¹Samuel D. Crossley,¹Richard D. Ash,^1,2Jessica M. Sunshine,³Catherine M. Corrigan,³Timothy J. McCoy,⁴David W. Mittlefehldt,¹Igor S. Puchtel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13558]
¹Department of Geology, University of Maryland, College Park, Maryland, 20742 USA
²Department of Astronomy, University of Maryland, College Park, Maryland, 20742 USA
³Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, 20560‐0119 USA
⁴Mail Code SR, NASA/Johnson Space Center, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

Petrogenetic relationships among members of the brachinite family were established by analyzing major and trace element concentrations of minerals for 9 representative specimens: Al Huwaysah 010, Eagles Nest, Northwest Africa (NWA) 4882, NWA 5363, NWA 7297, NWA 7299, NWA 11756, Ramlat as Sahmah (RaS) 309, and Reid 013. The brachinite family, which includes brachinites and ungrouped achondrites with compositional and isotopic similarities to brachinites, comprises FeO‐rich, olivine‐dominated achondrites whose compositional and mineralogic variability is correlated with oxidation state. Most classical brachinites are derived from precursors that were more oxidized and sulfur‐rich than those of ungrouped “brachinite‐like” achondrites. This is manifest in the distinct Fe‐Ni‐S systems among brachinite family precursors, which were sulfide‐dominated for the most oxidized brachinites and metal‐dominated for the least oxidized brachinite‐like achondrites. Consequently, highly siderophile element behavior was controlled through melting and removal of their dominant host phase in the precursor, which was likely pentlandite in sulfide‐dominated systems and kamacite/taenite in metal‐dominated systems. Anomalous Ir/Os and Pt/Os ratios of oxidized brachinites may be attributed to selective complexing during melting of As‐rich pentlandite, consistent with our observations of impact‐melted sulfides in R chondrite NWA 11304, although further experimental work is needed to model this process. The apparent redox trend among the brachinite family is consistent with silicate FeO content and Fe/Mn ratios, which may be used as a proxy for determining the relative oxidation state of brachinite family members. Based on our analyses, we make several recommendations for reclassification of samples into a continuum of oxidized to reduced endmembers for the brachinite family. Along with a common range of Δ17O, this evidence is consistent with either formation on a common heterogeneous parent body, or at least from the same nebular reservoir, with variable O and S fugacities, resulting in mineralogically distinct igneous products for oxidized and reduced endmembers. Sulfur‐bearing, oxidized differentiation may extend to other bodies that formed at or beyond the snow line in the early solar system, and should be considered when interpreting observational data for asteroids in upcoming missions.

¹C. P. Opeil,^2,3D. T. Britt,⁴R. J. Macke,⁴G. J. Consolmagno
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13556]
¹Department of Physics, Boston College, 140 Commonwealth Ave., Chestnut Hill, Massachusetts, 02467 USA
²Department of Physics, University of Central Florida, 4111 Libra Dr., Orlando, Florida, 32816 USA
³The Center of Lunar and Asteroid Surface Science, 12354 Research Pkwy Suite 214, Orlando, Florida, 32826 USA
⁴Vatican Observatory, V‐00120 Vatican City State
Published by arrangement with John Wiley & Sons

Measurements of the low‐temperature thermodynamic and physical properties of meteorites provide fundamental data for the study and understanding of asteroids and other small bodies. Of particular interest are the CM carbonaceous chondrites, which represent a class of primitive meteorites that record substantial chemical information concerning the evolution of volatile‐rich materials in the early solar system. Most CM chondrites are petrographic type 2 and contain anhydrous minerals such as olivine and pyroxene, along with abundant hydrous phyllosilicates contained in the meteorite matrix interspersed between the chondrules. Using a Quantum Design Physical Property Measurement System, we have measured the thermal conductivity, heat capacity, and thermal expansion of five CM2 carbonaceous chondrites (Murchison, Murray, Cold Bokkeveld, Northwest Africa 7309, Jbilet Winselwan) at low temperatures (5–300 K) which span the range of possible surface temperatures in the asteroid belt and outer solar system. The thermal expansion measurements show a substantial and unexpected decrease in CM2 volume as temperature increases from 210 to 240 K followed by a rapid increase in CM2 volume as temperature rises from 240 to 300 K. This transition has not been seen in anhydrous CV or CO carbonaceous chondrites. Thermal diffusivity and thermal inertia as a function of temperature are calculated from measurements of density, thermal conductivity, and heat capacity. Our thermal diffusivity results compare well with previous estimates for similar meteorites, where conductivity was derived from diffusivity measurements and modeled heat capacities; our new values are of higher precision and cover a wider range of temperatures.

