¹Justina Novakova,^1,2Monika Jerigova,³Eduard Jane,²Vojtech Szoecs,^1,2DusanVelic
Planetary and Space Sience (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.105012]
¹Faculty of Natural Sciences, Comenius University, Ilkovičova 6, 842 48, Bratislava, Slovakia
²International Laser Centre, Ilkovičova 3, 842 48, Bratislava, Slovakia
³Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, 845 38, Bratislava, Slovakia

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¹Yayoi N.Miura,²Mamoru Okuno,²Yuichiro Cho,^1,2,3Kazuo Yoshiok,²Seiji Sugita
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.105046]
¹Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-0032, Japan
²Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033, Japan
³Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8561, Japan

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¹S.T.Port,¹V.F.Chevrier
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.105022]
¹University of Arkansas, Center for Space and Planetary Sciences, Fayetteville, AR, 72701, United State

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¹Jingyi Mah,¹Ramon Brasser
¹Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114052]
¹Earth Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8550, Japan
Copyright Elsevier

Combining isotopic constraints from meteorite data with dynamical models of planet formation proves to be advantageous in identifying the best model for terrestrial planet formation. Prior studies have shown that the probability of reproducing the distinct isotopic compositions of the Earth and Mars for both classical and Grand Tack models is very low. In the framework of the Grand Tack model, for Mars to be isotopically different from the Earth, it had to form under very specific conditions. Here, we subjected a fairly new and unexplored model—the depleted disc model—to the test. It presupposes that the region in the inner protoplanetary disc from Mars’ orbit and beyond is depleted in mass such that Mars is left with insufficient material to grow to a larger size. Our aim is to test the whether the distinct isotopic compositions of the Earth and Mars are a natural outcome of this model. We found that the terrestrial planets accrete material mostly locally and have feeding zones that are sufficiently distinct. The Earth and Mars, and by extension, Venus, can have distinct isotopic compositions if there is an isotopic gradient in the terrestrial planet region of the protoplanetary disc. Our results suggest that the material in the inner Solar System most likely did not undergo substantial mixing that homogenised the potential isotopic gradient, in contrast to the Grand Tack model where the feeding zones of the terrestrial planets are nearly identical due to the mixing of material by Jupiter’s migration.

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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