^1,2Flore Van Maldeghem et al. (>10)
Earth and Planetary Science Letters 641, 118837 Link to Article [https://doi.org/10.1016/j.epsl.2024.118837]
¹Archaeology, Environmental changes, and Geo-chemistry (AMGC), Vrije Universiteit Brussel, Pleinlaan 2, Brussels B-1050, Belgium
²Center for Star and Planet Formation, Globe Institute, University of Copenhagen, Oester Voldgade 5, 1350 Copenhagen K, Denmark
Copyright Elsevier

Each year, approximately 5000 tons of extraterrestrial material reaches the Earth’s surface as micrometeorites, cosmic dust particles ranging from 10 to 2000 μm in size. These micrometeorites, collected from diverse environments, mainly deep-sea sediments, Antarctic ice, snow and loose sediments, and hot deserts, are crucial in understanding our Solar System’s evolution. Chrome-rich spinel (Cr-spinel) minerals have gained attention as proxies for studying the extraterrestrial flux in sedimentary deposits, because these robust minerals occur, in various extraterrestrial materials, with compositions characteristic of their parent bodies. A total of 27 Cr-spinel bearing micrometeorites within the size range of 185–800 μm, were identified from approximately 6000 micrometeorites from the Transantarctic Mountains (n = 23) and the Sør Rondane Mountains (n = 4), in Antarctica, containing Cr-spinel (8–120 μm), were examined in this study for geochemical composition and high-precision oxygen isotope ratios to assess alteration and identify potential parent bodies.

Oxygen isotopes in the micrometeorite groundmass and in Cr-spinel grains reveal a predominance of ordinary chondritic precursors, with only 1 in 10 micrometeorites containing Cr-spinel minerals showing a carbonaceous chondritic signature. This may be further confirmed by an elevated Al content (> 12 wt% Al₂O₃) in Cr-spinel from specific carbonaceous chondrite types, but a more extensive dataset is required to establish definitive criteria. The first Cr-spinel bearing particle, in an Antarctic micrometeorite, that can be linked to R-chondrites based on oxygen isotopes, has been documented, demonstrating the potential for R-chondrites as a source of chrome-rich spinels. The study also highlights the potential for chemical modifications and alteration processes that Cr-spinel minerals may undergo during their time on the parent body, atmospheric entry, and terrestrial residence.

In the context of the broader micrometeorite flux, the results align with previous findings, showing a consistent contribution of micrometeorites containing Cr-spinel minerals related to ordinary chondrites over the past 2 to 4 million years. This is however a small fraction (∼ 1 %) of the total micrometeorite flux. The study further confirms that Cr-spinel minerals recovered from sedimentary deposits serve as valuable proxies for tracking events related to ordinary chondritic or achondritic materials. However, it is emphasized that Cr-spinel minerals alone cannot serve as exclusive indicators of the overall extraterrestrial flux, especially during periods dominated by carbonaceous chondritic dust in the inner Solar System. To comprehensively understand the complete extraterrestrial flux, additional proxies are needed to trace dust-producing events associated with various Solar System objects. The intricate nature of Cr-spinel compositions, and the potential for alteration processes emphasize the need for further research to refine our understanding of these extraterrestrial markers.

¹Helen Grant,¹Romain Tartèse,¹Rhian Jones,²Laurette Piani,²Yves Marrocchi
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.06.005]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester M13 9PL, UK
²CRPG, CNRS-Université de Lorraine, UMR 7358, Vandoeuvre les Nancy, France
Copyright Elsevier

