研究者業績
基本情報
- 所属
- 立教大学 理学部 物理学科 教授理学研究科 物理学専攻博士課程後期課程 教授Graduate School of Science Field of Study: Physics Professor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 特任教授(兼任)宇宙科学研究所 WSO-UVプロジェクト 特任教授
- 学位
- 博士(理学)(東京大学)
- 研究者番号
- 30455464
- J-GLOBAL ID
- 201101036293959472
- researchmap会員ID
- 6000028006
研究キーワード
1研究分野
1経歴
6-
2022年8月 - 現在
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2020年11月 - 現在
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2018年4月 - 現在
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2018年4月 - 現在
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2018年4月 - 現在
学歴
3-
2004年4月 - 2007年3月
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2002年4月 - 2004年3月
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1997年4月 - 2002年3月
受賞
1論文
125-
Astronomy & Astrophysics 639 A83-A83 2020年7月 査読有り<italic>Context.</italic> The Hayabusa2 spacecraft launched by Japan Aerospace Exploration Agency has been conducting observations of the asteroid (162173) Ryugu since June 2018. The Telescopic Optical Navigation Camera (ONC-T) onboard Hayabusa2 has obtained thousands of images under a variety of illumination and viewing conditions. <italic>Aims.</italic> Our objective is to examine and validate the camera calibration, derive a photometric correction for creating global albedo maps, and to interpret the photometric modeling results to characterize the surface of Ryugu. <italic>Methods.</italic> We observed (162173) Ryugu with the Gemini-South telescope, and combined these measurements with other published ground-based observations of the asteroid. The ground-based observations were compared with the data obtained by ONC-T in order to validate the radiometric calibration mutually. We used a combination of the Hapke disk-integrated and disk-resolved model equations to simultaneously analyze the combined ground- and spacecraft-based data. <italic>Results.</italic> The average spectrum of Ryugu was classified as Cb-type following the SMASSII taxonomy and C/F-type following the Tholen taxonomy based on spacecraft observations. We derived Hapke model parameters for all seven color filters, which allowed us to photometrically correct images to within an error of <10% for ~80% of the image pixels used in the modeling effort. Using this model, we derived a geometric albedo of 4.0 ± 0.5% (<italic>v</italic> band) for Ryugu. The average reflectance factor at the standard illumination condition was 1.87 ± 0.14% in the <italic>v</italic> band. Moreover we measured a phase reddening of (2.0 ± 0.7) × 10−3 <italic>μ</italic>m−1 deg−1 for Ryugu, similar to that observed for the asteroid (101955) Bennu. <italic>Conclusions.</italic> The global color map showed that the general trend was for darker regions to also be redder regions, however there were some distinct exceptions to this trend. For example, Otohime Saxum was bright and red while Kibidango crater was dark and blue. The darkness and flatness of Ryugu’s reflectance might be caused by a high abundance of organic materials.
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Science 368(6491) 654-659 2020年5月8日 査読有りThe near-Earth asteroid (162173) Ryugu is thought to be a primitive carbonaceous object that contains hydrated minerals and organic molecules. We report sample collection from Ryugu’s surface by the Hayabusa2 spacecraft on 21 February 2019. Touchdown images and global observations of surface colors are used to investigate the stratigraphy of the surface around the sample location and across Ryugu. Latitudinal color variations suggest the reddening of exposed surface material by solar heating and/or space weathering. Immediately after touchdown, Hayabusa2’s thrusters disturbed dark, fine grains that originate from the redder materials. The stratigraphic relationship between identified craters and the redder material indicates that surface reddening occurred over a short period of time. We suggest that Ryugu previously experienced an orbital excursion near the Sun.
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Science 368(6486) 67-71 2020年4月3日 査読有りThe Hayabusa2 spacecraft investigated the small asteroid Ryugu, which has a rubble-pile structure. We describe an impact experiment on Ryugu using Hayabusa2’s Small Carry-on Impactor. The impact produced an artificial crater with a diameter >10 meters, which has a semicircular shape, an elevated rim, and a central pit. Images of the impact and resulting ejecta were recorded by the Deployable CAMera 3 for >8 minutes, showing the growth of an ejecta curtain (the outer edge of the ejecta) and deposition of ejecta onto the surface. The ejecta curtain was asymmetric and heterogeneous and it never fully detached from the surface. The crater formed in the gravity-dominated regime; in other words, crater growth was limited by gravity not surface strength. We discuss implications for Ryugu’s surface age.