¹Philipp Gleißner,¹Harry Becker
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13557]
¹Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstr 74‐100, 12249 Berlin, Germany
Published by arrangement with John Wiley & Sons

Mass fractions of the siderophile volatile elements S, Se, and Te were determined together with highly siderophile elements (HSE) and osmium isotope ratios in multiple aliquots of five lunar mafic impact melt breccias. The impactites were sampled from presumably Imbrium‐related ejecta deposits at the Apollo 14, 15, and 16 landing sites. As in many mafic impact melt breccias, all studied impactites display fractionated siderophile element patterns characteristic of differentiated metal, interpreted to reflect metal‐rich impactor material from the core of a differentiated planetesimal. The compositional record of Fra Mauro crystalline matrix breccias and recent constraints on the time of their formation suggest that the admixture of this differentiated metal component to the Procellarum KREEP Terrane occurred before the Imbrium basin was formed. The impact melt rock portion of dimict breccia 61015 displays fractionations of HSE like other mafic impact melt breccias, but CI chondrite‐like ratios of S, Se, Te, and Ir. Preservation of these contrasting impactor signatures in a single impactite sample demonstrates mixing of differentiated metal and CI chondrite‐like impactor material and their homogenization in an impact melt sheet. Correlations of highly siderophile element ratios between impactites from different Apollo landing sites suggest that siderophile element inventories of many lunar impactites were affected by similar mixing processes. Mass fractions and ratios of S, Se, and Te in other mafic impact melt breccias closely resemble those of pristine mafic target rocks.

^1,2,3Jing Yang,³Yangting Lin,^3,4,5Hitesh Changela,³Liewen Xie,⁶Bin Chen,³Jinhui Yang
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13559]
¹Department of Earth and Space Sciences, Southern University of Science and Technology, Shenzhen, 518055 China
²School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026 China
³Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
⁴Qianxuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing, 100029 China
⁵Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, 87131 USA
⁶Department of Earth and Space Sciences, Southern University of Science and Technology, Shenzhen, 518055 China
Published by arrangement with John Wiley & Sons

The ungrouped achondrite Northwest Africa (NWA) 7325 parent body underwent a severe impact after primary crystallization, which completely melted plagioclase and partially melted pyroxene, followed by Mg diffusion into the adjacent plagioclase‐melt. The 26Al‐26Mg system was therefore modified, forming a pseudoisochron with an initial δ26Mg* of 0.094 ± 0.005‰ and an age of 4563.12 ± 0.33 Ma between the primary crystallization and subsequent impact event(s). The positive initial δ26Mg* can be interpreted by a model age of ~1.77 Ma after CAIs when a chondritic composition differentiated into a magma/rock with the Al/Mg ratio equivalent to that of NWA 7325 (~1.52). The LREE enrichments and a positive Eu anomaly suggest that the NWA 7325 parent magma formed by the melting of a plagioclase‐rich crustal lithology, which crystallized from a magma ocean. Differentiation of the magma ocean was prior to 1.77 Ma after CAIs. NWA 7325 is also unique by containing many rounded voids (5–6 vol%) interstitial to or enclosed in silicates, suggested to have formed by the leaching/vaporization of pre‐existing Fe‐Ca‐Mg‐Mn sulfides. This is supported by the similar morphology between voids and Cr‐bearing troilites, the discovery of relict oldhamite, and the highly reducing conditions of NWA 7325. The loss of pre‐existing sulfides could explain the unusual subchondritic Mn/Mg ratio of the bulk sample. Furthermore, the enrichment of moderately volatile elements (K/Th ratio ~2600–10,000) in the NWA 7325 parent body may result from the bonding with S2‐ in silicate melts under highly reducing conditions. NWA 7325 therefore provides evidence of sulfur‐rich magmatism in the early solar system.

