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・学際科学研究系 助教総合研究大学院大学 先端学術院・宇宙科学コース 助教慶應義塾大学大学院 システムデザインマネジメント研究科 特別招聘准教授(兼任)先端生命科学研究所 訪問准教授法政大学大学院 理工学研究科 連携准教授九州工業大学 工学部宇宙システム工学科 非常勤講師マサチューセッツ工科大学 ソルジャーナノテクノロジー研究所 訪問科学者
- 学位
- Ph.D.（宇宙科学）(1995年10月 英国ケント大学)
- 研究者番号
- 00321571
- J-GLOBAL ID
- 200901039611171139
- researchmap会員ID
- 1000292032
- 外部リンク
専門は、太陽系探査科学、アストロバイオロジー。特に小惑星や彗星、その破片である流星・宇宙塵など、太陽系小天体に関する探査・実験・分析・観測・理論的研究の融合から、惑星系、地球型惑星、生命前駆物質の起源と進化を実証的に解明すること。現在は、海洋天体を対象とした生命兆候探査の基礎研究にも注力している。
LDEF、EuReCa、HST、SFU、Leonid-MAC、のぞみ、スターダスト、はやぶさ、イカロス、はやぶさ２、たんぽぽ、みお、たんぽぽ2、エクレウス、たんぽぽ4、ゲートウェイ、DESTINY+、コメットインターセプタなど、多彩な日欧米の宇宙実験・探査プロジェクトに参画。深宇宙探査や宇宙実験等による、未踏・未知のフロンティアへの挑戦を重視している。自ら開発した宇宙観測機器であるLeonid-MAC HDTV-II，はやぶさサンプラ、イカロスALADDIN、たんぽぽ1&2捕集パネル、エクレウスCLOTH、ゲートウェイLVDMのPI(主任研究者)やたんぽぽ2プロジェクトマネージャー等を務めてきた。現在はISAS宇宙工学委員会OPENS WG共同代表を務める。
教育者としては、総合研究大学院大学先端学術院宇宙科学コース、東京大学大学院工学系研究科航空宇宙工学専攻、慶應義塾大学院システムデザインマネジメント研究科、慶応義塾大学先端生命科学研究所、法政大学大学院理工学研究科、九州工業大学工学部宇宙システム工学科、国際宇宙大学等で、学生研究指導や授業講義を担当。米国マサチューセッツ工科大学、海洋研究開発機構、大阪大学レーザー研究所等との共同研究も主導してきた。
現在、国際宇宙空間研究委員会（COSPAR）評議員および地球-月システム・惑星・太陽系小天体宇宙研究科学委員会・委員長、国際宇宙航行アカデミー(IAA)・アカデミシャンおよび宇宙物理科学委員会・幹事、日本学術会議・地球惑星科学委員会 国際連携分科会・COSPAR小委員会・幹事、JAXA惑星等保護審査部会・部会長代理。2007年よりPMI認定PMP。2014-2018年、アジア人で初めてCOSPAR惑星保護パネル(PPP)の副委員長を務めた。
小惑星帯に炭素質小惑星(B/Cb)「8906 Yano」(1995 WF2）がある。
研究キーワード
29研究分野
7主要な経歴
26学歴
8-
1992年4月 - 1995年10月
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1993年6月 - 1993年8月
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1987年4月 - 1991年6月
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1989年8月 - 1990年6月
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1983年4月 - 1987年3月
委員歴
37-
2023年10月 - 現在
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2022年9月 - 現在
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2021年10月 - 現在
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2021年7月 - 現在
受賞
47論文
297-
Astronomy and Computing 47 100828-100828 2024年4月 査読有り
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Space Science Reviews 220(1) 2024年1月24日 査読有りAbstract Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum $\varDelta $V capability of $600\text{ ms}^{-1}$. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule.
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Astroparticle Physics 154 2024年1月The Extreme Universe Space Observatory on a Super Pressure Balloon 1 (EUSO-SPB1) was launched in 2017 April from Wanaka, New Zealand. The plan of this mission of opportunity on a NASA super pressure balloon test flight was to circle the southern hemisphere. The primary scientific goal was to make the first observations of ultra-high-energy cosmic-ray extensive air showers (EASs) by looking down on the atmosphere with an ultraviolet (UV) fluorescence telescope from suborbital altitude (33 km). After 12 days and 4 h aloft, the flight was terminated prematurely in the Pacific Ocean. Before the flight, the instrument was tested extensively in the West Desert of Utah, USA, with UV point sources and lasers. The test results indicated that the instrument had sensitivity to EASs of ⪆3 EeV. Simulations of the telescope system, telescope on time, and realized flight trajectory predicted an observation of about 1 event assuming clear sky conditions. The effects of high clouds were estimated to reduce this value by approximately a factor of 2. A manual search and a machine-learning-based search did not find any EAS signals in these data. Here we review the EUSO-SPB1 instrument and flight and the EAS search.
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Earth, Planets and Space 75(121) 2023年6月4日 査読有りThe zodiacal light (ZL) is sunlight scattered by interplanetary dust (IPD) in the optical wavelengths. The spatial distribution of IPD in the Solar system may hold an important key to understanding the evolution of the Solar system and material transportation within it. The IPD number density can be expressed as n(r)∼r^{−α}, and the result of α∼1.3 was obtained by the previous observations from the interplanetary space by Helios 1/2 and Pioneer 10/11 in the 1970s and 1980s. However, no direct measurements of α based on the ZL observation from the interplanetary space outside the Earth's orbit have been conducted since then. Here we introduce the initial result of the ZL radial profile at optical wavelengths observed at 0.76-1.06 au by ONC-T with Hayabusa2# mission in 2021-2022. The obtained ZL brightness is well reproduced by the model brightness, but there is a small excess of the observed ZL brightness over the model brightness at around 0.9 au. The obtained radial power-law index is α=1.30±0.08, which is consistent with the previous results based on the ZL observations. The dominant uncertainty source in α arises from the uncertainty in the Diffuse Galactic Light estimation.
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Science 379(6634) eabn9057 2023年2月24日 査読有り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.
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Science 379(6634) eabn9033 2023年2月24日 査読有り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.
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Science 379(6634) 2023年2月24日 査読有りSamples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed 17 Ryugu samples measuring 1 to 8 millimeters. Carbon dioxide-bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu's parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and calcium- and aluminum-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed through aqueous alteration reactions at low temperature, high pH, and water/rock ratios of <1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate that Ryugu's parent body formed ~2 million years after the beginning of Solar System formation.
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NATURE ASTRONOMY 7(2) 170-181 2022年12月 査読有りWithout a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 mu m hydroxyl (-OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 mu m band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.
