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The spectral properties of anhydrous carbonates and nitrates are dominated by strong, sharp vibrational bands due to the CO32− and NO3− anions observed as absorption bands in near-infrared spectra, as Reststrahlen features or absorption bands in mid-IR spectra, depending on particle size, and as peaks in Raman spectra. These spectral features provide a reliable means to identify the occurrence of carbonates and nitrates on planetary surfaces, which in turn contribute to our understanding of the environment and chemistry of planetary bodies. Four modes occur for carbonates and nitrates due to symmetric stretching (ν1), out-of-plane bending (ν2), asymmetric stretching (ν3), and in-plane bending (ν4). The vibrational absorptions of these spectral features vary with the mineral structure and the size of the cation, where the calcite-, dolomite-, aragonite-, and alkali-type structures result in different spectral features. Mid-IR bands for carbonates and nitrates occur from 1,040 to 1,105 cm−1 for ν1, from 810 to 906 cm−1 for ν2, from 1,275 to 1,590 cm−1 for ν3, and from 670 to 756 cm−1 for ν4. In Raman spectra the carbonate and nitrate absorptions are observed near 1,050–1,080 cm−1 for ν1, near 880 cm−1 for ν2, near 1,415–1,430 cm−1 for ν3, and near 680–700 cm−1 for ν4. NIR spectra include bands due to overtones and combinations at ∼1.75, 1.9, 2.0, 2.3, 2.5, 3.4, 4.0, and 4.6 μm for carbonates and ∼1.8, 2.0, 2.2, 2.4, 2.6, 3.5, 4.1, and 4.8 μm for nitrates. This study provides data for remote determination of carbonate and nitrate chemistry and will enable better characterization of these minerals on planetary bodies including Mars, Ceres, and Bennu.

An asteroid family is a group of asteroids with similar orbital proper elements (e.g., Nesvorný et al. 2005), which could be fragments formed by large impact events. The heating temperature in primordial bodies is important to form various mineralogies observed in asteroids and meteorites. The short-lived radiogenic heat of 26Al is the plausible heat source for the early stages of planetesimal formation. After 5 Myr of CAIs, 26Al decreases by 26Al highly depend on the water-to-rock ratio (W/R) and accretion timing in the planetesimal. W/R can be a good indicator of the formation distance from the Sun. However, it should be noted that W/R can be changed by the differentiation process (Wakita et al. 2011, Neumann et al. 2020, Kurokawa et al. 2022). The taxonomic composition of a family can be a witness to the internal structure of a primordial body, before disruption to become a collisional family. The near-ultraviolet wavelengths (NUV; 0.3-0.5 µm) and 0.7-µm absorption band are sensitive to the presence of phyllosilicates (Feierberg et al. 1985, Vilas and Gaffey 1989). The presence or absence of the 0.7-µm band and the NUV absorption suggest a possible differentiation process. Methods: In this study, in order to cover the NUV to visible wavelength range, using two spectrophotometric surveys, we used SDSS MOC4 (Ivezić et al. 2001) and ECAS (Zellner et al. 1985), for evaluation of the taxonomic configuration of family members. The asteroid family members were classified based on Tholen’s taxonomy (Tholen 1984). Furthermore, the 0.7-µm band (HYD) was evaluated as the slope change between the SDSS r-i filters to i-z filters: HYD=[r-i-(r-i)_sun]-[i-z-(i-z)_sun]. Results: Some of these families had been studied spectroscopically and the fraction of members with 0.7-µm band absorption can be obtained from the literature (Mothé-Diniz et al. 2005, Morate et al. 2016, 2018, 2019, de León et al. 2016, De Prá et al. 2020). Families with negative HYD values have a majority of members with the 0.7-µm band absorption from the spectroscopic studies. Thus, we found the HYD is a good proxy for the 0.7-µm band absorptions, even though the SDSS filters are not optimized for characterizing the 0.7-µm band. Furthermore, a strong correlation (correlation coefficient of -0.69) exists between HYD and the NUV absorption, suggesting that the NUV absorption can be also used for evaluating the presence of Fe-bearing phyllosilicates. The NUV absorption strength decreases from G > C/B > F/CP > P > D, which is in good agreement with the percentage of objects showing 0.7-µm band found by Vilas (1994) and Fornasier et al. (2014). Thus, G types might be dominated by Fe-bearing phyllosilicates in composition, while F types might be dominated by Fe-poor phyllosilicates. The figure shows the taxonomic compositions for primitive asteroid families that have greater than 30 asteroid members. We found several families consist of relatively homogeneous taxonomic types. The collisional families with majority of G type (the highest NUV absorption) are composed of Fe-rich phyllosilicates, and those with majority of F type (the lowest NUV absorption) are composed of Mg-rich phyllosilicates or dehydrated phyllosilicates. There are also intermediate families which consist of variety of taxonomic classes, which may inhere compositional heterogeneity. This heterogeneous families are larger than 200 km, indicating the size of primordial bodies may play a great role to differentiate or produce different lithologies inside the bodies. Figure. Taxonomic structure of primitive asteroid families. References: Nesvorný et al. (2005) Icarus 173, 132-152. Wakita et al. (2011) EPS 63, 1193-1206. Neumann et al. (2020) A&A 633, A117. Kurokawa et al. (2022) AGU Acvances 3, e2021AV000568. Feierberg et al. (1985) Icarus 63, 183-191. Vilas and Gaffey (1989) Science 246, 790-792. Ivezić et al. (2001) Astron. J 122, 2749-2784. Zellner et al. (1985) Icarus 61, 355-416. Tholen (1984) PhD thesis from University of Arizona. Mothé-Diniz et al. (2005) Icarus 174, 54-80. Morate et al. (2016) A&A 586, A129. Morate et al. (2018) A&A 610, A25. Morate et al. (2019) 630, A141. De Prá et al. (2020) A&A 643, A102. Vilas (1994) Icarus 111, 456-467.