Deuterium to hydrogen isotope ratios in unequilibrated ordinary chondrites (UOCs) which have undergone little-to-no thermal metamorphism pose an interesting problem when looking at water in the early Solar System. Bulk chondrite studies have shown that UOCs of the lowest subtypes have D/H ratios as high as comets from the outer Solar System, which, along with bulk UOC water abundances, decrease with thermal metamorphism. Since bulk UOC analyses represent a complex mixture of organic and hydrated phases, it is not clear what phase(s) is responsible for the high bulk D/H values. In this study, we report in situ secondary ion mass spectrometry (SIMS) measurements of the H isotope composition of the fine-grained matrix of UOCs with petrological subtypes ranging from 3.00 to 3.9. We find that for matrix areas in UOCs of petrologic subtype ≥3.2, correlations between D-rich organic material and D-poor phyllosilicates give relatively D-poor intrinsic water isotopic compositions, with δD values between −320 ± 91 ‰ and −71 ± 71 ‰, which are inherited from parent body accretion. Therefore, we conclude that OC parent bodies accreted D-poor water ice that had an H isotopic composition similar to that of CM and CV chondrite parent bodies. We find that matrix in UOCs of the lowest subtypes (Semarkona, Bishunpur, and Ngawi) show similar water and organic H isotope compositions to higher type UOCs. Our in situ analyses also show that matrix areas in these pristine UOCs contain a third, thus far unidentified, component that carries the high D/H signature, with δD values up to ∼6000 ‰. We propose that this component is pristine amorphous silicates preserved from the molecular cloud or early protoplanetary disc that is extremely sensitive to thermal and aqueous alteration on asteroidal parent bodies.

^1,2Makoto Kimura,³Motoo Ito,²Akira Monoi,¹Akira Yamaguchi,⁴Richard C. Greenwood
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.06.002]
¹National Institute of Polar Research, 10-3 Midoricho, Tachikawa, Tokyo 190-8513, Japan
²Faculty of Science, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512, Japan
³Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200-Monobe-otsu, Nankoku, Kochi 783-8502, Japan
⁴Planetary and Space Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom
Copyright Elsevier

CI chondrites are the most significant extra-terrestrial samples for estimating the composition of primordial materials in the Solar System. However, CIs lose many primary features because of heavy parent body aqueous alteration. However, CI and CI-related Ryugu particles contain small amounts of relict anhydrous minerals, indicating primary occurrences of chondrules and refractory inclusions. In this study, we estimated the primordial abundance of chondrules in CIs from calculations of the bulk major element compositions. The constraints for the calculation were as follows: 1) CI chondrites primarily comprised chondrules, refractory inclusions, opaque minerals, and a matrix similar to other carbonaceous (C) chondrites. 2) The chemical compositions of these components were similar to those of the unaltered C chondrites. 3) The primary matrix composition of the CI was close to the mean bulk composition. 4) The alteration occurred isochemically. We used the mean major elemental compositions of chondrules and refractory inclusions in an almost unaltered chondrite, Y-81020, CO3.05. Our results were within the range of previously reported CI bulk chemical compositions in the case where chondrule abundances are ≲10 wt%. We also calculated the bulk chemical composition of Tagish Lake, ungrouped C2, which primarily contained ≲20 wt% chondrules. The CI chondrites and Tagish Lake were formed in the outer Solar System. The low primary abundance of chondrules in CIs is closely related to the formation conditions of chondrules in such regions. We suggest that dust with abundant ice and minor chondrules accreted onto the parent bodies of the CI and Tagish Lake in the outer Solar System. Primordial chondrule abundance is the key to clarifying the physical and chemical conditions and evolution of the early Solar System.

¹H. C. Bates,²R. Aspin,³C. Y. Fu,^1,4C. S. Harrison,⁵E. Feaver,^1,6E. Branagan-Harris,¹A. J. King,²J. F. J. Bryson,²S. Sridhar,²C. I. O. Nichols
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14224]
¹Planetary Materials Group, Natural History Museum, London, UK
²Department of Earth Sciences, University of Oxford, Oxford, UK
³Department of Earth Science & Engineering, Imperial College London, London, UK
⁴Department of Earth & Environmental Sciences, The University of Manchester, Manchester, UK
⁵Physics & Astronomy Department, University College London, London, UK
⁶Atmospheric, Oceanic & Planetary Physics, University of Oxford, Oxford, UK
Published by arrangement with John Wiley & Sons