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Icarus 338 113527-113527 2020年3月 査読有りAsteroid 162173 Ryugu has numerous craters. The initial measurement of impact craters on Ryugu, by Sugita et al. (2019), is based on Hayabusa2 ONC images obtained during the first month after the arrival of Hayabusa2 in June 2018. Utilizing new images taken until February 2019, we constructed a global impact crater catalogue of Ryugu, which includes all craters larger than 20 m in diameter on the surface of Ryugu. As a result, we identified 77 craters on the surface of Ryugu. Ryugu shows variation in crater density which cannot be explained by the randomness of cratering; there are more craters at lower latitudes and fewer at higher latitudes, and fewer craters in the western bulge (160 degrees E - 290 degrees E) than in the region around the meridian (300 degrees E - 30 degrees E). This variation implies a complicated geologic history for Ryugu. It seems that the variation in crater density indicates that the equatorial ridge located in the western hemisphere is relatively young, while that located in the eastern hemisphere is a fossil structure formed during the short rotational period in the distant past.
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Proceedings of the International Astronautical Congress, IAC 2020-October 2020年During the touchdowns of the "Hayabusa2" spacecraft on the asteroid Ryugu, some of the ejected surface materials were scattered toward the spacecraft. Apart from impact sampling by firing a metallic projectile, another mechanism of this phenomenon is surface material ejecta from formation of a crater by RCS thrusts of the spacecraft during its ascent from the asteroid surface after the touchdown. We conducted ground experiments of gas injection into simulated soil under vacuum in order to investigate the interaction between thruster plume and asteroidal regolith.
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Advances in the Astronautical Sciences 171 3101-3120 2020年The Hayabusa2 spacecraft successfully landed on the asteroid Ryugu on February 22nd, 2019. Because of the abundance of boulders, the touchdown operation required high accuracy for spacecraft safety. This research, therefore, investigates a precision landing sequence using retroreflective marker tracking. The trajectory for the touchdown operation is computed based on a high-fidelity gravity model to minimize the landing error. This paper provides trajectory reconstruction results based on actual flight data. Consequently, it is demonstrated that a landing accuracy of 3 m can be achieved, resulting in the successful touchdown.
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Astronomy & Astrophysics 632 L5-L5 2019年12月 査読有りAfter its release and a descent and bouncing phase, the Hayabusa2 lander MASCOT came to a final rest and MASCOT’s camera MASCam acquired a set of images of the surface of Ryugu. With MASCam’s instantaneous field of view of about 1 mrad, the images provide pixel scales from 0.2 to 0.5 mm pixel−1 in the foreground and up to 1 cm pixel−1 for surface parts in the background. Using a stereo-photogrammetric analysis of the MASCam images taken from slightly different positions due to commanded and unintentional movements of the MASCOT lander, we were able to determine the orientation for the different measurement positions. Furthermore, we derived a 3D surface model of MASCOT’s vicinity. Although the conditions for 3D stereo processing were poor due to very small stereo angles, the derived 3D model has about 0.5 cm accuracy in the foreground at 20 cm distance and about 1.5 cm at a distance of 40–50 cm.
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Astronomy & Astrophysics 632 L4-L4 2019年12月 査読有りA high-resolution 3D surface model, map-projected to a digital terrain model (DTM), and precisely ortho-rectified context images (orthoimages) of MASCOT landing site area are important data sets for the scientific analysis of relevant data that have been acquired with MASCOT’s image camera system MASCam and other instruments (e.g., the radiometer MARA and the magnetometer MASMag). We performed a stereo-photogrammetric (SPG) analysis of 1050 images acquired from the Hayabusa2 Optical Navigation Camera system (ONC) during the asteroid characterization phase and the MASCOT release phase in early October 2018 to construct a photogrammetric control point network of asteroid (162173) Ryugu. We validated existing rotational parameters for Ryugu and improved the camera orientation (position and pointing) of the ONC images to decimeter accuracy using SPG bundle block adjustment. We produced a high-resolution DTM of the entire MASCOT landing site area. Finally, based on this DTM, a set of orthoimages from the highest-resolution ONC images around MASCOT’s final rest position complements the results of this analysis.
