¹Yves Marrocchi,¹Alizé Longeau,¹Rosa Lozano Goupil,¹Valentin Dijon,^1,2,3Gabriel Pinto,¹Julia Neukampf,¹Johan Villeneuve,⁴Emmanuel Jacquet 
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.03.001]
¹Centre de Recherches Pétrographiques et Géochimiques (CRPG), CNRS, UMR 7358, Nancy, France
²Royal Belgian Institute of Natural Sciences, Geological Survey of Belgium, 1000, Brussels, Belgium
³Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Valdivia, Chile
⁴Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Muséum national d’Histoire naturelle, Sorbonne Université, CNRS, CP52, 57 rue Cuvier, 75005 Paris, France
Copyright Elsevier

The systematic isotopic difference between refractory inclusions and chondrules, particularly for oxygen, has long indicated an isotopic evolution of the solar protoplanetary disk. However, it remains underconstrained whether such evolution continued during chondrule formation. Intrigued by past reports of the size-dependent oxygen isotopic compositions of chondrules in ordinary chondrites (OC), we analyzed type I olivine-rich chondrules of various sizes in two LL3 chondrites. Although most chondrules show positive Δ17O values comparable to bulk ordinary chondrites, a population of smaller (less than about 0.1 mm2 in cross-section), including many isolated olivine grains (sensu lato), are 16O-enriched (with Δ17O values down to −13.2 ‰). Literature data allow the same observation for R chondrites. All sub-TFL type I chondrules (i.e., Δ17O < 0) chondrules have Mg# > 97 mol% while the supra-TFL type I chondrule olivines extend to the formal boundary with type II chondrules (i.e., Mg# = 90 mol%). The sub-TFL chondrules are likely genetically related to isotopically similar aluminum-rich chondrules described in the literature. They therefore must have formed earlier than most OC and R chondrules when the inner disk was still sub-TFL. This interpretation is supported by the presence of similarly 16O-rich relict grains in supra-TFL OC and R chondrules that must be remains of this incompletely recycled precursor material. The non-carbonaceous reservoir was thus still evolving isotopically towards 16O-poorer composition when chondrule formation began, whether by mixing with outer disk material, late accretion streamers and/or an increase in the solid/gas ratio due to magnetothermal disk winds.

¹Shiori Matsubara,¹Hidenori Terasaki,²Takashi Yoshino,¹Satoru Urakawa,¹Daisuke Yumitori
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14149]
¹Department of Earth Sciences, Graduate School of Science and Technology, Okayama University, Okayama, Japan
²Institute for Planetary Materials, Okayama University, Tottori, Japan
Copyright Elsevier

In differentiated planetesimals, the liquid core starts to crystallize during secular cooling, followed by the separation of liquid–solid phases in the core. The wetting property between liquid and solid iron alloys determines whether the core melts are trapped in the solid core or they can separate from the solid core during core crystallization. In this study, we performed high-pressure experiments under the conditions of the interior of small bodies (0.5–3.0 GPa) to study the wetting property (dihedral angle) between solid Fe and liquid Fe-S as a function of pressure and duration. The measured dihedral angles are approximately constant after 2 h and decrease with increasing pressure. The dihedral angles range from 30° to 48°, which are below the percolation threshold of 60° at 0.5–3.0 GPa. The oxygen content in the melt decreases with increasing pressure and there are strong positive correlations between the S + O or O content and the dihedral angle. Therefore, the change in the dihedral angle is likely controlled by the O content of the Fe-S melt, and the dihedral angle tends to decrease with decreasing O content in the Fe-S melt. Consequently, the Fe-S melt can form interconnected networks in the solid core. In the obtained range of the dihedral angle, a certain amount of the Fe-S melt can stably coexist with solid Fe, which would correspond to the “trapped melt” in iron meteorites. Excess amounts of the melt would migrate from the solid core over a long period of core crystallization in planetesimals.

