¹Renbiao Tao,¹Yingwei Fei
Earth and Planetary Science Letters 562, 116849 Link to Article [https://doi.org/10.1016/j.epsl.2021.116849]
¹Earth and Planets Laboratory, Carnegie Institution for Science, 5251 Broad Branch Road, NW, Washington, DC 20015, USA
Copyright Elsevier

The partitioning of light elements between liquid and solid at the inner core boundary (ICB) governs compositional difference and density deficit between the outer and inner core. Observations of high S and low Fe concentration on the surface of Mercury from MESSENGER mission indicate that Mercury is formed under much more reduced conditions than other terrestrial planets, which may result in a Si and S-bearing metallic Fe core. In this study, we conducted high-pressure experiments to investigate the partitioning behavior of Si and S between liquid and solid in the Fe-Si-S system at 15 and 21 GPa, relevant to Mercury’s ICB conditions. Experimental results show that almost all S partitions into liquid. The partitioning coefficient of Si (D_Si) between liquid and solid is strongly correlated with the S content in liquid (XSliquid) as: ⁎log10⁡(DSi)=0.0445+5.9895⁎log10⁡(1−XSliquid). Within our experimental range, pressure has limited effect on the partitioning behavior of Si and S between liquid and solid. For Mercury with an Fe-Si-S core, compositional difference between the inner and outer core is strongly dependent on the S content of the core. The lower S content is in the core, the smaller compositional difference and density deficit between the liquid outer core and solid inner core should be observed. For a core with 1.5 wt% bulk S, a model ICB temperature would intersect with the melting curve at ∼17 GPa, corresponding to an inner core with a radius of ∼1600 km.

¹KeZhu朱柯,¹Frédéric Moynier,² Martin Schiller,³ConelM. O’D. Alexander,⁴Jemma Davidson,⁴Devin L.Schrader,^1,2Elishevah van Kooten,^1,2Martin Bizzarro
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.02.031]
¹Université de Paris, Institut de Physique du Globe de Paris, CNRS UMR 7154, 1 rue Jussieu, Paris 75005, France
²Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5–7, Copenhagen DK-1350, Denmark
³Earth and Planetary Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, Washington, DC 20015, USA
⁴Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287-6004, USA
Copyright Elsevier

Chondrites are meteorites from undifferentiated parent bodies that provide fundamental information about early Solar System evolution and planet formation. The element Cr is highly suitable for deciphering both the timing of formation and the origin of planetary building blocks because it records both radiogenic contributions from ⁵³Mn-⁵³Cr decay and variable nucleosynthetic contributions from the stable ⁵⁴Cr nuclide. Here, we report high-precision measurements of the mass-independent Cr isotope compositions (ε⁵³Cr and ε⁵⁴Cr) of chondrites (including all carbonaceous chondrites groups) and terrestrial samples using for the first time a multi-collection inductively-coupled-plasma mass-spectrometer to better understand the formation histories and genetic relationships between chondrite parent bodies. With our comprehensive dataset, the order of decreasing ε⁵⁴Cr (per ten thousand deviation of the ⁵⁴Cr/⁵²Cr ratio relative to a terrestrial standard) values amongst the carbonaceous chondrites is updated to CI = CH ≥ CB ≥ CR ≥ CM ≈ CV ≈ CO ≥ CK > EC > OC. Resolvable ε⁵⁴Cr (with 2SE uncertainty) differences between CV and CK chondrites rule out an origin from a common parent body or reservoir as has previously been suggested. The CM and CO chondrites share common ε⁵⁴Cr characteristics, which suggests their parent bodies may have accreted their components in similar proportions. The CB and CH chondrites have low-Mn/Cr ratios and similar ε⁵³Cr values to the CI chondrites, invalidating them as anchors for a bulk Mn-Cr isochron for carbonaceous chondrites. Bulk Earth has a ε⁵³Cr value that is lower than any chondrite group, including enstatite chondrites. This depletion may constrain the timing of volatile loss from the Earth or its precursors to be within the first million years of Solar System formation and is incompatible with Earth’s accretion via any of the known chondrite groups as main contributors, including enstatite chondrites.

