¹R. J. Curtis,¹H. C. Bates,¹T. J. Warren,¹K. A. Shirley,¹E. C. Brown,¹A. J. King,¹N. E. Bowles
Meteoritics & Planetary Scince (in Press) Link to Article [https://doi.org/10.1111/maps.14055]
¹Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford, UK
²Earth Sciences, Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

A laboratory study was performed using the Visible Oxford Space Environment Goniometer in which the broadband (350–1250 nm) bidirectional reflectance distribution function (BRDF) of the Winchcombe meteorite was measured, across a range of viewing angles—reflectance: 0°–70°, in steps of 5°; incidence: 15°, 30°, 45°, and 60°; and azimuthal: 0°, 90°, and 180°. The BRDF dataset was fitted using the Hapke BRDF model to (1) provide a method of comparison to other meteorites and asteroids, and (2) to produce Hapke parameter values that can be used to extrapolate the BRDF to all angles. The study deduced the following Hapke parameters for Winchcombe: w = 0.152 ± 0.030, b = 0.633 ± 0.064, and h_S = 0.016 ± 0.008, demonstrating that it has a similar w value to Tagish Lake (0.157 ± 0.020) and a similar b value to Orgueil (0.671 ± 0.090). Importantly, the surface profile of the sample was characterized using an Alicona 3D® instrument, allowing two of the free parameters within the Hapke model φ and �¯, which represent porosity and surface roughness, respectively, to be constrained as φ = 0.649 ± 0.023 and �¯ = 16.113° (at 500 μm size scale). This work serves as part of the characterization process for Winchcombe and provides a reference photometry dataset for current and future asteroid missions.

¹Guy Libourel,²Pierre Beck,³Akiko M. Nakamura,⁴Pierre Vernazza,⁵Clement Ganino,¹Patrick Michel
The Planetary Science Journal 4, 123 Open Access Link to Article [DOI 10.3847/PSJ/ace114]
¹Université Côte d’Azur, Lagrange, Observatoire de la Côte d’Azur, CNRS, Nice, France
²UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble, Grenoble, France
³Graduate School of Science, Kobe University, Japan
⁴Université Aix-Marseille, CNRS, Laboratoire d’Astrophysique de Marseille, Marseille, France
⁵Université Côte d’Azur, Géoazur, Observatoire de la Côte d’Azur, CNRS, Valbonne, France

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¹Aimee Smith,¹Rhian H. Jones
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14051]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester, UK
Published by arrangement with John Wiley & Sons

In the CR (Renazzo-like) chondrite group, many chondrules have successive igneous rim (IR) layers, with an outer layer that contains a silica mineral and/or silica-rich glass (silica-rich igneous rims, SIRs). Models for SIR formation include (1) accretion of Si-rich dust onto solid chondrule surfaces, followed by heating and cooling and (2) condensation of SiO(gas) onto the surface of partially molten chondrules. We evaluate these models, based on a petrographic study of five Antarctic CR chondrites that have undergone minimal secondary alteration. We obtained electron microprobe analyses of minerals and glass with quantitative wavelength-dispersive spectroscopy mapping, and identified silica polymorphs with Raman spectroscopy. Common SIRs contain silica, low-Ca pyroxene, Ca-rich pyroxene, Fe,Ni metal, ± glass ± plagioclase ± rare olivine. We also describe near-monomineralic SIRs where a narrow zone of cristobalite occurs at the outer edge of the chondrule. All crystalline silica is cristobalite, except for one SIR that consists of tridymite. Some rims contain silica-rich glass (>80 wt% SiO2) but no silica mineral. Features such as sharp interfaces and compositional boundaries between chondrules and SIRs indicate that SIRs were formed from solid precursors. Consideration of the stability fields of silica polymorphs and computed liquidus temperatures indicates that SIRs were heated to >1500°C for limited time periods, followed by rapid cooling, similar to conditions for chondrule formation. We infer that in the CR chondrule formation region, the same heating mechanism was repeated multiple times while the chemical composition of the nebular gas evolved to highly fractionated silica-rich compositions.

