¹Shuai Li, ^2,3,4Daniel P. Moriarty III, ⁵Carle M. Pieters, ⁶Rachel L. Klima, ⁶Angela M. Dapremont
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116668]
¹Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI, USA
²NASA Goddard Space Flight Center, Greenbelt, MD, USA
³Department of Astronomy, University of Maryland, College Park, MD, USA
⁴Center for Research and Exploration in Space Science & Technology II, University of Maryland, College Park, MD, USA
⁵Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, USA
⁶Johns Hopkins University Applied Physics Laboratory (JHUAPL), Laurel, MD, USA
Copyright ELsevier

This study presents high-resolution (140 m/pixel) controlled mosaics of Moon Mineralogy Mapper (M3) data in the lunar polar regions (80°–90° N/S), with a focus on assessing mineralogy and water content across the Artemis exploration zone. M3 extensively sampled the lunar polar regions, providing a high spatial resolution, hyperspectral imaging dataset that uniquely covers reflectance absorptions of major minerals and water on the lunar surface. We developed a methodology to preferentially use M3 image cubes acquired when the star tracker was operational to ensure accurate spatial registration of M3 pixels in our new mosaics. Integrated band depth (IBD) analyses were conducted to map distributions of hematite and other mineral species at the Artemis exploration zone. We also derived water contents at the Artemis sites from our new M3 mosaics. Our findings indicate that the Artemis exploration zone is largely dominated by mature regolith that is probably rich in plagioclase. Hematite is predominantly concentrated on east-facing slopes, likely due to enhanced oxidation from Earth wind oxygen interacting with the lunar regolith. Pyroxene-rich exposures are observed in three Artemis candidate landing regions and they are all associated with fresh impact craters. The water distribution is highly variable, with higher concentrations on pole-facing slopes and near permanently shadowed regions, likely controlled by low surface temperatures. High water contents are observed at hematite exposures, which reinforces that water may play a crucial role in hematite formation on the Moon. These results provide valuable insights for future lunar exploration, aiding in the selection of landing sites, planning of traverse routes, and informing in situ resource utilization (ISRU) for the Artemis missions.

^1,2,3Kengo T.M. Ito, ¹Sota Niki, ⁴Hikaru Hasegawa, ¹Kanoko Kurihara, ²Tokiyuki Morohoshi, ⁴Takashi Mikouchi, ¹Takafumi Hirata, ⁵Martin Bizzarro, ²Tsuyoshi Iizuka
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.05.022]
¹Geochemical Research Center, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan
²Department of Earth and Planetary Science, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan
³Division of Sustainable Energy and Environmental Engineering, The University of Osaka, Yamadaoka 2-1, Suita, Osaka 565-0871, Japan
⁴The University Museum, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan
⁵Center for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, Denmark
Copyright Elsevier

Brachinites are a group of primitive achondrites composed mostly of ferroan olivine, which may have formed as partial melting residues or cumulates on an incompletely differentiated planetesimal. To constrain the petrogenetic origin of brachinites and the thermal history of the parent body, we report the first study that integrates mineralogical, rare earth element (REE), and U–Pb age data for brachinite Ca-phosphates, apatite and merrillite, using very coarse grains up to ∼ 500 µm in diameter found in Northwest Africa 10932. The mineralogical data reveal partial replacement of apatite by merrillite concurrent with the reaction of olivine and a S-rich vapor to form symplectitic clinopyroxene-troilite/Fe-Ni metal intergrowths during thermal metamorphism. Apatite cores surrounded by merrillite rims exhibit REE zoning resulting from diffusion during metamorphism. Diffusion modeling of the REE zoning using the olivine-chromite equilibration temperature of 978 ± 11 ˚C constrains the duration of the metamorphism to be 104 yr. This timescale is far longer than that of shock metamorphism, and therefore requires an internal heat source such as adjacent magma. The apatite cores and merrillite rims yielded identical U–Pb ages of 4482 ± 29 Ma (2σ) reflecting complete resetting of the U–Pb system during metamorphism. This metamorphic age is distinctly younger than the Mn–Cr age of 4565 Ma reported for the Brachina meteorite, revealing indigenous thermal activity over ∼ 80 Myr on the parent body. Reconciling the protracted thermal activity with the primitive brachinite composition suggests that brachinites were derived from a moderately shallow region of the parent body, whose interior was differentiated into a core and mantle. Moreover, the metamorphic age is identical to the reported U–Pb age of apatite in the andesitic meteorites Graves Nunataks 06128 and 06129 [4460 ± 30 Ma (2σ)]. This correspondence supports the hypothesis that the andesitic meteorites are samples of partial melts extracted from the ultramafic residues represented by brachinites and further suggests that the transformation from apatite to merrillite in the brachinite source region released a metasomatic Cl-rich fluid to form chlorapatite in the shallower crustal region.

