^1,2Yan Fan et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13925]
¹State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi’an, 710069 China
²Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081 China
Published by arrangement with John Wiley & Sons

Shidian is a recent meteorite which fell in Yunnan province, China, on November 27, 2017, and has been classified as a CM2 chondrite. Petrography, mineralogy, oxygen and chromium isotopic composition, reflectance spectrum, and density studies of Shidian are reported in this study. Clasts with different aqueous alteration degree, two type 1 clasts with nontypical CM petrography, and one metamorphic clast are observed in Shidian. Mineralogically, Shidian main body consists of phyllosilicates (∼70 vol%), forsterite (∼13 vol%), fayalitic olivine, carbonates, sulfide, high-Ca pyroxene, magnetite framboids, and Fe-Ni metal. The average electron microprobe analysis (EMPA) analytical totals of phyllosilicates are 84.07 ± 1.75 wt%, with average FeO/SiO2 of tochilinite–cronstedtite intergrowths (TCIs) in different clasts ranging from 1.18 to 3.29. The bulk geochemical composition is characterized by flat rare earth element pattern, and by depletion of highly volatile elements. The whole rock oxygen isotopic composition is −0.51 ± 0.73‰, 5.44 ± 1.01‰, and −3.38 ± 0.20‰ for δ17O, δ18O, and Δ17O, respectively, with bulk chromium isotopic composition as ε54Cr = 1.00 ± 0.11. The grain density, bulk density, and porosity are 2.758 ± 0.008 g cm−3, 2.500 ± 0.004 g cm−3, and 9.37 ± 0.59%, respectively. The reflectance spectrum shows “blue” (negative) continuum slope across the visible and near-infrared range, with characteristic absorption features (such as 0.765, 0.923, and 1.160 μm for phyllosilicates). These characteristics indicate that Shidian is an unheated, brecciated CM chondrite and may be an analog of asteroid Bennu.

¹Kayla Iacovino,²Francis M.McCubbin,³Kathleen E.Vander Kaaden,¹Joanna Clark,⁴Axel Wittmann,¹Ryan S.Jakubek,¹Gordon M.Moore,²Marc D.Fries,¹Doug Archer,²Jeremy W.Boyce
Earth and Planetary Science Letters 602, 117908 Link to Article [https://doi.org/10.1016/j.epsl.2022.117908]
¹ARES, Jacobs/NASA Johnson Space Center, 2101 E NASA Pkwy, Houston, TX 77058 USA
²ARES, NASA Johnson Space Center, 2101 E NASA Pkwy, Houston, TX 77058 USA
³NASA Headquarters, Mary W. Jackson Building, Washington, D.C., 20546 USA
⁴Eyering Materials Center, Arizona State University, 1001 S. McAllister Ave., Tempe, AZ 95287-8301 USA
Copyright Elsevier

Here we present the results of experiments designed to reproduce the interaction between super-solidus mercurian magmas and graphite at high temperatures (ramped up from ambient temperature to 1195–1390 °C) and low pressure (10 mbar). The compositions of resultant gases were measured in situ with a thermal gravimeter/differential scanning calorimeter connected to a mass spectrometer configured to operate under low pressures and reducing conditions. Solid run products were analyzed by electron microprobe and Raman spectroscopy. Three magma starting compositions were based on the composition of the Borealis Planitia region (termed NVP for the Northern Volcanic Plains) on Mercury ± alkali metals, sulfur, and transition metal oxides. Smelting between FeOmelt and graphite was observed above 1100 °C, evidenced by the generation of CO and CO2 gas and the formation of Fe-Si metal alloys, which were found in contact with residual graphite grains. Experiments with transition metal oxide-free starting compositions did not produce metal alloys and showed no significant gas production. In all runs that produced gas, C-O-H±S species dominated the degassing vapor. Our results suggest that the consideration of graphite smelting processes can significantly increase calculated eruption velocities and that gas produced by smelting alone can account for >75% of the pyroclastic deposits identified on Mercury. A combination of S-H-degassing and CO-CO2 production from smelting can explain all but the single largest pyroclastic deposit on Mercury.

