研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 宇宙機応用工学研究系 はやぶさ２プロジェクト 准教授
- 学位
- 理学博士(1989年3月 東京大学)
- 連絡先
- yoshikawa.makoto
jaxa.jp - J-GLOBAL ID
- 200901037361657011
- researchmap会員ID
- 1000304540
研究キーワード
6経歴
5-
2003年10月 - 現在
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1998年4月 - 2003年9月
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1991年4月 - 1998年3月
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1996年12月 - 1997年12月
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1989年4月 - 1991年3月
学歴
2-
1984年4月 - 1989年3月
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1980年4月 - 1984年3月
委員歴
9-
2020年10月 - 現在
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1994年4月 - 現在
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2013年1月 - 2015年3月
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2011年1月 - 2012年12月
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2009年 - 2011年
受賞
2-
2019年11月
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2018年12月
論文
260-
Journal of Geophysical Research: Planets 127(11) 2022年11月 査読有り
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Nature Astronomy 6(10) 1163-1171 2022年10月Volatile and organic-rich C-type asteroids may have been one of the main sources of Earth’s water. Our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but the meteorite record is biased: only the strongest types survive atmospheric entry and are then modified by interaction with the terrestrial environment. Here we present the results of a detailed bulk and microanalytical study of pristine Ryugu particles, brought to Earth by the Hayabusa2 spacecraft. Ryugu particles display a close compositional match with the chemically unfractionated, but aqueously altered, CI (Ivuna-type) chondrites, which are widely used as a proxy for the bulk Solar System composition. The sample shows an intricate spatial relationship between aliphatic-rich organics and phyllosilicates and indicates maximum temperatures of ~30 °C during aqueous alteration. We find that heavy hydrogen and nitrogen abundances are consistent with an outer Solar System origin. Ryugu particles are the most uncontaminated and unfractionated extraterrestrial materials studied so far, and provide the best available match to the bulk Solar System composition.
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Geochemical Perspectives Letters 24 1-6 2022年10月 査読有りThe Hayabusa2 spacecraft has returned samples from the Cb-type asteroid (162173) Ryugu to Earth. Previous petrological and chemical analyses support a close link between Ryugu and CI chondrites that are presumed to be chemically the most primitive meteorites with a solar-like composition. However, Ryugu samples are highly enriched in Ca compared to typical CI chondrites. To identify the cause of this discrepancy, here we report stable Ca isotopic data (expressed as δ44/40CaSRM915a) for returned Ryugu samples collected from two sites. We found that samples from both sites have similar δ44/40CaSRM915a (0.58 ± 0.03 % and 0.55 ± 0.08 %, 2 s.d.) that fall within the range defined by CIs. This isotopic similarity suggests that the Ca budget of CIs and Ryugu samples is dominated by carbonates, and the variably higher Ca contents in Ryugu samples are due to the abundant carbonates. Precipitation of carbonates on Ryugu likely coincided with a major episode of aqueous activity dated to have occurred ∼5 Myr after Solar System formation. Based on the pristine Ryugu samples, the average δ44/40CaSRM915a of the Solar System is defined to be 0.57 ± 0.04 % (2 s.d.).
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Nature Astronomy 6(10) 1172-1177 2022年9月1日
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2022年8月29日Abstract Chondrule-like objects and Ca-Al-rich inclusions (CAIs) are discovered in the retuned samples from asteroid Ryugu. Three chondrule-like objects, which are 16O-rich and -poor with D17O (= d17O – 0.52 × d18O) values of ~ − 23‰ and ~ − 3‰, are dominated by Mg-rich olivine, resembling what proposed as earlier generations of chondrules. The 16O-rich objects are likely to be melted amoeboid olivine aggregates that escaped from incorporation into 16O-poor chondrule precursor dust. Two CAIs composed of spinel, hibonite, and perovskite are 16O-rich with D17O of ~ − 23‰ and possibly as old as the oldest CAIs. The chondrule-like objects and CAIs (< 30 µm) are as small as those from comets, suggesting radial transport favoring smaller objects from the inner solar nebula to the formation location of the Ryugu original parent body, which is farther from the Sun and scarce in chondrules. The transported objects may have been mostly destroyed during aqueous alteration.
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2022年8月3日Abstract Hayabusa2 spacecraft successfully collected rock samples through two touchdowns from the surface of C-type near-Earth asteroid 162173 Ryugu and brought them back to Earth in 2020. At the Extraterrestrial Sample Curation Center in JAXA, we performed initial description to all samples to obtain the fundamental information and prepare the database for sample allocation. We propose morphological classifications for the returned samples based on the initial description of 205 grains described in the first 6 months. The returned samples can be distinguished by four morphological characteristics: dark, glossy, bright, and white. According to coordinated study of initial description and detailed investigation by scanning electron microscopy and X-ray diffraction analysis in this study, these features reflect the differences in the degree of space weathering and mineral assemblages. The degree of space weathering of the four studied grains is heterogeneous: weak for A0042 (dark group) and C0041 (white group); moderate for C0094 (glossy); and severe for A0017 (bright). The white phase in a grain belonging to white group is identified as large carbonate minerals. This is the first effort to classify Ryugu returned samples. Based on these results, researchers can estimate sample characteristics only from the information on the JAXA curation public database. It could be an important reference for sample selection for further investigation.