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Astronomy & Astrophysics 632 L3-L3 2019年12月 査読有りImages from the Optical Navigation Camera system (ONC) onboard the Hayabusa2 spacecraft show the MASCOT lander during its descent to the surface of asteroid (162173) Ryugu. We used results from a previous stereo-photogrammetric analysis that provided precise ONC image orientation data (camera position and pointing), ONC orthoimages, and an ONC-based 3D surface model to combine them with the visibilities of MASCOT itself and its shadow on-ground within the ONC images. We integrated additional information from instruments onboard MASCOT (MASMag, MARA, MASCam) and derived MASCOT’s release position and modeled its free-fall descent path and its velocity over 350 s from its release at ∼41 m altitude above ground until its first contact with the surface of Ryugu. After first contact, MASCOT bounced over the surface of Ryugu for 663 s and came to rest at its first settlement point after four intermediate surface contacts. We again used ONC images that show MASCOT and partly its shadow and reconstructed the bouncing path and the respective velocities of MASCOT. The achieved accuracy for the entire descent and bouncing path is ∼0.1 m (1<italic>σ</italic>).
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Journal of Astronomical Telescopes, Instruments, and Systems 5(04) 1-1 2019年10月23日 査読有り
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Icarus 331 179-191 2019年10月 査読有りIn 2018, the Japanese spacecraft Hayabusa2, arrived at the small asteroid Ryugu. The surface of this C-type asteroid is covered with numerous boulders whose size and shape distributions are investigated in this study. Using a few hundred Optical Navigation Camera (ONC) images with a pixel scale of approximately 0.65 m, we focus on boulders greater than 5 m in diameter. Smaller boulders are also considered using five arbitrarily chosen ONC close-up images with pixel scales ranging from 0.7 to 6 cm. Across the entire surface area (~2.7 km ) of Ryugu, nearly 4400 boulders larger than 5 m were identified. Boulders appear to be uniformly distributed across the entire surface, with some slight differences in latitude and longitude. At ~50 km , the number density of boulders larger than 20 m is twice as large as on asteroid Itokawa (or Bennu). The apparent shapes of Ryugu's boulders resemble laboratory impact fragments, with larger boulders being more elongated. The ratio of the total volume of boulders larger than 5 m to the total excavated volume of craters larger than 20 m on Ryugu can be estimated to be ~94%, which is comparatively high. These observations strongly support the hypothesis that most boulders found on Ryugu resulted from the catastrophic disruption of Ryugu's larger parent body, as described in previous papers (Watanabe et al., 2019; Sugita et al., 2019). The cumulative size distribution of boulders larger than 5 m has a power-index of −2.65 ± 0.05, which is comparatively shallow compared with other asteroids visited by spacecraft. For boulders smaller than 4 m, the power-index is even shallower and ranges from −1.65 ± 0.05 to −2.01 ± 0.06. This particularly shallow power-index implies that some boulders are buried in Ryugu's regolith. Based on our observations, we suggest that boulders near the equator might have been buried by the migration of finer material and, as a result, the number density of boulders larger than 5 m in the equatorial region is lower than at higher latitudes. 2 −2
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Development of high-efficiency reflective grating by holographic processing for UV exoplanet scienceProceedings of the SPIE 11116 2019年9月9日 査読有り
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Astronomy & Astrophysics 2019年8月23日 査読有り
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Science 365(6455) 817-820 2019年8月23日 査読有り© 2017 The Authors. The near-Earth asteroid (162173) Ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu’s surface on 3 October 2018. We present images from the MASCOT camera (MASCam) taken during the descent and while on the surface. The surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. Rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. Close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. The inclusions appear similar to those in carbonaceous chondrite meteorites.
