¹Daniel P.Glavin et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13560]
¹NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA
Published by arrangement with John Wiley & Sons

The Asuka (A)‐12236 meteorite has recently been classified as a CM carbonaceous chondrite of petrologic type 3.0/2.9 and is among the most primitive CM meteorites studied to date. Here, we report the concentrations, relative distributions, and enantiomeric ratios of amino acids in water extracts of the A‐12236 meteorite and another primitive CM chondrite Elephant Moraine (EET) 96029 (CM2.7) determined by ultra‐high‐performance liquid chromatography time‐of‐flight mass spectrometry. EET 96029 was highly depleted in amino acids and dominated by glycine, while a wide diversity of two‐ to six‐carbon aliphatic primary amino acids were identified in A‐12236, which had a total amino acid abundance of 360 ± 18 nmol g−1, with most amino acids present without hydrolysis (free). The amino acid concentrations of A‐12236 were double those previously measured in the CM2.7 Paris meteorite, consistent with A‐12236 being a highly primitive and unheated CM chondrite. The high relative abundance of α‐amino acids in A‐12236 is consistent with formation by a Strecker‐cyanohydrin dominated synthesis during a limited early aqueous alteration phase on the CM meteorite parent body. The presence of predominantly free glycine, a near racemic mixture of alanine (d/l ~0.93–0.96), and elevated abundances of several terrestrially rare non‐protein amino acids including α‐aminoisobutyric acid (α‐AIB) and racemic isovaline indicate that these amino acids in A‐12236 are extraterrestrial in origin. Given a lack of evidence for biological amino acid contamination in A‐12236, it is possible that some of the l‐enantiomeric excesses (lee ~34–64%) of the protein amino acids, aspartic and glutamic acids and serine, are indigenous to the meteorite; however, isotopic measurements are needed for confirmation. In contrast to more aqueously altered CMs of petrologic types ≤2.5, no l‐isovaline excesses were detected in A‐12236. This observation strengthens the hypothesis that extensive parent body aqueous activity is required to produce or amplify the large l‐isovaline excesses that cannot be explained solely by exposure to circularly polarized radiation or other chiral symmetry breaking mechanisms prior to incorporation into the asteroid parent body.

¹Jan L.Hellmann,^1,2Timo Hopp,¹Christoph Burkhardt,¹ThorstenKleine
Earth and Planetary Science Letters 549, 116508 Link to Article [https://doi.org/10.1016/j.epsl.2020.116508]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
²Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA
Copyright Elsevier

Compared to the composition of CI chondrites and the Sun, all other carbonaceous chondrites are variably depleted in volatile elements. However, the origin of these depletions, and how they are related to volatile loss during high-temperature processes within the solar nebula, are unclear. To better understand the processes that caused volatile element fractionations among carbonaceous chondrites, we obtained mass-dependent Te isotopic compositions and Te concentrations for a comprehensive set of samples from the major carbonaceous chondrite groups. The chondrites exhibit well-resolved inter-group Te isotope variations towards lighter isotopic compositions for increasingly volatile-depleted samples. The Te isotopic compositions and concentrations are also correlated with the mass fraction of matrix and with nucleosynthetic Cr anomalies. Combined, these correlations indicate mixing between volatile-rich, isotopically heavy, and ⁵⁴Cr-rich CI-like matrix with volatile-poor, isotopically light, and ⁵⁴Cr-poorer chondrules or chondrule precursors. The Te-Cr isotopic correlation suggests that all carbonaceous chondrites contain CI-like matrix, and that chondrules and this CI-like matrix formed from isotopically distinct material originating from different regions of the disk. The only samples plotting off the Te-Cr correlation are CR chondrites, indicating that CR chondrules formed from different precursor material than chondrules from other carbonaceous chondrites, either because they formed at greater heliocentric distance and/or at a later time. Plots of volatile element abundances versus matrix mass fraction reveal that chondrules/chondrule precursors display CI-chondritic ratios for volatile elements with 50% condensation temperatures below ∼750 K, with an overall abundance of ∼0.13 × CI. Mixing between these two components, therefore, naturally results in CI-like ratios for these elements in all carbonaceous chondrites, in spite of different degrees of volatile depletion. A corollary of this observation is that the CI-like ratios of volatile elements in the bulk silicate Earth may result from the accretion of volatile-depleted materials and do not require accretion of CI chondrites themselves.

¹Shirai, N.,¹Hozumi, T.,²Toh, Y.,^1,3Ebihara, M.
Journal of Radioanalytical and Nuclear Chemistry (in Press) Link to Article [DOI: 10.1007/s10967-020-07273-8]
¹Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan
²Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Shirakata, Tokai-mura, Ibaraki 319-1195, Japan
³Department of Earth Sciences, Waseda University, 1-6-1 Nishi-Waseda, Shinjuku-ku, Tokyo, 169-8050, Japan

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¹Sloane, J.B.,¹Sedwick, R.J.
Journal of Propulsion and Power 36, 551-559 Link to Article [DOI: 10.2514/1.B37566]
¹University of Maryland, College Park, MD 20742, United States

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¹Shu, J.
Earth Science Frontier 27, 133-153 Link to Article [DOI: 10.13745/j.esf.sf.2019.12.3]
¹Center for High Pressure Science & Technology Advanced Research, Beijing, 100094, China

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¹Wang, K.,²Li, W.,²Li, S.
Earth Science Frontiers 27, 104-122 Link to Article [DOI: 10.13745/j.esf.sf.2020.4.5]
¹Department of Earth and Planetary Sciences, Washington University in St. Louis, MO 63130, United States
²School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023, China