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Publications of the Astronomical Society of Japan 74(4) 877-903 2022年8月1日We report the results of video observations of tiny (diameter less than 100 m) near-Earth objects (NEOs) with Tomo-e Gozen on the Kiso 105 cm Schmidt telescope. The rotational period of a tiny asteroid reflects its dynamical history and physical properties since smaller objects are sensitive to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. We carried out video observations of 60 tiny NEOs at 2 fps from 2018 to 2021 and successfully derived the rotational periods and axial ratios of 32 NEOs including 13 fast rotators with rotational periods less than 60 s. The fastest rotator found during our survey is 2020 HS7 with a rotational period of 2.99 s. We statistically confirmed that there is a certain number of tiny fast rotators in the NEO population, which have been missed with all previous surveys. We have discovered that the distribution of the tiny NEOs in a diameter and rotational period (D-P) diagram is truncated around a period of 10 s. The truncation with a flat-top shape is not explained well by either a realistic tensile strength of NEOs or the suppression of YORP by meteoroid impacts. We propose that the dependence of the tangential YORP effect on the rotational period potentially explains the observed pattern in the D-P diagram.
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Monthly Notices of the Royal Astronomical Society 514(4) 6173-6182 2022年8月1日The JAXA Hayabusa2 mission accomplished the formation of an artificial crater on the asteroid Ryugu. The aim of this work is to analyse the area surrounding the artificial crater and reveal spectral variability compared to the same region before the crater formation, to mineralogically and physically characterize the subsurface exposed material. The crater's investigation focused on the analysis of two regions corresponding to the inner part of crater (the pit and the crater wall/floor), two areas related to ejecta deposited close to the crater, two areas of ejecta moved far from the crater, and two external areas. Each area was investigated both before and after the crater formation, by the study of the photometrically corrected spectral parameters: the 1.9 μm reflectance, the near-infrared spectral slope, and the depth of the bands at 2.7 and 2.8 μm. The subsurface material of the post-crater areas shows deeper absorption bands, a decrease in reflectance, and a reddening in spectral slope with respect to the surface material of pre-crater areas. The subsurface regolith could have experienced a lower OH devolatilization due to space weathering and/or could be composed of finer dark grains than the surface layer. The ejecta reached distances of ~20 m from the impact point, mainly moving in the northern direction; nevertheless, a few ejecta also reached the south-eastern part of crater.
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Planetary Science Journal 3(7) 2022年7月1日Hera is a planetary defense mission under development in the Space Safety and Security Program of the European Space Agency for launch in 2024 October. It will rendezvous in late 2026 December with the binary asteroid (65803) Didymos and in particular its moon, Dimorphos, which will be impacted by NASA’s DART spacecraft on 2022 September 26 as the first asteroid deflection test. The main goals of Hera are the detailed characterization of the physical properties of Didymos and Dimorphos and of the crater made by the DART mission, as well as measurement of the momentum transfer efficiency resulting from DART’s impact. The data from the Hera spacecraft and its two CubeSats will also provide significant insights into asteroid science and the evolutionary history of our solar system. Hera will perform the first rendezvous with a binary asteroid and provide new measurements, such as radar sounding of an asteroid interior, which will allow models in planetary science to be tested. Hera will thus provide a crucial element in the global effort to avert future asteroid impacts at the same time as providing world-leading science.
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Planetary and Space Science 219 105519-105519 2022年6月
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Publications of the Astronomical Society of Japan 74(2) 308-317 2022年4月On 2020 December 5 at 17:28 UTC, Japan Aerospace Exploration Agency's Hayabusa2 sample return capsule (SRC) re-entered Earth's atmosphere. The capsule passed through the atmosphere at supersonic speeds, emitting sound and light. The inaudible sound was recorded by infrasound sensors installed by Kochi University of Technology and Curtin University. Based on analysis of the recorded infrasound, the trajectory of the SRC in two cases, one with constant-velocity linear motion and the other with silent flight, could be estimated with an accuracy of 0° 5 in elevation and 1° in direction. A comparison with optical observations suggests a state of flight in which no light is emitted but sound is emitted. In this paper, we describe the method and results of the trajectory estimation.
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Icarus 115007-115007 2022年3月
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Science 375(6584) 1011-1016 2022年3月The Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. The mission performed two landing operations to collect samples of surface and subsurface material, the latter exposed by an artificial impact. We present images of the second touchdown site, finding that ejecta from the impact crater was present at the sample location. Surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to Ryugu’s boulders, and shapes from quasi-spherical to flattened. The samples were returned to Earth on 6 December 2020. We describe the morphology of >5 grams of returned pebbles and sand. Their diverse color, shape, and structure are consistent with the observed materials of Ryugu; we conclude that they are a representative sample of the asteroid....