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Earth, Planets and Space 74(1) 2022年12月 査読有りJapanese Hayabusa2 spacecraft has successfully carried out an impact experiment using a small carry-on impactor (SCI) on an asteroid (162173) Ryugu. We examine the size distribution of particles inside and outside an artificial impact crater (the SCI crater) based on the images taken by the optical navigation camera onboard the Hayabusa2 spacecraft. The circumferential variation in particle size distribution inside the SCI crater is recognized and we interpret that major circumferential variation is caused by the large boulders inside the SCI crater that existed prior to the impact. The size distribution inside the SCI crater also shows that the subsurface layer beneath the SCI impact site had a large number of particles with a characteristic size of – 9 cm, which is consistent with the previous evaluations. On the other hand, the size distribution outside the SCI crater exhibits the radial variation, implying that the deposition of ejecta from the SCI crater is involved. The slope of the size distribution outside the crater at small sizes differs from the slope of the size distribution on the surface of Ryugu by approximately 1 or slightly less. This is consistent with the claim that some particles are buried in fine particles of the subsurface origin included in ejecta from the SCI crater. Thus, the particle size distributions inside and outside the SCI crater reveal that the subsurface layer beneath the SCI impact site is rich in fine particles with – 9 cm in size while the particles on the surface have a size distribution of a power-law form with shallower slopes at small sizes due to the deposition of fine ejecta from the subsurface layer. Finally, we discuss a process responsible for this difference in particle size distribution between the surface and the subsurface layers. The occurrence of segregation in the gravitational flow of particles on the surface of Ryugu is plausible. Graphical Abstract: [Figure not available: see fulltext.].
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Science advances 8(46) eabo7239 2022年10月20日 査読有りThe Hayabusa2 spacecraft returned to Earth from the asteroid 162173 Ryugu on December 6, 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 3He/4He and 20Ne/22Ne ratios, along with some contaminant terrestrial atmospheric gases. A mixture of solar and Earth's atmospheric gas is the best explanation of the container gas composition. Fragmentation of Ryugu grains within the sample container is discussed based on 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.
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Science (New York, N.Y.) 379(6634) eabo0431 2022年10月20日 査読有りThe near-Earth carbonaceous asteroid (162173) Ryugu is expected to contain volatile chemical species that could provide information on the origin of Earth's volatiles. Samples of Ryugu were retrieved by the Hayabusa2 spacecraft. We measure noble gas and nitrogen isotopes in Ryugu samples, finding they are dominated by pre-solar and primordial components, incorporated during Solar System formation. Noble gas concentrations are higher than those in Ivuna-type carbonaceous (CI) chondrite meteorites. Several host phases of isotopically distinct nitrogen have heterogeneous abundances between the samples. Our measurements support a close relationship between Ryugu and CI chondrites. Noble gases produced by galactic cosmic rays, indicating ~5 Myr exposure, and from implanted solar wind, record the recent irradiation history of Ryugu after it migrated to its current orbit.
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Science (New York, N.Y.) 379(6634) eabn7850 2022年6月9日 査読有り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 measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples. They are mainly composed of materials similar to 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, [Formula: see text] (Stat.) [Formula: see text] (Syst.) million years after 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 the Sun's photosphere than other natural samples do.
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Proceedings of Science 395 2022年3月18日We present the status of the development of a Cherenkov telescope to be flown on a long-duration balloon flight, the Extreme Universe Space Observatory Super Pressure Balloon 2 (EUSO-SPB2). EUSO-SPB2 is an approved NASA balloon mission that is planned to fly in 2023 and is a precursor of the Probe of Extreme Multi-Messenger Astrophysics (POEMMA), a candidate for an Astrophysics probe-class mission. The purpose of the Cherenkov telescope on-board EUSOSPB2 is to classify known and unknown sources of backgrounds for future space-based neutrino detectors. Furthermore, we will use the Earth-skimming technique to search for Very-High-Energy (VHE) tau neutrinos below the limb (E > 10 PeV) and observe air showers from cosmic rays above the limb. The 0.785 m2 Cherenkov telescope is equipped with a 512-pixel SiPM camera covering a 12.8° x 6.4° (Horizontal × Vertical) field of view. The camera signals are digitized with a 100 MS/s readout system. In this paper, we discuss the status of the telescope development, the camera integration, and simulation studies of the camera response.
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Proceedings of Science 395 2022年3月18日The Fluorescence Telescope is one of the two telescopes on board the Extreme Universe Space Observatory on a Super Pressure Balloon II (EUSO-SPB2). EUSO-SPB2 is an ultra-long-duration balloon mission that aims at the detection of Ultra High Energy Cosmic Rays (UHECR) via the fluorescence technique (using a Fluorescence Telescope) and of Ultra High Energy (UHE) neutrinos via Cherenkov emission (using a Cherenkov Telescope). The mission is planned to fly in 2023 and is a precursor of the Probe of Extreme Multi-Messenger Astrophysics (POEMMA). The Fluorescence Telescope is a second generation instrument preceded by the telescopes flown on the EUSO-Balloon and EUSO-SPB1 missions. It features Schmidt optics and has a 1-meter diameter aperture. The focal surface of the telescope is equipped with a 6912-pixel Multi Anode Photo Multipliers (MAPMT) camera covering a 37.4 x 11.4 degree Field of Regard. Such a big Field of Regard, together with a flight target duration of up to 100 days, would allow, for the first time from suborbital altitudes, detection of UHECR fluorescence tracks. This contribution will provide an overview of the instrument including the current status of the telescope development.
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Proceedings of Science 395 2022年3月18日The Extreme Universe Space Observatory Super Pressure Balloon 2 (EUSO-SPB2) is under development, and will prototype instrumentation for future satellite-based missions, including the Probe of Extreme Multi-Messenger Astrophysics (POEMMA). EUSO-SPB2 will consist of two telescopes. The first is a Cherenkov telescope (CT) being developed to identify and estimate the background sources for future below-the-limb very high energy (E>10 PeV) astrophysical neutrino observations, as well as above-the-limb cosmic ray induced signals (E>1 PeV). The second is a fluorescence telescope (FT) being developed for detection of Ultra High Energy Cosmic Rays (UHECRs). In preparation for the expected launch in 2023, extensive simulations tuned by preliminary laboratory measurements have been performed to understand the FT capabilities. The energy threshold has been estimated at 1018.2 eV, and results in a maximum detection rate at 1018.6 eV when taking into account the shape of the UHECR spectrum. In addition, onboard software has been developed based on the simulations as well as experience with previous EUSO missions. This includes a level 1 trigger to be run on the computationally limited flight hardware, as well as a deep learning based prioritization algorithm in order to accommodate the balloon's telemetry budget. These techniques could also be used later for future, space-based missions.
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Proceedings of Science 395 2022年3月18日The field of UHECRs (Ultra-High energy cosmic Rays) and the understanding of particle acceleration in the cosmos, as a key ingredient to the behaviour of the most powerful sources in the universe, is of outmost importance for astroparticle physics as well as for fundamental physics and will improve our general understanding of the universe. The current main goals are to identify sources of UHECRs and their composition. For this, increased statistics is required. A space-based detector for UHECR research has the advantage of a very large exposure and a uniform coverage of the celestial sphere. The aim of the JEM-EUSO program [1] is to bring the study of UHECRs to space. The principle of observation is based on the detection of UV light emitted by isotropic fluorescence of atmospheric nitrogen excited by the Extensive Air Showers (EAS) in the Earth's atmosphere and forward-beamed Cherenkov radiation reflected from the Earth's surface or dense cloud tops. In addition to the prime objective of UHECR studies, JEM-EUSO will do several secondary studies due to the instruments' unique capacity of detecting very weak UV-signals with extreme time-resolution around 1 μs: meteors, Transient Luminous Events (TLE), bioluminescence, maps of human generated UV-light, searches for Strange Quark Matter (SQM) and high-energy neutrinos, and more. The JEM-EUSO program includes several missions from ground (EUSO-TA [2]), from stratospheric balloons (EUSO-Balloon [3], EUSO-SPB1 [4], EUSO-SPB2 [5]), and from space (TUS [6], Mini-EUSO [7]) employing fluorescence detectors to demonstrate the UHECR observation from space and prepare the large size missions K-EUSO [8] and POEMMA [9]. A review of the current status of the program, the key results obtained so far by the different projects, and the perspectives for the near future are presented.
