¹A. Emran, ¹K.M. Stack
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116576]
¹NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
Copyright Elsevier

Hollows on Mercury are small depressions formed by volatile loss, providing important clues about the volatile inventory of the planet’s surface and shallow subsurface. We investigate the composition of hollows in various phases of devolatilization at Dominici crater. By applying a machine learning approach to MESSENGER Mercury Dual Imaging System data, we defined surface units within the study area and extracted their reflectance spectra. We applied linear (areal) spectral modeling using laboratory sulfides, chlorides, graphite, and silicate mineral spectra to estimate the composition of hollows and their surrounding terrains. At Dominici, the hollow on the crater rim/wall is interpreted to be active, while that in the center of the crater is interpreted as a waning hollow. We find that the active hollow predominantly comprises silicates (augite and albite), with a trace amount of graphite and CaS. In contrast, waning hollows contain marginally elevated sulfides (MgS and CaS) and graphite, but slightly lower silicates than the active hollow. The spectra of low reflectance terrain surrounding the hollows appear to be dominated by graphite and sulfides, which contribute to its darker appearance. We suggest that hollow at the crater forms due to thermal decomposition of sulfides, primarily MgS possibly mixed with CaS, as well as possible the depletion of graphite. As devolatilization wanes, a mixture of predominantly silicate minerals remains in the hollows — impeding further vertical growth.

^1,2Roshan Nath et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14342]
¹Indian Institute of Science Education and Research, Bhopal, Madhya Pradesh, India
²Physical Research Laboratory, Ahmedabad, Gujarat, India
Published by arrangement with John Wiley & Sons

Meteorites, remnants of asteroids that successfully survive their passage through the Earth’s atmosphere, hold critical information about the evolution and history of the solar system. Traditional methods of analyzing these rare and precious specimens often involve destructive geochemical techniques, which deplete the sample and limit subsequent analyses. The accurate classification of meteorites, typically determined through petrological examination, is crucial before any further analytical steps. Reflectance spectroscopy, which interprets a sample’s characteristics by analyzing reflected light, has emerged as a nondestructive alternative with significant potential for meteorite classification. In this technique, apparently, sometimes we do not need to process the sample. This technique allows for the examination of spectral features such as absorption bands, symmetry, band centers, inflection points, and overall slope. In this study, we employed spectral reflectance data from 1781 meteorite samples to develop and fine-tune a deep learning model capable of accurate classification. The model was trained on 75% of the dataset and validated on the remaining 25%, achieving a validation accuracy of 93%. These results demonstrate the efficiency of using deep learning and reflectance spectroscopy for meteorite classification, offering a nondestructive and accurate alternative to traditional methods.

^1,2Zhi Cao et al. (>10)
Earth and Planetary Science Letters 658, 119327 Link to Article [https://doi.org/10.1016/j.epsl.2025.119327]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, 550081 Guiyang, China
²Planetary Environmental and Astrobiological Research Laboratory, School of Atmospheric Sciences, Sun Yat-Sen University, 519082 Zhuhai, China
Copyright Elsevier

The space weathering processes modify the microstructure and physicochemical properties of the surface of regolith mineral grains. We report microcraters and space-weathered rims on the surface of plagioclase, pyroxene, olivine, ilmenite and troilite grains in Chang’e-5 scooped lunar soil by electron microscopy. Micro-analysis shows that low-speed secondary impact events indicated by microcraters dominated the evolution of Chang’e-5 regolith materials, which may have driven the formation of a potential microscale redox environment under a special mineral combination. Solar wind and cosmic ray irradiation lead to significant differences in space-weathered rims of mineral surfaces. This indicates the correlation between the nature of different space-weathered rims and the inherent structure and composition of minerals. According to the statistical correlation between space-weathered rim width and track density, the average exposure ages of plagioclase and olivine in Chang’e-5 lunar soil are 2.180−0.222+0.229 Ma and 0.842−0.469+1.120 Ma, respectively. This rule applies to regolith materials with short exposure time. The in situ mineralogical evidence clarifies that compared with Apollo mature lunar soil, Chang’e-5 lunar soil seems to have undergone weaker space weathering modification and shorter exposure history, and the essence is a weakly space-weathered lunar soil from young basalt. The nature of the space-weathered rims on the mineral surface of Chang’e-5 lunar soil reflects the response of regolith material to space weathering in a short exposure history, which is of great significance for the interpretation of spectral data of returned samples.