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METEORITICS & PLANETARY SCIENCE 54 . 2019年8月
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Icarus 325 153-195 2019年6月 査読有り
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Science 364(6437) 268-272 2019年4月19日 査読有り
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Astrophysical Journal Letters 874(1) 2019年3月20日© 2019. The American Astronomical Society. All rights reserved.. 162173 Ryugu, the target of Hayabusa2, has a round shape with an equatorial ridge, which is known as a spinning top shape. A strong centrifugal force is a likely contributor to Ryugu's top-shaped features. Observations by the Optical Navigation Camera on board Hayabusa2 show a unique longitudinal variation in geomorphology; the western side of this asteroid, later called the western bulge, has a smooth surface and a sharp equatorial ridge, compared to the other side. Here, we propose a structural deformation process that generated the western bulge. Applying the mission-derived shape model, we employ a finite element model technique to analyze the locations that experience structural failure within the present shape. Assuming that materials are uniformly distributed, our model shows the longitudinal variation in structurally failed regions when the spin period is shorter than ∼3.75 hr. Ryugu is structurally intact in the subsurface region of the western bulge while other regions are sensitive to structural failure. We infer that this variation is indicative of the deformation process that occurred in the past, and the western bulge is more relaxed structurally than the other region. Our analysis also shows that this deformation process might occur at a spin period between ∼3.5 and ∼3.0 hr, providing the cohesive strength ranging between ∼4 and ∼10 Pa.
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50th Lunar and Planetary Science Conference 2132 1732-1733 2019年3月
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Science 364(6437) 2019年 査読有り
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Science 364(6437) 272-275 2019年 査読有り© 2019 American Association for the Advancement of Science. All rights reserved. The near-Earth asteroid 162173 Ryugu, the target of the Hayabusa2 sample-return mission, is thought to be a primitive carbonaceous object. We report reflectance spectra of Ryugu's surface acquired with the Near-Infrared Spectrometer (NIRS3) on Hayabusa2, to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micrometers was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, which is consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.
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Astronomy & Astrophysics 2018年11月28日 査読有り
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EXPERIMENTAL ASTRONOMY 46(1) 135-209 2018年11月 査読有りThousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet's birth, and evolution. ARIEL was conceived to observe a large number (1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25-7.8m spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10-100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed - using conservative estimates of mission performance and a full model of all significant noise sources in the measurement - using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL - in line with the stated mission objectives - will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.
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Journal of Astronomical Telescopes, Instruments, and Systems 4(4) 2018年10月1日 査読有り
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Review of Scientific Instruments 2018年2月15日 査読有り
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日本惑星科学会誌遊星人 27(3) 207-215 2018年<p>火星衛星Phobosからのサンプルリターンに挑む火星衛星探査計画 (Martian Moons eXploration: MMX) は，現在，宇宙航空研究開発機構 (JAXA) プリプロジェクトとして，2024年の打ち上げと5年の往還期間を設定し，精力的な検討・初期開発が進められている．MMXは，サンプル分析，Deimosを加えた火星衛星の近接観測，そして火星大気および火星圏のモニタリング観測を組み合わせることにより，惑星に寄りそう衛星という切り口と視座から，太陽系における大気と水を湛えたハビタブル惑星の形成と進化の解明に迫ろうとしている．</p>
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ICARUS 300 341-359 2018年1月 査読有りHayabusa2, the first sample return mission to a C-type asteroid was launched by the Japan Aerospace Exploration Agency (JAXA) on December 3, 2014 and will arrive at the asteroid in the middle of 2018 to collect samples from its surface, which may contain both hydrated minerals and organics. The optical navigation camera (ONC) system on board the Hayabusa2 consists of three individual framing CCD cameras, ONC-T for a telescopic nadir view, ONC-W1 for a wide-angle nadir view, and ONC-W2 for a wide-angle slant view will be used to observe the surface of Ryugu. The cameras will be used to measure the global asteroid shape, local morphologies, and visible spectroscopic properties. Thus, image data obtained by ONC will provide essential information to select landing (sampling) sites on the asteroid. This study reports the results of initial inflight calibration based on observations of Earth, Mars, Moon, and stars to verify and characterize the optical performance of the ONC, such as flat-field sensitivity, spectral sensitivity, point-spread function (PSF), distortion, and stray light of ONC-T, and distortion for ONC-W1 and W2. We found some potential problems that may influence our science observations. This includes changes in sensitivity of flat fields for all bands from those that were measured in the pre-flight calibration and existence of a stray light that arises under certain conditions of spacecraft attitude with respect to the sun. The countermeasures for these problems were evaluated by using data obtained during initial in-flight calibration. The results of our inflight calibration indicate that the error of spectroscopic measurements around 0.7 mu m using 0.55, 0.70, and 0.86 mu m bands of the ONC-T can be lower than 0.7% after these countermeasures and pixel binning. This result suggests that our ONC-T would be able to detect typical strength (similar to 3%) of the serpentine absorption band often found on CM chondrites and low albedo asteroids with >= 4 sigma confidence. (C) 2017 Elsevier Inc. All rights reserved.
