¹Ming Ma,¹Jingran Chen,²Clive R. Neal,^3,4Shengbo Chen,¹Bingze Li,¹Chenghao Han,¹Peng Tian
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115464]
¹School of Surveying and Exploration Engineering, Jilin Jianzhu University, Changchun, China
²Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA
³School of Geo-Exploration Science and Techniques, Jilin University, Changchun, China
⁴Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei, China
Copyright Elsevier

High alumina (HA) mare basalts play unique roles in understanding the heterogeneity of lunar mantle. Their presence was confirmed by the Apollo and Luna samples, and their remote sensing identification was implemented using HA sample FeO, TiO₂ and Th concentration constraints. This study selected the surfaces with ~0.5% rock abundance as windows into HA basalts identification. The lithology of these rock pixels was first classified based on thorium maps from the Lunar Prospector and major element oxide products from Diviner data onboard the Lunar Reconnaissance Orbiter (LRO). Then, the LRO Diviner Al₂O₃ (~11 wt%) concentration constraint was applied in the mare basalt rock pixels across the Moon. The mare-highland mixtures were distinguished from HA basalt rocks based on the positive linear relationships between Al₂O₃ and Mg# in the adjacent pixels for four impact vector directions away from each candidate HA pixel. These HA basalts rock pixels identified by this study indicate that HA basalts are concentrated locally in South Pole-Aitken (SPA) basin, Schiller-Schickard region and 13 maria such as southern and northern Oceanus Procellarum, central Humorum, Tranquillitatis, Fecunditatis and Serenitatis, northern Imbrium and southern Nubium, but are seldom found in Mare Moscoviense and Orientale regions on the farside. Detailed investigations in Mare Fecunditatis found that fifteen HA basalt units or patches could be confidently identified. These HA basalts have the total area and volume of <77,658 km² and < 54,301 km³, and the maximum depth and thickness of 1147 m and 1062 m respectively. In addition, analyses of the HA rocks indicated that the HA basalts are discontinuous and have variable thicknesses.

¹Zhongtian Zhang,¹David Bercovici,²Linda T. Elkins-Tanton
Earth and Planetary Science Letters (in Press) Link to Article [https://doi.org/10.1016/j.epsl.2023.118019]
¹Department of Earth and Planetary Sciences, Yale University, New Haven, CT, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
Copyright Elsevier

Primitive achondrites represent residual mantle material of planetesimals from which up to 20% partial melts were extracted. Melting experiments on chondritic compositions suggest that melts produced by ≲20% partial melting are rich in silica and alkali elements. Such melts are highly viscous (≳103Pa⋅s), and percolation models predict that they would only migrate negligible distances over timescales of 1–10Myr. After these timescales, a planetesimal would either be melted into a magma ocean by radiogenic heating from Al26, if it formed early; or it would cool below solidus, if it formed relatively late. However, melt migration is also controlled by permeability, which could be high for aggregates of rock boulders (compared to those of mineral grains). Specifically, the theory of planet formation suggests that collisions occurred frequently between planetesimals in the early solar system. These collisions may have shattered the planetesimals into fragments with sizes of meters to tens of meters, which would have accreted gravitationally into one or more daughter bodies. We develop a model to investigate melt migration in “rubble-pile” planetesimals; in particular, the melt exchange between partially molten rock boulders and the void space between them. The results suggest that, with typical properties of primitive achondrite materials at the conditions of low-degree partial melting, melts may have been squeezed into the voids between boulders, and migrated rapidly through these channels. Therefore, primitive achondrites may record melt migration in rubble-pile bodies reaccreted from fragments of partially molten planetesimals.