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Publications of the Astronomical Society of Japan 74(1) 50-63 2022年2月1日On 2020 December 5 at 17:28 UTC, the Japan Aerospace Exploration Agency's Hayabusa-2 sample return capsule came back to the Earth. It re-entered the atmosphere over South Australia, visible for 53 seconds as a fireball from near the Northern Territory border toward Woomera where it landed in the the Woomera military test range. A scientific observation campaign was planned to observe the optical, seismo-acoustic, radio, and high energy particle phenomena associated with the entry of an interplanetary object. A multi-institutional collaboration between Australian and Japanese universities resulted in the deployment of 49 instruments, with a further 13 permanent observation sites. The campaign successfully recorded optical, seismo-acoustic, and spectral data for this event which will allow an in-depth analysis of the effects produced by interplanetary objects impacting the Earth's atmosphere. This will allow future comparison and insights to be made with natural meteoroid objects.
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Nature Astronomy 6(2) 221-225 2022年2月
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Nature Astronomy 6(2) 214-220 2022年2月Abstract C-type asteroids1 are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing2–7 and on-asteroid measurements8,9 with Hayabusa2 (ref. 10). However, the ground truth provided by laboratory analysis of returned samples is invaluable to determine the fine properties of asteroids and other planetary bodies. We report preliminary results of analyses on returned samples from Ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for Ca–Al-rich inclusions (CAIs) and chondrules. The bulk sample mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. The power index of its size distribution is shallower than that of the surface boulder observed on Ryugu11, indicating differences in the returned Ryugu samples. The average of the estimated bulk densities of Ryugu sample particles is 1,282 ± 231 kg m−3, which is lower than that of meteorites12, suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements5,9. The extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of Ryugu3,4 and confirming that the sample is representative of the asteroid. Together with the absence of submillimetre CAIs and chondrules, these features indicate that Ryugu is most similar to CI chondrites but has lower albedo, higher porosity and more fragile characteristics.
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Proceedings of the International Astronautical Congress, IAC 2022-September 2022年The Hayabusa2 extended mission is designed to rendezvous with the fast-rotating asteroid 1998 KY26 in 2031. The asteroid's diameter and rotation period are as small as 20-40 m and 10:7 min, respectively. Consequently, the low gravity and rapid rotation of the asteroid form distinctive dynamical environments. This paper rst characterizes orbital and surface environments about 1998 KY26. Then, possible orbital operations are investigated, particularly focusing on the hovering and descent operations. Our research, therefore, contributes to exploring one of the smallest members of the solar system.
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Astronomy and Astrophysics 666 2022年 査読有りContext. JAXA's Hayabusa2 mission rendezvoused the Ryugu asteroid for 1.5 years to clarify the carbonaceous asteroids' record for Solar System origin and evolution. Aims. We studied the photometric behavior of the spectral parameters characterizing the near-infrared (NIR) spectra of Ryugu provided by the Hayabusa2/NIRS3 instrument, that is to say 1.9 µm reflectance, 2.7 and 2.8 µm band depths (ascribed to phyllosilicates), and NIR slope. Methods. For each parameter, we applied the following empirical approach: (1) retrieval of the equigonal albedo by applying the Akimov disk function (this step was only performed for the reflectance photometric correction); (2) retrieval of the median spectral parameter value at each phase angle bin; and (3) retrieval of the phase function by a linear fit. Results. Ryugu's phase function shows a steepness similar to Ceres, according to the same taxonomy of the two asteroids. Band depths decrease with increasing phase angle: this trend is opposite to that observed on other asteroids explored by space missions and is ascribed to the very dark albedo. NIR and visible phase reddening are similar, contrary to other asteroids, where visible phase reddening is larger: this could be due to surface darkness or to particle smoothness. Albedo and band depths are globally uncorrelated, but locally anticorrelated. A correlation between darkening and reddening is observed.
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Hayabusa2 Asteroid Sample Return Mission: Technological Innovation and Advances 541-556 2022年1月1日Hayabusa2 was a mission with a series of challenging operations and a scientific goal that related to the origins of life. These attributes presented an opportunity to engage with a wide range of people beyond the scientific community who might be inspired by the difficulty of the engineering or relate to a search for how life on Earth began. The mission's outreach program aimed to share news throughout the mission in Japan and overseas, with regular updates on mission operations, real-time events for an immersive feel during major operations and campaigns to allow people to connect with the team.