^1,2Kainen L.Utt,^1,2Ryan C.Ogliore,^1,2Nan Liu,³Alexander N.Krot,³John P.Bradley,⁴Donald E.Brownlee,⁴David J.Joswiak
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.11.020]
¹Department of Physics, Washington University in St. Louis, St. Louis, MO 63130
²McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO 63130
³Hawaii Institute of Geophysics and Planetology, University of Hawaii at Mānoa, Honolulu, HI 96822
⁴Department of Astronomy, University of Washington, Seattle, WA 98195
Copyright Elsevier

Filamentary enstatite crystals, formed by gas-solid condensation in the solar nebula, are found in chondritic porous interplanetary dust particles of probable cometary origin. We measured the oxygen isotopic composition of four filamentary enstatite grains, two whiskers (1.8μm and 2.3μm in length) and two ribbons (3.4μm and 6.1μm in length), from the giant cluster interplanetary dust particle U2-20 GCP using NanoSIMS ion imaging. These grains represent both the ¹⁶O-rich solar (δ^17,18O ≈-70 ‰) and ¹⁶O-poor planetary (δ^17,18O ≈0 ‰) isotope reservoirs. Our measurements provide evidence for very early vaporization of dust-poor and dust-rich regions of the solar nebula, followed by condensation and outward transport of crystalline dust to the comet-forming region very far from the Sun. Similar processes are likely responsible for the crystalline silicates observed in the outer regions of protoplanetary disks elsewhere in the Galaxy.

¹Tait, Alastair W.,^1,2Wilson, Siobhan A.,¹Tomkins, Andrew G.,^1,3Hamilton, Jessica L.,^4,5Gagen, Emma J.,⁶Holman, Alex I.,⁶Grice, Kliti,⁷Preston, Louisa J.,³Paterson, David J.,⁴Southam, Gordon
Astrobiology 22, 399-415 Link to Article [DOI 10.1089/ast.2020.2387]
¹School of Earth, Atmosphere and Environment, Monash University, Room 109, 9 Rainforest Walk, Melbourne, 3800, Vic, Australia
²Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada
³Australian Synchrotron, ANSTO, Clayton, VIC, Australia
⁴School of Earth and Environmental Sciences, University of Queensland, St. Lucia, QLD, Australia
⁵Australian Centre for Ecogenomics, School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, QLD, Australia
⁶Western Australian Organic and Isotope Geochemistry Centre, Institute for Geoscience Research, Curtin University, Perth, WA, Australia
⁷Department of Earth Sciences, Natural History Museum, London, United Kingdom

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Baziotis I.P.,²Ma C.,²Guan Y.,³Ferrière L.,¹Xydous S.,²Hu J.,⁴Kipp M.A.,⁴Tissot F.L.H.,²Asimow P.D.
Scientific Reports 12, 5520 Open Access Link to Article [DOI 10.1038/s41598-022-09465-6]
¹Agricultural University of Athens, Iera Odos 75, Athens, 11755, Greece
²Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, 91125, CA, United States
³Natural History Museum Vienna, Burgring 7, Vienna, 1010, Austria
⁴The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, 91125, CA, United States

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Cyril Sturtz,¹Angela Limare,¹Stephen Tait,¹Édouard Kaminski
Journal of Geophysical research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2021JE007000]
¹Université de Paris, Institut de Physique du Globe de Paris, CNRS, F-75005 Paris, France
Published by arrangement with John Wiley & Sons

This paper is the first of two companion papers presenting a theoretical and experimental study of the evolution of crystallizing magma oceans in planetesimals. We aim to understand the behavior of crystals formed in a convective magma ocean, and the implications of crystal segregation for the thermal and structural evolution of the convective system. In particular, we wish to constrain the possibility to form and preserve cumulates and/or flotation crusts by sedimentation or flotation of crystals respectively. We use lab-scale analog experiments to study the stability and the erosion of a floating lid composed of plastics beads lying over a convective viscous fluid volumetrically heated by microwave absorption. We propose a law for erosion and re-entrainment that depends only on two dimensionless numbers that govern these phenomena: (i) the Rayleigh-Roberts number, characterizing the vigor of convection and (ii) the Shields number, that encompasses the physics of the flow-particle interaction. We further consider the formation of a cumulate at the base of the convective layer by sedimentation of beads that are denser than the fluid. We find that particle deposition occurs at a velocity that scales with the Stokes velocity, a result consistent with previous experimental studies. We build up a model that describes the transient evolution of the convective system’s thermal state and the fraction of particles that segregated from the flow or that remain in suspension.