¹Robert M. Hazen,¹Shaunna M. Morrison,²Anirudh Prabhu
American Mineralogist 106, 325-350 Link to Article[http://www.minsocam.org/MSA/AmMin/TOC/2021/Abstracts/AM106P0325.pdf]
¹Earth and Planets Laboratory, Carnegie Institution for Science, 5251 Broad Branch Road NW, Washington, D.C. 20015, U.S.A.
²Tetherless World Constellation, Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180, U.S.A.
Copyright: The Mineralogical Society of America

Information-rich attributes of minerals reveal their physical, chemical, and biological modes of
origin in the context of planetary evolution, and thus they provide the basis for an evolutionary system
of mineralogy. Part III of this system considers the formation of 43 different primary crystalline and
amorphous phases in chondrules, which are diverse igneous droplets that formed in environments with
high dust/gas ratios during an interval of planetesimal accretion and differentiation between 4566 and
4561 Ma. Chondrule mineralogy is complex, with several generations of initial droplet formation via
various proposed heating mechanisms, followed in many instances by multiple episodes of reheating
and partial melting. Primary chondrule mineralogy thus reflects a dynamic stage of mineral evolution,
when the diversity and distribution of natural condensed solids expanded significantly

^1,2Makiko K. Haba,^1,3Yi-Jen Lai,¹Jörn-Frederik Wotzlaw,⁴Akira Yamaguchi,^5,6,7Maria Lugaro,¹Maria Schönbächler
Proceedings of the National Academy of Sciences of the United States of America (PNAS) (in Press) Link to Article [https://doi.org/10.1073/pnas.2017750118]
¹Institute of Geochemistry and Petrology, ETH Zürich, 8092 Zürich, Switzerland;
²Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan;
³Macquarie GeoAnalytical, Department of Earth and Environmental Sciences, Macquarie University, Sydney, NSW 2109, Australia;
⁴Antarctic Meteorite Research Center, National Institute of Polar Research, 190-8518 Tokyo, Japan;
⁵ Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH), 1121 Budapest, Hungary;
⁶Institute of Physics, ELTE Eötvös Loránd University, 1117 Budapest, Hungary;
⁷Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, VIC 3800, Australia

The niobium-92–zirconium-92 (92Nb–92Zr) decay system with a half-life of 37 Ma has great potential to date the evolution of planetary materials in the early Solar System. Moreover, the initial abundance of the p-process isotope 92Nb in the Solar System is important for quantifying the contribution of p-process nucleosynthesis in astrophysical models. Current estimates of the initial 92Nb/93Nb ratios have large uncertainties compromising the use of the 92Nb–92Zr cosmochronometer and leaving nucleosynthetic models poorly constrained. Here, the initial 92Nb abundance is determined to high precision by combining the 92Nb–92Zr systematics of cogenetic rutiles and zircons from mesosiderites with U–Pb dating of the same zircons. The mineral pair indicates that the 92Nb/93Nb ratio of the Solar System started with (1.66 ± 0.10) × 10−5, and their 92Zr/90Zr ratios can be explained by a three-stage Nb–Zr evolution on the mesosiderite parent body. Because of the improvement by a factor of 6 of the precision of the initial Solar System 92Nb/93Nb, we can show that the presence of 92Nb in the early Solar System provides further evidence that both type Ia supernovae and core-collapse supernovae contributed to the light p-process nuclei.