Spectral and mineralogical analyses were performed using nine naturally hydrated and dehydrated carbonaceous chondritesamples which were classified into heating stages (HS) from I to IV based on previous X-ray diffraction results.In-situheating of samples at 120–400°C was performed during spectral measurements and successfully removed absorbed water and part of rehydrated water from chondrite samples. Reflectance spectra of HS-I samples show the positive slope in visible (Vis)-infrared (IR) range and the significant 0.7- and 3-μm absorption bands. The 0.7-μm band appears in only HS-I sample spectra. With increasing temperature of heating, (1) Vis-IR slope decreases, (2) the 3-μm band becomes shallower, and (3) Christiansen feature (CF) and Reststrahlen bands (RB) shift toward longer wavelength. TEM-EDX analyses showed that the matrix of strongly-heated chondrites consists of tiny olivine, low-Ca pyroxene, and FeNi metallic particles mostly smaller than 100nm in diameter, instead of Fe-rich serpentinesand tochilinite observed in the HS-I chondrite. Therefore, in proportion to the heating degree, amorphization and dehydration of serpentine and tochilinite from HS-I to HS-II may cause the 0.7- and 3-μm band weakening, spectral bluing and darkening of chondrite spectra. In addition, formation of secondary anhydrous silicates and FeNi-rich metal grains at HS-IV would be responsible for the 3-μm band depth decrease, spectral reddening and brightening, CF peak shift, and RB changes of chondrite spectra. Those spectral changes in response to mineralogical alteration processes will be useful to interpret planetary surfacecomposition by remote-sensing observations using ground-based or airborne/space telescopes or spacecraft missions.

Many small boulders with reflectance values higher than 1.5 times the average reflectance have been found on the near-Earth asteroid 162173 Ryugu. Based on their visible wavelength spectral differences, Tatsumi et al. (2021) 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 its 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 0.1-1 Myr, which is consistent with the crater retention age (, Comment: 21 pages, 20 Figures, 1 Table, Published in Icarus, November 15 2021, 369 114591

Ryugu is a carbonaceous rubble-pile asteroid visited by the Hayabusa2 spacecraft. Small rubble pile asteroids record the thermal evolution of their much larger parent bodies. However, recent space weathering and/or solar heating create ambiguities between the uppermost layer observable by remote-sensing and the pristine material from the parent body. Hayabusa2 remote-sensing observations find that on the asteroid (162173) Ryugu both north and south pole regions preserve the material least processed by space weathering, which is spectrally blue carbonaceous chondritic material with a 0–3% deep 0.7-µm band absorption, indicative of Fe-bearing phyllosilicates. Here we report that spectrally blue Ryugu’s parent body experienced intensive aqueous alteration and subsequent thermal metamorphism at 570–670 K (300–400 °C), suggesting that Ryugu’s parent body was heated by radioactive decay of short-lived radionuclides possibly because of its early formation 2–2.5 Ma. The samples being brought to Earth by Hayabusa2 will give us our first insights into this epoch in solar system history., Both poles of asteroid Ryugu, the target of space mission Hayabusa2, preserve the least processed material by space weathering. Here, the authors show detection of 700 nm absorption band in the polar spectra of Ryugu, that allows to constrain the hydrothermal history of its spectrally blue parent body.

Almahata Sitta (AhS), an anomalous polymict ureilite, is the first meteorite observed to originate from a spectrally classified asteroid (2008 TC(3)). However, correlating properties of the meteorite with those of the asteroid is not straightforward because the AhS stones are diverse types. Of those studied prior to this work, 70–80% are ureilites (achondrites) and 20–30% are various types of chondrites. Asteroid 2008 TC(3) was a heterogeneous breccia that disintegrated in the atmosphere, with its clasts landing on Earth as individual stones and most of its mass lost. We describe AhS 91A and AhS 671, which are the first AhS stones to show contacts between ureilitic and chondritic materials and provide direct information about the structure and composition of asteroid 2008 TC(3). AhS 91A and AhS 671 are friable breccias, consisting of a C1 lithology that encloses rounded to angular clasts (

