¹Alexander N. Krot,²Michail I. Petaev,¹Kazuhide Nagashima
Progress in Earth and Planetary Science 8, 61 Link to Article [DOI https://doi.org/10.1186/s40645-021-00437-4]
¹Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Mānoa, Honolulu, HI, 96822, USA
²Department of Earth and Planetary Sciences, Harvard University and Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, 02138, USA

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^1,2Kimur,^3,4Weisberg M.K.,²Takaki A.,^1,5Imae N.,^1,5Yamaguchi A.
Progress in Earth and Planetary Science 8, 55 Link to Article [DOI10.1186/s40645-021-00447-2]
¹National Institute of Polar Research, Tokyo, Japan
²Ibaraki University, Mito, Japan
³Kingsborough College and Graduate Center of the City University of New York, New York, United States
⁴American Museum of Natural History, New York, United States
⁵SOKENDAI, Tokyo, Japan

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¹Abdu Y.A.
Hyperfine Interactions 242, 5 Link to Article [DOI 10.1007/s10751-021-01729-3]
¹Department of Applied Physics and Astronomy, University of Sharjah, P.O. Box 27272, Sharjah, United Arab Emirates

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¹Hiroaki Kaneko,²Sota Arakawa,¹Taishi Nakamoto
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114726]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
²Division of Science, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka-shi, Tokyo 181-8588, Japan
Copyright Elsevier

Coarse objects in chondrites such as chondrules and CAIs are mostly coated with fine-grained rims (FGRs). FGRs can be formed on the surface of free floating chondrules in a turbulent nebula, where dust aggregation also occurs. A former study has reported that the morphology of the dust populations accreting onto chondrules affects the initial structures of FGRs. It was revealed that, if monomer grains accrete onto chondrules, the smaller grains tend to accumulate near the surface of chondrules, and FGRs exhibit grain size coarsening from the bottom to the top. However, the study did not consider the effect of temporal growth of dust aggregates on FGRs formation. In this study, we calculate the aggregation of polydisperse monomer grains and their accretion onto chondrules. The following two different stages of dust aggregation can be identified: the monomer-aggregation stage and the BCCA-like stage. In the monomer-aggregation stage, monomer grains are incorporated into aggregates when the average aggregate size reaches the size of the monomer. In the BCCA-like stage, aggregates evolve fractally in a fashion similar to that of single size monomer grains. Based on the results of the previous study, we obtain the requisite conditions for chondrules to acquire monomer-accreting FGRs with grain size coarsening observed in some chondrites. In the case of similar size distribution as that of Inter Stellar Medium (ISM), the maximum grain size of m is widely () required for monomer accretion, while if turbulent intensity in a nebula is extremely weak (), a maximum grain size m is required. The monomer size distributions having larger mass fraction in the large grains compared to ISM might be necessary for the effective grain size coarsening.

¹Kenneth A. Farley,²Susan Taylor,¹Jonathan Treffkorn,²James H. Lever,²Anthony L. Gow
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13759]
¹California Institute of Technology, Pasadena, California, 91125 USA
²US Army Engineer Research and Development Center Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire, 03755 USA
Published by arrangement with John Wiley & Sons

Researchers have characterized extraterrestrial (ET) helium, likely carried by interplanetary dust particles (IDPs), in deep-sea sediments spanning more than the last 100 Myr. Here we complement those low resolution and deep time studies by measuring He in modern Antarctic air and recent ice. We analyzed 180 air filter samples collected in 2017 and 2018 at the South Pole and detected 3He above blank levels in 178. The filters collected during the austral springs had elevated 3He in multiple subsamples indicating the presence of many individual IDPs and potentially, a temporal variation in the ET small particle flux. Our calculated mean 3He flux of 1.4 ± 1.2 × 10−12 cc STP cm−2 ka−1 is the first such measurement from air samples. We also melted, filtered, and analyzed one hundred and forty-one 1 m-long ice sections from a ˜2000-yr-old South Pole core. We detected 3He above blank levels in 139 of the 141 ice core samples and calculated an average flux of 1.2 ± 0.3 × 10−12 cc STP cm−2 ka−1. Our two flux values are within a factor of two of those calculated from stratospheric IDP concentrations, those previously measured for sections of the GISP2 and Vostok ice cores, and from sediment cores from different locations and ages. The similarity of these flux values over disparate time scales (1–108 yr) and geographic locations (90° S to equator) indicates modest temporal variability and remarkable agreement among diverse IDP archives. These data provide a compelling link from IDPs collected in the stratosphere to those recorded in deep time sedimentary archives.