¹Isaac J. Onyett,¹Martin Schiller,¹Georgy V. Makhatadze,¹Zhengbin Deng,^1,2Anders Johansen,^1,3Martin Bizzarro
Nature 619, 539-544 Open Access Link to Article [DOI https://doi.org/10.1038/s41586-023-06135-z]
¹Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Copenhagen, Denmark
²Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Lund, Sweden
³Institut de Physique du Globe de Paris, Université de Paris Cité, Paris, France

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¹Katelyn R. Frizzell,¹Lujendra Ojha,²Suniti Karunatillake
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115700]
¹Department of Earth and Planetary Sciences, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
¹Louisiana State University, Baton Rouge, LA, USA
Copyright Elsevier

The thermal evolution of terrestrial planets is primarily modulated by the distribution of heat-producing elements (HPE) within the crust and mantle. Chemical data from Martian meteorites suggest that Mars differentiated early, which led to an early partitioning of incompatible heat-producing elements in the crust. Previous estimates of Martian crustal heat flow that used the bulk regolith abundances of HPEs from the Gamma-Ray Spectrometer (GRS) suite on Mars Odyssey spacecraft have further corroborated this view of Mars, albeit with poorly known crustal column representativeness. Here we couple the GRS-derived chemical maps of Mars with estimates of crustal thickness and density from the InSight lander to revise the estimated Martian crustal heat flow. The mean crustal heat flow values range from 3.0 to 13.9 mW m⁻² for the endmember gravity-derived crustal thickness models anchored by constraints from InSight. We also estimate the crustal heat flow from other factors such as the distribution of HPEs with depth and the Uranium content of the crust. Our results suggest that the mean crustal heat flow varies substantially across models, with the highest mean values being associated with higher densities and an increased enrichment of HPEs with depth. Further work is needed to constrain the crustal thickness of Mars, as the largest uncertainties in the estimate of crustal heat flow stem from uncertainty in the crustal thickness estimates, not geochemical variability. The results from this work corroborate previous estimates of a strong fractionation of heat-producing elements into the Martian crust.

• ¹Craig Robert Walton et al. (>10)
  Geochmica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.07.012]
  ¹University of Cambridge, Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, United Kingdom
  Copyright Elsevier
  

The thermal history of asteroids is recorded by the radioisotopic ages of meteorites that derive from them. Radioisotopic ages may date a number of events, such as the cooling of a parent body during waning radiogenic metamorphism, rapid cooling experienced upon parent body break-up, and/or subsequent collision-induced reheating of material. However, sampling statistics for meteorite radioisotope ages are currently relatively low and most are derived from analyses of bulk material, therefore lacking the in-situ microtextural context that aids in distinguishing collisional events. Here, we present new in-situ apatite U-Pb ages for nine L chondrite meteorites using secondary ionisation mass spectrometry.

Our measurements greatly expand the L chondrite phosphate U-Pb age record and provide evidence for distinct stages in the thermal evolution of the L chondrite parent asteroid, including: early collisions driving parent body fragmentation- and/or exhumation-associated cooling at > 4530 Ma; onion-shell-style cooling with waning radiogenic metamorphism until 4500 Ma; late collisional reheating from 4480–4460 Ma; parent body break-up at 474± 22 Ma; and recent ejection events within several 10s of Myr of present day. We show that meteorite shock stage correlates with upper intercept age but is uncorrelated with lower intercept age. This outcome links the upper intercept ages alone to the preserved high-energy impact-related features in strongly shocked meteorites, which has important implications for our interpretation of the L chondrite U-Pb record.

We see no evidence in our record for collisional episodes between 3000–4400 Ma, i.e., the Late Heavy Bombardment. Our upper intercept age record hints that collision rates changed as a result of some dynamical instability at 4460–4480 Ma, which may have strongly depleted the main asteroid belt, and/or that L asteroid physical structure changed such that the shock metamorphic response to collisions was muted after this time, e.g., by the formation of weak rubble pile bodies. L chondrite phosphate U-Pb ages provide evidence for a heterogeneous early and shared late (less than 500 Ma) thermal history for the majority of L chondrite meteorites falling to Earth today. From this observation, we infer that most L chondrites derive from a single parent asteroid (in existence from around 4500–4440 Ma to 474± 22 Ma), which has since been disturbed to create an asteroid family. Our record of meteorite U-Pb ages traces out the thermal and dynamical evolution of the L chondrite asteroid. These observations can be used in future to benchmark dynamical models of Solar System evolution.