Tarda is an ungrouped, hydrated carbonaceous chondrite (C2-ung) that was seen to fall in Morocco in 2020. Early studies showed that Tarda chemically resembles another ungrouped chondrite, Tagish Lake (C2-ung), which has previously been linked to the dark D-type asteroids. Samples of D-type asteroids provide an important opportunity to investigate primitive conditions in the outer solar system. We show that Tarda contains few intact chondrules and refractory inclusions and that its composition is dominated by secondary Mg-rich phyllosilicates (>70 vol%), carbonates, oxides, and Fe-sulfides that formed during extensive water–rock reactions. Quantitative assessment of first-order reversal curve (FORC) diagrams shows that Tarda’s magnetic mineralogy (i.e., framboidal magnetite) is comparable to that of the CI chondrites and differs notably from that of most CM chondrites. These traits support a common formation process for magnetite in Tarda and the CI chondrites. Furthermore, Tarda’s pre-terrestrial paleomagnetic remanence is similar to that of Tagish Lake and samples returned from asteroid Ryugu, with a very weak paleointensity (<0.6 μT) suggesting that Tarda’s parent body accreted more distally than that of the CM chondrites, possibly at a distance of >5.4–8.3 AU. An origin in the cold, outer regions of the solar system is further supported by the presence of distinct, porous clasts enriched in aliphatic-rich organics that potentially retain a pristine interstellar composition. Together, our observations support a genetic relationship between Tarda and Tagish Lake.

J. Storz^a, M.P. Reitze^a, A.N. Stojic^a, I. Kerraouch^a,b, A. Bischoff^a, H. Hiesinger^a, T. John^c
Icarus (in Press)
Link to Article [https://doi.org/10.1016/j.icarus.2024.116189]
^aInstitut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany.
^bBuseck Center for Meteorite Studies (BCMS), Arizona State University, Tempe, AZ 85827, USA.
^cFreie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, D-12249 Berlin, Germany.

Although C1 clasts in carbonaceous chondrites are usually mineralogically similar to CI chondrites, they often exhibit distinct chemical or isotope characteristics, indicating that the diversity of carbonaceous matter is larger than represented by currently known meteorites. Samples returned by the Hayabusa2 mission provide an excellent opportunity to directly compare remote sensing data with laboratory spectra and elaborate on meteorite-asteroid links.

We obtained reflectance spectra from 10 carbonaceous samples of extraterrestrial origin to identify spectral differences in the wavelength region between 2.5 and 16.5 μm. We investigated seven volatile-rich clasts, two CI chondrites, and a fragment from the asteroid Ryugu, recently returned by the Hayabusa2 mission. To obtain representative spectra from a lithology, we performed multiple analysis with an aperture size of 100 μm × 100 μm. Subsequently, spectral features were correlated with petrographic and chemical data.

The phyllosilicate composition of the investigated C1 and C2 clasts is on average more Fe-rich compared to bulk CI chondrites, which is spectrally reflected in lower Christiansen feature (CF)/Reststrahlenband (RB) ratios. Our results confirm previous studies that indicate that the band area of the OH absorption band at 2.7 μm is dependent on the phyllosilicate composition. A high Mg abundance in phyllosilicates leads to a stronger OH absorption band. Varying degrees of aqueous alteration cause mineralogic differences that are observable in the reflectance spectra. Either in form of a band center shift towards smaller or longer wavelengths, depending on the metal cation giving rise to the M-OH absorption band, and/or a generally weaker OH absorption band, and a broad Reststrahlen band (RB) at 10 μm, with two minor RBs emerging at 11.3 and 12 μm. In contrast, most C1 clasts show a single RB at ≈10 μm, and a constant OH band position at 2.70 μm. The abundance of minor constituents, such as sulfides and carbonates, can also affect the spectrum. Dolomite produces two diagnostic bands at 6.5 and 11.3 μm, whereas pyrrhotite, devoid of diagnostic bands in this wavelength region, increases the background while decreasing the RB intensity.

Our findings indicate that within a laboratory framework, subtle mineralogic differences among hydrated carbonaceous materials can be spectroscopically detected. The spectra of Ryugu sample A0008 show a distinctive OH absorption band, as seen in the globally retrieved data by the NIRS3 instrument for Ryugu (Kitazato et al., 2019). Under specific circumstances, micro-FTIR reflectance spectra can be qualitatively compared to remote sensing spectra, and help to further elaborate on meteorite-asteroid links.