¹Thierry Fouchet et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114773]
¹LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
Copyright Elsevier

We present the Infrared spectrometer of SuperCam Instrument Suite that enables the Mars 2020 Perseverance Rover to study remotely the Martian mineralogy within the Jezero crater. The SuperCam IR spectrometer is designed to acquire spectra in the 1.3–2.6 µm domain at a spectral resolution ranging from 5 to 20 nm. The field-of-view of 1.15 mrad, is coaligned with the boresights of the other remote-sensing techniques provided by SuperCam: laser-induced breakdown spectroscopy, remote time-resolved Raman and luminescence spectroscopies, and visible reflectance spectroscopy, and micro-imaging. The IR spectra can be acquired from the robotic-arm workspace to long-distances, in order to explore the mineralogical diversity of the Jezero crater, guide the Perseverance Rover in its sampling task, and to document the samples’ environment. We present the design, the performance, the radiometric calibration, and the anticipated operations at the surface of Mars.

¹Nao NAKANISHI,¹Tetsuya YOKOYAMA,^1,2Satoki OKABAYASHI,³Hikaru IWAMORI,⁴Takafumi HIRATA
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.11.009]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
²Department of Applied Chemistry for Environment, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan
³Earthquake Research Institute, The University of Tokyo, Bunkyo, Tokyo 113-0032, Japan
⁴Geochemical Research Center, Graduate School of Science, The University of Tokyo, Bunkyo, Tokyo 113-0032, Japan
Copyright Elsevier

CR chondrites are suitable for understanding the genetic linkage between metals and chondrules due to the unique characteristics of the coexisting metal phases with chondrules. Metal grains are found in three different locations of CR chondrites; chondrule interior (“interior grain”), chondrule surficial shells (“margin grain”), and the matrix (“isolated grain”). Here we report the abundances of highly siderophile elements (HSEs) and major elements in three types of metals (interior, margin, and isolated grains) from three CR chondrites (NWA 801, NWA 7184, and Dhofar 1432) by using femtosecond LA-ICP-MS (fs LA-ICP-MS) and EPMA. Additionally, we report the isotopic compositions of Os and Fe in the metals by using micro-milling sampling coupled with N-TIMS and MC-ICP-MS. The CR metals have variations in 187Os/188Os and δ57Fe values ranging from 0.1193 to 0.1314 and from –1.05 to +0.25, respectively. HSE abundances, except for Pd and Au, in the three types of metals increase as the abundance of Ir increases. A possible explanation for the variations of HSE abundances within and among grains, 187Os/188Os values within each grain, and δ57Fe values among grains, is the condensation of liquid metal from a gaseous reservoir followed by fractional crystallization. Most of the CR metals have negative δ57Fe values, suggesting that Fe in metal phases might have formed by condensation prior to Fe condensation in silicate phases. The chondrules and three types of metal grains in CR chondrites are believed to have formed contemporaneously in the same region. The existence of large isolated metals in matrix and compound chondrules might be the result of collision and merging of the metal and silicate droplets.

¹M. F. Rabbi,²L. A. J. Garvie,³D. Cotto-Figueroa,⁴E. Asphaug,¹K. H. Khafagy,¹S. Datta,¹A. Chattopadhyay
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13761]
¹School for Engineering of Matter Transport and Energy, Arizona State University, PO Box 879106, Tempe, Arizona, 85287 USA
²School of Earth and Space Exploration, Arizona State University, PO Box 876004, Tempe, Arizona, 85287 USA
³Department of Physics and Electronics, The University of Puerto Rico at Humacao, Call Box 860, Humacao, Puerto Rico, 00792 USA
⁴Lunar and Planetary Laboratory, University of Arizona, PO Box 210092, Tucson, Arizona, 85721 USA
Published by arrangement with John Wiley & Sons

A comprehensive understanding of the mechanical strength and failure mechanisms of asteroids is essential for the development of hazard mitigation strategies and in situ resource extraction. In this study, the Aba Panu (L3) ordinary chondrite meteorite is investigated to understand its failure response under compressive loading. Compression experiments were conducted on ten 1 cm cubes under quasi-static conditions in constant displacement control mode at room temperature. Three-dimensional (3-D) digital image correlation (DIC) was used to measure the full-field deformation and strain. These data were used to determine the elastic modulus and local strain distribution, and investigate the effects of the mineralogical and structural heterogeneity on the crack formation and growth sites. Aba Panu exhibits brittle failure during compression with a range of failure strength from 361.7 to 578.0 MPa. Axial splitting and multiple fracturing occur during the uniaxial compressive state of stress. Ultrasonic tests were used to calculate elastic moduli from sound speeds and compared with the results of L-type ordinary chondrites from the literature. Characterization results from electron microprobe analysis identified different elements and areal distribution of mineral phases and pre-existing cracks. In general, the DIC results did not show correlations between crack initiation and specific mineralogical or textural components in this meteorite, such as chondrules or metals/sulfide grains, suggesting that the pre-existing microcracks and porosity control the Aba Panu failure mechanisms.