¹Nancy L. Chabot,^1,2Colin D. Hamill,¹Evangela E. Shread,³Richard D. Ash,⁴Catherine M. Corrigan
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14341]
¹Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
²American Astronomical Society, Washington, DC, USA
³Department of Geology, University of Maryland, College Park, Maryland, USA
⁴Smithsonian Institution, National Museum of Natural History, Washington, DC, USA
Published by arrangement with John Wiley & Sons

Troilite is a common phase in iron meteorites, but there are limited data available for the partitioning behavior of elements between troilite and solid metal. In this study, we present the results of experiments with coexisting Fe-Ni solid metal, an S-rich metallic liquid, and troilite, conducted at 800–925°C in evacuated silica tubes at 1 atm. We report solid metal–troilite partition coefficients for 22 elements commonly studied in iron meteorites. We find that elements with chalcophile behavior have an affinity for troilite and that the majority of siderophile elements are incompatible in troilite. A notable exception to this generalization is for the siderophile element Mo, which partitions roughly equally between solid metal and troilite. We find that Ni and Co are largely concentrated in the solid metal, but given their higher concentrations in iron meteorites, their partitioning behavior indicates that measurable amounts of Ni and Co should be present in iron meteorite troilite when it forms. Our work motivates the need for additional measurements of the trace element composition of iron meteorite troilite and validates the assumption made in iron meteorite crystallization models that partitioning into troilite can be neglected for the majority of siderophile elements, with the exception of Mo.

^1,2,3Denton S. Ebel,^1,4Marina E. Gemma,^1,3,5Michael K. Weisberg,^1,6Jon M. Friedrich
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14328]
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, US
⁵Department of Physical Sciences, Kingsborough College, City University of New York, Brooklyn, New York, USA
⁶Department of Chemistry, Fordham University, Bronx, New York, USA
Published by arrangement with John Wiley & Sons

Compared to the carbonaceous chondrites (CCs), ordinary chondrites (OCs) are depleted in Mg and refractory lithophile elements. The OCs are classified by a trend from high metal (H) to low total iron (L) to low total iron and low metal (LL) compositions with increasing heavy O isotopes and refractory siderophile enrichment. We surveyed many CC for primitive materials that might be analogs of components that formed in, and then escaped, originally solar composition reservoirs from which OCs formed. Amoeboid olivine aggregates (AOA) are nodular accretions with discrete refractory Ca-, Al-, Ti-rich mineral assemblages and often with separate Fe-metal alloy nodules, all surrounded by 16O-rich, near-pure olivine Mg2SiO4 rinds. Most AOAs contain the daughter products of extinct 26Al revealing their very early ages. We find relatively large metal grains with olivine rims forming isolated or clumped nodules or “metal–olivine inclusions” in AOAs in many carbonaceous chondrites, particularly the highly primitive CO-like chondrite Acfer 094 (C2 ungr). Similar nodules have been reported in samples returned from the highly altered, CI-like asteroid Bennu by the OSIRIS-REx mission. In discrete regions and times in the protoplanetary disk, differing drift velocities of these 10s of micron scale components could have caused the correlated loss of both refractory siderophiles (in metal), refractory lithophiles, and Mg and 16O (in olivine). Varying degrees of loss of nodules similar to these “MOI,” from the chondrule-forming reservoirs from which H, L, and LL chondrites accreted could, simultaneously, explain the multiple aspects of their chemical compositions.

^1,2Wenqing Chang, ^1,2Zhiguo Meng, ²Yi Xu, ²Xiaoping Zhang, ²Roberto Bugiolacchi, ^2,3Long Xiao, ^4,5Jinsong Ping, ⁴Hongbo Zhang, ^4,5Yuanzhi Zhang
Earth and Planetary Science Letters 658, 119326 Link to Article [https://doi.org/10.1016/j.epsl.2025.119326]

¹College of Geoexploration Science and Technology, Jilin University, No.6 Ximinzhu Street, Changchun 130026, China
²State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau 999078, China
³Planetary Science Institute, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
⁴Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, CAS, Beijing 100101, China
⁵School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China
Copyright Elsevier

The Apollo basin, situated on the northeastern edge of the South Pole-Aitken (SPA) basin, is the sampling area for the Chang’e -6 (CE-6) mission. In this study, we investigated the microwave thermophysical properties of surface deposits in the region by comparing brightness temperature (TB) and TB difference (dTB) maps derived from CE-2 Microwave Radiometer data combined with topography, chemical elements, and Moon Mineralogy Mapper products. The main results are as follows. (1) High dTB anomaly: A significant high dTB anomaly is identified near the CE-6 landing region, characterized by the highest FeO and TiO2 contents estimated from the small-fresh craters; (2) Basaltic Volcanism: High dTB anomaly is proposed as a new basaltic unit in late stage of mare infill, and, by combining derived ages and geomorphology, we provide a new perspective on the basaltic volcanism with four episodes of magma infill in the CE-6 landing region; (3) Thermophysical Parameters: The high dTB anomaly indicates the potential importance of analyzing the returned CE-6 samples to enhance our understanding of the Moon’s surface deposits using the passive microwave remote sensing data.