¹Jean‐Pierre Lorand^2,3,4Jabrane Labidi,⁴Claire Rollion‐Bard,⁵Emilie Thomassot,⁶Jeremy J. Bellucci,⁷Martin Whitehouse,⁷Alexander Nemchin,⁸Munir Humayun,³James Farquhar,^9,10Roger H. Hewins,⁹Brigitte Zanda,⁹Sylvain Pont
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13564]
¹Laboratoire de Planétologie et Géodynamique à Nantes, CNRS, UMR 6112, Université de Nantes, 2 Rue de la Houssinère, BP 92208, 44322 Nantes Cédex 3, France
²Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, 20015 USA
³Department of Geology, University of Maryland, College Park, Maryland, 20740 USA
⁴Institut de physique du globe de Paris, CNRS, Université de Paris, F‐75005 Paris, France
⁵CRPG‐CNRS, Nancy, 54500 France
⁶Department of Applied Geology, Curtin University, Perth, Western Australia, 6845 Australia
⁷Laboratory for Isotope Geology, Swedish Mus. of Nat History, Stockholm, SE‐104 05 Sweden
⁸Department of Earth, Ocean & Atmospheric Science and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, 32310 USA
⁹Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC) ‐ Sorbonne, Université‐ Muséum National d’Histoire Naturelle, UPMC Université Paris 06, UMR CNRS 7590, IRD, UMR 206, 61 rue Buffon, 75005 Paris, France
¹⁰Department of Earth & Planetary Sciences, Rutgers University, Piscataway, New Jersey, 08854 USA
Published by arrangement with John Wiley & Sons

The sulfur isotope budget of Martian regolith breccia (NWA 7533) has been addressed from conventional fluorination bulk rock analyses and ion microprobe in situ analyses. The bulk rock analyses yield 865 ± 50 ppm S in agreement with LA‐ICP‐MS analyses. These new data support previous estimates of 80% S loss resulting from terrestrial weathering of NWA 7533 pyrite. Pyrite is by far the major S host. Apatite and Fe oxyhydroxides are negligible S carriers, as are the few tiny igneous pyrrhotite–pentlandite sulfide grains included in lithic clasts so far identified. A small nonzero Δ33S (−0.029 ± 0.010‰) signal is clearly resolved at the 2σ level in the bulk rock analyses, coupled with negative CDT‐normalized δ34S (−2.54 ± 0.10‰), and near‐zero Δ36S (0.002 ± 0.09‰). In situ analyses also yield negative Δ33S values (−0.05 to −0.30‰) with only a few positive Δ33S up to +0.38‰. The slight discrepancy compared to the bulk rock results is attributed to a possible sampling bias. The occurrence of mass‐independent fractionation (MIF) supports a model of NWA 7533 pyrite formation from surface sulfur that experienced photochemical reaction(s). The driving force that recycled crustal S in NWA 7533 lithologies—magmatic intrusions or impact‐induced heat—is presently unclear. However, in situ analyses also gave negative δ34S values (+1 to −5.8‰). Such negative values in the hydrothermal setting of NWA 7533 are reflective of hydrothermal sulfides precipitated from H2S/HS‐ aqueous fluid produced via open‐system thermochemical reduction of sulfates at high temperatures (>300 °C).

¹Ramakant R. Mahajan
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13565]
¹Physical Research Laboratory, Ahmedabad, Gujarat, 380009 India
Published by arrangement with John Wiley & Sons

Noble gases and nitrogen are investigated in eight individual chondrules of the Dhajala H3.8 chondrite. The mean cosmic ray exposure age of the chondrules using 21Ne and 38Ar is 5.9 ± 3.0 Ma. There is no significant evidence of a pre‐exposure for these chondrules. All the measured chondrules contain variable amounts of radiogenic 129Xe. Noble gas analysis indicates Q‐type gas incorporated in the chondrules. The chondrules have variable amounts of N2. The chondrules have distinct trapped N isotopic composition (δ15Nt varies from −24.1 ± 8.4‰ to 89.1 ± 12.7‰), which is inconsistent with Q‐gas and solar wind. These inconsistencies can be considered preliminary evidence in support of multiple trapped components in the chondrules. A heavy N signature component is observed in the chondrules studied contrasted with the solar wind composition. There is no correlation between the concentration of N2 and noble gases. Derivations of variable nitrogen observed in Dhajala (H3.8) chondrules reflect the gas captured at the time of formation, having heterogeneous isotopic signature in the nebula.