¹Zichen Wei, ¹Yan Zhuang, ^1,2Hao Zhang, ³Pengfei Zhang, ³Yang Li, ⁴Menghua Zhu, ¹Te Jiang, ³Ronghua Pang
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116665]
¹School of Earth Sciences, China University of Geosciences, Wuhan, China
²CAS Center for Excellence in Planetology, Hefei, China
³Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
⁴State Key Laboratory of Lunar and Planetary Science, Macau University of Science and Technology, Macau, China
Copyright Elsevier

Space weathering processes, including micrometeoroid impact and solar wind irradiation typically redden, darken, and attenuate the fingerprint absorption features in the visible and near-infrared (VNIR) reflectance spectra of planetary surface materials. The so-called lunar style space weathering typically produces nanophase metallic iron (npFe0) and amorphous mineral layers. This paradigm has been known to be inadequate in describing the weathering processes on many other airless bodies and many open questions are waiting to be answered. For example, the greater flux of micrometeorite impacts or higher surface temperature on Mercury may produce larger npFe0 particles; the gardening effects on space weathering remain largely unknown; on asteroids such as Vesta, random regolith mixing and contamination by exogenic material from impacts are believed to be the dominant space weathering processes. To understand these and other questions in non-lunar style space weathering, we conducted pulsed laser irradiations on low-iron olivine grains in powders and pellets at various energy levels. By performing transmission electron microscope and reflectance spectroscopic measurements, we found that progressive irradiation caused continuous darkening. Meanwhile, the VNIR spectral slope changed from reddening to bluing after reaching a “saturation point”, and the absorption band depth transitioned from weakening to stabilization. At the same time, repeated irradiations led to limited growth of npFe0 particles in low-iron olivine. In all simulated irradiations, significant spectral alterations occurred in early stages, implying that fresh surfaces are more sensitive to space weathering. The rates of spectral modification of powder samples were found to be remarkably lower than those of the pellet samples. We also observed that exogenous metal contaminants could evaporate and condense into an opaque layer during simulated bombardments, obscuring the original spectral features of regolith.

¹Torii Douglas-Song, ¹Tsutomu Ota, ¹Masahiro Yamanaka, ¹Hiroshi Kitagawa, ¹Ryoji Tanaka, ¹Christian Potiszil, ¹Tak Kunihiro
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.05.038]
¹The Pheasant Memorial Laboratory Institute for Planetary Materials, Okayama University Yamada 827, Misasa, Tottori 682-0193, Japan
Copyright Elsevier

Here we report the in situ ion-microprobe analyses of the Li- and O-isotope compositions of enstatite, FeO-rich pyroxene, olivine, glass, and cristobalite grains from six chondrule-related objects from the Sahara 97103 EH3 chondrite. The O-isotope composition of the enstatite grains scattered around the intersection between the terrestrial fractionation and primitive chondrule minerals lines. Whereas, that of olivine varied along the primitive chondrule minerals line. Based on the mineralogy, we found cristobalite formed as a result of Si saturation, instead of the reduction of FeO-rich silicates, consistent with Si-enrichment of whole rock enstatite chondrites. Based on the mineralogy and O-isotope compositions, we infer that olivines in some chondrules are relict grains. In chondrules that contained olivine, no abundant niningerite [(Mg,Fe,Mn)S] was observed. Thus, enstatite formation can be explained by the interaction of an olivine precursor with additional SiO2 (Mg2SiO4 + SiO2 → Mg2Si2O6), instead of sulfidation (Mg2SiO4 + S → 1/2 Mg2Si2O6 + MgS + ½O2). Using the equation Mg2SiO4 + SiO2 → Mg2Si2O6 and the O-isotope compositions of enstatite and olivine, the O-isotope composition of the additional SiO2 was estimated. Based on the O-isotope composition, we infer that there could be a Si-rich gas with an elevated Δ17O value similar to, or greater than the second trend line (Δ17O = 0.9 ‰) suggested by Weisberg et al. (2021), during chondrule formation. The variation in the Li-isotope compositions of enstatite and olivine grains from EH3 chondrules is smaller than that for the same phases from CV3 chondrules. The variation in the Li-isotope compositions of the enstatite and olivine grains from EH3 chondrules is also smaller than that of their O-isotope compositions. During the recycling of enstatite-chondrite chondrules, both Li- and O-isotope compositions were homogenized. Although enstatite is the major carrier of Li in EH3 chondrules, the Li-isotope composition (δ7Li) of enstatite is lower than that of whole rock EH3 chondrites, suggesting the existence of a phase with higher δ7Li. Meanwhile, the Li-isotope composition and concentration (δ7Li, [Li]) of enstatite is higher than that of olivine. The Li-isotope composition of the Si-rich gas was estimated to be δ7Li = 1 ‰, using a similar mass-balance calculation as applied for the O-isotope composition. The Li-isotope composition of the Si-rich gas from the enstatite-chondrite-chondrule forming-region, is consistent with that of whole rock EH3 chondrites, and differs significantly from that of the Si-rich gas from the carbonaceous-chondrite-chondrule-forming region (δ7Li = −11 ‰) determined by a previous study. We speculate that the Si-rich gas in the carbonaceous-chondrite-chondrule-forming region maintained the Li-isotope heterogeneity inherited from light lithium synthesized by galactic cosmic-ray spallation in the interstellar medium.

