¹Megan Broussardet al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.701381]
¹Department of Earth, Environmental, and Planetary Sciences and the McDonnell Center for the Space Sciences,Washington University in St. Louis, St. Louis, Missouri, USA
Published by arrangement with John Wiley & Sons

CI chondrites are a compositionally primitive group of meteorites that haveundergone extensive aqueous alteration, providing insights into the evolution of primitiveplanetesimals. Oued Chebeika 002 is the most pristine CI chondrite to date. In this work,we report its mineralogy, bulk chemistry, oxygen and potassium isotope ratios, andcosmogenic radionuclides 10 Be, 26 Al, and 36 Cl. The 10 Be cosmic ray exposure ages of OuedChebeika 002 samples are 2.6 0.5 and 2.9 0.7 Myr. The d41 K of two samples is0.114 0.019 and 0.247 0.044 &. We find that the mineralogy, oxygen isotopes,potassium isotopes, and bulk chemistry of Oued Chebeika 002 overlap with those ofsamples returned from the asteroids Ryugu and Bennu. We therefore propose that CI chondrites and the asteroids Bennu and Ryugu may have originated from a common parentbody, for which we propose the name “Naunet,” after an Egyptian goddess of primordialwater. Naunet formed in the outer solar system and underwent aqueous alteration. In themain belt, Naunet broke up, producing rubble-pile asteroids, including Bennu, Ryugu, andthe secondary CI chondrite parent body/bodies, fragments of which survived passage to theEarth’s surface, becoming CI chondrites.

¹Tetsuya Yokoyama et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.701411]
¹Department of Earth & Planetary Sciences, Institute of Science Tokyo, Meguro, Japan
Published by arrangement with John Wiley & Sons

Sample return missions play a significant role in planetary science by providing
pristine extraterrestrial materials. JAXA’s Hayabusa2 and NASA’s OSIRIS-REx missions
have returned samples from the C-type asteroids Ryugu and Bennu, respectively. The
chemical and mineralogical compositions of these samples closely resemble those of CI
chondrites, the traditional reference material for solar system abundances. Based on the
findings of the Hayabusa2 mission, JAXA launched the Ryugu Reference Project (RRP) to
maximize the scientific value of the returned samples and formed the RRP Measurement
Definition Team (RRP-MDT) to elucidate the RRP’s scientific goal and objectives. The
RRP-MDT defined the goal of RRP to reassess the elemental abundances and isotopic
compositions of the solar system through comprehensive analyses of the returned asteroid
samples and CI chondrites. To this end, the team recommended preparing homogeneously
powdered Ryugu reference materials (RRM) using approximately 750 and 400mg of
samples from Chambers A and C, respectively, to address observed compositional
heterogeneities. The team proposed to measure the elemental abundances and isotopic
compositions of the RRM by analytical techniques involving seven specific measurement
groups. Through comprehensive analytical methodologies, interlaboratory calibration, and
statistical evaluation, the RRP aims to refine our understanding of solar system formation
and evolution

^1,2Anna E. Engle, ³Helen E. Maynard-Casely, ^2,1Jennifer Hanley, ³Christopher Baldwin
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117069]
¹Northern Arizona University, Flagstaff, 86011, AZ, USA
²Lowell Observatory, Flagstaff, 86001, AZ, USA
³Australian Centre for Neutron Scattering, ANSTO, Kirrawee DC, 2232, NSW, Australia
Copyright Elsevier

Ethane (CH), propane (CH), and butane (CH₁₀) are present on many outer solar system bodies but our understanding of their solid phase behaviors is still limited. Linear alkanes are known to exhibit multiple solid phases, with at least one of them being a disordered crystalline phase, wherein the molecules remain in a structured placement but have a freedom of rotation about one or multiple axes. Elucidating the properties of these solid phases is critical for understanding the geochemical and geomorphological processes occurring on icy bodies, thus we undertook an investigation of these three simple alkanes at temperatures relevant to the outer solar system via neutron diffraction. We report on extracted thermal expansion properties, observed phase behaviors, and subsequent analysis of their ’loosely packed’ crystal structures through calculations of crystal voids, contact parameters, and fingerprint plots.