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Proceedings of Science 395 2022年3月18日K-EUSO is a planned mission of the JEM-EUSO program for the study of ultra-high energy cosmic rays (UHECR) from space, to be deployed on the International Space Station. The K-EUSO observatory consists of a UV telescope with a wide field of view, which aims at the detection of fluorescence light emitted by extensive air showers (EAS) in the atmosphere. The EAS events will be sampled with a time resolution of 1-2.5 μs to reconstruct the entire shower profile with high precision. The detector consisting of ∼ 105 independent pixels will allow a spatial resolution of ∼700 m on ground. From a 400 km altitude, K-EUSO will achieve a large and full sky exposure to sample the highest energy range of the UHECR spectrum. In this contribution, we present estimates of the performance of the observatory: an estimation of the expected exposure and triggered event rate as a function of energy and the event reconstruction performance, including resolution of arrival directions and energy of UHECRs.
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Proceedings of Science 395 2022年3月18日The Extreme Universe Space Observatory on a Super Pressure Balloon II (EUSO-SPB2) is a second generation stratospheric balloon instrument for the detection of Ultra High Energy Cosmic Rays (UHECRs, E > 1 EeV) via the fluorescence technique and of Very High Energy (VHE, E > 10 PeV) neutrinos via Cherenkov emission. EUSO-SPB2 is a pathfinder mission for instruments like the proposed Probe Of Extreme Multi-Messenger Astrophysics (POEMMA). The purpose of such a space-based observatory is to measure UHECRs and UHE neutrinos with high statistics and uniform exposure. EUSO-SPB2 is designed with two Schmidt telescopes, each optimized for their respective observational goals. The Fluorescence Telescope looks at the nadir to measure the fluorescence emission from UHECR-induced extensive air shower (EAS), while the Cherenkov Telescope is optimized for fast signals (∼10 ns) and points near the Earth's limb. This allows for the measurement of Cherenkov light from EAS caused by Earth skimming VHE neutrinos if pointed slightly below the limb or from UHECRs if observing slightly above. The expected launch date of EUSO-SPB2 is Spring 2023 from Wanaka, NZ with target duration of up to 100 days. Such a flight would provide thousands of VHECR Cherenkov signals in addition to tens of UHECR fluorescence tracks. Neither of these kinds of events have been observed from either orbital or suborbital altitudes before, making EUSO-SPB2 crucial to move forward towards a space-based instrument. It will also enhance the understanding of potential background signals for both detection techniques. This contribution will provide a short overview of the detector and the current status of the mission as well as its scientific goals.
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Proceedings of Science 395 2022年3月18日The JEM-EUSO (Joint Experiment Missions for Extreme Universe Space Observatory) program aims at the realization of the ultra-high energy cosmic ray (UHECR) observation using wide field of view fluorescence detectors in orbit. Ultra-violet (UV) light emission from the atmosphere such as airglow and anthropogenic light on the Earth’s surface are the main background for the space-based UHECR observations. The Mini-EUSO mission has been operated on the International Space Station (ISS) since 2019 which is the first space-based experiment for the program. The Mini-EUSO instrument consists of a 25 cm refractive optics and the photo-detector module with the 2304-pixel array of the multi-anode photomultiplier tubes. On the nadir-looking window of the ISS, the instrument is capable of continuously monitoring a ∼300 km × 300 km area. In the present work, we report the preliminary result of the measurement of the UV light in the nighttime Earth using the Mini-EUSO data downlinked to the ground. We mapped UV light distribution both locally and globally below the ISS obit. Simulations were also made to characterize the instrument response to diffuse background light. We discuss the impact of such light on space-based UHECR observations and the Mini-EUSO science objectives.
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Proceedings of Science 395 2022年3月18日The Extreme Universe Space Observatory - Super Pressure Balloon (EUSO-SPB2) mission will fly two custom telescopes that feature Schmidt optics to measure Čerenkov- and fluorescence-emission of extensive air-showers from cosmic rays at the PeV and EeV-scale, and search for τ-neutrinos. Both telescopes have 1-meter diameter apertures and UV/UV-visible sensitivity. The Čerenkov telescope uses a bifocal mirror segment alignment, to distinguish between a direct cosmic ray that hits the camera versus the Čerenkov light from outside the telescope. Telescope integration and laboratory calibration will be performed in Colorado. To estimate the point spread function and efficiency of the integrated telescopes, a test beam system that delivers a 1-meter diameter parallel beam of light is being fabricated. End-to-end tests of the fully integrated instruments will be carried out in a field campaign at dark sites in the Utah desert using cosmic rays, stars, and artificial light sources. Laser tracks have long been used to characterize the performance of fluorescence detectors in the field. For EUSO-SPB2 an improvement in the method that includes a correction for aerosol attenuation is anticipated by using a bi-dynamic Lidar configuration in which both the laser and the telescope are steerable. We plan to conduct these field tests in Fall 2021 and Spring 2022 to accommodate the scheduled launch of EUSO-SPB2 in 2023 from Wanaka, New Zealand.
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Proceedings of Science 395 2022年3月18日The TurLab facility is a laboratory, equipped with a 5 m diameter and 1 m depth rotating tank, located in the fourth basement level of the Physics Department of the University of Turin. In the past years, we have used the facility to perform experiments related to the observations of Extreme Energy Cosmic Rays (EECRs) from space using the fluorescence technique for JEM-EUSO missions with the main objective to test the response of the trigger logic. In the missions, the diffuse night brightness and artificial and natural light sources can vary significantly in time and space in the Field of View (FoV) of the telescope. Therefore, it is essential to verify the detector performance and test the trigger logic under such an environment. By means of the tank rotation, a various terrestrial surface with the different optical characteristics such as ocean, land, forest, desert and clouds, as well as artificial and natural light sources such as city lights, lightnings and meteors passing by the detector FoV one after the other is reproduced. The fact that the tank located in a very dark place enables the tests under an optically controlled environment. Using the Mini-EUSO data taken since 2019 onboard the ISS, we will report on the comparison between TurLab and ISS measurements in view of future experiments at TurLab. Moreover, in the forthcoming months we will start testing the trigger logic of the EUSO-SPB2 mission. We report also on the plans and status for this purpose.