¹Cody Schultz,¹Ralph E. Milliken,¹Joseph Boesenberg,^2,3Imene Kerraouch
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14339]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, Rhode Island, USA
²BCMS, Arizona State University, Tempe, Arizona, USA
³Institute für Planetologie, University of Münster, Münster, Germany
Published by arrangement with John Wiley & Sons

CM carbonaceous chondrites are complex brecciated meteorites that exhibit significant chemical, mineralogic, and petrographic diversity both between and within individual samples. As most reflectance spectroscopy studies of carbonaceous chondrites are performed on bulk powders, important questions remain about the true spectral diversity of these complex breccias and the degree to which lab-based meteorite spectra can be reliably related to remotely acquired spectra of primitive asteroids. The Aguas Zarcas meteorite is a unique CM chondrite in that it has been found to exhibit at least five chemically and isotopically distinct lithologies that are all associated with a single fall event. Here, we describe a coordinated petrographic and spectroscopic study to further investigate the thermochemical and collisional history of the Aguas Zarcas parent body and to better understand how to interpret remotely acquired spectra of primitive asteroids. Four intact sections of the Aguas Zarcas meteorite, which together represent at least three to four distinct lithologies, were analyzed using microscope FT-IR (μFT-IR) spectroscopy and electron probe microanalysis (EPMA) elemental mapping. Our study found significant variations in spectral features, particularly in the mid-infrared (MIR) wavelength region, that can be linked to petrographic diversity between lithologies. The relative abundance of matrix phyllosilicates and pyroxene appears to have the strongest influence on the shape, position, and strength of MIR spectral features. Linear spectral unmixing models as a method for compositional interpretation showed varying accuracy when compared to EPMA-based estimates, with integrated μFT-IR spectral maps showing better results compared to unmixing of bulk (larger spot size) FT-IR spectra. A notable discovery in two sections of the Aguas Zarcas meteorite was the presence of carbonate veins along the boundary of chemically and petrographically separate lithologies, which provide important constraints on the nature and timing of pre- and post-brecciation aqueous alteration.

^1,2Fridolin Spitzer, ^1,2Christoph Burkhardt, ³Thomas S. Kruijer, ^1,2Thorsten Kleine
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.03.021]
¹Max Planck Institute for Solar System Research, Department for Planetary Sciences, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
²Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
³Nuclear & Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Avenue (L-231), Livermore, CA 94550, USA
Copyright Elsevier

Isotope anomalies in meteorites reveal a fundamental dichotomy between Non-Carbonaceous- (NC) and Carbonaceous-type (CC) planetary bodies. Until now, this dichotomy is established for the major meteorite groups, representing about 36 distinct parent bodies. Ungrouped meteorites represent an even larger number of additional parent bodies, but whether they conform to the overall NC-CC dichotomy is unknown. Here, the genetics and chronology of 26 ungrouped iron meteorites is considered through nucleosynthetic Mo and radiogenic W isotopic compositions. Secondary cosmic ray-induced modifications of these isotope compositions are corrected using Pt isotope measurements on the same samples. We find that all of the ungrouped irons have Mo isotope anomalies within the range of the major meteorite groups and confirm the NC-CC dichotomy for Mo, where NC and CC meteorites define two distinct, subparallel s-process mixing lines. All ungrouped NC irons fall on the NC-line, which is now precisely defined for 41 distinct parent bodies. The ungrouped CC irons show scatter around the CC-line indicative of small r-process Mo heterogeneities among these samples. These r-process Mo isotope variations correlate with O isotope anomalies, most likely reflecting mixing of CI chondrite-like matrix, chondrule precursors and Ca-Al-rich inclusions. This implies that CC iron meteorite parent bodies accreted the same nebular components as the later-formed carbonaceous chondrites. The Hf-W model ages of core formation for the ungrouped irons overlap with those of the iron meteorite groups from each reservoir and reveal a narrow age peak at ∼3.3 Ma after Ca-Al-rich inclusions for the CC irons. By contrast, the NC irons display more variable ages, including younger ages indicative of impact-induced melting events, which seem absent among the CC irons. This is attributed to the more fragile and porous nature of the CC bodies, making impact-induced melting on their surfaces difficult. The chemical characteristics of all iron meteorites together reveal slightly more oxidizing conditions during core formation for CC compared to NC irons. More strikingly, strong depletions in moderately volatile elements, typical of many iron meteorite parent bodies, predominantly occur among CC irons, for reasons that remain unclear at present.