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EARTH PLANETS AND SPACE 69 2017年12月 査読有りWe provide an overview of data products from observations by the Japanese Venus Climate Orbiter, Akatsuki, and describe the definition and content of each data-processing level. Levels 1 and 2 consist of non-calibrated and calibrated radiance (or brightness temperature), respectively, as well as geometry information (e.g., illumination angles). Level 3 data are global-grid data in the regular longitude-latitude coordinate system, produced from the contents of Level 2. Non-negligible errors in navigational data and instrumental alignment can result in serious errors in the geometry calculations. Such errors cause mismapping of the data and lead to inconsistencies between radiances and illumination angles, along with errors in cloud-motion vectors. Thus, we carefully correct the boresight pointing of each camera by fitting an ellipse to the observed Venusian limb to provide improved longitude-latitude maps for Level 3 products, if possible. The accuracy of the pointing correction is also estimated statistically by simulating observed limb distributions. The results show that our algorithm successfully corrects instrumental pointing and will enable a variety of studies on the Venusian atmosphere using Akatsuki data.
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ADVANCES IN SPACE RESEARCH 60(7) 1453-1462 2017年10月 査読有りMass spectrometry has been widely used in lander missions to characterize the volatiles in rocks and soils on planetary surfaces. A good vacuum seal is very important for introducing such solid samples to a vacuum chamber and ejecting them. However, multiple measurements require many metal gaskets, leading to extra weight and complexity for the instruments. In this study, we investigate the capability of three kinds of elastomeric O-rings (Viton, Nexus-SLT, and Nexus-FV) as vacuum seals for mass spectrometric measurements, particularly for in situ K-Ar dating on Mars. First, thermal cycle tests revealed that low-temperature-resistant O-rings can maintain pressure < 10(-5) Pa at -60 degrees C under 1 bar ambient pressure, whereas Viton O-rings leaked at -25 degrees C. Then, the amount of Ar-40 due to out gassing from the O-rings and permeation under the ambient pressure of 650 Pa or 3 Pa was measured and compared with the amounts of Ar-40 that a flight-equivalent laser would liberate from potential target Martian rocks. The measured amounts were < 1% of that a target rock with 5000 ppm K2O and an age of 4.2 Ga would yield. These results suggest that a Viton O-ring can maintain the AT blank low under the Mars atmospheric pressure when temperatures are higher than -25 degrees C. A double O-ring seal using the low-temperature resistant elastomers would be an alternative approach at lower temperatures. The elastomeric O-rings would be useful for constructing a small and light-weighted mass spectrometric instrument for in situ K-Ar dating on Mars. (C) 2017 COSPAR. Published by Elsevier Ltd. All rights reserved.
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SPACE SCIENCE REVIEWS 208(1-4) 17-31 2017年7月 査読有りThe optical navigation camera telescope (ONC-T) is a telescopic framing camera with seven colors onboard the Hayabusa2 spacecraft launched on December 3, 2014. The main objectives of this instrument are to optically navigate the spacecraft to asteroid Ryugu and to conduct multi-band mapping the asteroid. We conducted performance tests of the instrument before its installation on the spacecraft. We evaluated the dark current and bias level, obtained data on the dependency of the dark current on the temperature of the charge-coupled device (CCD). The bias level depends strongly on the temperature of the electronics package but only weakly on the CCD temperature. The dark-reference data, which is obtained simultaneously with observation data, can be used for estimation of the dark current and bias level. A long front hood is used for ONC-T to reduce the stray light at the expense of flatness in the peripheral area of the field of view (FOV). The central area in FOV has a flat sensitivity, and the limb darkening has been measured with an integrating sphere. The ONC-T has a wheel with seven bandpass filters and a panchromatic glass window. We measured the spectral sensitivity using an integrating sphere and obtained the sensitivity of all the pixels. We also measured the point-spread function using a star simulator. Measurement results indicate that the full width at half maximum is less than two pixels for all the bandpass filters and in the temperature range expected in the mission phase except for short periods of time during touchdowns.