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Proceedings of Science 395 2022年3月18日The TUS observatory was the first orbital detector aimed at the detection of ultra-high energy cosmic rays (UHECRs). It was launched on April 28, 2016, from the Vostochny cosmodrome in Russia and operated until December 2017. It collected ∼ 80, 000 events with a time resolution of 0.8 μs. A fundamental parameter to be determined for cosmic ray studies is the exposure of an experiment. This parameter is important to estimate the average expected event rate as a function of energy and to calculate the absolute flux in case of event detection. Here we present results of a study aimed to calculate the exposure that TUS accumulated during its mission. The role of clouds, detector dead time, artificial sources, storms, lightning discharges, airglow and moon phases is studied in detail. An exposure estimate with its geographical distribution is presented. We report on the applied technique and on the perspectives of this study in view of the future missions of the JEM-EUSO program.
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Proceedings of Science 395 2022年3月18日Mini-EUSO is a detector observing the Earth in the ultraviolet band from the International Space Station through a nadir-facing window, transparent to the UV radiation, in the Russian Zvezda module. Mini-EUSO main detector consists in an optical system with two Fresnel lenses and a focal surface composed of an array of 36 Hamamatsu Multi-Anode Photo-Multiplier tubes, for a total of 2304 pixels, with single photon counting sensitivity. The telescope also contains two ancillary cameras, in the near infrared and visible ranges, to complement measurements in these bandwidths. The instrument has a field of view of 44◦, a spatial resolution of about 6.3 km on the Earth surface and of about 4.7 km on the ionosphere. The telescope detects UV emissions of cosmic, atmospheric and terrestrial origin on different time scales, from a few µs upwards. On the fastest timescale of 2.5 µs, Mini-EUSO is able to observe atmospheric phenomena as Transient Luminous Events and in particular the ELVES, which take place when an electromagnetic wave generated by intra-cloud lightning interacts with the ionosphere, ionizing it and producing apparently superluminal expanding rings of several 100 km and lasting ' 100 µs. These highly energetic fast events have been observed to be produced in conjunction also with Terrestrial Gamma-Ray Flashes and therefore a detailed study of their characteristics (speed, radius, energy ...) is of crucial importance for the understanding of these phenomena. In this paper we present the observational capabilities of ELVE detection by Mini-EUSO and specifically the reconstruction and study of ELVE characteristics.
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Proceedings of Science 395 2022年3月18日Mini-EUSO is a telescope launched on board the International Space Station in 2019 and currently located in the Russian section of the station. Main scientific objectives of the mission are the search for nuclearites and Strange Quark Matter, the study of atmospheric phenomena such as Transient Luminous Events, meteors and meteoroids, the observation of sea bioluminescence and of artificial satellites and man-made space debris. It is also capable of observing Extensive Air Showers generated by Ultra-High Energy Cosmic Rays with an energy above 1021 eV and detect artificial showers generated with lasers from the ground. Mini-EUSO can map the night-time Earth in the UV range (290 - 430 nm), with a spatial resolution of about 6.3 km and a temporal resolution of 2.5 μs, observing our planet through a nadir-facing UV-transparent window in the Russian Zvezda module. The instrument, launched on 2019/08/22 from the Baikonur cosmodrome, is based on an optical system employing two Fresnel lenses and a focal surface composed of 36 Multi-Anode Photomultiplier tubes, 64 channels each, for a total of 2304 channels with single photon counting sensitivity and an overall field of view of 44◦. Mini-EUSO also contains two ancillary cameras to complement measurements in the near infrared and visible ranges. In this paper we describe the detector and present the various phenomena observed in the first year of operation.
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Proceedings of Science 395 2022年3月18日Mini-EUSO is a mission of the JEM-EUSO program flying onboard the International Space Station since August 2019. Since the first data acquisition in October 2019, more than 35 sessions have been performed for a total of 52 hours of observations. The detector has been observing Earth at night-time in the UV range and detected a wide variety of transient sources all of which have been modeled through Monte Carlo simulations. Mini-EUSO is also capable of detecting meteors and potentially space debris and we performed simulations for such events to estimate their impact on future missions for cosmic ray science from space. We show here examples of the simulation work done in this framework to analyze the Mini-EUSO data. The expected response of Mini-EUSO with respect to ultra high energy cosmic ray showers has been studied. The efficiency curve of Mini-EUSO as a function of primary energy has been estimated and the energy threshold for Cosmic Rays has been placed to be above 1021 eV. We compared the morphology of several transient events detected during the mission with cosmic ray simulations and excluded that they can be due to cosmic ray showers. To validate the energy threshold of the detector, a system of ground based flashers is being used for end-to-end calibration purposes. We therefore implemented a parameterization of such flashers into the JEM-EUSO simulation framework and studied the response of the detector with respect to such sources.
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Proceedings of Science 395 2022年3月18日EUSO-TA is a ground-based experiment, placed at Black Rock Mesa of the Telescope Array site as a part of the JEM-EUSO (Joint Experiment Missions for the Extreme Universe Space Observatory) program. The UV fluorescence imaging telescope with a field of view of about 10.6◦ x 10.6◦ consisting of 2304 pixels (36 Multi-Anode Photomultipliers, 64 pixels each) works with 2.5-microsecond time resolution. An experimental setup with two Fresnel lenses allows for measurements of Ultra High Energy Cosmic Rays in parallel with the TA experiment as well as the other sources like flashes of lightning, artificial signals from UV calibration lasers, meteors and stars. Stars increase counts on pixels while crossing the field of view as the point-like sources. In this work, we discuss the method for calibration of EUSO fluorescence detectors based on signals from stars registered by the EUSO-TA experiment during several campaigns. As the star position is known, the analysis of signals gives an opportunity to determine the pointing accuracy of the detector. This can be applied to space-borne or balloon-borne EUSO missions. We describe in details the method of the analysis which provides information about detector parameters like the shape of the point spread function and is the way to perform absolute calibration of EUSO cameras.
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Proceedings of Science 395 2022年3月18日Mini-EUSO is the first detector of the JEM-EUSO program deployed on the ISS. It is a wide field of view telescope currently operating from a nadir-facing UV-transparent window on the ISS. It is based on an array of MAPMTs working in photon counting mode with a 2.5 μs time resolution. Among the different scientific objectives it searches for light signals with time duration compatible to those expected from Extensive Air Showers (EAS) generated by EECRs interacting in the atmosphere. Although the energy threshold for cosmic ray showers is above E > 1021eV, due the constraints given by the size of the UV-transparent window, the dedicated trigger logic has been capable of the detection of other interesting classes of events, like elves and ground flashers. An overview of the general performance of the trigger system is provided, with a particular focus on the identification of classes of events responsible for the triggers.