¹Sakiko Kikuchi,¹Takazo Shibuya,¹Mariko Abe,²Katsuyuki Uematsu
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.11.006]
¹Super-cutting-edge Grand and Advanced Research (SUGAR) program, Institute for Extra-cutting-edge Science and Technology Avant-garde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa, 2370061, Japan
²Department of Marine & Earth Sciences, Marine Works Japan, Ltd., 3-54-1 Oppamahigashi, Yokosuka, Kanagawa 2370061, Japan
Copyright Elsevier

The presence of hydrous minerals in carbonaceous chondrites has been considered as an important evidence for the former presence of liquid water in parent asteroids. However, the evolution of water–rock reactions in hydrous asteroids remains not well constrained. Here, we conduct water–rock type experiments and chemical equilibria calculations under low-temperature hydrothermal and reducing conditions to investigate the alteration process and secondary mineral assemblages of chondritic rock in the earliest alteration stage. Using synthetic chondrite (mixtures of olivine (forsterite95), orthopyroxene (enstatite95), silicate glass, troilite and Femetal) as a starting material, our experiments were conducted at temperatures of 25°C–80°C for time periods between 1 to 460 days at a water-to-rock mass ratio of 10. A combination of X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses revealed that the primary secondary phases consisted of pyrrhotite, an amorphous SiO2-rich phase and saponite at 80°C, while the secondary phase consisted of an amorphous SiO2-rich phase and saponite at 25°C. At both temperatures, the SiO2-rich phases and saponite densely covered the surface of the primary phases. The Fe/Mg ratios of saponite and amorphous SiO2-rich phases showed clear difference between 80°C and 25°C. Saponite that was formed at 80°C was richer in Fe than the initial silicate phases, and the highest Fe/Mg ratios were obtained in the saponite encrusting the troilite and Femetal. These results suggest that the Fe distributed from the troilite and Femetal induced the formation of Fe-rich saponite. Some of the secondary minerals observed from our alteration experiments were consistent with those expected by chemical equilibria calculations. However, the formation of serpentine, the dominant secondary mineral expected from chemical equilibria calculations, was not observed in our experiments up to 460 days, probably because the preferential dissolution of SiO2-rich silicate glass in the earliest stage of alteration induced the formation of saponite rather than serpentine. The secondary mineral assemblage and its morphological characteristics, as observed by our alteration experiments, showed similarities with carbonaceous chondrites such as CM2 and CO3 chondrites. This alteration might be explained by water–rock reactions at low temperatures and by the short time alteration. These findings better constrain the temperatures and timescales of aqueous alterations in hydrous asteroids, as well as the role of water in the early solar system bodies.

¹Denggao Qiu,¹Fei Li,¹Jianguo Yan,¹Wutong Gao,¹Zheng Chong
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114778]
¹State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, Wuhan 430070, China
Copyright Elsevier

The FeO and TiO2 contents are critical for distinguishing petrological properties of the Moon and for studying the distribution of the lunar maria and its multi-period volcanic activity. Traditional methods used the ratio between spectral reflectances to estimate FeO and TiO2 contents, which are empirical models. The development of machine learning algorithms offered new ideas for solving inversion problems, and these algorithms can automatically mine the data for potential correlations wherever possible. In this work, by using the Kaguya Multiband Imager data, we construct an optimized spectral inversion model using the Convolutional Neural Network (CNN) algorithm to produce a map of the FeO and TiO2 content on the lunar surface. The CNN models were compared with the traditional linear model and the Random Forest (RF) model. The results were indicated that the CNN models had higher accuracy and the CNN model eliminated the shortcoming of the RF model that the inversion results were limited by the training data, and certainly optimizes the impact of data striping. The CNN models can better describe the nonlinear relationship between spectral reflectance and oxide content. This also provides the basis for the inversion of the other oxides (e.g., MgO, Al2O3, CaO and SiO2). These new maps from the CNN model provide reference information for further studies of the geological evolution of the Moon.