¹Mizuho Koike,^2,3Yuji Sano,^1,2Naoto Takahat,⁴ Tsuyoshi Iizuka,^4,5Haruka Ono,^4,5Takashi Mikouchi
Earth and Planetary Science Letters 549, 116497 Link to Article [https://doi.org/10.1016/j.epsl.2020.116497]
¹Earth and Planetary Systems Science Program, Graduate School of Advanced Science and Engineering, Hiroshima University, 1-3-1 Kagamiyama, Higashihiroshima-shi, Hiroshima, 739-8526, Japan
²Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, 277-8564, Japan
³Institute of Surface-Earth System Science, Tianjin University, Nankai District, Tianjin, 300072, PR China
⁴Department of Earth and Planetary Science, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan
⁵The University Museum, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan
Copyright Elsevier

The late heavy bombardment (LHB) hypothesis, wherein the terrestrial planets are thought to have suffered intense collisions ca. 3.9 billion years ago, is under debate. Coupled with new dynamical calculations, re-examination of geochronological data seem to support an earlier solar system instability and a smooth monotonic decline in impacts, as opposed to a “cataclysm.” To better understand this collisional history, records from the asteroidal meteorites are required. Here, we report a uranium–lead (U–Pb) chronological dataset for eucrite meteorites thought to originate from the asteroid 4 Vesta; this dataset indicates to a continuous history of collisions prior to 4.15 Ga. Our 207Pb⁎/206Pb⁎ model ages of apatite [Ca5(PO4)3(F,Cl,OH)] and merrillite [Ca9NaMg(PO4)7] from three brecciated basaltic eucrites—Juvinas (4150.3 ± 11.6 million years ago (Ma); merrillite only), Camel Donga (disturbed around 4570–4370 Ma), and Stannern (4143.0 ± 12.5 Ma)—record multiple thermal metamorphic events during the period of ∼4.4–4.15 Ga. We interpret this to mean that Vesta or the vestoid cluster underwent multiple impacts and moderate high-temperature reheating during this time. The ages of ∼4.4–4.15 Ga are distinctly younger than the initial magmatic process on Vesta (>4.5 Ga) but are significantly older than a later “impact peak” based on some interpretations of 40Ar–39Ar chronologies (∼3.9–3.5 Ga). The intense collisions prior to 4.15 Ga on Vesta are at odds with the conventional LHB hypothesis but not inconsistent with the much earlier bombardment and monotonic decline scenario. Different radiometric chronologies of the asteroid likely represent the different stages of a continual collisional process. Conversely, the model 207Pb⁎/206Pb⁎ ages of apatite in the unbrecciated basaltic eucrite, Agoult, returned an age of 4524.8 ± 9.6 Ma. This may represent slow cooling from an earlier global reheating of the crust on Vesta at 4.55 Ga, as documented by other radiometric chronologies. The apatite in Juvinas recorded a coincident timing of 4516.9 ± 10.4 Ma, which could be due to either slow crustal cooling or impact.

¹Giampaolo P. Sighinolfi,^1,2Federico Lugli,¹Federica Piccione,³Vincenzo DE Michele,^1,4Anna Cipriani
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13550]
¹Department of Chemical and Geological Sciences, University of Modena and Reggio Emilia, Via Campi 103, Modena, 41225 Italy
²Department of Cultural Heritage, University of Bologna, Via degli Ariani 1, Ravenna, 48121 Italy
³Museo di Storia Naturale, Milan, 20121 Italy
⁴Lamont‐Doherty Earth Observatory, Columbia University, Palisades, New York, 10964 USA
Published by arrangement with john Wiley & Sons