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Science 375(6584) 1011-1016 2022年3月 査読有り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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Nature Astronomy 6(2) 214-220 2022年2月 査読有り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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日本地球化学会年会要旨集 69 9 2022年地球上での生命の誕生に必要とされるアミノ酸などの生体有機物の起源としては，原始大気からの生成や，地球外で生成したアミノ酸の隕石などによる供給が考えられる。本研究では 太陽エネルギー粒子による弱還元型大気(二酸化炭素・一酸化炭素・窒素・水混合気体)からのアミノ酸生成の可能性、および宇宙塵によるアミノ酸供給の可能性を調べるため、加速器を用いた模擬初期地球大気への陽子線照射実験や，宇宙におけるアミノ酸の安定性に関する宇宙実験「たんぽぽ」「たんぽぽ２」により行った。地球起源アミノ酸および地球外起源アミノ酸に関して，供給量やアミノ酸不斉の起源等の観点から比較を行い，今後の展望についても述べる。
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GEOCHEMICAL JOURNAL 56(6) 197-222 2022年 査読有りThe Hayabusa2 spacecraft explored C-type near-Earth asteroid (162173) Ryugu and returned asteroidal materials, collected during two touchdown operations, to the Earth as the first sample from carbonaceous-type asteroid. The sample container, in which similar to 5 g of Ryugu sample was enclosed, was safely opened in the clean chamber system with no severe exposure to the terrestrial atmosphere. In the course of preparation operation of the sample container, two dark-colored millimeter- to sub-millimeter-sized particles were found outside the sealing part of the sample container. Because they look similar to the Ryugu particles inside the sample container, the particles were named as Q particles (Q from questionable). In this study, we investigated Q particles (Q001 and Q002) mineralogically and petrographically to compare them with potential contaminants (the ablator material of the reentry capsule and fine sand particles at the capsule landing site), Ryugu sample, and CI chondrites. The Q particles show close resemblance to Ryugu sample and CI chondrites, but have no evidence of terrestrial weathering that CI chondrites experienced. We therefore conclude that the Q particles are originated from Ryugu and were expelled from the sample catcher (sample storage canister) in space prior to the enclosure operation of the sample catcher in the sample container. The most likely scenario is that the Q particles escaped from the sample catcher during the retrieval of the sample collection reflector, which was the necessary operation for the sample container closing.
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Nature Astronomy 6(10) 1163-1171 2022年 査読有り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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Proceedings of the Japan Academy. Series B, Physical and biological sciences 98(6) 227-282 2022年 査読有り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, Δ17O, 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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Earth, Planets and Space 74(1) doi: 10.1186/s40623-022-01628-z. 2022年 査読有り
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Astrobiology 21(12) 1479-1493 2021年12月1日 査読有りAmino acids have been detected in extraterrestrial bodies such as carbonaceous chondrites (CCs), which suggests that extraterrestrial organics could be the source of the first life on Earth, and interplanetary dust particles (IDPs) or micrometeorites (MMs) are promising carriers of extraterrestrial organic carbon. Some amino acids found in CCs are amino acid precursors, but these have not been well characterized. The Tanpopo mission was conducted in Earth orbit from 2015 to 2019, and the stability of glycine (Gly), hydantoin (Hyd), isovaline (Ival), 5-ethyl-5-methylhydantoin (EMHyd), and complex organics formed by proton irradiation from CO, NH3, and H2O (CAW) in space were analyzed by high-performance liquid chromatography and/or gas chromatography/mass spectrometry. The target substances showed a logarithmic decomposition over 1-3 years upon space exposure. Recoveries of Gly and CAW were higher than those of Hyd, Ival, and EMHyd. Ground simulation experiments showed different results: Hyd was more stable than Gly. Solar ultraviolet light was fatal to all organics, and they required protection when carried by IDPs/MMs. Thus, complex amino acid precursors (such as CAW) were possibly more robust than simple precursors during transportation to primitive Earth. The Tanpopo 2 mission is currently being conducted to expose organics to more probable space conditions.
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Icarus 369 2021年11月15日 査読有りMany small boulders with reflectance values higher than 1.5 times the average reflectance have been found on the near-Earth asteroid 162,173 Ryugu. Based on their visible wavelength spectral differences, Tatsumi et al. (2021, Nature Astronomy, 5, doi:10.1038/s41550-020-1179-z) defined two bright boulder classes: C-type and S-type. These two classifications of bright boulders have different size distributions and spectral trends. In this study, we measured the spectra of 79 bright boulders and investigated their detailed spectral properties. Analyses obtained a number of important results. First, S-type bright boulders on Ryugu have spectra that are similar to those found for two different ordinary chondrites with different initial spectra that have been experimentally space weathered the same way. This suggests that there may be two populations of S-type bright boulders on Ryugu, perhaps originating from two different impactors that hit Ryugu's parent body. Second, the model space-weathering ages of meter-size S-type bright boulders, based on spectral change rates derived in previous experimentally irradiated ordinary chondrites, are 105–106 years, which is consistent with the crater retention age (<106 years) of the ~1-m deep surface layer on Ryugu. This agreement strongly suggests that Ryugu's surface is extremely young, implying that the samples acquired from Ryugu's surface should be fresh. Third, the lack of a serpentine absorption in the S-type clast embedded in one of the large brecciated boulders indicates that fragmentation and cementation that created the breccias occurred after the termination of aqueous alteration. Fourth, C-type bright boulders exhibit a continuous spectral trend similar to the heating track of low-albedo carbonaceous chondrites, such as CM and CI. Other processes, such as space weathering and grain size effects, cannot primarily account for their spectral variation. Furthermore, the distribution of the spectra of general dark boulders, which constitute >99.9% of Ryugu's volume, is located along the trend line in slope/UV-index diagram that is occupied by C-type bright boulders. These results indicate that thermal metamorphism might be the dominant cause for the spectral variety among the C-type bright boulders on Ryugu and that general boulders on Ryugu may have experienced thermal metamorphism under a much narrower range of conditions than the C-type bright boulders. This supports the hypothesis that Ryugu's parent body experienced uniform heating due to radiogenic energy rather than impact heating.
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Proceedings of the International Astronomical Union 15 259-261 2021年10月1日 査読有りCircumstellar discs are known to exist in great variety, from gas-rich discs around the youngest stars to evolved debris discs such as the solar system's zodiacal cloud. Through gravitational interaction, exoplanets embedded in these discs can generate density variations, imposing potentially observable structural features on the disc such as rings or gaps. Here we report on a mirrored double crescent pattern arising in simulations of discs harbouring a small, moderately eccentric planet - such as Mars. We show that the structure is a result of a directed apsidal precession occurring in particles that migrate the planet's orbital region under Poynting-Robertson drag. We further analyze the strength of this effect with respect to planet and particle parameters.
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Advances in Space Research 69(7) 2787-2797 2021年10月 査読有り責任著者Capturing and analyzing cometary coma dust lead to elucidate the origin of water and organics within the Solar System. For future sample return missions of fragile organic microparticles from a cometary nucleus, rendezvous operations will become more favorable than flyby missions because the comet rendezvous can reduce impacting velocity of cometary dust particles slow enough to capture them intact, rather than hypervelocity flyby sampling like the Stardust mission to the Comet Wild 2. At JAXA/ISAS, we are developing a core technology for sample return of microparticles ejected at as a lower velocity as an order of 0.1 m/s to 100 m/s after rendezvous with a cometary nucleus. We have devised “Vertically Aligned Carbon Nanotube (VA-CNT)” carpets as an effective capture medium for such a purpose. The VA-CNT carpets can amplify van der Waals force with impacting particles due to the large contact area and can capture intact the microparticles of sub-mm in size or smaller in the vacuum space environment while preserving its adhesive strength. In this study, we modelled capturing mechanism of microparticles on the VA-CNT carpets by the impact analysis software “LS-DYNA” to further improve its particle capture performance. The stress–strain constitutive laws for the VA-CNT carpets were derived via indentation and inputted to our simulations that were consistent with impact experiment results. The simulations reveal that the mechanical property of the VA-CNT carpets is the key for the improvement of its particle capture performance suitable for sampling the cometary dust.
