¹Borlina C.S., ¹Weiss B.P.,²Bryson J.F.J.,³Bai X.-N.,¹Lima E.A.,¹Chatterjee N.,¹Mansbach E.N.
Science Advances 42, eabj6928 Link to Article [DOI 10.1126/sciadv.abj6928]
¹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
²Department of Earth Sciences, Oxford University, Oxford, United Kingdom
³Institute for Advanced Study and Department of Astronomy, Tsinghua University, Beijing, China

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^1,2,3Tatsumi E. et al. (>10)
Nature Communications 12, 5837 Link to Articles [DOI 10.1038/s41467-021-26071-8]
¹Instituto de Astrofísica de Canarias (IAC), La Laguna, Tenerife, Spain
²Department of Astrophysics, University of La Laguna, La Laguna, Tenerife, Spain
³The University of Tokyo, Bunkyo, Tokyo, Japan

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¹I.Blanchard,¹D.C.Rubie,³E.S.Jennings,³I.A.Franchi,³X.Zhao,¹S.Petitgirard,¹N.Miyajima,⁴S.A.Jacobson,⁵A.Morbidelli
Earth and Planetary Science Letters 580, 117374 Link to Article [https://doi.org/10.1016/j.epsl.2022.117374]
¹Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany
²Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet Street, London WC1E 7HX, UK
³School of Physical Sciences, Open University, Milton Keynes MK7 6AA, UK
⁴Department of Earth and Environmental Sciences, Michigan State University, East Lansing, MI 48824, USA
⁵Laboratoire Lagrange, Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
Copyright Elsevier

Carbon is an essential element for the existence and evolution of life on Earth. Its abundance in Earth’s crust and mantle (the Bulk Silicate Earth, BSE) is surprisingly high given that carbon is strongly siderophile (metal-loving) at low pressures and temperatures, and hence should have segregated almost completely into Earth’s core during accretion. Estimates of the concentration of carbon in the BSE lie in the range 100–260 ppm and are much higher than expected based on simple models of core–mantle differentiation. Here we show through experiments at the putative conditions of Earth’s core formation (49–71 GPa and 3600–4000 K) that carbon is significantly less siderophile at these conditions than at the low pressures (≤13 GPa) and temperatures (≤2500 K) of previous large volume press studies, but at least an order of magnitude more siderophile than proposed recently based on an experimental approach that is similar to ours. Using our new data along with previously published results, we derive a new parameterization of the pressure–temperature dependence of the metal–silicate partitioning of carbon. We apply this parameterization in a model that combines planet formation and core-mantle differentiation that is based on astrophysical N-body accretion simulations. Because differentiated planetesimals were almost completely depleted in carbon due to sublimation at high temperatures, almost all carbon in the BSE was added by the accretion of fully-oxidized carbonaceous chondrite material from the outer solar system. Carbon is added to the mantle continuously throughout accretion and its concentration reaches values within the BSE range (e.g. 140+-40 ppm) at the end of accretion. The corresponding final core and bulk Earth carbon concentrations are 1270+-300 ppm and 495+-125 ppm respectively.

¹L.Chimiak,²J.Eiler,²A.Sessions,³C.Blumenfeld,⁴M.Klatte,⁵B.M.Stoltz
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.01.015]
¹Department of Geological Sciences, University of Colorado—Boulder, Boulder, CO, 80309 USA
²Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, USA
³Dantari, Inc, Westlake Villiage, CA, 91361, USA
⁴Dottikon Exlusive Synthesis AG, Dottikon, 5605, CH
⁵Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
Copyright Elsevier

Strecker synthesis creates α–amino acids from prebiotically plausible substrates (cyanide, ammonia, and aldehydes) and is widely hypothesized to be a key mechanism in the chemistry that led to life on Earth and on other planets. To better constrain the synthetic environments and precursors of abiotic α–amino acids, and to determine unique signatures of abiogenic amino acids, we measured the molecular-averaged and site-specific carbon and nitrogen isotope effects for the Strecker synthesis of alanine. The reaction steps of the Strecker synthesis can be divided into two groups: an initial series of reversible amination and nitrile-addition reactions (‘equilibration’) and a second series of irreversible hydrolysis reactions (‘hydrolysis’). The equilibration of cyanide, acetaldehyde, and ammonia with the intermediate, α–aminopropionitrile (α-APN), has a measured 55.1 ‰ equilibrium nitrogen isotope effect between the 15N–rich amine nitrogen in α-aminopropionitrile and the 15N–poor ammonia and a 20.0 ‰ equilibrium carbon isotope effect between the 13C-poor C–2 site in α–aminopropionitrile and the 13C–rich carbonyl carbon in acetaldehyde. The first irreversible hydrolysis step is inferred to have an up to 10 ‰ normal carbon fractionation (i.e., faster for 12C, slower for 13C) for the whole molecule, but it also has one or more side reactions that deplete the reactive α-APN reservoir by up to 15 ‰. The second hydrolysis step has a 15.4 ‰ normal kinetic isotope effect on the amide (C–1) site of alaninamide, which becomes the carboxyl site of alanine. Other α–amino acids will likely experience similar nitrogen isotope fractionations between ammonia and their amine sites, and similar carbon isotope fractionations between the carbonyl carbon in reactant aldehydes or ketones and the intermediate α–aminonitrile, and between cyanide and the carboxyl site. Therefore, these isotope effects allow us to predict the carbon and nitrogen isotopic contents and intramolecular structures of α-amino acids formed by Strecker synthesis based on their substrates’ isotopic compositions, or to infer the isotopic compositions of substrates from which amino acids formed, for example in the case of the amino-acid-rich carbonaceous chondrites. The site-specific C and N isotopic compositions of amino acids formed by Strecker chemistry contrast with those typical of terrestrial biosynthetic amino acids, so these data also provide a means of discriminating between biogenic and abiogenic α–amino acids.