^1,2,3Christopher J. Barnes,⁴Aleksander Błasiak,⁵Helge Vinje Birgerheim,⁵Matthias Konrad-Schmolke,⁵Delia Rösel,^3,4Jarosław Majka,⁵Thomas Zack
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70137]
¹Institute of Geological Sciences, Polish Academy of Sciences, Krakow, Poland
²Department of Earth and Environmental Sciences, University of British Columbia Okanagan, Kelowna, British Columbia,Canada
³Department of Earth Sciences, Uppsala University, Uppsala, Sweden
⁴Faculty of Geology, Geophysics & Environmental Protection, AGH University of Krakow, Krakow, Poland
⁵Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden
Published by arrangement with John Wiley & Sons

The mineralogy and textures of several fragments from the Ribbeck aubrite were analyzed using a combination of scanning electron microscopy, electron microprobe analysis, μRaman spectroscopy, and laser ablation inductively coupled reaction cell mass spectrometry (LA-ICP-MS/MS). The meteorite fragments are strongly brecciated and show evidence of shock melting. The silicate phases of the fragments predominantly consist of enstatite, albite, and roedderite, with subordinate forsterite, diopside, K-feldspar. Non-silicate phases include kamacite, troilite, oldhamite, and Fe-Ti, Fe-Mn, and Fe-Cr rich sulfides. Tridymite and cristobalite, the latter contained in Si-rich glass, are also present within one enstatite grain. Vesicular fusion crust is apparent in several fragments. The discovery of roedderite is the first reported for the Ribbeck aubrite. In situ Rb/Sr dating combined with chemical analysis of the roedderite was performed via laser ablation ICP-MS/MS using the single-spot dating approach. The average chemistry of 20 roedderite analyses is 68.7 wt% of SiO2, 23.1 wt% of MgO, 4.9 wt% of K2O, and 3.3 wt% of Na2O and is <0.1 wt% of FeO. The total concentrations of Rb and Sr are 282 and <1 μg g−1, respectively. Single-spot Rb/Sr dates from the same 20 analyses yielded a weighted average of 4570 ± 27 Ma, interpreted as the formation age of the Ribbeck aubrite parent body. The result highlights advantages of single-spot Rb/Sr dating compared to short-lived isotopic systems (e.g., 26Al-26Mg, 53Mn-53Cr, and 129I-129Xe), long-lived systems with radiogenic noble gasses (e.g., 40K-40Ar and 238/235U-232Th-4He), and the conventional Rb/Sr isochron approach for meteorite cosmochronology.

¹Jiawei Zhao et al. (>10)
American Mineralogist 111, 376-393 Link to Article [https://doi.org/10.2138/am-2025-9877]
¹State Key Laboratory of Geological Processes and Mineral Resources, Planetary Science Institute, School of Earth Sciences, China University of Geosciences, Wuhan 430074,
China
Copyright: The Mineralogical Society of America

Pyroxene is a primary constituent mineral in basaltic lunar regolith. These minerals form through the cooling and crystallization of lunar basaltic magma and are subsequently altered by impact events. Thus, pyroxene can serve as a significant indicator for interpreting lunar magmatic processes and impact phenomena. For lunar samples that are mostly mafic and frequently shocked to various degrees, deciphering the effect of shock on pyroxene is necessary for a better understanding of the primary magmatic processes. However, previous studies have neglected to investigate the impact metamorphism of pyroxene in lunar regolith and the potential compositional changes that may result from such impacts. Lunar regolith samples returned by the Chang’E-5 (CE-5) mission are reworked from a monolithic mafic protolith with well-constrained compositions and record strong to mild shock effects that are widespread in the samples. The returned samples provide an excellent chance to distinguish the signatures of impact processes from magmatic activities. Here we report microstructural and compositional variations in a shocked pyroxene within a basaltic clast from CE-5 lunar regolith, which were analyzed by Raman spectroscopy, analytical scanning electron microscopy, electron probe microanalysis, and scanning transmission electron microscopy. The shock microstructures are characterized by the glide system of dislocation [001](100), pigeonite formation induced by shock-related deformations, and solid-melt partitioning and localized frictional melting at grain boundaries or within pyroxene. Combined with the occurrence of shock twins in ilmenite adjacent to the shock melt vein, these shock phenomena are approximately indicative of low-to-moderate shock pressure (9–17 GPa). Most parts of the pyroxene have abnormal Raman peaks at ∼822 cm−1, suggesting the substitution of Si4+ by Al3+ in the tetrahedral site of this shocked pyroxene structure, and this characteristic is recognized as a shock indicator. Evidence from the morphology and elemental distribution of pigeonite within host augite suggests that the Si-Al substitution is consistent with the pigeonite formation, which is triggered or modified by shock-induced deformations and local frictional melting under the fast shear stress. The multiple trends of composition evolution in this single shocked pyroxene reflect sequential processes of magma crystallization, shock-related exsolution, and frictional melting. Our findings indicate that shock effects in pyroxene under low-to-moderate shock conditions can induce changes in composition and structure, and may obscure the evidence of magmatic evolution in pyroxene.