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Icarus 366 2021年9月15日 査読有りThe resurfacing process on Ryugu accompanying the artificial impact crater formation by Hayabusa2's Small Carry-on Impactor (SCI) was studied by comparing pre- and post-impact images of this region captured by an optical navigation camera. Three different aspects of the resurfacing process were examined: the crater rim profiles, the motion of boulders and the appearance of new boulders, and the motion vectors of Ryugu's surface around the SCI crater. The averaged crater rim height, h, was derived as follows: h = hr exp [−(r/Rrim − 1)/λrim], where Rrim is the SCI crater rim radius of 8.8 m, the fitted parameter, hr, is 0.475 m, and the λrim is 0.245. The ejecta blanket thickness of the SCI crater was thinner than that estimated from both the observation of natural craters and the crater formation theory. However, this discrepancy of the ejecta blanket thickness was resolved by taking into account the new boulders appearing in the post-impact images in the volume. The motion of the discovered boulders could be classified by its mechanisms as follows: a dragging motion created by excavation flow during the crater formation, a pushing motion created by falling-back ejecta, a dragging motion created by the slight motion of the Okamoto boulder, and a motion caused by seismic shaking induced by the SCI impact itself. The seismic shaking caused boulders to move farther than 3 cm from the original site in most of the region within 15 m distance from the SCI crater center, where the maximum acceleration of the impact induced seismic waves 7 times larger than the surface gravity of Ryugu based on the laboratory experiments (Matsue et al. [2020] Icarus, 338, 113520), and the evidence of the seismic shaking for boulders with a movement of >3 cm was detected in about 10% of the boulders in the region between 15 m and 30 m from the crater center, which region was inferred to experience acceleration larger than the Ryugu's surface gravity based on previous laboratory experiments (Matsue et al. [2020] Icarus, 338, 113520).
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Astrobiology 21(12) 1451-1460 2021年8月27日 査読有り最終著者The Tanpopo experiment was the first Japanese astrobiology mission on board the Japanese Experiment Module Exposed Facility on the International Space Station (ISS). The experiments were designed to address two important astrobiological topics, panspermia and the chemical evolution process toward the generation of life. These experiments also tested low-density aerogel and monitored the microdebris environment around low Earth orbit. The following six subthemes were identified to address these goals: (1) Capture of microbes in space: Estimation of the upper limit of microbe density in low Earth orbit; (2) Exposure of microbes in space: Estimation of the survival time course of microbes in the space environment; (3) Capture of cosmic dust on the ISS and analysis of organics: Detection of the possible presence of organic compounds in cosmic dust; (4) Alteration of organic compounds in space environments: Evaluation of decomposition time courses of organic compounds in space; (5) Space verification of the Tanpopo hyper-low-density aerogel: Durability and particle-capturing capability of aerogel; (6) Monitoring of the number of space debris: Time-dependent change in space debris environment. Subthemes 1 and 2 address the panspermia hypothesis, whereas 3 and 4 address the chemical evolution. The last two subthemes contribute to space technology development. Some of the results have been published previously or are included in this issue. This article summarizes the current status of the Tanpopo experiments.
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Astrobiology 21(12) 1461-1472 2021年8月27日 査読有りThe Tanpopo experiment was the first Japanese astrobiology mission on board the International Space Station. It included exposure experiments of microbes and organic compounds as well as a capture experiment of hypervelocity impacting microparticles. We deployed three Exposure Panels, each consisting of 20 Exposure Units that contained microbes, organic compounds, an alanine UV dosimeter or an ionizing radiation dosimeter. The three Exposure Panels were situated on the zenith face of the Exposed Experiment Handrail Attachment Mechanism (ExHAM) that was pointing in zenith direction toward space, which was attached on a handrail of the Japanese Experiment Module (Kibo) Exposed Facility (JEM-EF) outside the International Space Station. The three Exposure Panels were one by one retrieved and returned to the ground after approximately 1, 2, and 3 years of exposure to the space environment. Capture Panels, each of which contained one or two blocks of amorphous silica aerogel, were exposed to collect hypervelocity impact microparticles. Possible captured particles may include micrometeoroids, human-made orbital debris, and natural terrestrial particles. Each year, Capture Panels containing from 11 to 12 aerogel blocks were attached to the three faces of the ExHAM (pointing to zenith, ram, and port); they remained in place for about 1 year and were then returned to the laboratory. This process was repeated three times, in total, during 2015-2018. Additional exposure of a Capture Panel facing ram was conducted between 2018 and 2019. Once the aerogel blocks were returned to the laboratory, they were encapsulated in dedicated transparent plastic cases and optically inspected by a specially designed microscopic system. Once located and recorded, hypervelocity impact signatures were excavated one by one and distributed for further detailed analyses. The apparatus, operation, and environmental factors of all the Tanpopo experiments are summarized in this article.
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Astrobiology 21(12) 1473-1478 2021年8月4日 査読有りRadiation dosimetry was carried out at the exposure facility (EF) and the pressurized module (PM) of the Japanese Kibo module installed in the International Space Station as one study on environmental monitoring for the Tanpopo mission. Three exposure panels and three references including biological and organic samples and luminescence dosimeters were launched to obtain data for different exposure durations during 3 years from May 2015 to July 2018. The dosimeters were equipped with additional shielding materials (0.55, 2.95, and 6.23 g/cm2 mass thickness). The relative dose variation, as a function of shielding mass thickness, was observed and compared with Monte Carlo simulations with respect to galactic cosmic rays (GCRs) and typical solar energetic particles (SEPs). The mean annual dose rates were DEF = 231 ± 5 mGy/year at the EF and DPM = 82 ± 1 mGy/year at the PM during the 3 years. The PM is well shielded, and the GCR simulation indicated that the measured mean dose reduction ratio inside the module (DPM/DEF = 0.35) required ∼26 g/cm2 additional shielding mass thickness. Observed points of the dose reduction tendency could be explained by the energy ranges of protons (10-100 MeV), where the protons passed through, or were absorbed in, the shielding materials of different mass thickness that surrounded dosimeters.
