¹Annarita Franza,²Marco Morelli,²Daniela Faggi,^1,3Giovanni Pratesi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13654]
¹Department of Earth Sciences, University of Firenze, via G. La Pira 4, 50122 Florence, Italy
²Fondazione PARSEC, Via Galcianese 20/h, 59100 Prato, Italy
³INAF‐IAPS, Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Rome, Italy
Published by arrangement with John Wiley & Sons

This work focuses on the historical and scientific investigation of a presumed meteorite fall that occurred in the Sicilian township of Marsala in 1834. Preliminary studies have classified this phenomenon as a “doubtful meteorite.” This term describes, according to the Nomenclature Committee of the Meteoritical Society, an object for which there was significant uncertainty over whether it was a real meteorite or, in some cases, whether it ever existed. Thanks to the analysis of untapped sources, the first objective of this work is to clarify the nature of the event. Subsequently, the results of the minero‐chemical analyses that were performed, in 1835, on two fragments recovered after the event are discussed for the first time. This work then shows the collecting history of one of the presumed meteorite specimens. Based on the results presented here, this work highlights the role of doubtful meteorites as a fundamental resource for the history of meteoritics and meteorite collecting as well as for studying the processes that have led to the scientific study of meteorites.

¹Aryavart Anand,^1,2Jonas Pape,¹Martin Wille,¹Klaus Mezger
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.04.029]
¹Institut für Geologie, Universität Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
²Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
Copyright Elsevier

The 53Mn-53Cr isotope systematics in ordinary chondrites constrains the accretion and thermal history of their parent bodies. Mineralogical observations and olivine-spinel geothermometry suggest that chromite in ordinary chondrites formed during prograde thermal metamorphism with the amount of chromite increasing with petrologic grades in type 3 to type 6 ordinary chondrites. Assuming a chondritic evolution of the respective parent bodies, 53Cr/52Cr model ages for chromite range from to Ma after the formation of calcium-aluminium-rich inclusions (CAIs). Chromite and silicate-metal-sulphide isochrons define an age range from to Ma. Both chromite model ages and isochron ages correlate with the petrological grade of the samples, which is consistent with an onion-shell structure of the chondrite parent bodies. The study shows that unlike the isochron ages, which are prone to impact-related disturbances or partial re-equilibration during cooling from high temperatures, the chromite model ages are not easily affected by thermal metamorphism or later events and yield robust mineral growth ages. The results are consistent with a homogenous distribution of 53Mn and an initial canonical 53Mn/55Mn = 6.28 x 10-6. The estimated closure temperatures for the Mn-Cr system in chromites range from ∼760 °C for type 6 to ∼540-620 °C for type 3 ordinary chondrites. The high closure temperatures estimated for type 3 and type 6 ordinary chondrites imply that the chromite ages correspond to the peak metamorphic temperature reached during the thermal history of the chondrite parent bodies. The oldest chromite model age obtained for type 3 samples along with the established Al-Mg chondrule formation ages constrain the accretion of the parent bodies to > 2.1 Ma after CAI formation, implying that planetesimal accretion immediately followed chondrule formation.

^1,2Du, K.,^1,3Li, S.,⁴Leya, I.,^4,5Smith, T.,⁶Zhang, D.,⁷Wang, P.
Advances in Space research (in Press) Link to Article [DOI: 10.1016/j.asr.2021.02.020]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China
²University of Chinese Academy of Sciences, Beijing, 100049, China
³Chinese Academy of Sciences Center for Excellence in Comparative Planetology, Hefei, 230026, China
⁴Physics Institute, University of Bern, Bern, CH-3012, Switzerland
⁵State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
⁶Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education, School of Geosciences and Info-physics, Central South University, Changsha, 410083, China
⁷Division of Mines and Geology, Sixth Geological Brigade, Hami, 839000, China