^1,2Xinxin Yan, ³Xinzhuan Guo, ³Yun Zhou, ^1,2Yuping Song, ⁴Qingshan Zhang, ^1,2Meng Lv
Earth and Planetary Science Letters 684, 120009 Link to Article [https://doi.org/10.1016/j.epsl.2026.120009]
¹Key Laboratory of High-Temperature and High-Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou 550081, China
²University of Chinese Academy of Sciences, Beijing 100049, China
³State Key Laboratory of Critical Mineral Research and Exploration, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou 550081, China
⁴China University of Mining and Technology, Xuzhou 221116, China
Copyright Elsevier

The thermal conductivity and diffusivity of mantle minerals fundamentally control planetary cooling rates. Orthopyroxene is a major constituent of the lunar mantle, yet the influence of trace water on its thermophysical properties under high-pressure and high-temperature conditions relevant to the lunar interior has remained unquantified. Here, we present high P–T measurements of these properties for synthetic enstatite containing 0–427 ppm H2O using an enhanced transient plane source method. Our results demonstrate that even trace water drastically reduces thermal transport efficiency by enhancing phonon scattering. Incorporating these data into lunar thermal evolution models reveals that a hydrated mantle maintains significantly higher internal temperatures than an anhydrous system over geologic time. By reconciling our model geotherms with the solidus of various lunar mantle constituents and with seismic constraints on the largely solid modern mantle, we constrain the bulk water content of the lunar mantle to around 300 ppm. This work redefines the thermal state of the Moon and provides a critical mechanism for explaining its prolonged magmatic evolution.

^1,2Yao Sun, ²Jonas Tusch, ¹Xiaorui Fan, ¹Jifeng Xu, ³Chao Li, ⁴Kristoffer Szilas, ²Carsten Münker, ¹Jingao Liu, ²Mario Fischer-Gödde
Earth and Planetary Science Letters 684, 120012 Link to Article [https://doi.org/10.1016/j.epsl.2026.120012]
¹State Key Laboratory of Geological Processes and Mineral Resources, and Frontiers Science Center for Deep‐time Digital Earth, China University of Geosciences, Beijing 100083, China
²Institut für Geologie und Mineralogie, Universität zu Köln, Cologne 50674, Germany
³National Research Center for Geoanalysis, Beijing 100037, China
⁴Natural History Museum of Denmark, University of Copenhagen, Copenhagen 1350, Denmark
Copyright Elsevier

The mass-independent Mo isotope composition of the Bulk Silicate Earth (BSE) bears great potential to investigate the origin of the Earth’s latest 10–20% planetary building blocks. However, currently different estimates for the Mo isotope composition of the BSE render constraints on the composition of late-stage accretionary materials difficult. To address this issue and to revisit the Mo isotope composition of the BSE, we report high-precision molybdenum isotope data for a comprehensive set of terrestrial molybdenites from different locations around the globe covering mineralization ages that extend from the Archean to the Phanerozoic. The molybdenite results are used to constrain the Mo isotope composition of the BSE as follows: ε92Mo = 0.04 ± 0.06, ε94Mo = 0.03 ± 0.03, ε95Mo = 0.01 ± 0.01, ε97Mo = 0.02 ± 0.02, ε100Mo = 0.05 ± 0.06 (n = 16, 95% confidence interval, relative to the NIST SRM 3134 Mo standard). In contrast to previous studies, no resolvable ε94Mo and ε95Mo anomalies were observed, suggesting a BSE composition with predominantly non-carbonaceous chondrite provenance. Considering the analytical uncertainties of our new BSE estimate and literature data for carbonaceous and non-carbonaceous meteorites, it remains a viable option that 12±10% of the present-day Mo budget in the BSE derives from carbonaceous meteorite material delivered during late-stage accretion. This amount of Mo is consistent with the fraction of Mo that was delivered to Earth during its final 0.5% of accretion by the late veneer.

¹Roger L. Gibson,¹S’lindile S. Wela,¹Leonidas C. Vonopartis,¹Marco A. G. Andreoli
Meteoritics & Planetary Science (in Press) Open Access Link to Articles [https://doi.org/10.1111/maps.70136]
¹School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
Published by arrangement with John Wiley & Sons