¹Laura E. Jenkins,¹Martin R. Lee,^1,2,3Luke Daly,⁴Ashley J. King,¹Cameron J. Floyd,¹Pierre-Etienne Martin,⁴Natasha V. Almeida,⁵Matthew J. Genge
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13949]
¹School of Geographical and Earth Sciences, The University of Glasgow, Glasgow, G12 8RZ UK
²Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, 6845 Australia
³Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, New South Wales, 2006 Australia
⁴Planetary Materials Group, Natural History Museum, London, SW7 5BD UK
⁵Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ UK
Published by arrangement with John Wiley & Sons

Winchcombe is a CM chondrite that fell in England on February 28, 2021. Its rapid retrieval was well characterized. Within two polished sections of Winchcombe, terrestrial phases were observed. Calcite and calcium sulfates were found in a sample recovered from a field on March 6, 2021, and halite was observed on a sample months after its recovery from a driveway on March 2, 2021. These terrestrial phases were characterized by scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. Calcite veins crosscut the fusion crust and therefore postdate it. The calcite likely precipitated in the damp environment (sheep field) where the meteorite lay for six days prior to its retrieval. The sulfates occur on the edges of the sample and were identified as three minerals: gypsum, bassanite, and anhydrite. Given that the sulfates occur only on the sample’s edges, including on top of the fusion crust, they formed after Winchcombe fell. Sulfate precipitation is attributed to the damp fall environment, likely resulted from sulfide-derived H2S reacting with calcite within the meteorite. Halite occurs as euhedral crystals only on the surface of a polished section and exclusively in areas relatively enriched in sodium. It was likely produced by the interaction of the polished rock slice with the humid laboratory air over a period of months. The sulfates, fusion crust calcite, and halite all post-date Winchcombe’s entry into the Earth’s atmosphere and showcase how rapidly meteorite falls can be terrestrially altered.

^1,2Guy Libourel,²Kazuhide Nagashima,³Marc Portail,²Alexander N. Krot
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.01.026]
¹Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
²Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96821, USA
³CNRS-CRHEA (Centre de Recherches sur l’Hétéro-Epitaxie et ses Applications), Université Côte d’Azur, Sophia Antipolis, Rue Bernard Grégory, 06560 Valbonne, France
Copyright Elsevier

Oxygen-isotope studies of carbonaceous chondrite chondrules are of pivotal importance for understanding of the evolution of the solar protoplanetary disk. It has been previously concluded that the observed variations in Δ17O (= δ17O – 0.52×δ18O) of chondrule olivines and pyroxenes are intimately tied to their Mg# (= MgO/(MgO+FeO) ×100, mol%) and the inferred oxygen fugacity (fO2) of gaseous reservoirs produced by evaporation of disk regions with different (silicate dust ± water ice)/gas ratios. Using high resolution cathodoluminescence and secondary ion mass spectrometry, we show, in contrast to host chondrule data, that Δ17O of chondrule olivines from the Yamato 81020 CO3.05 carbonaceous chondrite is independent of their Mg# and of the imposed fO2. Instead, there is a Δ17O bimodal distribution of Mg-rich olivines that gradually turns into a unimodal distribution as Mg# decreases. We suggest that chondrules recorded an evolution of an isotopically heterogeneous vapor plume resulting from a high temperature mixing of the 16O-enriched (Δ17O ≈ −6±2‰) and 16O-depleted (Δ17O ≈ −2.5±1‰) reservoirs. Drop in the vapor plume temperature under unbuffered redox conditions favors the dissolution of Fe,Ni-metal of chondrules and the subsequent crystallization of FeO-rich olivines at saturation; the 16O-depleted signature being the most resilient at lower temperature. Chondrules are thus inferred to have formed in a same turbulent heterogeneous environment in which locally high temperatures and reducing conditions prevailed (Type I), adjacent in space and/or in time to areas submitted to lower temperatures and more oxidizing conditions (Type II). Subtracting of chondrules at different stages of the gaseous plume evolution by fast cooling rates give rise to the chemical and isotopic diversity of chondrules. No extrinsic oxidizing agents (e.g., water ice) are needed in this scenario.