^1,2Eric M. MacLennan,^2,3Joshua P. Emery,²Michael P. Lucas,^3,4Lucas M. McClure,^2,4Sean S. Lindsay
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14150]
¹Department of Physics, University of Helsinki, Helsinki, Finland
²Earth and Planetary Sciences Department, Planetary Geosciences Institute, The University of Tennessee, Knoxville, Tennessee, USA
³Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, Arizona, USA
⁴Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee, USA
Published by arrangement with John Wiley & Sons

The exposure to irradiation from high-energy particles alters the reflectance properties of asteroid surfaces and is referred to as space weathering. This process leads to an increase in spectral slope in visible and near-infrared wavelengths. However, changes in the regolith particle size, which can vary dramatically among the asteroid population, are known to influence the spectral properties of meteorites and asteroids. In this context, we investigate the changes in spectral slope and absorption band depths of fresh and irradiated ordinary chondrite meteorites to quantitatively compare the effects of space weathering and grain size variations. To do so, we develop and employ the Spectral Analysis for Asteroid Reflectance Investigation routine that calculates the band parameters of reflectance spectra. We then formulate a parameter called the Space Weathering Index (SWI) that is designed to encapsulate spectral changes due to space weathering. We find that the SWI is strongly dependent on the spectral slope which complicates the interpretation of asteroid spectra in the context of grain size variations and space weathering. We also show that a second parameter, the Band Depth Index, is indicative of petrologic type. Finally, we use a linear discriminant analysis to classify asteroid reflectance spectra into H, L, LL, and unequilibrated ordinary chondrites.

^1,2Eric M. MacLennan,^2,3Joshua P. Emery,^3,4Lucas M. McClure,²Michael P. Lucas,^2,4Sean S. Lindsay,^2,5Noemi Pinilla-Alonso
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14151]
¹Department of Physics, University of Helsinki, Helsinki, Finland
²Earth and Planetary Sciences Department, The University of Tennessee, Knoxville, Tennessee, USA
³Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, Arizona, USA
⁴Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee, USA
⁵Florida Space Institute, University of Central Florida, Orlando, Florida, USA
Published by arrangement with John Wiley & Sons

Spacecraft missions to asteroids have revealed surfaces that have variations in albedo and spectral properties. Such variations are also detected across the asteroid population with ground-based observations, and are controlled by the physical characteristics of the regolith and by processes such as space weathering. Here, we investigate how space weathering and regolith grain size influence the spectra of ordinary chondrite-like asteroids observed from ground-based spectroscopy. The estimation of diagnostic band parameters from asteroid visible and near-infrared reflectance spectra allow us to estimate the degree of space weathering and their compositions, using results from an accompanying study (MacLennan et al., 2024). We use grain size estimations gleaned from the thermal inertia to show that regolith particle size differences have similar effect as space weathering on asteroid spectra. Finally, we quantify changes in spectral slope and band depth among asteroids using the space weathering index developed by MacLennan et al (2024), and reassess the importance of previously-proposed surface freshening mechanisms.

¹Lan F. Xie,¹Hong Y. Chen,¹Bing K. Miao,²Wen L. Song,¹Zhi P. Xia,¹Chuan T. Zhang,¹Guo Z. Chen,¹Jin Y. Zhang,^1,3Si Z. Zhao,¹Xu K. Gao
American Mineralogist 109, 457-470 Link to Article [http://www.minsocam.org/msa/ammin/toc/2024/Abstracts/AM109P0457.pdf]
¹Key Laboratory of Planetary Geological Evolution of Guangxi Provincial Universities, Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources in Guangxi, and Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, College of Earth Sciences, Guilin University of Technology, Guilin 541006, China
²State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China
³Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
Copyright: The Mineralogical Society of America