¹Aditi Pandey,²Elizabeth B. Rampe,²Douglas W. Ming,¹Youjun Deng,^2,3Candice C. Bedford,¹Paul Schwab
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115362]
¹Department of Soil and Crop Sciences, Texas A&M University, College Station, TX, USA
²NASA Johnson Space Center, Houston, TX, USA
³Lunar and Planetary Institute, Universities Space Research Association, Houston, TX, USA
Copyright Elsevier

Data collected by orbiters and landers have consistently shown abundant amorphous materials on Mars. Developing analytical techniques that target amorphous materials in terrestrial analogs can help determine the environmental conditions under which the amorphous assemblages on Mars were formed. However, the inherent short-range order, chemical heterogeneity, and nanoscale phase interactions create challenges in characterizing these phases. This study is aimed to overcome these challenges by combining chemical dissolution rate analysis with spectroscopy-based mass balance calculations (MBC) to characterize different pools of amorphous materials in terrestrial analogs. The differences in dissolution rates between rapidly dissolving Si, Al, and Fe amorphous materials and the slowly dissolving crystalline minerals were modeled to predict amorphous composition in five palagonitic samples from Hawaii (Mauna Kea) and four hyaloclastite tuffs from the subglacial volcanoes in southwest Iceland. These samples were selected as potential analogs because of their spectral and compositional resemblance to Mars’s surface materials.

The amorphous Si, Al, and Fe compositions from both sites varied based on the degree of aqueous alteration, grain size, and location. The amorphous fractions of the unconsolidated palagonitic analogs from Hawaii are composed of alteration products such as opal CT and ferrihydrite with minor amounts of unaltered basaltic glass. In contrast, the amorphous fractions of the cemented Icelandic samples were composed mainly of unaltered glass and mixed Fe(II, III) iron phases. Amorphous compositions of the loose Hawaiian and the consolidated Icelandic palagonites are comparable with the Martian modern and ancient aeolian materials respectively. The amorphous compositions in the Hawaiian sample, HWMK101, closely resemble the amorphous materials in Rocknest, a modern aeolian material from the sand shadow, and the Icelandic samples are comparable to the ancient aeolian materials from the Stimson formation. Our analysis indicates the presence of hydrated secondary alteration products such as ferrihydrite and allophane in Rocknest, and a mixture of reduced iron phases and silicate glass outlined with finer altered opaline silicates in Greenhorn. The chemical extraction analysis combined with MBC can be used to characterize amorphous phases in terrestrial analogs to better constrain the formation and characterization of the abundant amorphous materials on Mars.

¹B.Sutter et al. (>10)
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2022JE007387]
¹Jacobs Technology, NASA Johnson Space Center, Houston, TX, USA
Publishes by arrangement with JohnWiley & Sons

Results from the Sample Analysis at Mars (SAM)-evolved gas analyzer (EGA) on board the Mars Science Laboratory Curiosity rover constrained the alteration history and habitability potential of rocks sampled across the Siccar Point unconformity in Gale crater.
The Glasgow member (Gm) mudstone just below the unconformity had evidence of acid sulfate or Si-poor brine alteration of Fe-smectite to Fe amorphous phases, leaching loss of Fe-Mg-sulfate and exchange of unfractionated sulfur 34S (δ34S=2±7‰) with enriched 34S (20±5‰, V-CDT). Carbon abundances did not significantly change (322-661 μgC/g) consistent with carbon stabilization by amorphous Al- and Fe-hydroxide phases. The Gm mudstone had no detectable oxychlorine and extremely low nitrate. Nitrate (0.06 wt.% NO3), oxychlorine (0.13 wt% ClO4), high C (1472 μg C/g), and low Fe/Mg-sulfate concentration (0.24 wt.% SO3) depleted in 34S (δ34S = -27‰ ± 7), were detected in the Stimson formation (Sf) eolian sandstone above the unconformity. Redox disequilibrium through the detections of iron sulfide and sulfate supported limited aqueous processes in the Sf sandstone. Si-poor brines or acidic fluids altered the Gm mudstone just below the unconformity but did not alter underlying Gm mudstones further from the contact. Chemical differences between the Sf and Gm rocks suggested that fluid interaction was minimal between the Sf and Gm rocks. These results suggested that the Gm rocks were altered by subsurface fluids after the Sf placement. Aqueous processes along the unconformity could have provided habitable conditions and in some cases, C and N levels could have supported heterotrophic microbial populations.