¹A. Berezhnoi,^2,3YuI. Velikodsky,⁴YuV. Pakhomov,¹C. Wöhler
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2023.105648]
¹Image Analysis Group, TU Dortmund University, Otto-Hahn-Straße 4, 44227, Dortmund, Germany
²National Aviation University, Liubomyra Huzara Ave. 1, Kyiv, 03058, Ukraine
³Institute of Astronomy, V.N. Karazin Kharkіv National University, 35 Sumska Str., Kharkіv, 61022, Ukraine
⁴Institute of Astronomy of Russian Academy of Sciences, Moscow, Russia

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¹Elena Dobrica et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.02.003]
¹Hawai‘i Institute of Geophysics & Planetology, the University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
Copyright Elsevier

We have investigated several particles collected during each of two touchdowns of the Hayabusa2 spacecraft at the surface of the C-type asteroid 162173 Ryugu using various electron microscope techniques. Our detailed transmission electron microscopy study shows the presence of magnetite with various morphologies coexisting in close proximity. This is characteristic of CI chondrite-like materials and consistent with the mineral assemblages and compositions in the Ryugu parent body. We describe the microstructural characteristics of magnetite with different morphologies, which could have resulted from the chemical conditions (growth vs. diffusion rate) during their formation. Furthermore, we describe the presence of magnetites with a spherulitic structure composed of individual radiating fibers and that are characterized by pervasive, homogeneously distributed euhedral to subhedral pores that have been described in previous chondrite studies. This particular spherulitic structure is consistent with crystallization under nonequilibrium conditions. Additionally, the presence of a high density of defects within the magnetite fibers, the high surface/volume ratio of this morphology, and the presence of amorphous materials in several pores and at the edges of the acicular fibers further support their formation under nonequilibrium conditions. We suggest that the growth processes that lead to this structure result from the solution reaching a supersaturated state, resulting in adjustment to a lower free energy condition via nucleation and rapid growth.

¹Alicia Vaughan et al. (>10)
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2022JE007437]
¹Apogee Engineering, LLC, Flagstaff, AZ, US
Published by arrangement with John Wiley & Sons

A multi-instrument study of the regolith of Jezero crater floor units by the Perseverance rover has identified three types of regolith: fine-grained, coarse-grained, and mixed-type. Mastcam-Z, WATSON, and SuperCam RMI were used to characterize regolith texture, particle size, and roundedness where possible. Mastcam-Z multispectral and SuperCam LIBS data were used to constrain the composition of the regolith types. Fine-grained regolith is found surrounding bedrock and boulders, comprising bedforms, and accumulating on top of rocks in erosional depressions. Spectral and chemical data show it is compositionally consistent with pyroxene and a ferric-oxide phase. Coarse-grained regolith consists of 1-2 mm well-sorted gray grains that are found concentrated around the base of boulders and bedrock, and armoring bedforms. Its chemistry and spectra indicate it is olivine-bearing, and spatial distribution and roundedness indicate it has been transported, likely by saltation-induced creep. Coarse grains share similarities with the olivine grains observed in the Séítah formation bedrock, making that unit a possible source for these grains. Mixed-type regolith contains fine- and coarse-grained regolith components and larger rock fragments. The rock fragments are texturally and spectrally similar to bedrock within the Máaz and Séítah formations, indicating origins by erosion from those units, although they could also be a lag deposit from erosion of an overlying unit. The fine- and coarse-grained types are compared to their counterparts at other landing sites to inform global, regional, and local inputs to regolith formation within Jezero crater. The regolith characterization presented here informs regolith sampling efforts underway by Perseverance.

¹Annemiek C. Waajen,^2,3R. Prescott,¹Charles S. Cockell
Astrobiology 22, 5 Link to Article [https://doi.org/10.1089/ast.2021.0089]
¹Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh EH9 3FD, United Kingdom
²Department of Environmental Health Sciences, University of South Carolina, Columbia South Carolina, USA.
³School of Life Sciences, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, USA.

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¹Nathalie Turenne,¹Sahejpal Sidhu,¹Daniel M. Applin,¹Edward A. Cloutis,¹Z.U. Wolf,²Stanley A. Mertzman,³Elisabeth M. Hausrath,⁴Teresa Fornaro,⁵Adrian Brown
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115448]
¹Centre for Terrestrial and Planetary Exploration, University of Winnipeg, Winnipeg, Manitoba R3B 2E9, Canada
²Department of Earth and Environment, Franklin and Marshall College, P.O. Box 3003, Lancaster, PA 17604-3003, USA
³Department of Geoscience, University of Nevada, Las Vegas, NV 89154, USA
⁴INAF-Astrophysical Observatory of Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁵Plancius Research, Severna Park, MD 21146, USA
Copyright Elsevier