Since 2002, we have obtained size frequency distributions (SFDs) of main belt asteroids (MBAs), Hildas, and Jupiter Trojans (JTs) by using the 8.2-m Subaru Telescope equipped with the wide-field CCD cameras: Suprime-Cam (SC) or Hyper Suprime-Cam (HSC). After combining these SFDs with SFDs obtained from other surveys, we performed a comparative study of SFDs for each group of small bodies in an attempt to obtain clues about planet migration that affected those populations. The large aperture of the Subaru Telescope and the wide field of view of SC or HSC allowed us to detect small moving objects up to apparent magnitudes 24.4–24.5 mag (Rc-band), which corresponds to sub–km in diameter (D) for MBAs and about 1 km for Hildas and JTs. We combined the SFDs obtained from our surveys with those derived from published data to obtain the individual representative SFD for MBAs, Hildas and JTs in the size range of sub–km to 1000 km. We found that the SFDs of JTs and Hildas are roughly flat in the R-plot while that of MBAs has a wavy structure. We also investigated the SFDs of MBAs in the inner, middle, and outer regions of the main belt. We found that the shape of the SFDs changes gradually with increasing heliocentric distance across these regions. This trend continues beyond the outer region, where the SFD becomes flatter as shown by the SFDs of JTs and Hildas. Recent planet migration models suggest that the current JTs originated in the trans-Neptunian region and were captured as Trojans during planet migration. The finding of a gradual change of the SFDs from the inner MBAs to JTs is in line with the idea that trans-Neptunian objects (TNOs) were implanted not only into the JT region, but also into the main belt outer region (including the Hildas) at the early solar system. In order to investigate this implantation hypothesis, we considered a synthetic population of TNOs assuming with a SFD represented by a power-law distribution of N > D ∝ D - 3 , (estimated from crater record on Pluto and Charon). We then added this synthetic population to the MBA populations in various proportions. We found that the higher the proportion, the flatter the wavy SFD of MBAs becomes. This simple model yields a rough explanation for the gradual change of SFDs found from the inner main belt to the JT region. However, the shape of the modelled SFDs does not match observations for all sizes. In particular, because important discrepancies are seen in the small size range, we need to consider the removal of small objects by collisional evolution and/or Yarkovsky effect in the future.

著者人数: 66名 (所属. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS): 岩田, 隆浩; 安部, 正真; 大竹, 真紀子; 仲内, 悠佑; 松岡, 萌; L. Riu; 中藤, 亜衣子; 横田, 康弘; 坂谷, 尚哉; 山本, 幸生; 岡田, 達明; 澤田, 弘崇, 早川, 雅彦; 白井, 慶; 嶌生, 有理; 尾川, 順子; 照井, 冬人; 竹井, 洋; 佐伯, 孝尚; 中澤, 暁; 田中, 智; 吉川, 真; 渡邊, 誠一郎; 津田, 雄一), Accepted: 2019-03-07, 資料番号: SA1180385000

The June 2, 2018, impact of asteroid 2018 LA over Botswana is only the second asteroid detected in space prior to impacting over land. Here, we report on the successful recovery of meteorites. Additional astrometric data refine the approach orbit and define the spin period and shape of the asteroid. Video observations of the fireball constrain the asteroid's position in its orbit and were used to triangulate the location of the fireball's main flare over the Central Kalahari Game Reserve. 23 meteorites were recovered. A consortium study of eight of these classifies Motopi Pan as a HED polymict breccia derived from howardite, cumulate and basaltic eucrite, and diogenite lithologies. Before impact, 2018 LA was a solid rock of about 156 cm diameter with high bulk density about 2.85 g/cm3, a relatively low albedo pV about 0.25, no significant opposition effect on the asteroid brightness, and an impact kinetic energy of about 0.2 kt. The orbit of 2018 LA is consistent with an origin at Vesta (or its Vestoids) and delivery into an Earth-impacting orbit via the nu_6 resonance. The impact that ejected 2018 LA in an orbit towards Earth occurred 22.8 +/- 3.8 Ma ago. Zircons record a concordant U-Pb age of 4563 +/- 11 Ma and a consistent 207Pb/206Pb age of 4563 +/- 6 Ma. A much younger Pb-Pb phosphate resetting age of 4234 +/- 41 Ma was found. From this impact chronology, we discuss what is the possible source crater of Motopi Pan and the age of Vesta's Veneneia impact basin., Comment: Meteoritics & Planetary Science (2021)

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. Hayabusa2 created an artificial crater on Ryugu to analyse the subsurficial material of the asteroid. Results show that the subsurface is more hydrated than the surface. It experienced alteration processes that can be traced back to Ryugu’s parent body.