¹Michael P. Lucas,¹Nicholas Dygert,²Jialong Ren,²Marc A. Hesse,²Nathaniel R. Miller,¹Harry Y. McSween
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13930]
¹Department of Earth & Planetary Sciences, University of Tennessee, 1621 Cumberland Ave., 602 Strong Hall, Knoxville, Tennessee, 37996 USA
²Department of Geological Sciences, University of Texas at Austin, 2275 Speedway Stop C9000, Austin, Texas, 78712 USA
Published by arrangement with John Wiley & Sons

Primitive achondrites of the acapulcoite–lodranite clan (ALC) are residues of partial melting that displays a continuum of thermal metamorphism and partial melting most likely set by burial depth within an internally heated, primordial acapulcoite–lodranite parent body (ALPB). New major and trace element data from eight ALC meteorites and the application of several thermometric methods suggest that the ALPB was affected by partial differentiation disrupted by rapid cooling from peak, magmatic temperatures. Application of rare earth element-in-two-pyroxene thermometry recovers temperatures of 1125–1250 °C for lodranites, while two-pyroxene solvus and Ca-in-olivine thermometry recover lower temperatures for ALC meteorites (941–1114 °C and 686–850 °C, respectively). Major and trace element disequilibrium in acapulcoite and transitional groups provides evidence for cryptic melt infiltration and melt rock reaction within these layers of the ALPB. From lodranites, we determined rapid cooling rates of ~1 to ~26 °C yr−1 from peak temperatures, consistent with collisional fragmentation of the parent body during differentiation. After this initial period of rapid cooling, cooling rates decreased by two to four orders of magnitude through Ca-in-olivine closure temperatures (~750 °C). We hypothesize that the primordial ALPB possessed an onion shell-type layered structure that was disrupted by collisional breakup during partial differentiation. Thermal modeling suggests that ALC samples originate from ~300 m to ~10 km radius collisional fragments that cooled rapidly over time scales of several to ~20,000 yr, then reaccreted to form a slower cooling, second-generation rubble-pile asteroid. The source of ALC meteorites is a second-generation (or later) rubble-pile body of S-type spectral class located near the Jupiter 3:1 mean motion resonance in the Main Belt of asteroids.

^1,2Guillaume Florin,^1,3Olivier Alard,²Béatrice Luais,¹Tracy Rushmer
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.11.014]
¹Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia
²Université de Lorraine, CNRS, CRPG, F-54000 Nancy, France
³Géosciences Montpellier, UMR 5243, CNRS & Université Montpellier, 34095 Montpellier, France
Copsright Elsevier

Understanding the evolution of metal in the protoplanetary disk is necessary to constrain the first steps of metal-silicate formation and the early stages of the evolution of the protoplanetary disk. We measured the siderophile elemental compositions (PGE, Ni, Co, Fe, Cu, Ga, Ge) of individual metal grains in H ordinary chondrites by laser ablation inductively coupled plasma mass spectrometry to investigate their formation. We analyzed unequilibrated ordinary chondrites (H3) to constrain processes affecting the metal before accretion, and inferred the effects of metamorphism by comparing their elemental compositions to those of equilibrated chondrites (H4–H6). Our results highlight large variations of refractory (Re, Os, W, Ir, Ru, Mo, Pt) and moderately volatile siderophile element (Pd, Au, Ga, Ge) concentrations among metal grains in H3 samples that permit to classify them according to their Ge/Ir ratios and HSE contents. These intergrain variations are progressively homogenized in H4–H6 samples due to their increasing degrees of metamorphism. To constrain the origin of the metal, we modeled its evolution during melting and crystallization. Our melting model of a single metallic precursor containing 1.5 wt.% C and up to 12 wt.% S reproduces well the observed range of siderophile element compositions in the metal. Metal grains show a range of W, Mo, and Ga compositions that we interpret to reflect various local (grain-scale) oxidation states during the melting event(s) due to the heterogeneous distribution of various oxidizing components within the precursors. The very similar HSE compositions of H and L/LL metal grains suggests that the variations of bulk metal abundance and HSE concentrations observed among the different classes of ordinary chondrites (H, L, LL) result from the heterogeneous physical distribution of a relatively chemically homogeneous metal component among OC parent bodies, and not from a chemical (sensu lato) gradient between H and LL chondrites.