Denton S. EBEL^1,2,3, Marina E. GEMMA^1,4, Samuel P. ALPERT^1,3, Jasmine BAYRON⁵, Ana H. LOBO⁶, and Michael K. WEISBERG^1,3,7
Meteoritics & Planetary Science (in Press)
Link to Article [https://doi.org/10.1111/maps.14191]
¹Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
²Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA
³Department of Earth and Environmental Sciences, Graduate Center of the City University of New York, New York,
New York, USA
⁴Department of Geosciences, Stony Brook University, Stony Brook, New York, USA
⁵Department of Geography, Hunter College, City University of New York, New York, New York, USA
⁶Department Physics & Astronomy, University of California Irvine, Irvine, California, USA
⁷Department of Physical Sciences, Kingsborough College, City University of New York, Brooklyn, New York, USA
Published by arrangement with John Wiley & Sons

Abundances, apparent sizes, and individual chemical compositions of chondrules, refractory inclusions, other objects, and surrounding matrix have been determined for Semarkona (LL3.00) and Renazzo (CR2) using consistent methods and criteria on X-ray element intensity maps. These represent the non-carbonaceous (NC, Semarkona) and carbonaceous chondrite (CC, Renazzo) superclans of chondrite types. We compare object and matrix abundances with similar data for CM, CO, K, and CV chondrites. We assess, pixel-by-pixel, the major element abundance in each object and in the entire matrix. We determine the abundance of “metallic chondrules” in LL chondrites. Chondrules with high Mg/Si and low Fe/Si and matrix carrying opposing ratios complement each other to make whole rocks with near-solar major element ratios in Renazzo. Similar Mg/Si and Fe/Si chondrule–matrix relationships are seen in Semarkona, which is within 11% of solar Mg/Si but significantly Fe-depleted. These results provide a robust constraint in support of single-reservoir models for chondrule formation and accretion, ruling out whole classes of astrophysical models and constraining processes of chondrite component formation and accretion into chondrite parent bodies.

Vincent GUIGOZ ¹, Anthony SERET² , Marc PORTAIL¹ , Ludovic FERRIERE³,
Guy LIBOUREL^2,4, Harold C. CONNOLLY Jr^5,6,7 , and Dante S. LAURETTA⁶
Meteoritics & Planetary Science (in Press) Open Access
Link to Article [https://doi.org/10.1111/maps.14225]
¹DCNRS, CRHEA, Universite C^ote d’Azur, Valbonne, France
²Observatoire de la C^ote d’Azur, CNRS, Laboratoire Lagrange, Universite Cote d’Azur, Nice, France
³Natural History Museum Abu Dhabi, Abu Dhabi, United Arab Emirates
⁴Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai‘i at
Manoa, Honolulu, Hawai‘i, USA
⁵Department of Geology, Rowan University, Glassboro, New Jersey, USA
⁶Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
⁷Department of Earth and Planetary Science, American Museum of Natural History, New York, New York, USA
Published by arrangement with John Wiley & Sons

Carbonates, as secondary minerals found in CM chondrites, have been widely employed for reconstructing the composition of the fluids from which they precipitated. They also offer valuable insights into the hydrothermal evolution of their parent bodies. In this study, we demonstrate that high-resolution cathodoluminescence (HR-CL) analyses of calcites derived from the brecciated Cold Bokkeveld CM2 chondrite can effectively reveal subtle compositional features and intricate zoning patterns. We have identified two distinct types of cathodoluminescence (CL) centers: a blue emission band (approximately 375–425 nm), associated with intrinsic structural defects, and a lower energy orange extrinsic emission (around 620 ± 10 nm), indicating the presence of Mn cations. These compositional variations enable discrimination between the calcite grain types previously designated as T1 and T2 in studies of CM chondrites. T1 calcites exhibit variable CL and peripheral Mn enrichments, consistently surrounded by a rim composed of Fe-S-rich serpentine–tochilinite assemblage. Conversely, T2 calcites display homogeneous CL and more abundant lattice defects. These polycrystalline aggregates of calcite grains, devoid of serpentine, contain Fe-Ni sulfide inclusions and directly interface with the matrix. We propose that changes in the Mn content of calcite (indicated by the intensity of orange CL emission) are influenced by variations in redox potential (Eh) and pH of the fluid phase. This proposed hydrothermal evolution establishes a parallel between terrestrial serpentinization followed by carbonation processes and the aqueous alteration of CM chondrites, warranting further exploration and investigation of this intriguing similarity.