The near-Earth asteroid (162173) Ryugu displays a Cb-type average spectrum and a very low average normal albedo of 0.04. Although the majority of boulders on Ryugu have reflectance spectra and albedo similar to the Ryugu average, a small fraction of boulders exhibit anomalously high albedo and distinctively different spectra. A previous study (Tatsumi et al., 2021) based on the 2.7-km observations and a series of low-altitude (down to 68 m) descent observations conducted prior to the first touchdown have shown that the spectra of these anomalous boulders can be classified into two distinct groups corresponding to S and C type asteroids. The former originate most likely from an impactor that collided with Ryugu's parent body, whereas the latter may be from portions of Ryugu's parent body that experienced a different temperature history than experienced by the majority of boulder materials. In this study, we analyzed images captured after the first touchdown to determine the quantitative properties of these bright boulders on Ryugu. We measured the sizes of more than a thousand bright boulders and characterized the morphologic properties of the largest ones. Analyses revealed many properties of bright boulders important for the evolution of Ryugu and its parent body. The size-frequency distributions of S- and C-type bright boulders follow power laws. We obtained the ratios of the total volume and surface area of S-type bright boulders to those of average dark boulders on the Ryugu surface. Also, many of the bright boulders are embedded in a larger substrate boulder, suggesting that they have experienced mixing and conglomeration with darker fragments on the parent body, rather than gently landing on Ryugu during or after its formation by reaccumulation. This is consistent with the hypothesis that S-type bright boulders were likely mixed during and/or before a catastrophic disruption., Comment: 19 pages, 11 figures, 3 Tables, published in Icarus, 369, 15 November, 2021, 114529

Antarctic carbonaceous chondrite (CC) meteorite chip samples in the Japanese and US collections have been studied by an ultraviolet (UV), visible (Vis), and near-infrared (NIR) (UVVNIR) spectrometer and a Fourier-transform infrared (FTIR) spectrometer, targeting small areas of about 2–6 mm in diameter. UVVNIR and FTIR reflectance spectra of 169 spots on 148 CC chips were measured on their naturally broken surfaces with no sample preparation. Among them, 83 spectra were accepted as reasonably free of terrestrial weathering or surface texture effects. X-ray diffraction (XRD) and FTIR measurements of a weathered sample revealed that gypsum likely formed on its surface after recovery from Antarctica. Principal component analysis (PCA) of the UVVNIR-FTIR combined spectra allowed distinguishing powder and chip or surface texture and identifying their class and thermal metamorphism. Gaussian fitting of the 3 μm absorption band of hydrous CC samples allowed for removal of the spectral effects of adsorbed H2O and for the extraction of structural absorption bands which are characteristic of CC classes and degree of aqueous alteration. These results suggest that CC-like rocks on small asteroids without fine regolith can be identified through spectral reflectance measurements by spacecraft, landers, or rovers.

著者人数: 120名(所属. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS): 澤田, 弘崇; 横田, 康弘; 坂谷, 尚哉; 岡田, 達明; 田中, 智; 飯島, 祐一; 早川, 雅彦; 松岡, 萌; R.-L. Ballouz; 嶌生, 有理; 水野, 貴秀; 石原, 吉明; 長谷川, 直; 藤本, 正樹; 吉川, 真; 山本, 幸生; 白井, 慶; R. Noguchi; 尾川, 順子; 照井, 冬人; 菊地, 翔太; 山口, 智宏; 竹内, 央, 三桝, 裕也; 高橋, 忠輝; 竹井, 洋; 藤井, 淳; 中澤, 暁; 細田, 聡史; 森, 治; 嶋田, 貴信; Soldini, Stefania; 岩田, 隆浩; 安部, 正真; 矢野, 創; 月崎, 竜童; 尾崎, 正伸; 西山, 和孝; 佐伯, 孝尚; 渡邊, 誠一郎; 津田, 雄一), Accepted: 2019-03-12, 資料番号: SA1180387000

Accepted: 2016-06-07, 資料番号: SA1160169000

The Near-Earth Asteroid 162173 Ryugu (1999 JU3) was investigated by the JAXA Hayabusa2 mission from June 2018 to November 2019. The data acquired by NIRS3 spectrometer revealed a dark surface with a positive near-infrared spectral slope. In this work we investigated the spectral slope variations across the Ryugu surface, providing information about physical/chemical properties of the surface. We analysed the calibrated, thermally and photometrically corrected NIRS3 data, and we evaluated the spectral slope between 1.9 μm and 2.5 μm, whose values extend from 0.11 to 0.28 and the mean value corresponds to 0.163±0.022. Starting from the mean value of slope and moving in step of 1 standard deviation (0.022), we defined 9 “slope families”, the Low-Red-Slope families (LR1, LR2 and LR3) and the High-Red-Sloped families (HR1, HR2, HR3, HR4, HR5, HR6). The mean values of some spectral parameters were estimated for each family, such as the reflectance factor at 1.9 μm, the spectral slope, the depth of bands at 2.7 μm and at 2.8 μm. A progressive spectral reddening, darkening and weakening/narrowing of OH bands is observed moving from the LR families to the HR families. We concluded that the spectral variability observed among families is the result of the thermal metamorphism experienced by Ryugu after the catastrophic disruption of its parent body and space weathering processes that occurred on airless bodies as Ryugu, such as impact cratering and solar wind irradiation. As a consequence, the HR1, LR1, LR2 and LR3 families, corresponding to equatorial ridge and crater rims, are the less altered regions on Ryugu surface, which experienced the minor alteration and OH devolatilization; the HR2, HR3, HR4, HR5 families, coincident with floors and walls of impact craters, are the most altered areas, result of the three processes occurring on Ryugu. The strong reddening of the HR6 family (coincident with Ejima Saxum) is likely due to the fine-sized material covering the large boulder.