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Hayabusa2 Asteroid Sample Return Mission: Technological Innovation and Advances 1-3 2022年1月1日Hayabusa2 is the second Japanese small body sample return exploration mission, targeting the carbonaceous asteroid (162173) Ryugu. The spacecraft was launched with Japan's H2A launch vehicle from the Tanegashima Space Center in December 2014 and arrived at Ryugu in June 2018. After completing detailed remote sensing observations, two sampling operations, one kinetic impact experiment, and multiple deployments of robotic smaller probes, the spacecraft left the asteroid in November 2019. It was a six-year journey that the spacecraft traveled approximately 5.2 billion km. In December 2020, the spacecraft returned to the Earth with extraterrestrial materials. A special volume is developed as a primary reference to collect engineering efforts from mission planning through in-orbit operations that made Hayabusa2’s achievements. This chapter introduces a brief overview of this book.
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Proceedings of the Japan Academy Series B: Physical and Biological Sciences 98(6) 227-282 2022年Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the C-type asteroid Ryugu by the Hayabusa2 mission. On average Ryugu particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. The abundances of 70 elements from the particles are in close agreement with those of CI chondrites. Bulk Ryugu particles show higher δ18O, ∆17O, and ε54Cr values than CI chondrites. As such, Ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. Such a finding is consistent with multi-scale H-C-N isotopic compositions that are compatible with an origin for Ryugu organic matter within both the protosolar nebula and the interstellar medium. The analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the Ryugu progenitor planetesimal (several 10’s of km), <2.6 Myr after CAI formation. Subsequently, the Ryugu progenitor planetesimal was fragmented and evolved into the current asteroid Ryugu through sublimation.
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Hayabusa2 Asteroid Sample Return Mission 5-23 2022年
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Hayabusa2 Asteroid Sample Return Mission 113-136 2022年
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Hayabusa2 Asteroid Sample Return Mission 241-257 2022年
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Nature Communications 12(1) 2021年12月<title>Abstract</title>Ryugu is a carbonaceous rubble-pile asteroid visited by the Hayabusa2 spacecraft. Small rubble pile asteroids record the thermal evolution of their much larger parent bodies. However, recent space weathering and/or solar heating create ambiguities between the uppermost layer observable by remote-sensing and the pristine material from the parent body. Hayabusa2 remote-sensing observations find that on the asteroid (162173) Ryugu both north and south pole regions preserve the material least processed by space weathering, which is spectrally blue carbonaceous chondritic material with a 0–3% deep 0.7-µm band absorption, indicative of Fe-bearing phyllosilicates. Here we report that spectrally blue Ryugu’s parent body experienced intensive aqueous alteration and subsequent thermal metamorphism at 570–670 K (300–400 °C), suggesting that Ryugu’s parent body was heated by radioactive decay of short-lived radionuclides possibly because of its early formation 2–2.5 Ma. The samples being brought to Earth by Hayabusa2 will give us our first insights into this epoch in solar system history.
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Advances in Space Research 68(8) 3093-3140 2021年10月15日One of the major challenges in the Hayabusa2 sample-return mission was the second touchdown on the asteroid Ryugu, which was designed to collect subsurface materials near the artificial crater formed by a small carry-on impactor. Due to engineering and scientific requirements, a narrow area with a radius as small as 3.5 m was selected as the target landing site. To achieve pinpoint touchdown at the selected site, an artificial landmark called a target marker (TM) was used for optical navigation. The key to a successful touchdown was precise deployment of the TM in the microgravity environment of the asteroid. This study therefore investigates a viable trajectory for TM deployment, incorporating the uncertainty in the impact and rebound motions of the TM. Following the TM deployment operation, a detailed survey of the landing site around the TM settlement point is performed to assess the terrain conditions. To guarantee the observation quality and spacecraft safety, multi-impulse low-altitude trajectories are introduced in this paper, along with covariance analyses based on the high-fidelity polyhedral gravity model of Ryugu. Subsequently, a pinpoint touchdown trajectory that satisfies various engineering requirements, such as landing accuracy and velocity, is designed, taking advantage of optical TM tracking. The feasibility of the touchdown sequence is further validated by a Monte Carlo dispersion analysis. Consequently, Hayabusa2 successfully touched down within the target site on 11 July 2019. The current research also conducts a post-operation trajectory reconstruction based on the flight data to demonstrate the actual guidance performance in the TM deployment, landing site observations, and pinpoint touchdown.
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Nature Astronomy 5(8) 766-774 2021年8月Planetesimals—the initial stage of the planetary formation process—are considered to be initially very porous aggregates of dusts1,2, and subsequent thermal and compaction processes reduce their porosity3. The Hayabusa2 spacecraft found that boulders on the surface of asteroid (162173) Ryugu have an average porosity of 30–50% (refs. 4–6), higher than meteorites but lower than cometary nuclei7, which are considered to be remnants of the original planetesimals8. Here, using high-resolution thermal and optical imaging of Ryugu’s surface, we discovered, on the floor of fresh small craters (<20 m in diameter), boulders with reflectance (~0.015) lower than the Ryugu average6 and porosity >70%, which is as high as in cometary bodies. The artificial crater formed by Hayabusa2’s impact experiment9 is similar to these craters in size but does not have such high-porosity boulders. Thus, we argue that the observed high porosity is intrinsic and not created by subsequent impact comminution and/or cracking. We propose that these boulders are the least processed material on Ryugu and represent remnants of porous planetesimals that did not undergo a high degree of heating and compaction3. Our multi-instrumental analysis suggests that fragments of the highly porous boulders are mixed within the surface regolith globally, implying that they might be captured within collected samples by touch-down operations10,11.