¹Panerai F.,²Bessire B.,²Haskins J.,¹Foster C.,³Barnard H.,²Stern E.,²Feldman J.
Planetary Science Journal 2, 179 Link to Article [DOI 10.3847/PSJ/ac1749]
¹Center for Hypersonics and Entry System Studies (CHESS), Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, 104 S. Wright Street, Urbana, 61801, IL, United States
²NASA Ames Research Center, Moffett Field, 94035, CA, United States
³Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, 94720, CA, United States

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^1,2Christopher H. House et al. (>10)
Proceeding sof the National Academy of Sciences of the United States of America 119, e2115651119 Link to Article [https://doi.org/10.1073/pnas.2115651119]
¹Department of Geosciences, The Pennsylvania State University, University Park, PA 16802
²Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, PA 16802

Obtaining carbon isotopic information for organic carbon from Martian sediments has long been a goal of planetary science, as it has the potential to elucidate the origin of such carbon and aspects of Martian carbon cycling. Carbon isotopic values (δ13CVPDB) of the methane released during pyrolysis of 24 powder samples at Gale crater, Mars, show a high degree of variation (−137 ± 8‰ to +22 ± 10‰) when measured by the tunable laser spectrometer portion of the Sample Analysis at Mars instrument suite during evolved gas analysis. Included in these data are 10 measured δ13C values less than −70‰ found for six different sampling locations, all potentially associated with a possible paleosurface. There are multiple plausible explanations for the anomalously depleted 13C observed in evolved methane, but no single explanation can be accepted without further research. Three possible explanations are the photolysis of biological methane released from the subsurface, photoreduction of atmospheric CO2, and deposition of cosmic dust during passage through a galactic molecular cloud. All three of these scenarios are unconventional, unlike processes common on Earth.

^1,4,5,6Famiano M.A.,²Boyd R.N.,^3,7Onaka T.,^4,5,8Kajino T.
Physical Review Research 3, 033025 Link to Article [DOI 10.1103/PhysRevResearch.3.033025]
¹Department of Physics, Western Michigan University, Kalamazoo, 49008-5252, MI, United States
²Department of Physics, Department of Astronomy, The Ohio State University, Columbus, 43210, OH, United States
³Department of Physics, Meisei University, 2-1-1 Hodokubo, Hino, 191-8506, Tokyo, Japan
⁴School of Physics, Beihang University (Beijing University of Aeronautics and Astronautics), International Research Center for Big-Bang Cosmology and Element Genesis, Beijing, 100083, China
⁵National Astronomical Observatory of Japan, 2-21-1 Mitaka, Tokyo, 181-8588, Japan
⁶Joint Institute for Nuclear Astrophysics
⁷Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
⁸Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan

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^1,2Qin K.,¹Zou X.
Yanshi Xuebao/Acta Petrologica Sinica 37, 2276 – 2286 Link to Article [DOI 10.18654/1000-0569/2021.08.03]
¹Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
²College of Earth and Planetary Sciences, University of Chinese, Academy of Sciences, Beijing, 100049, China

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¹Cao H.,¹Chen J.,¹Fu X.,^1,2Xin Y.,¹Qi X.,¹Shi E.,¹Ling Z.
Journal of Raman Spectroscopy (in Press) Link to Article [DOI 10.1002/jrs.6254]
¹Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Institute of Space Sciences, Shandong University, Weihai, 264209, China
²Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100101, China

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^1,2F.Miozzi,^1,3G.Morard,¹D.Antonangeli,¹M.A.Baron,⁵A.Pakhomova,^1,4A.N.Clark,⁶M.Mezoua,¹G.Fiquet
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.01.013]
¹Sorbonne Université, Muséum National d’Histoire Naturelle, UMR CNRS 7590, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005 Paris, France
²Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA1
³Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, UGE, ISTerre, Grenoble 38000, France1
⁴University of Colorado, Boulder, CO 80309-0399, USA
⁵Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany
⁶European Synchrotron Radiation Facility (ESRF), Grenoble, France
Copyright Elsevier

Several characteristics of a planet, including its internal dynamics, hinge on the composition and crystallization regime of the core, which, in turn, depends on the phase relations, melting behaviour and thermodynamic properties of constituent materials. The Fe-Si-C ternary system can serve as a proxy for core composition and formation processes under reducing conditions. We conducted laser-heated diamond anvil cell experiments coupled with in situ X-ray diffraction and electron microscopy analysis of the recovered samples, on four different starting compositions in the Fe-Si-C ternary system. Phase relations up to 200 GPa and up to 4000 K were determined. An FeSi phase with a B2 structure and iron carbides with different stoichiometries (i.e. Fe₃C and Fe₇C₃) are the main observed phases, along with pure C (diamond) that has an extended stability field in the subsolidus regime. Carbon is largely soluble in B2-structured FeSi, whereas Si does not partition into the carbides. The melting curve determined for the starting material containing the least amount of light elements is consistent with the one for the Fe-C system. The other starting materials display higher melting temperatures than that of Fe-C, suggesting the existence of at least two different invariant points in the Fe-Si-C system. Applied to planetary interiors, our observations highlight how a small variation in light elements content would deeply affect the solidification style of a core. Bottom-up (Fe-enriched systems) and top-down regimes (C-rich systems), as well as solidification of a crystal mush (Si-enriched systems). These three crystallization regimes influence significantly the possibility of starting and sustaining a dynamo. Our results provide new insights into the differentiation of terrestrial planets in the Solar System and beyond, contributing to the study of planetary diversity.