¹David W. Mittlefehldt
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.08.010]
¹Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Boulevard, Houston, TX 77058, USA
Copyright Elsevier

I have done major element analyses by electron microprobe, in-situ trace element analyses by laser ablation inductively coupled plasma mass spectrometry, and instrumental neutron activation analyses on bulk samples of olivine grains separated from main-group and Eagle-Station pallasites. Most main-group pallasite olivines have homogeneous Fe/Mg yet have varying Fe/Mn. Those few with anomalously ferroan olivine have Fe/Mn within the range of other main-group pallasites. High-temperature redox process coupled with diffusional exchange resulted in the homogeneous compositions of most main-group pallasites; simple diffusional exchange alone is insufficient. The Eagle-Station pallasites have Fe/Mn twice that of main-group pallasites with similar Fe/Mg, a result of having roughly half the Mn content. The Ni/Co ratio of main-group pallasite olivines is relatively constant and was imposed by the same high-temperature redox/diffusion process that established Fe/Mg-Fe/Mn relationships. Variability in trace lithophile element contents within individual pallasites and within individual olivine grains, coupled with very low contents for some that are inconsistent with formation from a magma, indicate that the current mm-sized olivine grains were recrystallized from a fragmental olivine breccia; grain fragments from different portions of an original dunitic mantle were juxtaposed in the breccia. Main-group pallasites are dimict breccias formed of fragmented and mixed monomict dunite breccia and metallic breccia that were formed in the walls and floor of a large basin that penetrated the mantle of their parent asteroid. Limited data indicate that Eagle-Station pallasites may have been formed by a similar process. Given that Eagle-Station and main-group pallasites were formed in distinct regions of the early Solar System, the pallasite forming process likely was common in early Solar System history.

¹Mario Fischer-Gödde et al.(>10)
Science 385, 752-756 Link to Article [DOI: 10.1126/science.adk4868]
¹Institut für Geologie und Mineralogie, University of Cologne, 50674 Cologne, Germany.
Reprinted with permission from AAAS

An impact at Chicxulub, Mexico, occurred 66 million years ago, producing a global stratigraphic layer that marks the boundary between the Cretaceous and Paleogene eras. That layer contains elevated concentrations of platinum-group elements, including ruthenium. We measured ruthenium isotopes in samples taken from three Cretaceous-Paleogene boundary sites, five other impacts that occurred between 36 million to 470 million years ago, and ancient 3.5-billion- to 3.2-billion-year-old impact spherule layers. Our data indicate that the Chicxulub impactor was a carbonaceous-type asteroid, which had formed beyond the orbit of Jupiter. The five other impact structures have isotopic signatures that are more consistent with siliceous-type asteroids, which formed closer to the Sun. The ancient spherule layer samples are consistent with impacts of carbonaceous-type asteroids during Earth’s final stages of accretion.

¹Z. Váci,²P.M. Kruttasch,¹M.J. Krawczynski,³R.C. Oglior,²K. Mezger
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.08.011]
¹Department of Earth and Planetary Sciences, Washington University in St. Louis, MO, USA
²Institut für Geologie, Universität Bern, Switzerland
³Department of Physics, Washington University in St. Louis, MO, USA
Copyright Elsevier

The ungrouped dunitic achondrite Northwest Africa (NWA) 12,217 contains symplectic spinel-pyroxene veins that are mineralogically identical to symplectites in other ultramafic planetary materials. The morphology and amount of chromite present in these features relative to the Cr in their olivine hosts suggest an exogenous origin. Petrological experiments show that a Cr laden sulfide liquid reacts with olivine to produce pyroxene by scavenging Mg and Fe from olivine to crystallize chromite. The liquid infiltrates cracks and grain boundaries within the olivine and produces a vein-like symplectic chromite-pyroxene mineralogy similar to that observed in NWA 12217. This process is likely responsible for forming the symplectites in the related ultramafic achondrites NWA 12217, 12319, 12562, and 13954, along with many other achondrites. The nucleosynthetic Cr isotopic composition of chromites appears to be in disequilibrium with that of silicates in NWA 12217, suggesting that the liquids responsible for the symplectite forming reaction are at least partially sourced from a different parent body and result from an impact .

¹Pascal M. Kruttasch,^1,2Aryavart Anand,³Paul H. Warren,⁴Chi Ma,¹Klaus Mezger
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.08.012]
¹Institut für Geologie, Universität Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
²Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
³Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA
⁴Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
Copyright Elsevier

Establishing the temporal evolution of the ureilite parent body(ies) is crucial for understanding the quantitative timescale of planetesimal formation and evolution in the protoplanetary disk. In order to establish a timeline for these early processes, age constraints on the accretion, differentiation and secondary reduction were obtained with the short-lived ⁵³Mn-⁵³Cr chronometer to whole-rock and sequentially digested fractions of main group ureilites. A whole-rock isochron dates the reservoir-scale Mn-Cr fractionation in the ureilite parent body(ies), associated with magmatic differentiation, to 2.89-0.51+0.56 Ma after CAI formation. This age implies that the ureilite parent body(ies) accreted no later than ∼1.5 Ma after CAI formation, at a time when the NC-CC dichotomy was already established. The ⁵³Mn-⁵³Cr systematics of fractions from chromite-bearing ureilites yield an age of 4.29-0.45+0.49 Ma after CAI formation for a secondary reduction event on the parent body. This event is commonly associated with the catastrophic disruption of the ureilite parent body while still hot. The chromite model ages are consistent with the isochron ages obtained from chromite-bearing ureilites. Collectively these ages indicate that chemical differentiation processes were underway on the ureilite parent body(ies) during the time interval when undifferentiated meteorite parent bodies were forming, and may have paused at the peak of planetesimal formation when planetary collisions were common.