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Nature Astronomy 5(8) 766-774 2021年8月 査読有り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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Nature Astronomy 5(3) 246-250 2021年3月 査読有りAnalyses of meteorites and theoretical models indicate that some carbonaceous near-Earth asteroids may have been thermally altered due to radiative heating during close approaches to the Sun1–3. However, the lack of direct measurements on the subsurface doesn’t allow us to distinguish thermal alteration due to radiative heating from parent-body processes. In April 2019, the Hayabusa2 mission successfully completed an artificial impact experiment on the carbonaceous near-Earth asteroid (162173) Ryugu4,5, which provided an opportunity to investigate exposed subsurface material and test potential effects of radiative heating. Here we report observations of Ryugu’s subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. The strength and shape of the OH feature suggests that the subsurface material experienced heating above 300 °C, similar to the surface. In contrast, thermophysical modelling indicates that radiative heating cannot increase the temperature above 200 °C at the estimated excavation depth of 1 m, even at the smallest heliocentric distance possible for Ryugu. This supports the hypothesis that primary thermal alteration occurred on Ryugu’s parent body.
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Astronomy and Astrophysics 647 2021年3月1日 査読有り最終著者A projectile accelerated by the Hayabusa2 Small Carry-on Impactor successfully produced an artificial impact crater with a final apparent diameter of 14.5 ± 0.8 m on the surface of the near-Earth asteroid 162173 Ryugu on April 5, 2019. At the time of cratering, Deployable Camera 3 took clear time-lapse images of the ejecta curtain, an assemblage of ejected particles forming a curtain-like structure emerging from the crater. Focusing on the optical depth of the ejecta curtain and comparing it with a theoretical model, we infer the size of the ejecta particles. As a result, the typical size of the ejecta particles is estimated to be several centimeters to decimeters, although it slightly depends on the assumed size distribution. Since the ejecta particles are expected to come from a depth down to ∼1 m, our result suggests that the subsurface layer of Ryugu is composed of relatively small particles compared to the uppermost layer on which we observe many meter-sized boulders. Our result also suggests a deficit of particles of less than ∼1 mm in the subsurface layer. These findings will play a key role in revealing the formation and surface evolution process of Ryugu and other small Solar System bodies.
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Planetary and Space Science 197 2021年3月 査読有りThe practical limitations inherent to human and robotic planetary exploration necessitate the development of specific protocols and methods. This non-standard approach requires testing and validation phases in order to optimise instrumental setups and improve data interpretation; this can occur prior to, during, or even after a mission. Flight instruments, and/or their spare models, may be evaluated using relevant terrestrial materials and/or locations. These materials are called analogues: “analogue sites” for large-scale locations, and “analogue samples” for smaller-scale materials. Depending on the scientific domain, the word “analogue” may carry different meanings but is invariably used to denote objects having compositions and/or physical properties similar to specific extraterrestrial objects. However, due to the variability in composition and properties of natural materials, there are always – inevitably – some differences between the analogue and the object(s) to which it refers. In analogue studies, it is, thus, important to focus on the specific properties that need to be imitated and to consider analogue properties rather than analogue sites or samples alone. Here, we introduce the concept of “functional analogues”. We first make an overview of the different types of analogues and sort them according to their utility. We then describe how different types of functional analogues can be used throughout the timeline of space missions, from the evaluation of different methods in the definition of a mission to understanding the results acquired by probes exploring extraterrestrial bodies. Finally, logical pathways are outlined that facilitate the selection of the best-suited functional analogue(s) according to their intended use and taking into account practical limitations.
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Journal of Geophysical Research: Planets 126(2) 2021年2月 査読有りSeismic shaking has been regarded as an essential source of resurfacing on asteroids. The Small Carry-on Impactor (SCI) operation on Hayabusa2 has been expected to be a unique opportunity for testing in situ seismic shaking whose energy is sufficiently large to excite observable surface modification. However, no obvious regolith hopping was identified even immediately outside of the crater formed by the SCI impact. To understand this discrepancy from the expectation, we simulate seismic wave propagation on Ryugu with a wide range of surface material properties and evaluate maximum acceleration on the surface. Numerical results reveal that low-quality factor or low seismic efficiency is required to explain the lack of geomorphological change after the SCI experiment. Considering that scattering under anhydrous conditions cannot efficiently dissipate energy, such a low-quality factor is not plausible. The weak yield strength in porous materials can efficiently decrease seismic wave energies, making the apparent seismic efficiency extremely low. Based on this hypothesis, we propose a formulation of surface mobility on asteroids that considers the physical properties of regolith. We consistently estimate the occurrence of seismic shaking with the existence of unstable boulders on Ryugu.
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Earth, Planets and Space 73(1) 21 2021年1月 査読有り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. [Figure not available: see fulltext.].
MISC
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Space Research Today 216 11-12 2023年4月 招待有り筆頭著者ISSN: 2647:9933
書籍等出版物
30
講演・口頭発表等
505担当経験のある科目(授業)
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2020年4月 - 現在宇宙工学 (法政大学理工学部)
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2019年4月 - 現在宇宙システム工学 (九州工業大学工学部宇宙システム工学科)
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2010年9月 - 現在フロンティアプロジェクトマネジメント (慶應義塾大学大学院システムデザインマネジメント研究科)
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2017年9月 - 2020年3月航空宇宙学特別講義II (東京大学大学院工学研究科航空宇宙工学専攻)
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2010年1月 - 2010年11月宇宙システム理工学 (慶應義塾大学大学院理工学研究科)
Works(作品等)
26共同研究・競争的資金等の研究課題