¹Samuel Ebert, ³Kazuhide Nagashima, ²Alexander N. Krot, ¹Addi Bischoff
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.05.029]
¹Institut für Planetologie, University of Münster, Münster, Germany
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
Copyright Elsevier

Refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)] in unmetamorphosed chondrites (petrologic type ≤ 3.0) have typically uniform 16O-rich solar-like compositions. The origin of oxygen-isotope heterogeneity within individual refractory inclusions from weakly metamorphosed (petrologic type > 3.0) chondrites remains controversial. It may reflect (i) condensation from a nebular gas having variable O-isotope composition, (ii) gas–solid or gas–melt O-isotope exchange with this gas, and/or (iii) O-isotope exchange with an 16O-depleted aqueous fluid in the host chondrite parent bodies. Here, we present the mineralogy, petrology and O-isotope compositions of refractory inclusions (12 CAIs and 2 AOAs) from the Rumuruti-type (R) chondrites of petrologic type 3 – Northwest Africa (NWA) 753, NWA 1471, and Dhofar 1123. The CAIs and AOAs are extensively altered: melilite is completely replaced by secondary minerals; perovskite is largely replaced by ilmenite; spinel and olivine are enriched in FeO. The polymineralic refractory inclusions have heterogeneous O-isotope compositions: Δ17O ranges from ∼−25 ‰ to ∼5 ‰ (2σ = ±∼2‰). The only exception is a spinel-hibonite inclusion having uniform 16O-depleted composition (Δ17O ∼ −14 ‰). Hibonite, most ferroan spinel, and some olivine and Al,(Ti)-diopside grains in Rumuruti-type chondrite (RC) fragments of low petrologic type (3.15 − 3.2) retained their initial Δ 17O values, which, however, range from −25 ‰ to ∼ −14 ‰, suggesting variations in O-isotope composition of nebular gas in the CAI-forming region. Most Al,Ti-diopside and some olivine and spinel grains in RC refractory inclusions are 16O-depleted compared to minerals most resistant to O-isotope exchange (hibonite and spinel) that retained their original compositions. The most 16O-depleted compositions of Al,Ti-diopside and ferroan olivine have Δ17O of ∼ +5‰ that is similar to Δ17O of the aqueously formed grossular and ferroan olivine. We infer that the 16O-depleted Al,Ti-diopside, olivine, and spinel in isotopically heterogeneous refractory inclusions experienced post-formation O-isotope exchange with aqueous fluids in the RC parent asteroid(s).

¹Christopher R. Glein, ² Yu (余馨婷),²Cindy N. Luu
The Astrophysical Journal 985, 187 Open Access Link to Article [DOI 10.3847/1538-4357/adced4]
¹Space Science Division, Space Sector, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, USA
²Department of Physics and Astronomy, University of Texas at San Antonio, 1 UTSA Circle, San Antonio, TX 78249, USA

The nature of sub-Neptunes is one of the hottest topics in exoplanetary science. Temperate sub-Neptunes are of special interest because some could be habitable. Here, we consider whether these planets might instead be rocky worlds with thick, hot atmospheres. Can recent James Webb Space Telescope observations of TOI-270 d be understood in terms of such a model? We perform thermochemical equilibrium calculations to infer conditions of quenching of C–H–O–N species. Our results indicate apparent CO2–CH4 equilibrium between ∼900 and ∼1100 K. The CO abundance should be quenched higher in the atmosphere where the equilibrium CO/CO2 ratio is lower, potentially explaining a lack of CO. N2 is predicted to dominate the nitrogen budget. We confirm that the atmosphere of TOI-270 d is strongly enriched in both C and Ogas relative to protosolar H, whereas N is likely to be less enriched or even depleted. We attempt to reproduce these enrichments by modeling the atmosphere as nebular gas that extracted heavy elements from accreted solids. This type of model can explain the C/H and Ogas/H ratios, but despite supersolar C/N ratios provided by solids, the NH3 abundance will probably be too high unless there is a nitrogen sink in addition to N2. A magma ocean may be implied, and indeed the oxygen fugacity of the deep atmosphere seems sufficiently low to support the sequestration of reduced N in silicate melt. The evaluation presented here demonstrates that exoplanetary geochemistry now approaches a level of sophistication comparable to that achieved within our own solar system.