^1,2,3Benoit Côté et al. (>10)
Science 371, 945-948 Link to Article [DOI: 10.1126/science.aba1111]
¹Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network, Konkoly Observatory, 1121 Budapest, Hungary.
²Institute of Physics, Eötvös Loránd University, 1117 Budapest, Hungary.
³National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824, USA.
Reprinted with permission from AAAS

The composition of the early Solar System can be inferred from meteorites. Many elements heavier than iron were formed by the rapid neutron capture process (r-process), but the astrophysical sources where this occurred remain poorly understood. We demonstrate that the near-identical half-lives (≃15.6 million years) of the radioactive r-process nuclei iodine-129 and curium-247 preserve their ratio, irrespective of the time between production and incorporation into the Solar System. We constrain the last r-process source by comparing the measured meteoritic ratio 129I/247Cm = 438 ± 184 with nucleosynthesis calculations based on neutron star merger and magneto-rotational supernova simulations. Moderately neutron-rich conditions, often found in merger disk ejecta simulations, are most consistent with the meteoritic value. Uncertain nuclear physics data limit our confidence in this conclusion.

¹Takashi Yoshizaki,^1,2,3William F.McDonough
Geochemistry [Chemie der Erde] (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2021.125746]
¹Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578, Japan
²Department of Geology, University of Maryland, College Park, MD 20742, USA
³Research Center for Neutrino Science, Tohoku University, Sendai, Miyagi 980-8578, Japan
Copyright Elsevier

Composition of terrestrial planets records planetary accretion, core–mantle and crust–mantle differentiation, and surface processes. Here we compare the compositional models of Earth and Mars to reveal their characteristics and formation processes. Earth and Mars are equally enriched in refractory elements (1.9 × CI), although Earth is more volatile-depleted and less oxidized than Mars. Their chemical compositions were established by nebular fractionation, with negligible contributions from post-accretionary losses of moderately volatile elements. The degree of planetary volatile element depletion might correlate with the abundances of chondrules in the accreted materials, planetary size, and their accretion timescale, which provides insights into composition and origin of Mercury, Venus, the Moon-forming giant impactor, and the proto-Earth. During its formation before and after the nebular disk’s lifetime, the Earth likely accreted more chondrules and less matrix-like materials than Mars and chondritic asteroids, establishing its marked volatile depletion. A giant impact of an oxidized, differentiated Mars-like (i.e., composition and mass) body into a volatile-depleted, reduced proto-Earth produced a Moon-forming debris ring with mostly a proto-Earth’s mantle composition. Chalcophile and some siderophile elements in the silicate Earth added by the Mars-like impactor were extracted into the core by a sulfide melt (∼0.5% of the mass of the Earth’s mantle). In contrast, the composition of Mars indicates its rapid accretion of lesser amounts of chondrules under nearly uniform oxidizing conditions. Mars’ rapid cooling and early loss of its dynamo likely led to the absence of plate tectonics and surface water, and the present-day low surface heat flux. These similarities and differences between the Earth and Mars made the former habitable and the other inhospitable to uninhabitable.

^1,2,3Michael K.Weisberg,⁴Noriko T.Kita,⁴Kohei Fukuda,⁴Guillaume Siron,^2,3Denton S.Ebel
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.02.027]
¹Dept. Physical Sci, Kingsborough College CUNY, Brooklyn, NY 11235
²Dept. Earth and Environmental Sci, CUNY Graduate Center, New York, NY 10016
³Dept. Earth and Planetary Sci, American Museum of Natural History, New York, NY 10024
⁴WiscSIMS, Dept. of Geoscience, University of Wisconsin-Madison, Madison, WI 53706
Copyright Elsevier