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ASTRONOMICAL JOURNAL 153(2) 2017年2月 査読有りThe water production rate of a comet is one of the. fundamental parameters necessary. to understand cometary activity when a comet approaches the Sun within 2.5 au, because water is the most abundant icy material in the cometary nucleus. Wide-field imaging observations of the hydrogen Ly alpha emission in comet 67P/Churyumov-Gerasimenko were performed by the Lyman Alpha Imaging Camera (LAICA) on. board the 50 kg class micro spacecraft, the Proximate Object Close Flyby with Optical Navigation (PROCYON), on UT 2015 September 7.40, 12.37, and 13.17 (corresponding to 25.31, 30.28, and 31.08 days after the perihelion passage of the comet, respectively). We derive the water production rates, QH(2)O, of the comet from Lya images of the comet by using a 2D axi-symmetric Direct Simulation Monte-Carlo model of the atomic hydrogen coma; (1.46. +/- 0.47) x 10(28), (1.24. +/- 0.40) x10(28), and (1.30. +/- 0.42) x 10(28) molecules s(-1) on 7.40, 12.37, and 13.17 September, respectively. These values are comparable to the values from in situ measurements by the Rosetta instruments in the 2015 apparition and the ground-based and space observations during the past apparitions. The comet did not show significant secular change in average water production rates just after the perihelion passage for the apparitions from 1982 to 2015. We emphasize that the measurements of absolute QH(2)O based on the wide field of view (e. g., by the LAICA/PROCYON) are so important to judge the soundness of the coma models used to infer QH(2)O based on in situ measurements by spacecraft, like the Rosetta.
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Proceedings of International Symposium on Radiation Detectors and Their Uses (ISRD2016) 2016年11月14日
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PLANETARY AND SPACE SCIENCE 128 14-29 2016年9月 査読有りAge is essential information for interpreting the geologic record on planetary surfaces. Although crater counting has been widely used to estimate the planetary surface ages, crater chronology in the inner solar system is largely built on radiometric age data from limited sites on the Moon. This has resulted in major uncertainty in planetary chronology. Because opportunities for sample-return missions are limited, in-situ geochronology measurements from one-way lander/rover missions are extremely valuable. Here we developed an in-situ isochron-based dating method using the K-Ar system, with K and Ar in a single rock sample extracted locally by laser ablation and measured using laser-induced breakdown spectroscopy (LIBS) and a quadrupole mass spectrometer (QMS), respectively. We built an experimental system combining flight equivalent instruments and measured K-Ar ages for mineral samples with known ages (similar to 1.8 Ga) and K contents (1-8 wt%); we achieved precision of 20% except for a mineral with low mechanical strength. Furthermore, validation measurements with two natural rocks (gneiss slabs) obtained K-Ar isochron ages and initial Ar-40 consistent with known values for both cases. This result supports that our LIBS-MS approach can derive both isochron ages and contributions of non-in situ radiogenic Ar-40 from natural rocks. Error assessments suggest that the absolute ages of key geologic events including the Noachian/Hesperian- and the Hesperian/Amazonian-transition can be dated with 10-20% errors for a rock containing similar to 1 wt% K2O, greatly reducing the uncertainty of current crater chronology models on Mars. (C) 2016 Elsevier Ltd. All rights reserved.