Context.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.Aims.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.Methods.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.Results.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 vband) for Ryugu. The average reflectance factor at the standard illumination condition was 1.87 ± 0.14% in thevband. Moreover we measured a phase reddening of (2.0 ± 0.7) × 10−3μm−1deg−1for Ryugu, similar to that observed for the asteroid (101955) Bennu.Conclusions.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.

The Ninth Symposium on Polar Science/Ordinary sessions: [OA] Antarctic meteorites / Hayabusa, Wed. 5 Dec. / Conference hall of the Research/Administration Building (2nd floor) at the JAXA Sagamihara Campus

We report the global distribution of areas exhibiting no absorption features (featureless or FL) on the lunar surface, based on the reflectance spectral data set obtained by the Spectral Profiler onboard Kaguya/SELENE. We found that FL sites are located in impact basins and large impact craters in the Feldspathic Highlands Terrane, while there are no FL sites in the Procellarum regions nor the South Pole-Aitken basin. FL sites in each impact basin/crater are mainly found at the peak rings or rims, where the purest anorthosite (PAN) sites are also found. At the local scale, most of the FL and PAN points are associated with impact craters and peaks. Most of the FL spectra show a steeper (redder) continuum than the PAN spectra, suggesting the occurrence of space weathering effects. We propose that most of the material exhibiting a FL spectrum originate from space weathered PAN. Taking into account all the occurrence trends of FL sites on the Moon, we propose that both the FL and PAN materials were excavated from the primordial lunar crust during ancient basin formations below the megaregolith in the highlands. Since the FL and PAN sites are widely distributed over the lunar surface, our new data may support the existence of a massive PAN layer below the lunar surface.

The Hayabusa2 spacecraft has three framing cameras (ONC-T, ONC-W1, and ONC-W2) for optical navigation to asteroid 1999 JU3. 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 JU3 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 μm 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 μm absorption in Jbilet Winselwan CM2 chondrite with decomposed Fe-rich serpentine.

We performed pulse-laser irradiation experiments of a primitive meteorite to simulate space weathering by micrometeorite bombardments on C-type asteroids. Pellets of powdered Murchison CM2 chondrite were set in vacuum and exposed to pulse laser with a diameter of 0.5 mm and delivered energies of 5, 10, and 15 mJ. We measured reflectance spectra of unirradiated and irradiated surfaces of the pellets. During analysis the pellet was heated to approximately 100 °C and purged in N2 gas in order to reduce absorption of ambient water. The spectra become darker and bluer with increasing laser energies. Their UV reflectance increases and 0.7- and 3-μm band depths decrease from 0 to 15 mJ. The spectral bluing observed in our experiments reproduces the bluing occurred during space weathering of C-type asteroids. High-resolution observation by a transmission electron microscope showed that the laser heating causes preferential melting and evaporation in FeS-rich fine-grained portions, which results in dispersion and deposition of numerous FeS-rich amorphous silicate particles 20–1000 nm in size on the surface of the pellet. In addition, at the laser-irradiated but unmelted areas, heat-induced amorphization and decomposition of serpentine occur. These mineralogical changes make the reflectance spectra of the Murchison CM chondrite darker and bluer.

Olivine-rich asteroids appear to be common in the main asteroid belt as well as present in the near-Earth asteroid population. There are a number of meteorite classes that are dominated by olivine ± metal. To determine whether relationships exist between these asteroids and meteorites, we spectrally characterized a number of olivine + meteoritic metal powder intimate and areal mixtures, pallasite slabs, and olivine powders on a metal slab. Our goal is to understand the spectral characteristics of olivine + metal assemblages and develop spectral metrics that can be used to analyze reflectance spectra of olivine-dominated asteroids. We found that the major olivine absorption band in the 1 μm region is resolvable in intimate mixtures for metal abundances as high as ∼90 wt.%. The wavelength position of the 1 μm region olivine absorption band center is sensitive to Fa content but insensitive to other variables. However, the band minimum position moves to shorter wavelengths with increasing metal abundance due to changes in spectral slope. The full width at half maximum (FWHM) of this band and reflectance at 1.8 μm are both most sensitive to olivine Fa content, metal abundance, and grain size, and much less to the presence of nanophase iron that reddens spectra. Reflectance at 0.56 μm and the 1.8/0.56 μm reflectance ratio are sensitive to these same parameters as well as to nanophase iron-associated spectral reddening. The wavelength position of the local reflectance maximum in the 0.7 μm region moves to longer wavelengths with increasing metal abundance and is most useful for constraining metal abundance in high metal-content mixtures. Pallasite slab spectra differ in a number of respects from powdered assemblages and multiple spectral parameters can be used to discriminate them. The spectra of increasingly fine-grained olivine + metal assemblages and those involving low-Fa olivine show increasing spectral dominance by metal. Systematic application of multiple spectral metrics allows olivine + metal assemblage properties such as Fa content, olivine/metal ratio, and grain size to be quantified or constrained. Analysis of reflectance spectra of 22 presumed olivine ± metal-rich asteroids indicates that most of them possess low- to medium-Fa content olivine (Fa 45 μm). Most asteroid spectra can be plausibly linked to specific olivine ± metal-bearing meteorite classes. Most of the asteroid spectra examined exhibit some degree of spectral reddening below ∼1.8 μm which is most consistent with the presence of fine-grained nanophase iron, likely produced by space weathering.