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Advances in Space Research 68(3) 1533-1555 2021年8月
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2021年6月21日<title>Abstract</title> 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 absorptions at 2.7 and 3.4 microns implying carbonaceous composition with indigenous aqueous alteration, respectively, match the global average of Ryugu, confirming the sample’s representativeness. Together with the absence of chondrule and Ca-Al-rich inclusion of larger than sub-mm, these features indicate Ryugu is most similar to CI chondrites but with darker, more porous and fragile characteristics.
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ICARUS 358 2021年4月Hayabusa2 deployed two artificial landmarks called "target markers (TMs)" on the asteroid Ryugu for autonomous landing control. To achieve precise deployment on target landing sites, the TMs were designed to dissipate kinetic energy and released near the asteroid surface (with an altitude of less than 40 m). This study evaluates the performance of the ballistic deployment in the actual microgravity environment by reconstructing the trajectories of the TMs from optical, altimetric, and radiometric data. In addition, based on the reconstructed trajectories, low-velocity impacts of the TMs on the surface of Ryugu are characterized with dynamical parameters, such as dissipated energy and a coefficient of restitution. The physical implications of the impact analysis are discussed in comparison with on-ground experimental data. Furthermore, the gravitational environment is investigated using the reconstructed trajectory data and a shape model of Ryugu, providing information on the local gravity anomaly. Consequently, this paper demonstrates the usefulness of deployable artificial landmarks for small-body landings and further offers insight on surface conditions and internal structures near the Hayabusa2 landing sites where samples of Ryugu were collected.
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Nature Astronomy 5(3) 246-250 2021年3月
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NATURE ASTRONOMY 5(2) 134-138 2021年2月Finding the basic mechanism governing the surface history of asteroids of various shapes is essential for understanding their origin and evolution. In particular, the asteroids (162173) Ryugu(1) and (101955) Bennu(2) currently being visited by Hayabusa2 and OSIRIS-REx appear to be top shaped. This distinctive shape, characterized by a raised equatorial bulge, is shared by other similarly sized asteroids, including Didymos A(3), 2008 EV5(4) and 1999 KW4 Alpha(5). However, the possibly common formation mechanism that causes the top-like shape is still under debate. One clue may lie in the boulders on their surfaces. The distribution of these boulders, which was precisely measured in unprecedented detail by the two spacecraft(1,2), constitutes a record of the geological evolution of the surface regolith since the origin of these asteroids. Here, we show that during the regolith migration driven by Yarkovsky-O'Keefe-Radzievskii-Paddack spin-up(6-9) the surface boulders coevolve with the underlying regolith and exhibit diverse dynamical behaviours: they can remain undisturbed, sink into the regolith layer and become tilted, or be totally buried by the downslope deposition, depending on their latitudes. The predominant geological features commonly observed on top-shaped asteroids, including the boulder-rich region near the pole(1,10), the deficiency of large boulders in the equatorial area(10,11) and partially buried, oblique boulders exposed on the regolith surface(12,13), are commensurate with this coevolution scenario. The surface regolith migration thus is the prevalent mechanism for the formation history of the top-shaped asteroids with stiffer cores.The distribution of boulders on the surface of top-shaped asteroids such as Bennu or Ryugu tells us about the processes driving their evolution. A model shows that the spin-up induced by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect can explain simultaneously both the latitudinal behaviour of the boulders and the regolith migration.
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Proceedings of the International Astronautical Congress, IAC A3 2021年Hayabusa2 is an asteroid sample return mission developed and operated by the Japan Aerospace Exploration Agency (JAXA). Hayabusa2 visited the C-Type asteroid Ryugu in 2018, stayed in the proximity of the asteroid for 1.5 years, and returned to Earth in 2020. Hayabusa2 succeeded in delivering three surface exploration robots to the asteroid surface, performing two landing and sample collection activities, generating one artificial crater impact, and deploying three small objects into orbit around the asteroid. The terrain of Ryugu was found to be unexpectedly harsh through the in-situ observations, and the operation strategy was obliged to be changed and aligned to the Ryugu environment. The project team overcame all the difficulties through tight and collaborative works between the team s scientists and engineers, and completed the planned missions perfectly. The total of 5.4 g of Ryugu sample was confirmed to contain in the returned capsule, which is now being analysed by specifically organized initial analysis teams, and will be delivered to international researchers through AO in 2022. This paper describes the entire flight result of the Hayabusa2 mission, and summarizes the engineering and scientific accomplishments of the mission.