Pink spinel anorthosite (PSA) and pink spinel troctolite (PST) are two lunar lithologies known to
contain Mg-rich spinel. PSA rich in spinel and lacking mafic minerals, was detected by the visible and
near-infrared reflectance spectroscopy. PST clasts were found in returned lunar samples and meteorites.
NWA 13191 is a recently approved lunar meteorite that contains a large amount of spinel-bearing clasts
and provides an opportunity to discuss its origin. Sixty-four spinel-bearing clasts were studied in this
research. These clasts are dominated by anorthitic feldspars (20.8–80.9 vol%, An90.9–96.8), mafic-rich
and aluminum-rich glass (14.7–72.1 vol%) quenched from a melt, and spinels (0.19–5.18 vol%). Fortynine of these clasts appear to have unusually low modal abundances of mafic silicates (avg. olivine
± pyroxene, 1.87 vol%), which distinguishes them from known spinel-bearing lunar samples (e.g.,
PST). The spinel compositions (avg. Mg# = 90.6, Al# = 97.4) and mafic minerals contents are basically
consistent with those of PSA. The absorption characteristics of glass in the reflection spectrum are not
obvious, so it is not clear if the PSA contains melt. The simulated crystallization experiment clearly
shows that it contains a large amount of melt at the spinel crystallization stage. These phenomena
provide experimental and sample evidence for the existence of glass in the lunar spinel-bearing lithologies. NWA 13191 records the highest known bulk Mg# (avg. 89.8), and the spinel records the highest
Al# (98.8) and Mg# (93.1) of lunar samples to date. The chemical properties of spinel-bearing clasts
in NWA 13191 are consistent with the slightly REE-enriched and alkali-poor Mg-suite rocks, such as
PST, magnesian anorthosites (MANs), and olivine-enriched Mg-suite rocks. These phenomena and
previous simulated crystallization experiments indicate that a Mg-Al-rich melt may be produced by
impact melting of Mg-rich anorthosite precursors. The spinel is a metastable crystallization product
along with plagioclase and vitric melt near the Moon’s surface. This realization provides observational
evidence for previous simulated crystallization experiments and theoretical speculations.

¹William Herbst,²James P. Greenwood
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14153]
¹Department of Astronomy, Wesleyan University, Middletown, Connecticut, USA
²Department of Earth and Environmental Sciences, Wesleyan University, Middletown, Connecticut, USA
Published by arrangement with John Wiley & Sons

Chondrules probably formed during a small window of time ~1–4 Ma after CAIs, when most solid matter in the asteroid belt was already in the form of km-sized planetesimals. They are unlikely, therefore, to be “building blocks” of planets or abundant on asteroids, but more likely to be a product of energetic events common in the asteroid belt at that epoch. Laboratory experiments indicate that they could have formed when solids of primitive composition were heated to temperatures of ~1600 K and then cooled for minutes to hours. A plausible heat source for this is magma, which is likely to have been abundant in the asteroid belt at that time, and only that time, due to the trapping of ²⁶Al decay energy in planetesimal interiors. Here, we propose that chondrules formed during low-speed (≲1kms−1) collisions between large planetesimals when heat from their interiors was released into a stream of primitive debris from their surfaces. Heating would have been essentially instantaneous and cooling would have been on the dynamical time scale, 1/(Gρ) ~30 min, where � is the mean density of a planetesimal. Many of the heated fragments would have remained gravitationally bound to the merged object and could have suffered additional heating events as they orbited and ultimately accreted to its surface. This is a hybrid of the splash and flyby models: We propose that it was the energy released from a body’s molten interior, not its mass, that was responsible for chondrule formation by heating primitive debris that emerged from the collision.

¹Aaron J. Cavosie,¹Phil A. Bland,²Noreen J. Evans,²Kai Rankenburg,³Malcolm P. Roberts,^4,5Luigi Folco
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.02.016]
¹Space Science and Technology Centre and The Institute for Geoscience Research, School of Earth and Planetary Science,Curtin University, Perth, WA 6102, Australia
²John de Laeter Centre, Curtin University, Perth, WA 6102, Australia
³Centre for Microscopy, Characterisation, and Analysis, University of Western Australia, Perth, WA 6009, Australia
⁴Dipartimento di Scienze della Terra, Università di Pisa, Pisa, 56126, Italy
⁵Centro per l’Integrazione della Strumentazione dell’Università di Pisa, Pisa 56126, Italy
Copyright Elsevier