Strontium isotopes and selected trace elements (Rb, Sr, REE, Zr, Hf, Th, and U) were measured on samples of Libyan Desert Glass (LDG) and a series of terrestrial materials (rocks, LDG‐bearing soils, eolic sand) collected over a large area of southwestern Egypt to identify the LDG terrestrial parent material and the site where impact melting occurred. Samples include Upper Cretaceous hypersilicic sandstones outcropping at or near the LDG strewn field and Lower Cretaceous to Silurian sandstones from the Gilf Kebir Plateau highlands. Strontium isotopes and partially Zr, Hf, Th, and U, possibly reflecting the composition of detrital zircon grains, are effective indicators of the geochemical affinity between terrestrial materials and LDG, unlike Rb, Sr, and REE abundances. The best geochemical affinity with LDG was found in LDG‐bearing soils collected at the base of intradunal corridors in the Great Sand Sea. Remarkably, abundances of the Zr group elements of the LDG Zr‐bearing phase are distinct from all terrestrial detrital zircons from the area. We suggest a mixture of weathering products from sandstones of different ages, including Devonian and Silurian rocks from the Gilf Kebir highlands, as the most likely source for LDG. A loose sedimentary formation exposed 29 Ma ago at the Earth’s surface, superimposed over hard bedrock, might have been the true terrestrial target of the impact, but because of its incoherent nature, it was rapidly destroyed, explaining the complete absence of any evidence of an impact structure.

^1,2James S. New,³Bahar Kazemi,²Mark C. Price,²Mike J. Cole,²Vassi Spathis,^1,3Richard A. Mathies,²Anna L. Butterworth
Meteoritics & Planetary Science (in Press) Link to Articie [https://doi.org/10.1111/maps.13554]
¹Space Sciences Laboratory, University of California, Berkeley, California, 94720 USA
²School of Physical Sciences, University of Kent, Canterbury, Kent, CT2 7NH UK
³Department of Chemistry, University of California, Berkeley, California, 94720 USA
Published by arrangement with John Wiley & Sons

Enceladus is a compelling destination for astrobiological analyses due to the presence of simple and complex organic constituents in cryovolcanic plumes that jet from its subsurface ocean. Enceladus plume capture during a flyby or orbiter mission is an appealing method for obtaining pristine ocean samples for scientific studies of this organic content because of the high science return, reduced planetary protection challenges, and lower risk and expense compared to a landed mission. However, this mission profile requires sufficient amounts of plume material for sensitive analysis. To explore the feasibility and optimization of the required capture systems, light gas gun experiments were carried out to study organic ice particle impacts on indium surfaces. An organic fluorescent tracer dye, Pacific Blue™, was dissolved in borate buffer and frozen into saline ice projectiles. During acceleration, the ice projectile breaks up in flight into micron‐sized particles that impact the target. Quantitative fluorescence microscopic analysis of the targets demonstrated that under certain impact conditions, 10–50% of the entrained organic molecules were captured in over 25% of the particle impacts. Optimal organic capture was observed for small particles (d ~ 5–15 µm) with velocities ranging from 1 to 2 km s−1. Our results reveal how organic capture efficiency depends on impact velocity and particle size; capture increases as particles get smaller and as velocity is reduced. These results demonstrate the feasibility of collecting unmodified organic molecules from the Enceladus ice plume for sensitive analysis with modern in situ instrumentation such as microfluidic capillary electrophoresis (CE) analysis with ppb organic sensitivity.

^1,2D. Ostrowski,^1,2K. Bryson
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13562]
¹NASA Ames Research Center, Mountain View, California, 94035 USA
²Bay Area Environmental Research Institute, NASA Ames Research Center, Mountain View, California, 94035 USA
Published by arrangement wit John Wiley & Sons

Meteorites provide vast amounts of information on the makeup and history of the solar system. The physical properties help to understand meteor behavior in the atmosphere, model characteristics of parent bodies, and determine methods to deflect potentially hazardous objects. Density and porosity are two of the most important physical properties. All the examined ordinary chondrite falls have bulk densities and porosities near their respected class averages. Most of the studied Antarctic ordinary chondrites have porosities around 12% or higher caused by weathering, placing them near the top of the range of values for chondritic falls. A trend is observed in acoustic velocity, where any meteorite with porosity over 10% has a longitudinal velocity near half the value of the class average. Low porosity meteorites such as Tenham, Chelyabinsk impact melt, and MIL07036 have velocities well above their class averages. Emissivities across all meteorites follow the trend of decreasing emissivity with increasing temperature.