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Proceedings of the International Astronautical Congress, IAC A3 2021年Hayabusa2 is the second asteroid sample return mission in the world following Hayabusa. The target asteroid was (162173) Ryugu, a C-Type near-Earth asteroid. The principal science purpose of the mission is to study the organic matter and water in the early stages of the Solar System, with the aim to understand the origin of the Earth s water and that of the substances that began life, as well as the origin and evolution of Solar System bodies. The mission successfully returned samples from Ryugu and collected a large amount of data on the asteroid through the onboard instruments, rovers, and lander. The mission completed several challenges such as two touchdowns, an impact experiment, and artificial satellite experiments. All of these challenges were important from the scientific point of view. The results revealed a range of the physical properties of Ryugu. With the samples of Ryugu now back on Earth, the sample analysis is currently underway to understand the materials from the early era of our Solar System. In addition to the scientific research, the mission also focused on outreach. We carried out a number of special campaigns, such as observations of the asteroid and spacecraft from Earth and an art contest, many talk events, web and twitter releases among other activities. We tried to inform people about our mission in real time and also tried to publish information both in Japanese and English simultaneously. Through these activities, we think we were able to make people feel connected with the Hayabusa2 mission and we hope that many more people have become interested in space activities. In this paper, we summarize the results of science and outreach for the Hayabusa2 mission.
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Proceedings of the International Astronautical Congress, IAC C4 2021年JAXA’s asteroid explorer Hayabusa2 completed its operation near the asteroid 162173 Ryugu, which started in June 2018, and carried out a maneuver away from the asteroid on November 13, 2019. In the outbound operation, the total delta-v performed by its ion propulsion was about 1,015 m/s, the space powered flight time reached 6,515 hours, 24 kg of propellant xenon was consumed, and 42 kg remained. On the return trip, 2,400 hours of operation was carried out in two parts, from December 2019 to February 2020 and from May to August 2020. Trajectory correction maneuver TCM-0 was carried out with one ion thruster from September 15 to 17, 2020, which was the last operation of the ion engine system, followed by several TCMs by chemical propulsion. The capsule returned to Earth on December 6, 2020. The total delta-v in the round trip was about 1.3 km/s, and the powered flight time was 9,398 hours. After consuming 31 kg of propellant xenon, 35 kg remained, a series of close flyby with an L-type asteroid 2001 CC21 in 2026 and rendezvous with a fast rotator asteroid 1998 KY26 in 2031 has been proposed as an extended mission of Hayabusa2 and its ion engine were restarted on January 5, 2021. The cumulative operating times for the four ion thrusters are 6,996, 2,880, 9,220, and 8,941 hours, respectively. 12,632-hour powered flight by the ion engine system produced about 1.7 km/s delta-v. An engineering model of Hayabusa2 neutralizer has been subjected to ground durability tests since the summer of 2012 prior to launch. 75,277 hours have passed by the end of September 2021, and it is still operating without failure and testing is ongoing.
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Proceedings of the International Astronautical Congress, IAC B6 2021年Hayabusa2 came back to Earth and the sample return capsule landed in Woomera Prohibited Area (WPA), Australia as planned on December 6, 2020. In the recovery operation all the function of the capsule system and finding system worked fine. The recovery operation teams found and recovered the capsule smoothly. After gas collection from the sample container, the capsule was quickly transported to Extraterrestrial Sample Curation Center in Sagamihara, Japan. The sample container was carefully opened, and 5.4g of C-type asteroid material was first confirmed in the world. Before these operations, the recovery operation team discussed with the government about the transport procedure and the environment impact even in the off-nominal cases with supported by Australian Space Agency (ASA). With reflecting the discussion, the recovery operation plan was applied to Australian government with safety plan and emergency plan in August 2019. However, the COVID-19 pandemic was increased in early 2020. It made the situation difficult. The entry to Australia was restricted and the regular international flight was almost suspended. After many discussions, the counter measure plan was added on the operation plan and we finally obtained Authorisation of Return of Overseas-Launched Space Object (AROLSO) in August 2020.
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Proceedings of the International Astronautical Congress, IAC C1 2021年The Hayabusa2 is an asteroid sample return mission. It returned to Earth on 5 Dec. 2020 and released the sample return capsule containing a confirmed 5.4 g sample. The AOCS (Attitude and Orbit Control System) then changed its trajectory and attitude for the capsule re-entry. This operation continued for about 24 hours and included six sequential attitude maneuvers. There was only one chance for this procedure to succeed, and it could not be aborted. The accurate estimation of this subsystem's operation was one of the most critical factors in the mission's success. The main difficulties were to realize several attitude maneuvers under control that had to be exceptionally strict because of the significant attitude disturbances Hayabusa2 was subjected to the sizable magnetic moment due to the Ion Engine System (IES) and the Earth's magnetic field, and the aerodynamic torque around the perigee point. The authors devised a precise timing control mode for switching and selection of RW unloading. This paper describes AOCS operation, the simulation model, and the results of an analysis of the re-entry operation. AOCS planning is described in detail, as are a comparison of actual operation results and planning.