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¹Williams, N.H.,^2,3Fehr, M.A.,^2,4Parkinson, I.J.,³Mandl, M.B.,^1,3Schönbächler, M.
Chemical Geology 568, 120009 Link to Article [DOI: 10.1016/j.chemgeo.2020.120009]
¹The University of Manchester, School of Earth, Atmospheric and Environmental Sciences, Manchester, M139PL, United Kingdom
²The Open University, School of Environment, Earth and Ecosystem Sciences, Milton Keynes, MK7 6AA, United Kingdom
³ETH Zürich, Institute of Geochemistry and Petrology, Zürich, 8092, Switzerland
⁴University of Bristol, School of Earth Sciences, Bristol, BS8 1RJ, United Kingdom

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^1,2Peter Jenniskens et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13653]
¹SETI Institute, 189 Bernardo Avenue, Mountain View, California, 94043 USA
²NASA Ames Research Center, Moffett Field, California, 94035 USA
Published by arrangement with John Wiley & Sons

The June 2, 2018 impact of asteroid 2018 LA over Botswana is only the second asteroid detected in space prior to impacting over land. Here, we report on the successful recovery of meteorites. Additional astrometric data refine the approach orbit and define the spin period and shape of the asteroid. Video observations of the fireball constrain the asteroid’s position in its orbit and were used to triangulate the location of the fireball’s main flare over the Central Kalahari Game Reserve. Twenty‐three meteorites were recovered. A consortium study of eight of these classifies Motopi Pan as an HED polymict breccia derived from howardite, cumulate and basaltic eucrite, and diogenite lithologies. Before impact, 2018 LA was a solid rock of ~156 cm diameter with high bulk density ~2.85 g cm−3, a relatively low albedo pV ~ 0.25, no significant opposition effect on the asteroid brightness, and an impact kinetic energy of ~0.2 kt. The orbit of 2018 LA is consistent with an origin at Vesta (or its Vestoids) and delivery into an Earth‐impacting orbit via the ν6 resonance. The impact that ejected 2018 LA in an orbit toward Earth occurred 22.8 ± 3.8 Ma ago. Zircons record a concordant U‐Pb age of 4563 ± 11 Ma and a consistent 207Pb/206Pb age of 4563 ± 6 Ma. A much younger Pb‐Pb phosphate resetting age of 4234 ± 41 Ma was found. From this impact chronology, we discuss what is the possible source crater of Motopi Pan and the age of Vesta’s Veneneia impact basin.

^1,2Pierre Beck,¹Olivier Poch
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114494]
¹Institut de Planetologie et d’Astrophysique de Grenoble, UGA-CNRS, Franc
²Institut Universitaire de France, Paris, France
Copyright Elsevier

The Sloan Digital Sky Survey provides colors for more than 100,000 moving objects, among which around 10,000 have albedos determined. Here we combined colors and albedo in order to perform a cluster analysis on the small bodies population, and identify a C-cluster, a group of asteroid related to C-type as defined in earlier work. Members of this C-cluster are in fair agreement with the color boundaries of B and C-type defined in DeMeo and Carry (2013). We then compare colors of C-cluster asteroids to those of carbonaceous chondrites powders, while taking into account the effect of phase angle. We show that only CM chondrites have colors in the range of C-cluster asteroids, CO, CR and CV chondrites being significantly redder. Also, CM chondrites powders are on average slightly redder than the average C-cluster. The colors of C-cluster members are further investigated by looking at color variations as a function of asteroid diameter. We observe that the visible slope becomes bluer with decreasing asteroids diameter, and a transition seems to be present around 20 km. We discuss the origin of this variation and, if not related to a bias in the dataset – analysis, we conclude that it is related to the surface texture of the objects, smaller objects being covered by rocks, while larger objects are covered by a particulate surface. The blueing is interpreted by an increased contribution of the first reflection in the case of rock-dominated surfaces, which can scatter light in a Rayleigh-like manner. We do not have unambiguous evidence of space weathering within the C-cluster based on this analysis, however the generally bluer nature of C-cluster objects compared to CM chondrites could be to some extent related to space weathering.