Detection of extra-terrestrial geochemical components in melt generated during meteorite impact provides diagnostic evidence that can be used to confirm a hypervelocity impact event, and in some cases, classify the projectile. However, projectile contamination is often present at sub-percent levels, and can be difficult to detect. In contrast, meteoritic abundances in glass from small impact craters (<1 km diameter) formed by iron meteorites can be anomalously high, which has been attributed to glass originating from the projectile-target interface. Emulsion textures, immiscible liquids, metal spherules, and non-meteoritic siderophile element ratios have been cited as evidence that the projectile component is typically fractionated in impact glass. Here we present compositional data for impact glass from the Henbury crater field in Australia, where the largest crater is 145 m in diameter and the subgreywacke target rock and IIIAB iron projectile are geochemically distinct. Mixing models (Fe-Si, Ni-Co, Cr-Ir) and high platinum group element abundances indicate average projectile contributions ranging from 3 to 13 % in Henbury glass, comparable to ranges reported in glass from the Kamil (Egypt) and Wabar (Saudi Arabia) impact craters. However meteoritic siderophile element ratios (Fe:Ni, Fe:Co, Ni:Co) in Henbury glass appear nearly unfractionated, whereas Wabar and Kamil glasses have more fractionated ratios. Observed variations are attributed to fractionation of meteoritic Ni by formation of immiscible Ni-rich spherules during oxidation of meteoritic iron, and subsequent separation of Ni-rich spherules from glass during ejection. The Henbury glass sample analyzed is interpreted as an example of an interface melt that quenched prior to extensive oxidation and phase separation, and thus may represent one of the least fractionated samples of melt from the projectile-target interface described thus far, whereas Wabar and Kamil glasses record more evidence of fractionation processes. These results further highlight the influence of metal spherule formation on the composition of ejected glass from small impact structures formed by iron meteorites and provide new insights that explain textural features observed in natural impact glasses.

¹Alice Aléon-Toppani et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.02.006]
¹Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
Copyright Elsevier

In order to better constrain the alteration history of the Ryugu parent body, we performed a multi-analytical study combining scanning electron microscopy, transmission electron microscopy and infrared spectroscopy on sections extracted from the three fragments A0064-FO019, A0064-FO021 and C0002-FO019 returned from Ryugu by the Hayabusa2 space mission. The three sections show large differences in terms of structure, mineralogy and infrared signature. Section A0064-FO019 resembles the major Ryugu lithology with the presence of both fine-grained phyllosilicates (fg-phyllos) with embedded nanosulfides and coarse-grained phyllosilicates (cg-phyllos), whereas section C0002-FO019 belongs to the group of the less altered lithologies with the presence of anhydrous minerals embedded in a partially amorphous matrix. Section A0064-FO021 also belongs to this group but shows two different lithologies, a compact amorphous one and a more porous and very fractured one showing the presence of Na-rich phosphate, calcite and olivine. The two less altered lithologies (sections A0064-FO021 and C0002-FO019) show the presence of numerous mineralogical features similar to those observed in cometary interplanetary dust particles, ultra-carbonaceous Antarctic micrometeorites or in the CM Paris meteorite, i.e. amorphous and partially crystallized matrix with GEMS-like ghosts objects, whisker olivine, phosphide, or FeNi metal. This supports an outer solar system origin common with that of cometary material for the Ryugu parent body. Combined with the results of Nakamura et al., (2022a, 2022b) reporting the presence of a lithology showing the presence of GEMS-like objects, we propose that section C0002-FO019 represents the onset of aqueous alteration of such primitive materials. The cg-phyllos and fg-phyllos of section A0064-FO019, i.e. of the major Ryugu lithology, representing the advanced stage of alteration, exhibit distinctive IR signatures with a higher abundance of oxygen-rich functional groups in the organic matter (OM) from the cg-phyllos. We thus suggest the following chronology of formation and evolution for Ryugu: (1) accretion of highly porous aggregate of GEMS-like units with fine-grained high-temperature anhydrous silicates, (2) onset of alteration with the dissolution of primary nanosulfides and development of amorphous/partially crystallized material in the pores, (3) crystallization of fg-phyllos with a second generation of sulfides, (4) later formation of cg-phyllos devoid of nanosulfides and their associated oxygen-rich OM in a more water-rich environment.

^1,2,3Xiaorong Qin,⁴Jiacheng Liu,^1,2Wei Tan,^1,2,3Hongping He,⁴Joseph Michalski,⁵Yu Sun,⁶Shangying Li,⁴Binlong Ye,^1,2Yiping Yang,⁴Yiliang Li
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116016]

¹CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
²CAS Center for Excellence in Deep Earth Science, Guangzhou, China
³University of Chinese Academy of Sciences, Beijing, China
⁴Laboratory for Space Research, University of Hong Kong, Hong Kong, China
⁵Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
⁶School of Land Engineering, Chang’an University, Xi’an, China
Copyright Elsevier