A core drilled through shocked and faulted Archean granitoid gneisses and dolerites in the eroded peak ring of the 70–80 km diameter Morokweng impact structure intersects multiple centimeter- to meter-wide clastic-matrix breccias containing a polymict clast population of lithic and mineral clasts and altered, millimeter- to centimeter -size, melt clasts. These polymict melt-bearing (PMB) breccias occur both as discrete dikes and in meter- to decameter-wide composite breccia intersections where they are intimately associated with cataclasite and pseudotachylite. Petrographic and bulk-rock geochemical analysis confirms that the PMB breccias comprise fragmental and melt material derived exclusively from the granitoid and doleritic wallrocks, with local geochemical deviations attributable to metasomatic hydrothermal alteration. Notwithstanding their almost complete replacement by smectite and zeolite assemblages, the melt clasts display textural and compositional characteristics identical to the pseudotachylite dikes. Composite lithic-melt clasts indicate an intimate association of melting with cataclasis and comminution prior to their incorporation into the PMB breccias. While most melt clasts display sharp, angular shapes, indicating brittle fracturing, local preservation of delicate filaments intruding the adjacent clastic matrix and bulbous to cuspate-lobate melt clast margins against the matrix indicate incorporation into the breccias while still molten and/or plastic. We propose that the PMB breccias formed by a combination of dynamic injection of friction melt into the cataclasite portions of large fault zones and the development of shear-induced Kelvin–Helmholz instabilities along the melt-cataclasite interface during ongoing fault slip. Melt injection into brecciated wallrock and smaller fractures hosting incoherent cataclasite may have been assisted by a pumping-suction mechanism driven by complex, rapidly changing, block movements during crater wall collapse and peak ring formation. Cooling of the pseudotachylite melts during continued shear or compression of the breccia zones led to their embrittlement and mechanical entrainment as fragments into the incohesive cataclastic fault material, producing the hybrid PMB breccia type. Although the complex strain patterns during peak ring formation could have played a role in extending the duration of shear movements affecting the breccias, we propose that the sequence of cataclasis, frictional melting, melt injection, quenching, brecciation of quenched melt, and melt clast entrainment necessary to produce the PMB breccias can be reconciled with a single, continuous, long-duration, large-magnitude, slip event during collapse of the transient crater wall.

¹Maximilian P. Reitze, ¹Iris Weber, ¹Andreas Morlok, ¹Harald Hiesinger, ¹Johannes Benkhoff, ¹Jan Hendrik Pasckert, ¹Nico Schmedemann, ¹Thomas Heyer, ²Solmaz Adeli
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2026.117073]
¹Institut für Planetologie, Universität Münster, Wilhelm-Klemm Str. 10, Münster, 48149, Germany
²Deutsches Zentrum für Luft- und Raumfahrt (DLR, Rutherfordstr. 2, Berlin, 12489, Germany
Copyright Elsevier

In this work, we propose a new potential mechanism for the formation of the so-called hollows on Mercury, hypothesizing that they are composed of carbonatites—volcanic rocks that are exceedingly rare on Earth. To evaluate this hypothesis, mid-infrared spectroscopic measurements were performed on a rare, unaltered terrestrial carbonatite sample from Mount Ol Doinyo Lengai, Tanzania, composed primarily of the carbonate minerals nyerereite and gregoryite. For comparison, spectra of several common terrestrial carbonate minerals were also acquired. The collected spectra display characteristic features of carbonate minerals. Our analysis suggests that carbonatite rocks should be taken into account for several physical properties required for the formation of hollows on Mercury’s surface. These include appropriate thermal stability, chemical composition, and surface coloration. In particular, the eruption temperatures of terrestrial carbonatite lavas are less than 100 °C below Mercury’s estimated daytime surface temperatures. This thermal similarity makes the measured spectra relevant for the MERTIS instrument onboard the BepiColombo spacecraft, which will investigate Mercury’s surface mineralogy in near future.

¹Dian Ji, ¹Rajdeep Dasgupta, ¹Cin-Ty Lee
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.03.042]
¹Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, United States of America
Copyright Elsevier

The theory of the Moon’s formation via a giant impact, along with initial early sample analyses, suggested that the Moon is extremely volatile-depleted relative to the Earth. Yet, the petrologic studies of lunar melt inclusions and volcanic glasses over the last two decades suggested that water content in the lunar mantle is much higher (as high as 133 – 292 μg/g) than expected and is similar to the Earth’s shallow upper mantle. This high water concentration of the lunar mantle challenged prevailing models of the formation and early evolution history of the Moon, suggesting that not all volatiles were lost, or that impactors supplied additional volatiles. However, previous petrologic models of lunar primary melt water content reconstruction did not consider many key magma differentiation processes. Here, we model lunar magmatism taking into consideration the process of magmatic recharge and show that such a process can explain the anomalously high water abundances, along with other volatile elements such as S, F, and Cl, in Apollo sample 74220 basaltic melt inclusions, as well as the available volatile data of Apollo 79135 and 15597 basaltic to andesitic melt inclusions. Moreover, the model can also explain the MgO content and high-Ti nature of 74220 inclusions, since recharge results in ever-increasing incompatible element concentrations while buffering major element compositions. Therefore, other than deriving from a wet background mantle, we propose an alternative scenario that the water-rich lunar melts could originate from a water-poor (as low as 1–22 μg/g), primitive, magma ocean cumulate. The estimated extent of volatile depletion of the lunar interior varies with the vigor of the magmatic recharge process. Further studies are necessary to independently assess evidence of magmatic recharge, the melt replenishment frequency, and the impact of such a magma reservoir process in our understanding of lunar mantle-crust evolution.