^1,2Yogita Kadlag,^1,3,4MichaelTatzel,³Daniel A.Frick, ¹Harry Becker,¹Philipp Kühne
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.04.022]
¹Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, 12249 Berlin, Germany
²Universität Bern, Physikalisches Institut, Sidlerstrasse 5, 3012 Bern, Switzerland
³GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany
⁴Universität Göttingen, Geowissenschaftliches Zentrum, Abteilung Sedimentologie & Umweltgeologie, Goldschmidtstr. 1, 37077 Göttingen, Germany
Copyright Elsevier

Chondrules in undifferentiated meteorites are former silicate melt droplets of variable texture and composition. Although widely studied, the chondrule formation mechanisms and conditions that explain all properties of chondrules are yet to be identified. To further constrain the processes that affected chondrules in the solar nebula and on the meteorite parent body, we determined in situ Si isotope ratios and major and trace element compositions of minerals in chondrules of variable types and sizes from the Allende CV3 chondrite.

The δ30Si in chondrule minerals ranges from -1.28 ± 0.19 to 0.55 ± 0.20 ‰ (2SE). The δ30Si in chondrules shows no direct relationship with chondrule sizes or with distance between core and rim. Barred olivine-rich chondrules record the highest δ30Si, likely because of faster cooling and less interaction with isotopically light nebular gas. Type I non-porphyritic and some porphyritic chondrules show overall higher δ30Si compared to type II porphyritic chondrules. Furthermore, Mg-rich olivine and Mg-rich pyroxene have systematically higher δ30Si compared to Fe-rich olivine and Fe-rich pyroxene.

The variable δ30Si of type I chondrule silicates (Mg-rich) compared to type II chondrule silicates (Fe-rich) may be explained by variable interaction of chondrule silicates with the nebular gas in the solar nebula. We envision a combination of equilibrium and kinetic isotope fractionation of Si between nebular gas and Fe-poor silicates (such as forsterite, anorthite, enstatite and mesostasis) and Fe-rich olivine and orthopyroxene. Petrographic evidence suggests that the enrichment of Fe in some highly altered porphyritic chondrules and at chondrule rims was likely caused by hydrothermal alteration on the parent body. Therefore, the correlation of Fe and δ30Si of the chondrule minerals might serve as an indicator for the extent of further secondary processing of some chondrule minerals. The sum of these observations suggests that the formation and alteration of type II chondrules occurred by oxidation of originally reduced, metal-rich type I chondrules, both in the solar nebula and later on the meteorite parent body. Remaining 30Si depleted gas contributed to the isotopic composition of matrix silicates. The evidence favours the formation of chondrules and matrix of the Allende meteorite in nebular settings rather than by asteroid impacts.

^1,2Klaus Mezger,¹Alessandro Maltese,^1,2Hauke Vollstaedt
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114497]
¹Institute for Geology, University of Bern, Baltzerstrasse 1+3, CH-3012 Bern, Switzerland
²Center for Space and Habitability, University of Bern, Switzerland
Copyright Elsevier

The abundances of the chemical elements and radiogenic isotopes in the silicate Earth provide key information on the composition of planetary building blocks, the accretion process, including its timing, and the early planetary-wide chemical differentiation. The abundances of the lithophile and highly siderophile elements in the bulk silicate Earth can be modeled as a mixture of three distinct components. Component A (proto-Earth) consisted of volatile-element depleted and strongly reduced material to which a highly oxidized component B (impactor, Theia) was added with chondritic element abundances for the refractory elements to slightly depleted in the volatile elements. Finally, a late veneer (component C) added more material with a composition similar to carbonaceous chondrites. These components make up ~85%, ~15% and ~ 0.4% of the mass of the silicate Earth, respectively. The sequence of their accretion led to a first core formation that produced a metallic core and depleted the silicate portion in siderophile elements including most of the Fe. Addition of the oxidized and volatile richer component B was followed by a second core formation event with removal of a sulfide melt and depletion of the mantle in chalcophile and siderophile elements. The final addition of a late chondritic veneer established a near CI-chondritic abundance among the highly siderophile elements, but also among S, Se and Te. The significant chemical differences between the two first and major components imply that they formed in different regions of the solar system and from isotopically distinct material. The homogeneity of the isotopes of refractory elements in the Earth-Moon system then requires a giant impact that was energetic enough to homogenize the material from the two bodies. The combination of the two major components that formed the Earth is contemporaneous with the formation of the Moon. The initial Sr-isotope composition of the Moon indicates that this impact occurred at 4.507 (15) Ga. The most-likely major source for the highly volatile elements, including water on Earth, is the Moon-forming impactor. Thus, the habitability of Earth and its ability to develop plate tectonic processes is the result of the chance collision of proto-Earth with a planetary body that had formed dominantly from material originating beyond the orbit where Earth formed and therefore had accreted a higher amount of volatile elements.