We report petrology and high precision, in situ oxygen isotope analyses of silicates in chondrules, fragments, metal-rich nodules, refractory inclusions from the ALH 81189 (EH3), ALH 85159 (paired with ALH 81189) and from the MAC 88136 (EL3) chondrite. This is the first report of oxygen isotope ratios for individual objects in an EL3 and for the silicates associated with the metal-rich nodules that are characteristic of unequilibrated enstatite (E3) chondrites. The oxygen isotopic data from the chondrules and other objects form a trend, on a 3-isotope plot, that coincides with the slope∼1 primitive chondrule mineral (PCM) line (initially defined by chondrules from the Acfer 094 primitive carbonaceous chondrite), with most objects clustering at the intersection of the PCM line with the terrestrial fractionation (TF) line, near whole rock E3. The data from EH3 and EL3 overlap and show a similar distribution, suggesting they formed from a similar pool of precursors or in similar gaseous environments, but their mineral compositions suggest differences in their nebular environments and/or parent bodies. Silicates in the metal-rich nodules we analyzed (in both EH3 and EL3) have oxygen isotope ratios (as well as mineral compositions) similar to the silicate (metal-free) chondrules. This is consistent with formation of the metal-rich nodules prior to chondrite accretion, in an environment and from a process similar to that which formed the coexisting chondrules, but from more metal-rich mixtures of precursors. Olivine in an AOA from ALH 81189 is 16O-rich with δ18O = –46.5‰, δ17O = –48.0‰, similar to the AOAs and refractory inclusions previously reported in E3 and in all other chondrite groups. There is a clear distinction in oxygen isotopic compositions between the chondrules in the E3 chondrites and those in the LL and R as well as those in CV and CM chondrite groups. Chondrules from CR and E chondrites plot closer to the PCM line than all other chondrite groups with E3 chondrules having a different distribution toward more 16O-poor compositions. Chondrules in other chondrite groups form trends above and below the PCM. From the distribution of EC chondrules along the PCM line, we propose that similar pools of chondrule precursors were present in the different (carbonaceous, CR and Acfer 094 and non-carbonaceous, E) chondrule forming regions in the protoplanetary disk but with different amounts of 16O-rich refractory materials, prior to development of the postulated Jupiter divide that potentially separated inner (non-carbonaceous) from outer (carbonaceous chondrite) Solar System materials or the Jupiter barrier was inefficient in completely separating these materials.

¹Thomas B.McCord,¹Jean-Philippe Combe,²Julie C.Castillo-Rogez,³Harry Y.McSween,⁴Thomas H.Prettyman
Geochemistry [Chemie der Erde] (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2021.125745]
¹The Bear Fight Institute, 22 Fiddler’s Road, P.O. Box 667, Winthrop, WA, 98862 USA
²Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109 USA
³Department of Earth & Planetary Sciences, University of Tennessee, Knoxville, TN, 37996-1410, USA
⁴Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ, 85719-2395, USA
Copyright Elsevier

Ceres, a nearly 1000-km diameter body located in the Solar System’s main asteroid belt, has been classified under many categories: planet, comet, asteroid, minor planet and, presently, dwarf planet. No matter what the designation, Ceres has experienced major planetary processes. Its evolution has been controlled by water, making it a most unusual, interesting and accessible inner Solar System object that can inform the evolution of outer Solar System moons and other dwarf planets. Early telescopic observations suggested a hydroxylated mineralogy similar to carbonaceous chondrite meteorites and a size and mass indicating a bulk density that implied a water content of 17−27 wt%. Thermodynamic modeling of Ceres’ evolution indicated that thermal aqueous evolution likely occurred. The Dawn Mission produced a huge increase in our understanding of Ceres, confirming but vastly extending the early knowledge. Dawn, carrying multispectral cameras, a visible-infrared imaging spectrometer and a nuclear spectrometer, orbited Ceres between 2015–2018 (after orbiting Vesta) at a number of different altitudes, ultimately reaching 35 km from the surface at periapsis. Observations of almost the entire surface and gravity field mapping revealed multiple geological and internal features attributed to the effects of water. The surface displays cryovolcanic-like and flow structures, exposed phyllosilicates, carbonates, evaporites and water ice. The subsurface shows partial differentiation, decreasing viscosity with depth, and lateral density heterogeneity. Ceres appears to be geologically active today and possesses liquid water/brine pockets or even an extended liquid layer in the interior, confirming an “Ocean World” designation in today’s vernacular.