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Proceedings of the International Astronautical Congress, IAC A3 2021年Hayabusa2, a Japanese asteroid sample return probe, was launched on December 3, 2014, and arrived at Ryugu, a C-Type asteroid, on June 27, 2018. It left Ryugu on November 13, 2019, after completing its 1.5-year asteroid proximity phase operation, including sample collections and a kinetic impact experiment. The propulsive return cruise with the ion thrusters began on December 3, 2019, and in October 2020, the spacecraft entered the precise guidance phase, in which the trajectory corrections with the chemical thrusters were conducted. After several trajectory correction maneuvers, the spacecraft was precisely guided to the landing point of the sample return capsule, and its reentry capsule entered Earth s atmosphere and successfully landed on December 5, 2020. The capsule recovery team immediately found and retrieved the capsule. This paper describes the results of Hayabusa2 Earth return and capsule reentry, including the cruising and precise guidance phase and capsule release operation.
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TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN 19(4) 584-590 2021年
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TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN 19(5) 654-659 2021年
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TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN 19(1) 52-60 2021年
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Nature Astronomy 5(1) 39-45 2021年1月The asteroid (162173) Ryugu and other rubble-pile asteroids are likely re-accumulated fragments of much larger parent bodies that were disrupted by impacts. However, the collisional and orbital pathways from the original parent bodies to subkilometre rubble-pile asteroids are not yet well understood . Here we use Hayabusa2 observations to show that some of the bright boulders on the dark, carbonaceous (C-type) asteroid Ryugu are remnants of an impactor with a different composition as well as an anomalous portion of its parent body. The bright boulders on Ryugu can be classified into two spectral groups: most are featureless and similar to Ryugu’s average spectrum , while others show distinct compositional signatures consistent with ordinary chondrites—a class of meteorites that originate from anhydrous silicate-rich asteroids . The observed anhydrous silicate-like material is likely the result of collisional mixing between Ryugu’s parent body and one or multiple anhydrous silicate-rich asteroid(s) before and during Ryugu’s formation. In addition, the bright boulders with featureless spectra and less ultraviolet upturn are consistent with thermal metamorphism of carbonaceous meteorites . They might sample different thermal-metamorphosed regions, which the returned sample will allow us to verify. Hence, the bright boulders on Ryugu provide new insights into the collisional evolution and accumulation of subkilometre rubble-pile asteroids. 1–3 4 4,5 6 7,8
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EARTH PLANETS AND SPACE 73(1) 2021年1月In this study, we determined the alignment of the laser altimeter aboard Hayabusa2 with respect to the spacecraft using in-flight data. Since the laser altimeter data were used to estimate the trajectory of the Hayabusa2 spacecraft, the pointing direction of the altimeter needed to be accurately determined. The boresight direction of the receiving telescope was estimated by comparing elevations of the laser altimeter data and camera images, and was confirmed by identifying prominent terrains of other datasets. The estimated boresight direction obtained by the laser link experiment in the winter of 2015, during the Earth's gravity assist operation period, differed from the direction estimated in this study, which fell on another part of the candidate direction; this was not selected in a previous study. Assuming that the uncertainty of alignment determination of the laser altimeter boresight was 4.6 pixels in the camera image, the trajectory error of the spacecraft in the cross- and/or along-track directions was determined to be 0.4, 2.1, or 8.6 m for altitudes of 1, 5, or 20 km, respectively.
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Astrodynamics 4(4) 349-375 2020年12月The Japanese interplanetary probe Hayabusa2 was launched on December 3, 2014 and the probe arrived at the vicinity of asteroid 162173 Ryugu on June 27, 2018. During its 1.4 years of asteroid proximity phase, the probe successfully accomplished numbers of record-breaking achievements including two touchdowns and one artificial cratering experiment, which are highly expected to have secured surface and subsurface samples from the asteroid inside its sample container for the first time in history. The Hayabusa2 spacecraft was designed not to orbit but to hover above the asteroid along the sub-Earth line. This orbital and geometrical configuration allows the spacecraft to utilize its high-gain antennas for telecommunication with the ground station on Earth while pointing its scientific observation and navigation sensors at the asteroid. This paper focuses on the regular station-keeping operation of Hayabusa2, which is called “home position” (HP)-keeping operation. First, together with the spacecraft design, an operation scheme called HP navigation (HPNAV), which includes a daily trajectory control and scientific observations as regular activities, is introduced. Following the description on the guidance, navigation, and control design as well as the framework of optical and radiometric navigation, the results of the HP-keeping operation including trajectory estimation and delta-V planning during the entire asteroid proximity phase are summarized and evaluated as a first report. Consequently, this paper states that the HP-keeping operation in the framework of HPNAV had succeeded without critical incidents, and the number of trajectory control delta-V was planned efficiently throughout the period.