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¹Sohei Wada,¹Noriyuki Kawasaki,²Changkun Park,^1,3Hisayoshi Yurimoto
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.08.004]
¹Department of Natural History Sciences, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
²Division of Earth-System Sciences, Korea Polar Research Institute, Incheon 21990, Republic of Korea
³Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo 001-0021, Japan
Copyright Elsevier

Fine-grained Ca-Al-rich inclusions (FGIs) in CV chondrites are suggested to be condensates from the solar nebular gas and thus captured O-isotopes from the gas. We conducted a combined study of petrographic observations and in situ O-isotope analysis using secondary ion mass spectrometry for an FGI, named HKD01, from the reduced CV chondrite Northwest Africa 8613. HKD01 has an irregular shape and petrographically three-layered structures: a hibonite-rich core, a spinel-rich core, and a mantle. Each petrographic domain contains melilite, hibonite, and spinel with variable proportions of those minerals. The O-isotopic compositions of the constituent minerals plotted along the slope-1 line on an O three-isotope diagram ranged between Δ¹⁷O ∼ −23‰ and 1‰. Hibonite and spinel are uniformly ¹⁶O-rich (Δ¹⁷O = −23‰) irrespective of their occurrences, while melilite crystals exhibit wide O-isotope variations ranging between Δ¹⁷O ∼ −23‰ and 1‰. The O-isotopic composition in a melilite crystal changes abruptly within ∼2 µm, indicating that disturbances of O-isotopes in melilite after condensation are less than ∼2 µm. Because the melilite in the FGI typically has grain sizes of 5−10 µm, the abrupt change of O-isotopic composition demonstrates that melilite crystals in the FGI preserve the O-isotopic composition of the nebular gas from which they condensed. In the mantle, aggregates of melilite crystals, having relatively large grain sizes (10−25 µm) and oscillatory chemical zoning, exhibit ¹⁶O-poor compositions with small variations ranging between Δ¹⁷O ∼ −4 and 1‰. Among them, a large melilite crystal (∼20 µm) with homogeneously ¹⁶O-poor composition (Δ¹⁷O ∼ 0‰) across the single crystal was found. The coexistence of ¹⁶O-poor and ¹⁶O-rich melilite crystals without O-isotope disturbances in the FGI reveals that ¹⁶O-poor (Δ¹⁷O ∼ 0‰) nebular gas existed in the formation region of the FGI HKD01 in addition to ¹⁶O-rich (Δ¹⁷O ∼ –23‰) nebular gas.

^1,2Druce, M.,^1,2Stirling, C.H.,³Rolison, J.M.
Geostandards and Geoanalytical Research (in Press) Link to Article [DOI: 10.1111/ggr.12341]
¹Department of Chemistry, University of Otago, PO Box 56, Dunedin, New Zealand
²Centre for Trace Element Analysis, University of Otago, PO Box 56, Dunedin, New Zealand
³Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-0808, United States

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¹Ted L.Roush
Icarsu (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114056]
¹Space Sciences Division, NASA Ames Research Center, Planetary Systems Branch, MS 245-3, Moffett Field, CA 94035-1000, United States of America
Copyright Elsevier

The visible, near-, and mid-infrared (≈0.4–6 μm) imaginary indices of refraction (k) are estimated from reflectance spectra for three carbonates germane to martian and terrestrial studies. The resulting values are combined with previous data at longer wavelengths and a subtractive Kramers-Konig analysis is used to estimate the real indices of refraction (n) as a function of wavelength. This process is iterated until neither the n or k vary significantly. The results provide estimated complex refractive indices spanning the ≈0.4–400 μm. The estimated visible, near-, and mid-infrared carbonate complex refractive indices are broadly consistent with previous studies, but extend the wavelength coverage and improve the spectral resolution for these materials.

¹Gordon M.Gartrelle,^1,2Paul S.Hardersen,^1,3Matthew R.M.Izawa,^1,4Matthew C.Nowinski
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114043]
¹University of North Dakota, Grand Forks, ND, USA
²Trouvaille LLC, Tucson, AZ, USA
³Institute of Planetary Materials, Okayama University, Misasa, Japan
⁴The Boeing Company, Washington, DC, USA
Copyright Elsevier

D-type asteroids are a prime example of the many dark, low-albedo asteroids which do not reflect sufficient light to reveal detectable mineral absorptions. While D-type asteroids are relatively rare in the inner solar system and the main asteroid belt, they are dominant among the Jovian Trojans. In this study, we have applied Shkuratov radiative transfer modeling to laboratory spectra of meteorites for which mineral abundances have been measured using X-ray diffraction (XRD) and Rietveld refinement. The general agreement of radiative transfer and XRD estimates of mineral abundances demonstrates the applicability of the radiative transfer approach to featureless, low-albedo spectra. Shkuratov modeling was then applied to new spectral observations of D-type asteroids, along with numerous previously published spectra. The surface mineral abundances of 81 D-type objects, including NASA’s Lucy Mission target (21900) Orus, were modeled using assemblages that are plausible based on meteorite analogues. Modeling results reveal D-types are composed of: low-iron olivine; magnesium saponite-dominant phyllosilicates; opaques such as pyrrhotite and tholin; as well as traces of water-ice and other constituents. Subtle compositional differences in model mineralogies exist between Trojan and non-Trojan D-types as well as between L4 and L5 Trojans suggesting differing formational as well as evolutional conditions have affected these bodies.