^1,2Alan E. Rubin
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14367]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, USA
²Maine Mineral & Gem Museum, Bethel, Maine, USA
Published by arrangement with John Wiley & Sons

Meteorite collection inventories show that many related meteorite groups have very different numerical abundances (e.g., lunar versus Martian meteorites; Eagle Station pallasites versus main-group pallasites; eucrites versus diogenites; ungrouped Antarctic irons versus ungrouped non-Antarctic irons; carbonaceous chondrite-related (CC) iron meteorites versus noncarbonaceous chondrite-related (NC) iron meteorites). The number of members of individual meteorite groups reflects the entire history of these rocks from excavation on their parent bodies to recovery on Earth. These numbers are functions of six main selection factors: (1) volume of the parent-body source region, (2) depth of this source region, (3) time spent in interplanetary space, (4) friability of meteoroids in space and during transit through the Earth’s atmosphere, (5) susceptibility of meteorite finds to terrestrial weathering, and (6) post-fall biases resulting from geography, demography, and preferences by meteorite collectors and analysts. The numerical ratio of lunar/Martian meteorites (~1.8) results from several factors including the Moon’s proximity, the short transit time of lunar meteoroids through interplanetary space, the lower crustal depth from which lunar meteorites were excavated, the lower energy required to launch samples off the Moon than off Mars, and the lower porosity and higher mechanical strength of lunar meteorites. The dunite shortage among asteroidal meteorites may have resulted from the deeply buried olivine-rich meteoroids being ejected hundreds of millions of years ago at the same time as pallasites and irons; however, the dunitic meteoroids (with their lower mechanical strength) would have eroded in interplanetary space on much shorter time scales than their metal-rich fellow travelers.

¹Emily L. Fischer, ¹Stephen W. Parman
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116664]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, 324 Brook St, Providence, RI 02912, United States of America
Copyright Elsevier

Enstatite chondrites are often used as models for the bulk composition of Mercury because they have similarly low oxygen fugacities. However, e-chondrites are too Si-rich to explain the observed composition of Mercury’s lavas. Here we explore a model in which an initially enstatite chondrite-like Mercurian silicate magma ocean loses Si to the large Fe core during early differentiation. We define a Mercury Fractionation Line (MFL) based on average basaltic geochemical terrane compositions and assume Mercury’s bulk silicate composition must fall along this line. We estimate that 26.5–36.7 ± 7.5 % (1σ) Si must be lost from an initial mantle to bring the e-chondrite compositions up to the MFL. Assuming that the Si is partitioned into the core, this implies a core Si content of 2.8–3.9 ± 0.8 wt% and an oxygen fugacity of IW–4.5 ± 1.0. We also show that a model where Mercury was initially ~2 times larger is consistent with more reducing oxygen fugacities (IW–5.0 ± 1.0) and a higher core Si content (~15 wt%). This estimated initial Mercury size is also consistent with predictions from dynamical simulations. We consider how Si partitioning into the core affects the δ30Si composition of the mantle. Though uncertainties are large, we show that as the initial radius of Mercury increases, δ30Si decreases, trending towards the δ30Si composition of enstatite chondrites. Our calculations do not constrain the mechanism by which Mercury’s mantle may have been lost. However, if they are correct, they imply that the mantle loss must have happened after core formation.

¹Lonnie D. Dausend,²Audrey C. Martin, ¹Joshua P. Emery
The Planetary Science Journal 6, 54 Open Access Link to Article [DOI 10.3847/PSJ/ada778]
¹Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, Arizona, 86011, USA
²Department of Physics, University of Central Florida, Orlando, Florida, 32816, USA

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¹Cristina A. Thomas et al. (>10)
The Planetary Science Journal 6, 115 Open Access Link to Article [DOI 10.3847/PSJ/adceba]
¹Northern Arizona University, Department of Astronomy and Planetary Science, P.O. Box 6010, Flagstaff, AZ 86011, USA

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