We present details of the global distribution of high-Ca pyroxene (HCP)-rich sites in the lunar highlands based on the global data set of hyperspectral reflectance obtained by the SELENE Spectral Profiler. Most HCP-rich sites in the lunar highlands are found at fresh impact craters. In each crater, most of the detection points are distributed on the ejecta, rim, and floor of the impact craters rather than the central peaks, while the central peaks are dominated by purest anorthosite (PAN). This indicates that HCP-rich materials originate from relatively shallower regions of the lunar crust than PAN. In addition, while all ray craters with sizes larger than ∼40 km possess HCP-rich materials, small fresh craters with sizes less than ∼6–10 km do not, indicating that the uppermost mixing layers in the lunar crust are not dominated by HCP. Based on these results, we propose that in the upper lunar crust, a HCP-rich zone overlying the PAN layer exists below the uppermost mixing layer. This HCP-rich zone may originate from interstitial melt during the formation of the flotation anorthositic cumulate, while an impact ejecta origin, impact melt origin, and/or magmatic intrusion into the upper lunar crust may also account for the occurrence of HCP-rich sites in the highlands.

Sulfate minerals are important indicators for aqueous geochemical environments. The geology and mineralogy of Mars have been studied through the use of various remote-sensing techniques, including thermal (mid-infrared) emission and visible/near-infrared reflectance spectroscopies. Spectral analyses of spacecraft data (from orbital and landed missions) using these techniques have indicated the presence of sulfate minerals on Mars, including Fe-rich sulfates on the iron-rich planet. Each individual Fe-sulfate mineral can be used to constrain bulk chemistry and lends more information about the specific formational environment [e.g., Fe 2+ sulfates are typically more water soluble than Fe 3+ sulfates and their presence would imply a water-limited (and lower Eh) environment; Fe 3+ sulfates form over a range of hydration levels and indicate further oxidation (biological or abiological) and increased acidification]. To enable better interpretation of past and future terrestrial or planetary data sets, with respect to the Fe-sulfates, we present a comprehensive collection of mid-infrared thermal emission (2000 to 220 cm −1 ; 5–45 μm) and visible/near-infrared (0.35–5 μm) spectra of 21 different ferrous- and ferric-iron sulfate minerals. Mid-infrared vibrational modes (for SO 4 , OH, H 2 O) are assigned to each thermal emissivity spectrum, and the electronic excitation and transfer bands and vibrational OH, H 2 O, and SO 4 overtone and combination bands are assigned to the visible/near-infrared reflectance spectra. Presentation and characterization of these Fe-sulfate thermal emission and visible/near-infrared reflectance spectra will enable the specific chemical environments to be determined when individual Fe-sulfate minerals are identified.

著者人数: 11名, Accepted: 2014-02-01, 資料番号: SA1004603000

We present a comprehensive description of petrologic, chemical and spectroscopic features of thermally metamorphosed CI-like and CM (and CM-like) chondrites. Only two such CI chondrites have so far been discovered i.e. Y-86029 and Y-82162. Thermal metamorphism in these chondrites is apparent in their low contents of H2O, C and the most thermally labile trace elements, partial dehydration of matrix phyllosilicates and abundance of thermally decomposed Ca–Mg–Fe–Mn carbonates, which apparently resulted from heating of Mg–Fe carbonate precursors. The CM chondrites exhibit a wide range of aqueous and thermal alteration characteristics. This alteration was almost complete in Y-86720 and Y-86789, which also escaped alternating episodes of oxidation and sulfidization experienced by the others. Thermal metamorphism in the CM chondrites is apparent in loss of thermally labile trace elements and also in partial to almost complete dehydration of matrix phyllosilicates: heating was less uniform in them than in CI chondrites. This dehydration is also evident in strength and shapes of integrated intensities of the 3 μm bands except in PCA 91008, which experienced extensive terrestrial weathering. Tochilinite is absent in all but Y-793321 probably due to heating. Textural evidence for thermal metamorphism is conspicuous in blurring or integration/fusion of chondrules with matrix in the more extensively heated (⩾600 °C) CM chondrites like PCA 91008 and B-7904. TEM and XRD analyses reveal that phyllosilicate transformation to anhydrous phases proceeds via poorly crystalline, highly desiccated and disordered ‘intermediate’ phases in the least and moderately heated (400–600 °C) carbonaceous chondrites like WIS 91600, PCA 91008 and Y-86029. These findings are significant in that they confirm that these phases occur in meteorites as well as terrestrial samples. Thermal alteration in these meteorites can be used to identify other carbonaceous chondrites that were thermally metamorphosed in their parent bodies. Combining RNAA trace element data for experimentally heated Murchison CM2 samples with petrographic and spectroscopic data, these thermally metamorphosed carbonaceous chondrites can be ordered by severity of open system heating as 400 °C ⩽ Y-793321