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TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN 14(30) Pk_111-Pk_116 2016年<p>DESTINY: the Demonstration and Experiment of Space Technology for Interplanetary Voyage, which is a candidate mission of Epsilon Launch Vehicle, plans to execute scientific observations using instruments with the mass of up to about 10 kg on the transfer and Halo orbit of the sun to earth Lagrangian point L1/L2 or on the fly-by orbit of near earth objects (NEO). Potential scientific objects include in-situ observation and remote sensing from these space are solar system explorations, such as, the observations of plasma and energetic particles around the terrestrial magnetosphere, inter-planetary and inter-stellar dust, and NEO. It is also considered to be useful for the pilot observations for future infrared, gamma-ray, and cosmic-ray space astronomical telescope in the deep space. Applied missions of DESTINY will be able to go to deep space with higher mass of payloads. Using the Epsilon Launch Vehicle, it will convey instruments of up to 50 kg to the space between Venus and Mars. DESTINY launched by the improved launch vehicle with the power of M-V rocket will carry payloads of up to 200 kg into the orbit of Venus and Mars. In these phases, Explorations for Venus, Mars, and multiple NEO, and astronomical observations from the deep space observatory will be realized by low cost deep space missions.</p>
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Aerospace Technology Japan 2016. 14(ists30) 89-94 2016年 査読有り
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ADVANCES IN SPACE RESEARCH 56(7) 1519-1524 2015年10月 査読有りThe Hayabusa2 spacecraft has three framing cameras (ONC-T, ONC-W1, and ONC-W2) for optical navigation to asteroid 1999 JU(3). The ONC-T is a telescopic camera with seven band-pass filters in the visible and near-infrared range. These filters are placed on a wheel, which rotates to put a selected filter for different observations, enabling multiband imaging. Previous ground-based observations suggesting that hydrous materials may be present on the surface of 1999 JU(3) and distributed in relatively limited areas. The presence of hydrous minerals indicates that this asteroid experienced only low to moderate temperatures during its formation, suggesting that primordial materials are preserved. In order to find the best sampling sites, we will perform reflectance spectroscopic observations using the ONC-T near the asteroid after arrival. Finding regions rich in hydrous minerals is the key for this remote sensing observation. In preparation for this, we conducted ground-based experiments for the actual ONC-T flight model to confirm the detectability of the absorption band of Fe-rich serpentine. As a result, we detected the absorption band near 0.7 mu m by reflectance spectroscopy of CM2 chondrites, such as Murchison and Nogoya, which are known to contain the Fe-rich serpentine, and did not detect any 0.7 mu m absorption in Jbilet Winselwan CM2 chondrite with decomposed Fe-rich serpentine. (C) 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.
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SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY 106 28-35 2015年4月1日 査読有り
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地球化学 48(4) 231-243 2014年Age is one of the most important observables in planetary science. The ages of geologic events on planets including Mars, however, are estimated with the crater chronology approach, which is largely based on radiometric age data derived from very limited places on the Moon. Obtaining age data for the inner planets, asteroids, or the satellites of the outer planets is essential for accurate understanding of the history of our solar system. Although sample-return missions can achieve this goal, they are technically very challenging and extremely expensive. Thus, in-situ geochronology measurements with one-way lander/rover missions would be very important. This paper reviews (1) primary scientific issues on planetary chronology, such as uncertainties in the crater chronology models on Mars, (2) recent developments for in-situ dating instruments based on K–Ar, Rb–Sr, or Pb–Pb dating methods, (3) in-situ K–Ar age measurements conducted by NASAs Curiosity rover, and (4) the development status of our in-situ K–Ar isochron dating method based on a combination of laser-induced breakdown spectroscopy and quadrupole mass spectrometry for measurements of potassium and argon, respectively. We also discuss perspectives for a future Japanese in-situ geochronology mission to Mars.
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Geophysical Research Letters 40(2) 250-254 2013年1月28日 査読有りThe Telescope of Extreme Ultraviolet (TEX) onboard Japan's lunar orbiter KAGUYA provided the first sequential images of the Earth's plasmasphere from the "side" (meridian) view. The TEX instrument obtained the global distribution of the terrestrial helium ions (He+) by detecting resonantly scattered emission at 30.4 nm. One of the most striking features of the plasmasphere found by TEX is an arc-shaped structure of enhanced brightness, which we call a "plasmaspheric filament". In the TEX image on 2 June 2008, the filament structure was clearly aligned to the dipole magnetic field line of L = 3.7 at 7.3 magnetic local time. Our analysis suggests that the filament represents an isolated flux tube filled with four times higher He + density than its neighbors. We found four events of plasmaspheric filament in the images obtained between March and June 2008, and in all four events, the geomagnetic activity was quite low. The plasmaspheric filament in the TEX image is the first evidence that a "finger" structure seen in the IMAGE-EUV image is the projection of an isolated flux tube. © 2013. American Geophysical Union. All Rights Reserved.