¹Keng-Hsien Chao,¹Rebecca deGraffenried,¹Mackenzie Lach,¹William Nelson,¹Kelly Truax,¹Eric Gaidos
Geochemistry [Chemie der Erde] (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2020.125735]
¹Department of Earth Sciences, University of Hawai’i at Mānoa, Honolulu, HI 96822, USA
Copyright Elsevier

The magma ocean concept was first conceived to explain the geology of the Moon, but hemispherical or global oceans of silicate melt could be a widespread “lava world” phase of rocky planet accretion, and could persist on planets on short-period orbits around other stars. The formation and crystallization of magma oceans could be a defining stage in the assembly of a core, origin of a crust, initiation of tectonics, and formation of an atmosphere. The last decade has seen significant advances in our understanding of this phenomenon through analysis of terrestrial and extraterrestrial samples, planetary missions, and astronomical observations of exoplanets. This review describes the energetic basis of magma oceans and lava worlds and the lava lake analogs available for study on Earth and Io. It provides an overview of evidence for magma oceans throughout the Solar System and considers the factors that control the rocks these magma oceans leave behind. It describes research on theoretical and observed exoplanets that could host extant magma oceans and summarizes efforts to detect and characterize them. It reviews modeling of the evolution of magma oceans as a result of crystallization and evaporation, the interaction with the underlying solid mantle, and the effects of planetary rotation. The review also considers theoretical investigations on the formation of an atmosphere in concert with the magma ocean and in response to irradiation from the host star, and possible end-states. Finally, it describes needs and gaps in our knowledge and points to future opportunities with new planetary missions and space telescopes to identify and better characterize lava worlds around nearby stars.

¹R.Brasser,^2,3S.J.Mojzsis,⁴S.C.Werner,⁵O.Abramov
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114389]
¹Earth Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8550, Japan
²Department of Geological Sciences, University of Colorado, Boulder, CO 80309, USA
³Origins Research Institute, Research Centre for Astronomy and Earth Sciences, H-1112 Budapest, Hungary
⁴Centre for Earth Evolution and Dynamics, University of Oslo, N-0315 Oslo, Norway
⁵Planetary Science Institute, Tucson, AZ 85719, USA
Copyright Elsevier

Subsequent to the Moon’s formation, late accretion to the terrestrial planets strongly modified the physical and chemical nature of silicate crusts and mantles. This alteration came in the form of melting through impacts, as well as the belated addition of volatiles and the highly siderophile elements (HSEs). Even though late accretion is well established as having been an important process in the evolution of the young solar system, its intensity and temporal decline remain subject to debate. Much of this deliberation hinges on what can be inferred about late accretion to the Moon from its computed mantle HSE abundances. Current debate centres on whether the lunar HSE record is representative of its whole late accretion history or alternatively that these were only retained in the mantle and crust after a particular time, and if so, when. Here we employ improved Monte Carlo impact simulations of late accretion onto the Moon and Mars and present an updated chronology based on new dynamical simulations of leftover planetesimals and the E-belt – a now-empty hypothesised inner extension of the asteroid belt (Bottke et al., 2012). We take into account the inefficient retention of colliding material. The source of impactors on both planetary bodies is assumed to be the same, hence we use constraints from both objects simultaneously. We compute the crater and basin densities on the Moon and Mars, the largest objects to strike these planets and the amount of material they accreted. Outputs are used to infer the mass in leftover planetesimals at a particular time period, which is then compared to the lunar HSE abundance. From this estimate we calculate a preferred lunar HSE retention age of ca. 4450 Ma which means that the modelled lunar mantle HSE abundances trace almost all of lunar late accretion. Based on our results, the surface ages of the lunar highlands are at least 4370 Ma. We find that the mass of leftover planetesimals with diameters Di < 300 km at 4500 Ma that best fits the crater chronology is approximately 2 × 10−3 Earth mass (ME) while the mass of the E-belt was fixed at 4.5 × 10−4 ME. We also find that a leftover planetesimal mass in excess of 0.01 ME results in a lunar HSE retention age younger than major episodes of lunar differentiation and crust formation, which in turn violates geochemical constraints for the timing and intensity of late accretion to the Earth (Mojzsis et al., 2019).