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自然科学研究機構アストロバイオロジーセンター 自然科学研究機構アストロバイオロジーセンター・サテライト研究 2022年4月 - 2025年3月
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大阪大学レーザー科学研究所 大阪大学レーザー科学研究所・共同利用研究B-1 2020年10月 - 2025年3月
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日本学術振興会 科学研究費助成事業 国際共同研究加速基金(国際共同研究強化(B)) 2018年10月 - 2024年3月
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公益財団法人・住友財団 基礎科学研究助成 2019年11月 - 2023年3月
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MIT International Science and Technology Initiatives The ULVAC-Hayashi MISTI Seed Fund 2020年1月 - 2022年8月
産業財産権
8学術貢献活動
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学術調査立案・実施米国・カリフォルニア工科大学・ケック宇宙研究所 (米国・カリフォルニア工科大学・ケック宇宙研究所) 2022年10月24日 - 2023年4月
社会貢献活動
2メディア報道
24その他
7教育内容やその他の工夫
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年月日（From）2012/04/01件名宇宙生命・物質科学研究室（LABAM)概要研究室理念： 宇宙塵をキーワードとする宇宙探査・実験によって可能となるアストロバイオロジーと地球外物質研究を融合して、惑星系、地球型惑星、生命の起源と進化を実証的に解明することを目指すとともに、近隣の学際研究への応用・連携を通じて人類社会の持続的なフロンティア拡大に貢献する。
その他教育活動上特記すべき事項
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年月日（From）1999/05年月日（To）2003/09件名文部科学省宇宙科学研究所・惑星科学研究系（本務）概要教授： 藤原顕
助手： 安部正真、矢野創 -
年月日（From）2003/10年月日（To）2012/03件名JAXA宇宙科学研究所・太陽系科学研究系（本務）概要助教：矢野創
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年月日（From）2012/04件名JAXA宇宙科学研究所・学際科学研究系・宇宙生命物質科学研究室（本務）概要助教：矢野創
(継続中) -
年月日（From）2003/10年月日（To）2023/03件名総合研究大学院大学・物理科学研究科・宇宙科学専攻（併任）概要助教： 矢野創
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年月日（From）2010/09件名慶応義塾大学大学院 システムデザインマネジメント研究科（兼任）概要特別招聘准教授： 矢野創
(継続中) -
年月日（From）2016/04件名法政大学大学院 理工学研究科（併任）概要連携准教授： 矢野創
JAXA-法政大学連携大学院協定に基づく。(継続中)
2016-2023年は客員准教授。 -
年月日（From）2019/04件名慶応義塾大学 先端生命科学研究所（兼任）概要訪問准教授： 矢野創
(継続中) -
年月日（From）2019/04件名九州工業大学 工学部宇宙システム工学科 （兼任）概要非常勤講師：矢野創
(継続中) -
年月日（From）2017/04年月日（To）2020/03件名東京大学大学院 工学系研究科航空宇宙工学専攻（兼任）概要非常勤講師：矢野創
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年月日（From）2023/04件名総合研究大学院大学・先端学術院・宇宙科学コース（併任）概要助教：矢野創
(継続中)
● 指導学生等の数
6-
年度2021年度(FY2021)博士課程学生数1修士課程学生数3連携大学院制度による学生数3技術習得生の数1
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年度2020年度(FY2020)修士課程学生数5連携大学院制度による学生数5技術習得生の数1
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年度2019年度(FY2019)修士課程学生数6連携大学院制度による学生数6技術習得生の数2
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年度2018年度(FY2018)修士課程学生数5連携大学院制度による学生数5技術習得生の数2その他留学生：1
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年度2022年度(FY2022)博士課程学生数1修士課程学生数2連携大学院制度による学生数2技術習得生の数2
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年度2023年度(FY2023)博士課程学生数1修士課程学生数3連携大学院制度による学生数3技術習得生の数3学術特別研究員数1その他留学生： 1
● 指導学生の表彰・受賞
4-
指導学生名芹澤遼太所属大学法政大学大学院（ISAS連携大学院生）受賞内容（タイトル、団体名等）COSPAR Student Travel Grant Award、COSPAR, 彗星サンプルリターンを目指したCNT微粒子捕集材の実験的研究と数値解析による形状設計受賞年月日2020年7月
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指導学生名中澤淳一郎所属大学総合研究大学院大学受賞内容（タイトル、団体名等）帝人久村奨学金授与、公益財団法人帝人奨学会受賞年月日2021年6月
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指導学生名中澤淳一郎所属大学総合研究大学院大学受賞内容（タイトル、団体名等）帝人久村奨学金授与、公益財団法人帝人奨学会受賞年月日2023年4月
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指導学生名中澤淳一郎所属大学総合研究大学院大学受賞内容（タイトル、団体名等）日本学術振興会特別研究員（DC)受賞年月日2023年4月
● 指導学生の顕著な論文
23-
指導学生名岩田 翔也所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文(2024)論文タイトルSmart MLI宇宙実証機の地上校正による有効性検証と地球―月圏ダスト分布計測
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指導学生名Francesc TINTO所属大学仏・国際宇宙大学院（夏季インターン学生）著者名, ジャーナル名, 巻号ページ（出版年）ISUーMSS修士論文 Individual Project Report (2002)論文タイトルEvaluation of Effects of Regolith Size Distribution on Visible Near IR Asteroid Spectroscopy
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指導学生名Serina DINIEGA所属大学仏・国際宇宙大学院著者名, ジャーナル名, 巻号ページ（出版年）ISUーMSS修士論文 Individual Project Report (2004)論文タイトルRegolith Distribution Model for Sub-kilometer Ellipsoidal Asteroids
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指導学生名寺元 啓介所属大学東京大学大学院著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2005）論文タイトルMeasurements of Sound Speed in Granular Materials Simulated Regolith
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指導学生名奥平 恭子所属大学総合研究大学院大学著者名, ジャーナル名, 巻号ページ（出版年）博士論文（2006）論文タイトルEvaluation of Micrometeoroid Analogs Alteration on Capturing by Aerogel
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指導学生名真壁 輝夫所属大学東京大学大学院著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2007）論文タイトルThe Determination of Projectile Shape for Asteroid Impact Sampling System
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指導学生名平井 隆之所属大学総合研究大学院大学著者名, ジャーナル名, 巻号ページ（出版年）博士論文（2014）論文タイトルA New Cosmic Dust Distribution Model inside the Earth’s Orbit Based on IKAROS-ALADDIN Results
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指導学生名望月 悠行所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2018）論文タイトル複層薄膜貫通型微粒子衝突センサへの信号積分回路付与による質量推定精度の向上
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指導学生名Maximilian SOMMER所属大学独・シュトッツガルト大学院(JSPSサマープログラム留学生)著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2018）論文タイトルModelling Resonant Features in the Zodiacal Cloud
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指導学生名實川 律子所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2019）論文タイトル多層断熱材一体型微粒子衝突センサの性能評価
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指導学生名石岡 英悟所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2019）論文タイトル小天体ランデブーミッションに向けた低中速衝突ダストの検出回路の開発
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指導学生名Maximilian EITEL所属大学独・シュトッツガルト大学院著者名, ジャーナル名, 巻号ページ（出版年）技術研修報告書（2019）論文タイトルTanpopo Particle Impact Analysis
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指導学生名山本 啓太所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2020）論文タイトルISSに搭載されたエアロゲル捕集材による超高速微粒子衝突頻度の経年変化に及ぼす二次イジェクタと遮蔽効果の影響
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指導学生名大泉 柊人所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2020）論文タイトル彗星ランデブーサンプルリターンを目指した垂直配向カーボンナノチューブの微粒子捕集性能の評価
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指導学生名中野 晴貴所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2020）論文タイトル圧電性薄膜センサに衝突した微粒子の質量推定のための出力信号周波数分析
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指導学生名神門 宏祐所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2021）論文タイトル宇宙科学研究に向けたレーザー励起微粒子衝突実験装置射出部の最適化
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指導学生名水上 恵利香所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2021）論文タイトル微粒子環境モデルの更新に向けたたんぽぽ捕集パネル 構造部上の衝突痕分析
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指導学生名芹澤 遼太所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2021）論文タイトル彗星サンプルリターンを目指したCNT微粒子捕集材の実験的研究と数値解析による形状設計
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指導学生名武田 悠希所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2022）論文タイトル宇宙往還した垂直配向カーボンナノチューブによる低速衝突不定形粒子の捕集
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指導学生名膽澤 宏太所属大学法政大学大学院（連携大学院生）著者名, ジャーナル名, 巻号ページ（出版年）修士論文（2022）論文タイトルエアロゲルによる宇宙固体微粒子の衝突捕集に関する実験および数値解析
● 専任大学名
1-
専任大学名総合研究大学院大学（SOKENDAI)
● 所属する所内委員会
3-
所内委員会名2006年4月 - 2019年3月 大学共同利用スペースプラズマ（現・超高速衝突実験）専門委員会・委員
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所内委員会名2016年12月 - 2018年12月 宇宙理工学合同委員会下・宇宙科学の今後20年の構想を検討する委員会・委員
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所内委員会名2023年6月ー現在 科学データ利用委員会・委員