¹G.David et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114481]
¹Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, CNES, Toulouse, France
Copyright Elsevier

The Curiosity rover has been characterizing mineralogical and chemical compositions of Gale crater soils on Mars since 2012. Given its sub-millimeter scale of analysis, the ChemCam instrument is well suited to study the composition of soil constituents. However, the interpretation of LIBS data on soils in the martian environment is complicated by the large diversity of particle sizes (from dust to sand), combined with the unknown physical arrangement of their mineral constituents (i.e., the type of grain mixtures). For example, martian soils contain a significant amount of X-ray amorphous materials whose physical form remains unclear. In this study, we reproduced martian soil analyses in the laboratory to understand how the LIBS technique can provide specific insights into the physical and chemical properties of granular soils. For this purpose, different types of samples were studied with various ranges of grain sizes, mimicking two possible mixtures that may occur in martian soils: mechanical mixtures of two populations of grains made of distinct chemical compositions; and material forming a compositionally distinct coating at the surface of grains. Our results, also supported by in situ ChemCam data, demonstrate that both the sizes and the type of mixture of soil particles have a strong influence on the LIBS measurement. For mechanical mixtures of two populations of grains larger than 125–250 μm, the scatter of the data provides information about the chemical composition of the end-members. On the other hand, the chemistry recorded by LIBS for grains with surface coatings is fully dominated by the outer material for grains smaller than 500 μm in diameter. This is due to the small penetration depth of the laser (~0.3–1.5 μm per shot), combined with the ejection of small grains at each shot, which leads to a constant replenishment of fresh material. This experimental work will thus improve our understanding of martian soils analyzed by ChemCam, and more broadly, will benefit LIBS studies of granular materials.

¹C.Pilorget,²J.Fernando
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114498]
¹Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS, Orsay 91405, France
²Independent scholar, Orsay 91400, France
Copyright Elsevier

Over the last few decades, visible and near-infrared spectroscopy has proven to be an efficient technique to characterize planetary surface mineralogy, in particular thanks to the presence of diagnostic features appropriate for the identification of most minerals of interest. A more quantitative analysis of the VIS-NIR reflectance spectra constitutes the next major step in understanding the planetary bodies’ history as the retrieval of the mineral assemblages and their relative abundances enables to constrain the chemical and physical conditions of their formation and, thus, the past and present geologic and climatic processes.

Here, we evaluate the capability to retrieve quantitative properties (abundance, grain size) of intimately mixed materials (the most common mineral mixture among planetary surfaces) from typical space VIS-NIR reflectance spectroscopic data. Such results are key to correctly assess the accuracy and relevance of the retrieved mineral information. For that purpose, we developed an inversion model based on a Monte-Carlo Markov Chains (MCMC) scheme with a Bayesian approach to invert VIS-NIR spectra. This approach allows to properly propagate the uncertainties from the data to the retrieved properties, and finally assess what such uncertainties imply for the interpretation. Different binary and ternary mixtures with minerals of interest in planetary sciences and displaying a large variety of albedos and spectral features were tested. Typical uncertainties, both for the abundance and the grain size, were derived and sensitivities on specific parameters/trends were identified. In particular, the role of absorption features in the spectra is quantified. Tests were performed using either the Hapke or the Shkuratov radiative transfer model. The case of unidentified endmembers in the mixture is also discussed. In particular, results show that if the unidentified phase does not display any significant spectral feature, the lack of knowledge about its optical properties does not significantly impact the inversion. These different results will be key in the quantitative analyses of VIS-NIR spectra from planetary bodies.

Finally, we analyze more specifically the case of phyllosilicates and carbonates, two families of minerals of high importance in understanding the Mars geologic and climate history. Typical uncertainties on their relative abundances and grain sizes are derived in various cases, providing a critical supporting dataset for the characterization of the martian mineralogy and the associated geological processes.