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Astrodynamics 4(4) 289-308 2020年12月Subsurface exploration is one of the most ambitious scientific objectives of the Hayabusa2 mission. A small device called small carry-on impactor (SCI) was developed to create an artificial crater on the surface of asteroid Ryugu. This enables us to sample subsurface materials, which will provide a window to the past. The physical properties of the resulting crater are also useful for understanding the internal structure of Ryugu. Accurate understanding of the crater and ejecta properties, including the depth of excavation of subsurface materials, requires accurate information on impact conditions. In particular, the impact angle is a critical factor because it greatly influences the size and shape of the crater. On April 5, 2019, the Hayabusa2 spacecraft deployed the SCI at 500 m of altitude above the asteroid surface. The SCI gradually reduced its altitude, and it shot a 2 kg copper projectile into the asteroid 40 min after separation. Estimating the position of the released SCI is essential for determining the impact angle. This study describes the motion reconstruction of the SCI based on the actual operation data. The results indicate that the SCI was released with high accuracy.
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Astrodynamics 4(4) 265-288 2020年12月In late 2018, the asteroid Ryugu was in the Sun’s shadow during the superior solar conjunction phase. As the Sun-Earth-Ryugu angle decreased to below 3°, the Hayabusa2 spacecraft experienced 21 days of planned blackout in the Earth-probe communication link. This was the first time a spacecraft had experienced solar conjunction while hovering around a minor body. For the safety of the spacecraft, a low energy transfer trajectory named Ayu was designed in the Hill reference frame to increase its altitude from 20 to 110 km. The trajectory was planned with the newly developed optNEAR tool and validated with real time data. This article shows the results of the conjunction operation, from planning to flight data.
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Nature Communications 11(1) 2020年12月1日Asteroid shapes and hydration levels can serve as tracers of their history and origin. For instance, the asteroids (162173) Ryugu and (101955) Bennu have an oblate spheroidal shape with a pronounced equator, but contain different surface hydration levels. Here we show, through numerical simulations of large asteroid disruptions, that oblate spheroids, some of which have a pronounced equator defining a spinning top shape, can form directly through gravitational reaccumulation. We further show that rubble piles formed in a single disruption can have similar porosities but variable degrees of hydration. The direct formation of top shapes from single disruption alone can explain the relatively old crater-retention ages of the equatorial features of Ryugu and Bennu. Two separate parent-body disruptions are not necessarily required to explain their different hydration levels.
MISC
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ASTROPHYSICAL JOURNAL LETTERS 935(1) 2022年8月16日We have conducted a NanoSIMS-based search for presolar material in samples recently returned from C-type asteroid Ryugu as part of JAXA's Hayabusa2 mission. We report the detection of all major presolar grain types with O- and C-anomalous isotopic compositions typically identified in carbonaceous chondrite meteorites: 1 silicate, 1 oxide, 1 O-anomalous supernova grain of ambiguous phase, 38 SiC, and 16 carbonaceous grains. At least two of the carbonaceous grains are presolar graphites, whereas several grains with moderate C isotopic anomalies are probably organics. The presolar silicate was located in a clast with a less altered lithology than the typical extensively aqueously altered Ryugu matrix. The matrix-normalized presolar grain abundances in Ryugu are 4.8$^{+4.7}_{-2.6}$ ppm for O-anomalous grains, 25$^{+6}_{-5}$ ppm for SiC grains and 11$^{+5}_{-3}$ ppm for carbonaceous grains. Ryugu is isotopically and petrologically similar to carbonaceous Ivuna-type (CI) chondrites. To compare the in situ presolar grain abundances of Ryugu with CI chondrites, we also mapped Ivuna and Orgueil samples and found a total of SiC grains and 6 carbonaceous grains. No O-anomalous grains were detected. The matrix-normalized presolar grain abundances in the CI chondrites are similar to those in Ryugu: 23 $^{+7}_{-6}$ ppm SiC and 9.0$^{+5.3}_{-4.6}$ ppm carbonaceous grains. Thus, our results provide further evidence in support of the Ryugu-CI connection. They also reveal intriguing hints of small-scale heterogeneities in the Ryugu samples, such as locally distinct degrees of alteration that allowed the preservation of delicate presolar material.
書籍等出版物
19講演・口頭発表等
32担当経験のある科目(授業)
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2019年4月 - 現在太陽と太陽系の科学 (放送大学)
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2011年4月 - 現在位置天文学・天体力学 (東京大学)
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2007年4月 - 現在宇宙科学 (玉川大学)
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2006年4月 - 現在宇宙システム工学特論 III (総合研究大学院大学)
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2006年 - 現在宇宙工学概論 (総合研究大学院大学)
共同研究・競争的資金等の研究課題
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日本学術振興会 科学研究費助成事業 2023年4月 - 2026年3月
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日本学術振興会 科学研究費助成事業 基盤研究(B) 2018年4月 - 2021年3月
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日本学術振興会 科学研究費助成事業 基盤研究(C) 2016年4月 - 2019年3月
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日本学術振興会 科学研究費助成事業 2003年 - 2006年
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日本学術振興会 科学研究費助成事業 2003年 - 2005年