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Transactions of the Japanese Society for Artificial Intelligence 8(27) Tn_23-Tn_28 2012年12月 査読有りWe have succeeded in imaging of the terrestrial plasmasphere by the Telescope of Extreme Ultraviolet (TEX) aboard Japan's lunar orbiter KAGUYA. The view afforded by the KAGUYA orbit encompasses the plasma distribution in a single exposure, enabling us to examine for the first time the globally-averaged properties of the plasmasphere from the "side" (meridian) perspective. This is the world first image of the plasmasphere from the moon.
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2nd International Conference on Space Technology, ICST 2011 2011年Laser-induced breakdown spectroscopy (LIBS) is a very useful elemental analysis tool in planetary exploration. In this study we conduct LIBS measurements under low pressure (1×10-3 mbar) to investigate the feasibility of LIBS measurement under vacuum conditions. Although the optical emission intensity decreases remarkably under low ambient pressure, our preliminary experimental results indicate that the precision of elemental abundance measurements does not decrease drastically even under 1×10 -3 mbar. This paper suggests that LIBS can be used at the surface of airless bodies, such as the Moon and asteroids and also can be utilized for quantitative analysis of elemental abundance of minerals under lunar surface environment. © 2011 IEEE.
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PLANETARY AND SPACE SCIENCE 58(12) 1660-1664 2010年10月 査読有りResonant scattering of the lunar sodium exosphere was measured from the lunar orbiter SELENE (Kaguya) from December 2008 to June 2009. Variations in line-of-sight integrated intensity measured on the night-side hemisphere of the Moon could be described as a spherical symmetric distribution of the sodium exosphere with a temperature of 2400-6000 K. Average surface density of sodium atoms in February is well above that in the other months by about 30%. A clear variation in surface density related to the Moon's passage across the Earth's magnetotail could not be seen, although sodium density gradually decreased (by 20 +/- 8%) during periods from the first through the last quarter of two lunar cycles. These results suggest that the supra-thermal components of the sodium exosphere are not mainly produced by classical sputtering of solar wind. The variation in sodium density (which depends on lunar-phase angle) is possibly explained by the presence of an inhomogeneous source distribution of photon-stimulated desorption (PSD) on the surface. (c) 2010 Elsevier Ltd. All rights reserved.
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Journal of Geophysical Research 2010年8月27日 査読有り
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Transactions of the Japan society for aeronautical and space sciences, space technology Japan 7(26) 27-32 2010年 査読有りThe Upper Atmosphere and Plasma Imager (UPI) was launched in 2007, and went to the moon. From the lunar orbit, two telescopes direct toward the Earth. The moon has no atmosphere, which leads no active emission near the spacecraft, thus we have a high quality image of the near-Earth environment. Moreover the moon orbits the Earth once a month and the Earth is observed from many different directions. This is called a "science from the Moon". The two telescopes are mounted on 2-axis gimbal system, Telescope of Extreme ultraviolet (TEX) and Telescope of Visible light (TVIS). TEX detects the O II (83.4nm) and He II (30.4nm) emissions scattered by ionized oxygen and helium, respectively. The targets of EUV imaging are the polar ionosphere, the polar wind, and the plasmasphere and the inner magnetosphere. The maximum spatial and time resolutions are 0.09 Re and 1 minute, respectively.
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Advances in Geosciences: Volume 19: Planetary Science (PS) 579-592 2010年1月 査読有り© 2010 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. An earth-orbiting Extreme Ultraviolet spectroscopic mission, EXtreme ultraviolet spectrosCope for ExosphEric Dynamics explore (EXCEED) that will be launched in 2012 is now under development. The EXCEED mission will carry out observations of Extreme Ultraviolet (EUV) emissions from tenuous plasmas around the planets. It is essential for planetary EUV spectroscopy to avoid the Earth’s atmospheric absorption, therefore it should be mandatory to observe above the Earth’s atmosphere. In this paper, we will introduce the general mission overview, the instrument, and the scientific targets.
MISC
83共同研究・競争的資金等の研究課題
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