^1,2Alan E. Rubin
Meteoritics & Planetary Science (in Press) Open Access
Link to Article [https://doi.org/10.1111/maps.14223]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, US
²Maine Mineral & Gem Museum, Bethel, Maine, USA
Published by arrangement with John Wiley & Sons

Type II chondrules have higher oxidation states than type I chondrules; in ordinary chondrites (OC), type II chondrules tend to be larger, richer in bulk Fe, and have higher densities than type I chondrules. Magnesian type IA chondrules tend to be richer in ¹⁶O than type II chondrules. Because the aerodynamic behavior of a particle is a function of the product of its size and density, type I and type II chondrules (or their precursors) were partly separated in the ordinary chondrite zone of the solar nebula prior to the accretion of OC parent asteroids. LL chondrites acquired a chondrule population with the highest type II/type I ratios, L chondrites acquired chondrules with an intermediate ratio, and H chondrites acquired chondrules with the lowest type II/type I ratios. This contributed to the observed differences among OC groups in oxidation state and O-isotopic composition: in going from H to L to LL, mean oxidation state increases and mean Δ¹⁷O values increase. Higher oxidation is marked by increases in the FeO contents of olivine, low-Ca pyroxene, chromite, and ilmenite; increases in the TiO₂ content of chromite; and increases in the Co content of kamacite.

^aJay Goguen, ^bAndrew Sharits, ^cAnn Chiaramonti, ^dThomas Lafarge, ^cEdward Garboczi
Icarus (in Press) Open Access
Link to Article [https://doi.org/10.1016/j.icarus.2024.116166]
^aSpace Science Institute, 4765 Walnut St STE B, Boulder, CO 80301, United States of America
^bUES, Inc. and Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force B, Fairborn, OH, United States of America
^cApplied Chemicals and Materials Division, National Institute of Standards and Technology, Boulder, CO 80305, United States of America
^dStatistical Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, United States of America

Samples of soils collected by the Apollo 11 mission (10084,2036) and the Apollo 14 mission (14163,940) were obtained from the NASA Curation and Analysis Planning Team for Extraterrestrial Materials (CAPTEM) program. The particle size, shape, and internal porosity were characterized in three dimensions (3D) using a combination of X-ray computed tomography (XCT) and mathematical analysis, with various size and shape parameters measured and calculated for each particle. High-resolution scanning electron microscopy (SEM) was used to image the particles that were too small for the two XCT instruments used. Similar characterization was carried out on samples of JSC-1A lunar soil simulant, updating a previous analysis. Approximately 14,000 lunar regolith particles and 128,000 JSC1-A particles, covering a wide range of size and shape, were characterized for this paper and the results stored in a publicly accessible database. This large number of particles enabled, for the first time, statistically valid particle shape distributions to be generated. The 3D shape distributions of the two regoliths and JSC-1A were quantitatively compared and it was found that the way particle shape and porosity depended on particle size was different between regolith and simulant. The measured size distribution of particles in the lunar soils was applied to estimate the relative contributions of different sizes to the ensemble average particle single scattering albedo and phase function. By linking our particle counts to published sieve weight fractions for the lunar samples, we find that ~80% of the total cross-section area is contributed by particles <20 μm diameter and ~ 50% by particles <8 μm diameter. The orientation-averaged two-dimensional projected areas of the actual regolith particles were computed so that this estimate was also based on real particle shapes. Such small sizes dominating the total cross-section area suggest that calculations of the elements of the scattering matrix for individual particles may be possible with modest computing capabilities leading to the development of improved models for the quantitative interpretation of remote sensing spectrophotometry and polarimetry. This 3D characterization and database will enable other computational work to be done with real lunar regolith particle shapes, including discrete element method mechanical modeling, packing simulations, further light scattering calculations, dust contamination modeling, and modeling of lunar rover interactions with collected and packed regolith particles.