¹Jeremy W. Boyce,¹Francis M. McCubbin,¹Nicole Lunning,^1,2Tyler Anderson
The Planetary Science Journal 5, 53 Open Access Link to Article [DOI 10.3847/PSJ/ad1830]
¹Astromaterials Research and Exploration Science Division, NASA Lyndon B. Johnson Space Center, 2101 E. NASA Parkway, Houston, TX 77058, USA; jeremy.w.boyce@nasa.gov
²Now at Lawrence Livermore National Laboratories, Livermore, CA 94550, USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Andrea Patzer,¹Julia Kowalski,¹Tommaso Di Rocco,¹Andreas Pack
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14155]
¹Geosciences Centre of the University of Göttingen, Göttingen, Germany
Published by arrangement with John Wiley & Sons

The ureilite parent body (UPB) was, in all likelihood, completely broken apart when hit by another object early in its history and reassembled into daughter bodies. We here present a study tailored to constrain the dimensions of the impact debris produced in the catastrophic disruption. Using a customized Python code to simulate the thermal evolution of the UPB fragments, we compared the FeO profiles modeled for different depths within those fragments with those measured across the reduction rims in olivines of 12 different ureilites (n = 37). Our profile data were fitted to the theoretical cooling profiles determined with a transient thermal model. The results are coherent and consistent with earlier studies and, despite using simplified boundary conditions (fragments described as ideal spheres and maximum radiation), our data provide valuable context on possible cooling pathways of the UPB debris. In detail, we found that the average depths within the given fragments from which our samples of ureilites originated were limited to 0.3–0.4 ± 0.1 m, with only few exceptions (e.g., one highly reduced sample lacked suitable reduction profiles suggesting either a depth of origin of >2 m or shielding of this fragment from rapid cooling, e.g., due to hovering in the center of a relatively dense cloud of debris). In addition, we calculated that the cooling from 1473 to 1100 K of the average fragment at the depth of our samples took no more than 3–4 days, suggesting that the reassembly of the ureilite daughter bodies could have been a very fast process.

^1,2Y. Li,^1,3A. Mei,^1,2W. Hsu,⁴S. Li
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2023JE008124]
¹Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, China
²CAS Center for Excellence in Comparative Planetology, Hefei, China
³School of Astronomy and Space Sciences, University of Science and Technology of China, Hefei, China
⁴Astronomical Research Center, Shanghai Science & Technology Museum, Shanghai, China
Published by arrangement with John Wiley & Sons

Ca-phosphates in Campo del Cielo (CdC) and Nantan were comprehensively studied to provide insights into the thermal histories of the IAB main group (MG) and related irons. In CdC, apatite grains are characterized by (a) close intergrowth with troilite/graphite in border area between silicate and metal in most cases and (b) near-flat rare earth elemental patterns (LaN/YbN = 0.6–0.7). This indicates they were formed during a metal-silicate mixing event at a relatively high temperature. Combining with petrographic textures, we suggest that the replacement of high-Ca pyroxene by low-Ca pyroxene at ∼950–1,000°C could release Ca and facilitate the formation of apatite grains. In the Nantan nodule, Ca-phosphates do not share a similar origin with those in CdC, as indicated by their different mineral chemistries and mineral associations. Ca-phosphates and associated silicates could crystallize from a P-C-S-rich metallic melt with the oxidation of lithophile elements. Combining all analyses from CdC and Nantan yielded a SIMS Pb-Pb isochron age of 4,558 ± 56 Ma. Considering that all the IAB-MG irons experienced a rapid high-temperature cooling process, the age of 4,558 ± 56 Ma provides another line of evidence that the parent body of IAB-MG and related irons experienced metal-silicate mixing in first 50 Myr of solar system. The previously reported Ar-Ar ages of ≤4.47 Ga could be related to the late reheating process(es). The degrees of late shock heating may vary from specimen to specimen.

¹Eng, A.M. et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE008033]
¹Western Washington University, Bellingham, WA, USA
Published by arrangement with John Wiley & Sons

Since leaving Vera Rubin ridge (VRr), the Mars Science Laboratory Curiosity rover has traversed though the phyllosilicate-bearing region, Glen Torridon, and the overlying Mg-sulfate-bearing strata, with excursions onto the Greenheugh Pediment and Amapari Marker Band. Each of these distinct geologic units were investigated using Curiosity’s Mast Camera (Mastcam) multispectral instrument which is sensitive to iron-bearing phases and some hydrated minerals. We used Mastcam spectra, in combination with chemical data from Chemistry and Mineralogy, Alpha Particle X-ray Spectrometer, and Chemistry and Camera instruments, to assess the variability of rock spectra and interpret the mineralogy and diagenesis in the clay-sulfate transition and surrounding regions. We identify four new classes of rock spectra since leaving VRr; two are inherent to dusty and pyroxene-rich surfaces on the Amapari Marker Band; one is associated with the relatively young, basaltic, Greenheugh Pediment; and the last indicates areas subjected to intense aqueous alteration with an amorphous Fe-sulfate component, primarily in the clay-sulfate transition region. To constrain the Mg-sulfate detection capabilities of Mastcam and aid in the analyses of multispectral data, we also measured the spectral response of mixtures with phyllosilicates, hydrated Mg-sulfate, and basalt in the laboratory. We find that hydrated Mg-sulfates are easily masked by other materials, requiring ≥90 wt.% of hydrated Mg-sulfate to exhibit a hydration signature in Mastcam spectra, which places constraints on the abundance of hydrated Mg-sulfates along the traverse. Together, these results imply significant compositional changes along the traverse since leaving VRr, and they support the hypothesis of wet-dry cycles in the clay-sulfate transition.

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.