Olivine exhibits highly diagnostic absorption features across visible to near-infrared (VNIR) wavelengths due to electronic transitions of Fe2+ in its crystal structure. The properties of these absorptions vary with composition, enabling compositional analysis of olivine through VNIR spectroscopy, both in the laboratory and through remote sensing. Previous analyses of these trends have relied on natural olivine samples, which are influenced by the presence of minor cations that can affect the diagnostic absorptions. We conduct a systematic analysis of a suite of synthetic (pure Mg/Fe) olivine samples with VNIR (300–2600 nm) reflectance spectroscopy and quantitative spectral deconvolutions. From the full suite of samples described and characterized by Dyar et al. (2009), we identify a small suite of well-characterized and chemically pure olivine samples that demonstrates consistent and reliable spectral reflectance properties across visible to near-infrared wavelengths. This suite covers the stoichiometric olivine solid solution from x = Mg/(Mg+Fe) = 0 to x = 70 (Fo to Fo70). Because of their tight compositional control, these synthetic samples improve on previous analyses of natural samples. The results of this study provide a new standard for spectral reflectance properties of olivine across visible to near-infrared wavelengths for the compositions present in the suite. We present updated data on the trends in olivine band position as a function of olivine composition, which are the basis for remote compositional evaluation of olivine with visible to near-infrared reflectance spectroscopy. For these reasons, these improved olivine band position trends are of major importance to remote compositional analyses of terrestrial planets.

[1] We present details of the identification of sites that show an absorption band at visible wavelengths and a strong 2 μm band using the SELENE Spectral Profiler. All the sites exhibiting the visible feature are found on the regional dark mantle deposit (DMD) at Sinus Aestuum. All the instances of the visible feature show a strong 2 μm band, suggestive of Fe- and Cr-rich spinels, which are different from previously detected Mg-rich spinel. Since no visible feature is observed in other DMDs, the DMD at Sinus Aestuum is unique on the Moon. The occurrence trend of the spinels at Sinus Aestuum is also different from that of the Mg-rich spinels, which are associated with impact structures. This may suggest that the spinel at Sinus Aestuum is a different origin from that of the Mg-rich spinel.

Identifying and mapping olivine on asteroid 4 Vesta are important components to understanding differentiation on that body, which is one of the objectives of the Dawn mission. Harzburgitic diogenites are the main olivine-bearing lithology in the howardite-eucrite-diogenite (HED) meteorites, a group of samples thought to originate from Vesta. Here, we examine all the Antarctic harzburgites and estimate that, on scales resolvable by Dawn, olivine abundances in putative harzburgite exposures on the surface of Vesta are likely at best in the 10–30% range, but probably lower due to impact mixing. We examine the visible/near-infrared spectra of two harzburgitic diogenites representative of the 10–30% olivine range and demonstrate that they are spectrally indistinguishable from orthopyroxenitic diogenites, the dominant diogenitic lithology in the HED group. This suggests that the visible/near-infrared spectrometer onboard Dawn (VIR) will be unable to resolve harzburgites from orthopyroxenites on the surface of Vesta, which may explain the current lack of identification of harzburgitic diogenite on Vesta.

CM chondrites are the most common type of hydrated meteorites, making up ∼1.5% of all falls. Whereas most CM chondrites experienced only low-temperature (∼0°C–120°C) aqueous alteration, the existence of a small fraction of CM chondrites that suffered both hydration and heating complicates our understanding of the early thermal evolution of the CM parent body(ies). Here, we provide new constraints on the collisional and thermal history of CM-like bodies from a comparison between newly acquired spectral measurements of main-belt Ch/Cgh-type asteroids (70 objects) and existing laboratory spectral measurements of CM chondrites. It first appears that the spectral variation observed among CM-like bodies is essentially due to variations in the average regolith grain size. Second, the spectral properties of the vast majority (unheated) of CM chondrites resemble both the surfaces and the interiors of CM-like bodies, implying a “low” temperature ( 100 km)—supposedly primordial—Ch/ Cgh-type main-belt asteroids likely expose the interiors of the primordial CM parent bodies, a possible consequence of impacts by small asteroids (D < 10 km) in the early solar system. The MIT component of this work is supported by NASA grant 09-NEOO009-0001, and by the National Science Foundation under grants Nos. 0506716 and 0907766. F.E.D. acknowledges support from NASA under grant No. NNX12AL26G issued through the Planetary Astronomy Program. E.A.C. thanks the Canada Foundation for Innovation, the Manitoba Research Innovations Fund, the Canadian Space Agency, the University of Winnipeg, and the Natural Sciences and Engineering Research Council of Canada for supporting the establishment and operation of the University of Winnipeg's Planetary Spectrophotometer Facility and this study. http://iopscience.iop.org/article/10.3847/0004-6256/152/3/54/meta