¹Helen Grant,¹Romain Tartèse,¹Rhian Jones,²Laurette Piani,²Yves Marrocchi,³Ashley King,²Thomas Rigaudier
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14041]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester, UK
²CNRS, CRPG, UMR 7358, Université de Lorraine, Vandoeuvre les Nancy, France
³Planetary Materials Group, Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

The origin and transport of water in the early Solar System is an important topic in both astrophysics and planetary science, with applications to protosolar disk evolution, planetary formation, and astrobiology. Of particular interest for understanding primordial water transport are the unequilibrated ordinary chondrites (UOCs), which have been affected by very limited alteration since their formation. Using X-ray diffraction and isotope ratio mass spectrometry, we determined the bulk mineralogy, H2O content, and D/H ratios of 21 UOCs spanning from petrologic subtypes 3.00–3.9. The studied UOC falls of the lowest subtypes contain approximately 1 wt% H2O, and water abundance globally decreases with increasing thermal metamorphism. In addition, UOC falls of the lowest subtypes have elevated D/H ratios as high as those determined for some outer Solar System comets. This does not easily fit with existing models of water in the protoplanetary disk, which suggest D/H ratios were low in the warm inner Solar System and increased radially. These new analyses confirm that OC parent bodies accreted a D-rich component, possibly originating from either the outer protosolar nebula or from injection of molecular cloud streamers. The sharp decrease of D/H ratios with increasing metamorphism suggests that the phase(s) hosting this D-rich component is readily destroyed through thermal alteration.

¹Rider-Stokes B.G. et al. (>10)
Nature Astronomy (in Press) Link to Article [DOI 10.1038/s41550-023-01968-0]
¹School of Physical Sciences, The Open University, Milton Keynes, United Kingdom

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¹Rochette, Pierre et al. (>10)
Comptes Rendus – Geoscience 355, 145-155 Open Access Link to Article [DOI 10.5802/crgeos.206]
¹Aix-Marseille Univ, CNRS, IRD, INRAE, UM 34 CEREGE, Aix-en-Provence, France

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¹Tadeusz A. Przylibski,²Magdalena Długosz-Lisiecka,¹Katarzyna Łuszczek,¹Konrad Blutstein
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14050]
¹Faculty of Geoengineering, Mining and Geology, Wrocław University of Science and Technology, Wrocław, Poland
²Institute of Applied Radiation Chemistry, Łódź University of Technology, Łódź, Poland
Published by arrangement with John Wiley & Sons

We used two different methods of statistical analysis—cluster analysis and principal component analysis—to analyze the concentrations of principal chemical components (Si, Mg, Ca, Fe, Ni) and Co in ordinary chondrites. The analysis is based predominantly on published data (metadata). In total, chemical composition data from 646 ordinary chondrites were used in the statistical analysis. The aim of this analysis was to establish whether it would be possible or not to distinguish H, L, and LL chondrites based on the concentrations of major elements and Co in their bulk chemical compositions. It was also important to determine what conclusions such an analysis could enable to draw about matter differentiation in the formation environments of primordial parent bodies of particular ordinary chondrite groups (H, L, and LL). Another aim of the statistical analysis was to determine whether the distribution of Fe and Ni (with Co admixtures) is independent of petrographic types within particular groups of chondrites. This is of crucial importance for determining the distribution of FeNi(Co) ore occurrences in potential extraterrestrial deposits on modern asteroids—the sources of ordinary chondrites. The obtained results of statistical analyses confirmed that a clear-cut distinction between particular groups of ordinary chondrites is only possible for group H, while distinguishing L chondrites from LL chondrites is not always obvious. The results of the statistical analyses relating to the question of the possible existence of several primordial parent bodies (formation environments) of each group of ordinary chondrites are consistent with the results of contemporary astronomical spectroscopy research. What is particularly interesting is obtaining indications of the existence of common formation environments of the matter of L and LL chondrites, possibly on a few primordial parent bodies. The statistical analyses indicate that there is no correlation between the concentration of principal chemical components and the petrographic type of ordinary chondrites. This proves homogenous distributions of these elements within the parent bodies of each group of ordinary chondrites. Hence, the distribution of these elements in individual present-day asteroids is also homogenous.