¹Kirsten Larsen,^1,Alexander N. Krot,¹Daniel Wielandt,²Kazuhide Nagashima,³Guy Libourel,^1,2Martin Bizzarro
Meteoritics & Planetary Society (in Press) Link to Article [https://doi.org/10.1111/maps.14325]
¹Centre for Star and Planet Formation, University of Copenhagen, Copenhagen, Denmark
²Hawaii Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawaii, USA
³Observatoire de la Côte d’Azur, UMR 7293 LAGRANGE, Nice, France
Published by arrangement with John Wiley & Sons

A coarse-grained igneous calcium-aluminum-rich inclusion (CAI) N-53, 4.3 × 5.9 mm in size, from the CR (Renazzo-type) carbonaceous chondrite Northwest Africa (NWA) 6043 is composed of two mineralogically, chemically, and isotopically distinct units—type B (B) and type C (C). Type B unit occurs in the CAI core and consists of melilite (Åk28–56), AlTi-diopside, anorthite, spinel, and minor Fe,Ni-metal. Type C unit forms islands in B (Cc) and mantle (Cm) around it and consists of Na-bearing åkermanitic melilite (Åk58–72, 0.18–0.86 wt% Na2O), anorthite, AlTi-diopside (up to 1.2 wt% Cr2O3), spinel (up to 2.1 wt% Cr2O3), perovskite, and minor wollastonite. The outermost portion of N-53 contains relict grains of olivine (Fa4) and low-Ca pyroxene (Fs4Wo5); Wark–Lovering rim is absent. Magnesian spinel in B and C is 16O-rich (Δ17O ~ −23‰); Cr-bearing spinel in Cm is 16O-depleted (Δ17O ~ −11‰). AlTi-diopside, anorthite, and melilite in B and Cc are 16O-depleted to various degrees (Δ17O ~ −22‰ to −19‰, −21‰ to −17‰, −13‰ to −8‰, respectively). AlTi-diopside, anorthite, and melilite in Cm show a range of compositions correlated with a distance from the CAI edge (Δ17O ~ −18‰ to −8‰, −16‰ to −8‰, ~ −8‰ to −2‰). Melilite in B has the heaviest Mg-isotope composition (Δ25Mg ~ 10‰); average Δ25Mg of melilite, AlTi-diopside, and spinel in C are ~9, ~8‰, and ~6‰, respectively; anorthite in both units has Δ25Mg of ~4‰. On the Al-Mg evolutionary diagram, melilite data in B oscillate around the canonical isochron. Melilite, AlTi-diopside, and spinel in C have resolvable δ26Mg* and deviate to the left of this isochron; anorthite in both units has barely resolvable δ26Mg*. Although these data are consistent with late-stage reprocessing of N-53, they provide no clear chronological information. We conclude that N-53 experienced multiple melting events. Initial melting of solid precursors took place in an 16O-rich gaseous reservoir and resulted in formation of the uniformly 16O-rich (Δ17O ~ −24‰) type B CAI. Subsequent single- or multi-stage partial melting of this CAI occurred in an 16O-depleted gaseous reservoir(s) and resulted in addition of SiO and Na to the CAI melt, O- and Mg-isotope exchange, and crystallization of C unit.

^1,2,3Harold C. Connolly Jr et al. (>10)
Meteoritics & Planetary Society (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14335]
¹Department of Geology, School of Earth and Environment, Rowan University, Glassboro, New Jersey, USA
²Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
³Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
Published by arrangement with John Wiley & Sons

The OSIRIS-REx mission returned a sample of regolith from the carbonaceous asteroid Bennu in September 2023. We present preliminary in situ investigations of the petrology and petrography of selected particles ranging in size from 0.5 to 3 mm. Using a combination of optical and electron beam techniques, we investigate whole specimens and polished sections belonging to morphologically and visually distinct categories of particles. We find that morphological differences in the particles are reflective of petrographic and petrologic differences, leading to the conclusion that we have at least two distinct major lithologies in the bulk sample. Our findings support predictions from remote sensing, suggesting that the morphological differences observed in the boulder population of Bennu correspond to petrologic differences. Our data provide insight into the geologic activity on Bennu’s parent body and the petrographic framework needed to contextualize the detailed analyses of this pristine asteroidal material.