Spectral reflectance properties of nontronite [a phyllosilicate with an ideal formula of Na0.3Fe23+(Si,Al)4O10(OH)2·nH2O] were investigated under simulated Mars surface conditions of atmospheric pressure and composition, and after heating to 110°, 180°, and 300 °C. The data can be used to determine the conditions to which nontronites on the martian surface may have been subjected. Nontronite’s spectral features include Fe3+ associated absorption features below 1000 nm, H2O/OH features near 1400 nm, H2O features near 1900 nm, a characteristic metal-OH (Fe3+) feature in the 2280–2290 nm region, and an additional Fe-OH absorption feature near 2400 nm. Heating in a low-pressure CO2 environment leads to the loss of Fe-OH-associated features below 1000 nm at temperatures as low as 110 °C. Both OH and H2O are progressively lost upon heating to 300 °C, but small, spectrally-detectable amounts remain at 300 °C. The longer wavelength Fe-OH absorption bands in the 2280 and 2400 nm region persist up to these temperatures. Comparison to other smectites and Fe-rich phyllosilicates show that a strong 2280–2290 nm absorption feature and weak or absent ~2320 nm feature are unique to nontronite. A broader absorption feature in the 2300 nm region suggests the presence of nontronite and one or more Mg-bearing phyllosilicate(s). A Mg+Fe3+ phyllosilicate is implausible because of the difficulty in incorporating Mg2+ into the dioctahedral structure of nontronite. With increasing grain size, nontronite spectra become darker and progressively more blue-sloped beyond ~1500 nm with absorption bands showing increasing depth until saturation is reached for some of them beyond a few hundred-micron grain size. The spectral changes documented in this study, as well as a comparison to previous studies, suggest that the absorption features associated with nontronite can be used to place constraints on conditions that nontronite may have been exposed to in the past. This study demonstrates that dehydration as well as dehydroxylation can occur at temperatures <300 °C.

^1,2Ildiko Gyollai,^3,4Elias Chatzitheodoridis,^2,5Ákos Kereszturi,^1,2Máté Szabó
Meteortics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13950]
¹Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, ELKH, Budapest, Hungary
²CSFK, MTA Centre of Excellence, Konkoly Thege Miklós út 15-17, Budapest, H-1121 Hungary
³Department of Geological Sciences, School of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, Greece
⁴Network of Researchers on the Chemical Evolution of Life (NoRCEL), Leeds, UK
⁵Konkoly Thege Miklos Astronomical Institute, Research Centre for Astronomy and Earth Sciences, ELKH, Budapest, Hungary
Published by arrangement with John Wiley & Sons

We studied the occurrence of secondary minerals and inferred their formation in the Yamato-000593 Martian meteorite using multiple technological approaches such as electron probe micro analysis, optical microscope, Raman spectroscopy, scanning electron microscopy, as well as Fourier transform-infrared microscopy and spectroscopy. Two separate hydrothermal alteration events and their sequence of formation (based on superpositional relationship) can be identified: an elevated temperature phase producing high-temperature sulfidic hydrothermal alteration and a lower temperature hydrothermal alteration phase by iron-rich fluids. This meteorite shows signatures more compatible with magmatic effects, rather than impact-induced hydrothermal alteration, as has been proposed earlier. The sulfidic alteration probably formed by magmatic hydrothermal fluids, whereas iron-rich hydrothermal fluid circulation after a possible early impact event has also been proposed, when the fluids cooled down to 50 °C. Most of the secondary minerals formed at alkaline-neutral conditions, and the few observed signatures (clay–silica-bearing veins, siderite-iron-oxide veins) of briny conditions are probably from local spatial effects in larger cavities. The ferrous minerals (hematite and siderite) along the fractures could be crystallized from Fe-HCO3-bearing fluids. Alternatively, the primary magmatic minerals could have been oxidized easily (Fe-rich olivines, magnetite) during the cooling to iron oxides (hematite, goethite). The results suggest the possible existence of at least ephemerally habitable environments on Mars, mainly at volcanically heated locations. Following published geochemical models, the carbonates formed within acidic-circumneutral condition, which was followed by formation of phyllosilicates in alkaline condition.