We have analyzed reflectance spectra (0.3–2.5 lm) of a number of ungrouped or tentatively grouped carbonaceous chondrites (CCs), possible CC-type xenoliths in an aubrite (Cumberland Falls) and a howardite (PRA 04401), a CH chondrite (PCA 91467), a CC polymict breccia (Kaidun), and some R chondrites. The best approach to analysis relies largely on characterizing spectrally active phases – i.e., those phases that contribute diagnostic absorption features, involving absorption band wavelength position, band depth, shape of absorption features, combined with albedo and spectral slope. Mafic silicate (hydrous and/or anhydrous) absorption features are ubiquitous in the CCs and R chondrites we have examined. Combining information on these features along with albedo and spectral slopes allows reasonable inferences to be made concerning their uniqueness. Reflectance spectra of Coolidge show contributions from both olivine and Fe oxyhydroxides (from terrestrial weathering), and its high reflectance and mafic silicate band depths are consistent with a petrologic grade >3 and inconsistent with CVs. The CC nature of the Cumberland Falls inclusions from spectral analysis is inconclusive, but they do exhibit spectral features consistent with their overall mineralogy. DaG 430, which has petrologic characteristics of both CV and CK chondrites, has a spectrum that is not fully consistent with either group. The spectrum of EET 96029 is consistent with some, but not all CM2 chondrites. GRO 95566, a meteorite with some affinities to CM2s, most resembles the Renazzo CR2 chondrite, consistent with their similar mineralogies, and its spectral properties can be related to its major mineralogic characteristics. Spectra of Kaidun are most consistent with CR chondrites, which form the bulk of this meteorite. The reflectance spectrum of MCY 92005 is consistent with its recent classification as a CM2 chondrite. The R3 chondrite MET 01149 shares many characteristics with CKs, but differs in terms of its slightly red slope and 2 lm region absorption feature. The combination of high reflectance, deep 1 lm band and, to a lesser extent, slightly red slope and weak 2 lm region absorption band, distinguishes PRE 95404 from CV3s, to which it was initially assigned. The LAP 04840 R6 spectrum is dominated by olivine, consistent with a petrologic grade >3. Its reflectance is somewhat lower than for the R3 chondrites, and falls within the range of many CCs. Its most characteristic feature is the metal–OH absorption bands in the 2.3 lm region. Analysis and assignment of PCA 91467 (CH3) is complicated by the presence of terrestrial weathering products. Its red spectral slope is consistent with its high metal content. Reflectance spectra of the howardite PRA 04401, which contains 40% CM2-like inclusions, is dominated by the howardite’s pyroxene absorption bands, and expected CM2-type absorption bands near 0.7 and 1.1 lm are not seen. The CC xenoliths do reduce overall reflectance and pyroxene absorption band depths significantly, and probably add an overall red slope, when compared to inclusion-free howardites. QUE 99038, which has been linked to CM2, CO, or CR chondrites is not spectrally consistent with any of these groups. The 2 lm band, high overall reflectance, and dominant olivine absorption band are all generally inconsistent with CM2 and CR2–3 chondrites. It resembles the CO3 chondrite ALH 77003 in the 1 lm region, but differs in the 2 lm region. The red-sloped, nearly featureless spectrum of Tagish Lake is unique among carbonaceous chondrites. It probably arises from the highly aromatic nature of the organic component and its intimate association with the phyllosilicate-rich matrix, which makes up a high proportion of this meteorite. Our results suggest that the meteorites included in this study can usually be determined to be either unique or to be placed with a reasonable degree of confidence into established CC groups. Our analysis has also provided

著者人数: 12名, Accepted: 2012-09-21, 資料番号: SA1004297000

We examined the spectral reflectance properties of 26 carbonaceous chondrites (CCs) that show evidence of aqueous alteration and subsequent thermal metamorphism (termed ATCCs). We also reviewed the thermal and aqueous alteration history of these meteorites and searched for trends between spectral parameters and temperature histories in order to uncover spectral–compositional relationships. Aqueous alteration results in the production of phyllosilicates from anhydrous silicate precursors – largely serpentine group phyllosilicates, and increasing amounts of saponite group phyllosilicates with increasing aqueous alteration. Thermal metamorphism results in dehydration of these phyllosilicates and production of abundant amorphous material except at the highest temperatures (≳900 °C), as well as alteration of carbonaceous components. ATCCs are a spectrally diverse group in almost all respects. Spectral slopes, as measured by the ratio of reflectance at 2.4 μm to the local peak or inflection in the 0.5–0.8 μm region and 2.4/1.5 μm ratios range from 0.78 to 1.48, and 0.93 to 1.24, respectively (blue-sloped spectra have ratio values of

著者人数: 11名, Accepted: 2011-12-14, 資料番号: SA1003071000

著者人数: 11名, Accepted: 2011-04-11, 資料番号: SA1003245000

著者人数: 20名, Accepted: 2011-07-28, 資料番号: SA1003065000