita, R. Honda, T. Motora, S. Kameda, H. Sawada, C. Honda, M. Yamada, H. Suzuki, K. Yoshioka, M. Hayakawa, K. Ogawa, Y. Cho, Y. Takei, T. Saiki, S. Nakazawa, S. Tanaka, M. Yoshikawa, S. Watanabe, Y. Tsuda. Brown University, Providence, RI, 02912, USA.The University of Aizu, JP.Institut of Space and Astronautical Science (ISAS/JAXA), JP. Kwansi Gakuin University, JP.Ashikaga Universty, JP.Tohoku University, JP.Chiba Institute of Technology, JP.Institut d’ Astrophysique Spatiale, FR.J...

After its release and a descent and bouncing phase, the Hayabusa2 lander MASCOT came to a final rest and MASCOT’s camera MASCam acquired a set of images of the surface of Ryugu. With MASCam’s instantaneous field of view of about 1 mrad, the images provide pixel scales from 0.2 to 0.5 mm pixel−1in the foreground and up to 1 cm pixel−1for surface parts in the background. Using a stereo-photogrammetric analysis of the MASCam images taken from slightly different positions due to commanded and unintentional movements of the MASCOT lander, we were able to determine the orientation for the different measurement positions. Furthermore, we derived a 3D surface model of MASCOT’s vicinity. Although the conditions for 3D stereo processing were poor due to very small stereo angles, the derived 3D model has about 0.5 cm accuracy in the foreground at 20 cm distance and about 1.5 cm at a distance of 40–50 cm.

Images from the Optical Navigation Camera system (ONC) onboard the Hayabusa2 spacecraft show the MASCOT lander during its descent to the surface of asteroid (162173) Ryugu. We used results from a previous stereo-photogrammetric analysis that provided precise ONC image orientation data (camera position and pointing), ONC orthoimages, and an ONC-based 3D surface model to combine them with the visibilities of MASCOT itself and its shadow on-ground within the ONC images. We integrated additional information from instruments onboard MASCOT (MASMag, MARA, MASCam) and derived MASCOT’s release position and modeled its free-fall descent path and its velocity over 350 s from its release at ∼41 m altitude above ground until its first contact with the surface of Ryugu. After first contact, MASCOT bounced over the surface of Ryugu for 663 s and came to rest at its first settlement point after four intermediate surface contacts. We again used ONC images that show MASCOT and partly its shadow and ...

Hayabusa2 at the asteroid RyuguAsteroids fall to Earth in the form of meteorites, but these provide little information about their origins. The Japanese mission Hayabusa2 is designed to collect samples directly from the surface of an asteroid and return them to Earth for laboratory analysis. Three papers in this issue describe the Hayabusa2 team's study of the near-Earth carbonaceous asteroid 162173 Ryugu, at which the spacecraft arrived in June 2018 (see the Perspective by Wurm). Watanabeet al.measured the asteroid's mass, shape, and density, showing that it is a “rubble pile” of loose rocks, formed into a spinning-top shape during a prior period of rapid spin. They also identified suitable landing sites for sample collection. Kitazatoet al.used near-infrared spectroscopy to find ubiquitous hydrated minerals on the surface and compared Ryugu with known types of carbonaceous meteorite. Sugitaet al.describe Ryugu's geological features and surface colors and combined resul...

Impact-degassed sulfur oxides would have played important roles in the mass extinction on the K/T boundary. We carried out chemical equilibrium calculation and mass spectroscopic experiment to estimate the SO2/SO3 ratio in the K/T impact vapor plume.

We conducted laser ablation experiments to investigate whether impact-induced high-temperature CN radicals are converted to HCN in a neutral atmosphere. The results indicate that this HCN formation mechanism is more efficient than pure shock heating of a

The geologic record indicates that the mass extinction at K/T boundary, 65 Myrs ago, was caused by a hypervelocity impact of an asteroid or a comet. During the K/T impact event, a large amount of sulfur was degassed from the impact site. The degassed sulfur converts to sulfuric acid aerosol and stays in the stratosphere for a long time. This reduces the sunlight significantly and leads to a mass extinction. However, if the degassed sulfur is dominated by SO3 not SO2, then the conversion to sulfuric acid aerosol occurs very rapidly and the blockage of sunlight does not last for a long time. The chemical reaction of sulfur-oxides in an impact vapor cloud, nevertheless, has not been studied in detail previously, and the SO2/SO3 ratio in a vapor cloud is yet highly uncertain. The purpose of this study is to estimate the SO2/SO3 ratio in the K/T impact vapor cloud. Here we discuss the results of calculation of chemical equilibrium and kinetics of sulfur-containing species in an impact va...

On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics.

We conducted laser heating experiments that simulate impact-induced vaporization to investigate the effects of SiO2-derived oxygen on carbon chemistry within vapor clouds. The results indicate that SiO2-derived oxygen oxidizes carbon significantly.