The compositional stratigraphy of Al-rich clays overlying Fe/Mg-rich clays on Mars has been viewed as a window to understanding the atmospheric conditions of early Mars. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) indicates that nontronite is a main component of Fe/Mg-rich clays. However, the role of the ancient climate in the alteration process, which produced and dissolved these phyllosilicates, remains under debate. The present study experimentally modeled the dissolution of nontronite and precipitation of kaolinite in an acidic solution, which enables us to enhance the interpretation of near-infrared remote sensing data from compositional stratigraphy on Mars. The obtained results show that the transformation started from the losses of both tetrahedral Si and interlayer alkali(earth) cations in nontronite, and Fe3+ in the dioctahedral sheet was released and formed hematite with progressive damage of Sisingle bondO tetrahedral sheets. TG analyses also show that the dissolution of nontronite and precipitation of kaolinite led to an increase in metal-OH (metal = Al, Fe3+ and Mg) content and a simultaneous decrease in H2O content. Accordingly, the gradual increasing trend of visible/near-infrared reflectance (VNIR) spectra ratios of BD1400/BD1900 (BD, band depth) in the kaolinized nontronite can be linked to a gradual upward transition from nontronite to a mixture of nontronite and kaolinite, and finally into kaolinite and hematite, by comparing their spectral features at different evolution stages. Such a trend suggests a weathering process known as ferrallitization, i.e., partial leaching of Si and enrichment of Fe3+ and Al3+. The observed weathering process is consistent with a warm and wet climate capable of sustaining acidic liquid water on its surface over extended geological periods.

¹Mingming Zhang,¹Noël Chaumard,¹Céline Defouilloy,²William O. Nachlas,³Donald E. Brownlee,³David J. Joswiak,⁴Andrew J. Westphal,⁴Zack Gainsforth,¹Kouki Kitajima,¹Noriko T. Kita
Geochimica et Cosmochimica acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.02.013]
¹WiscSIMS, Department of Geoscience, University of Wisconsin–Madison, Madison, WI 53706, USA
²Eugene Cameron Electron Microprobe Laboratory, Department of Geoscience, University of Wisconsin–Madison, Madison, WI 53706, USA
³Department of Astronomy, University of Washington, Seattle, WA 98195, USA
⁴Space Sciences Laboratory, University of California, Berkeley, California 94720, USA
Copyright Elsevier

We measured oxygen isotope ratios of 16 silicate fragments from seven aerogel tracks (turnip-like type B tracks 77, 149, 172, 191, and 220; carrot-like type A tracks 22 and 175) of the comet 81P/Wild 2 collector from NASA’s Stardust mission using secondary ion mass spectrometry. Thirteen were prepared by ultramicrotomy; three from track 220 were prepared by sputtering resin blocks using a SIMS Kohler beam, a new procedure aiming to mine as many cometary particles encased in aerogel/resin as possible. Combining new and literature results, we recognized that most silicate fragments of individual type B tracks have diverse mineralogy but consistent mass-independent fractionation of oxygen isotopes (Δ17O = δ17O − 0.52 × δ18O) or display negative Δ17O–Mg# relationship like CR chondrules. These observations suggest that their impactors are loosely bound aggregates of unequilibrated materials originating mainly from similar protoplanetary disk regions, resembling the cluster IDP U2-20-GCA. Furthermore, silicate fragments from type A track 22 have almost identical mineralogy and Δ17O values, confirming that its impactor is a single chondrule-like fragment. The terminal particle of type A track 175 is pure forsterite with Δ17O of ∼–23‰.

Six iron-rich fragments of this study have positive oxygen isotope ratios (Δ17O∼+2‰) and ordinary chondrite chondrule-like olivine compositions. Together with five similar fragments in the literature, a unique population (Mg# ≤86) of Wild 2 fragments that resemble chondrules from the inner solar system (O-E-R) chondrites or the outer solar system CH-CB chondrites was identified. The remaining 16O-poor Wild 2 fragments are Mg# ≥79 silicates with Δ17O∼–2‰ and a small amount of Mg# ≤79 silicates with Δ17O∼0‰, which are most consistent with CR chondrite chondrules. Thus, we conclude that in addition to the possible major source of CR chondrite chondrule-like materials, the inner solar system or CH-CB chondrule-like materials are a minor component of comet Wild 2, like the cluster IDP U2-20-GCA.