^1,2Shurui Chen et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116256]
¹College of Surveying & Geo-Informatics, Tongji University, Shanghai 200092, China
²The Shanghai Key Laboratory of Space Mapping and Remote Sensing for Planetary Exploration, Tongji University, Shanghai 200092, China
Copyright Elsevier

Exploring the concealed subsurface structures and materials beneath the lunar surface can reveal significant insights into geological history. This study offers a comprehensive analysis of the stratigraphic interpretation and subsurface material composition at the Chang’E-4 landing site, integrating both in-situ and orbital radar with multispectral datasets. We report the identification of a subsurface structure, which resembles a buried impact crater (~420 m in diameter) under the Yutu-2 rover’s path. This crater could degrade over a period of 0.42 to 0.53 Ga, with an initial diameter of 293 to 323 m and an initial depth of 45.9 to 51.4 m. Surface material above the buried crater, evaluated by the in-situ visible and near-infrared imaging spectrometer (VNIS) detector, shows a higher abundance of clinopyroxene compared to surrounding areas, where a near-equal mix of clinopyroxene and orthopyroxene is observed. Assessment of crater diameters in proximity to the Chang’E-4 landing site, along with the mineral compositions at their epicenters, reveals a decrease in the abundance of clinopyroxene and plagioclase with depth. Conversely, the quantities of orthopyroxene and olivine increase, implying that clinopyroxene-rich Finsen ejecta significantly influenced the Chang’E-4 landing site’s geological composition. Two potential stratigraphic boundary depths are identified at 13.5 and 22 m, based on pronounced variations in mineral abundance, offering fresh insights into subsurface delineation beyond radar data. Considering the VNIS and vertical mineral composition, we propose the buried crater’s formation resulted from Finsen crater’s ejecta. Also, we identify eight potential historical impacts by comparing subsurface relief variations with mineral composition ratios between clinopyroxene and orthopyroxene. The integration of subsurface structure, along with surface and subsurface mineral composition, enables a more robust stratigraphic interpretation, facilitates shallow material source analysis, and allows for historical impact tracing.

¹Philipp Zanon,¹Michelle Dunn, ¹Geoffrey Brooks
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.116257]
¹Swinburne University of Technology, John St, Hawthorn, Melbourne, 3122, Victoria, Australia
Copyright Elsevier

The detrimental effects and challenges of Lunar dust for Lunar exploitation were first identified during the Apollo missions. During the extra vehicle activities (EVAs) undertaken by astronauts, the dust clogged mechanisms, disrupted sensors, and caused several health issues for the astronauts. Despite numerous studies, there is no definite understanding as to why different Apollo missions experienced varying levels of dust disruptions. The variations in dust behavior could be attributed to the amount of radiation the Lunar soil is exposed to, as well as mineralogy and particle sizes. To enhance our understanding of Lunar dust behavior this study investigated Space Recourse Technologies, formally known as Exolith, simulant at different mineral compositions, and their surface detachment characteristics were measured. Experiments measuring the individual minerals and their mixed simulant-like counterparts were conducted using electrostatic fields. Inclusive to this, non-dried and dried samples were compared by measuring adhesion to target plates when subject to electrostatic forces. The results found that Highlands simulant exhibited a higher buildup on a target plate than its Mare counterpart by an average of 33% under the same conditions, likely due to particle size differences. In addition to these findings, evidence of particle reactivity decay was observed under repeated tests with up to 60% less Mare simulant and 36% Highlands deposition being measured compared to the first set of experiments. A possible explanation may be particle reactivity. Microscope images identified that particles are transported in groups as opposed to individual grains. These results will help researchers in tailoring dust mitigation solutions based on different regions on the Lunar surface and influence mission planning from the perspective of dust mitigation and contamination.

¹Lingzhi Sun,¹Paul G. Lucey
Earth and Planetary Science Letters 643, 118931 Link to Article [https://doi.org/10.1016/j.epsl.2024.118931]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
Copyright Elsevier

The South Pole-Aitken (SPA) basin, excavating more than 100 km depth, must have exposed extensive lunar mantle materials, making it a promising location for sampling mantle material. To investigate the distribution of potential mantle materials across the SPA basin, we mapped the distribution of Mg# and major minerals contents using Moon Mineralogy Mapping data and radiative transfer modeling. We found that the potential mantle material exposed by SPA is Mg-rich orthopyroxenite, and we identified the locations of seven mantle candidate sites. The Chang’E-6 sample return site is located near mantle candidate sites within the Apollo basin, making it promising to return the first unambiguous mantle sample. Our Mg# and mineral mapping results show that the SPA ejecta is enriched in low-Ca pyroxene (LCP) with Mg#≥85, consistent with a post-overturn upper mantle composition. The enrichment of LCP in the SPA upper mantle may result from a low content of dunite or incomplete overturn.

¹C. J. Floyd,²S. Benito,¹P.-E. Martin,¹L. E. Jenkins,³E. Dunham,^1,4,5L. Daly,¹M. R. Lee
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14250]
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK
²Ruhr-Universität Bochum, Chair of Materials Technology, Bochum, Germany
³Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, Los Angeles, California, USA
⁴Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, New South Wales, Australia
⁵Department of Materials, University of Oxford, Oxford, UK
Published by arrangement with John Wiley & Sons

The sizes of chondrules are a valuable tool for understanding relationships between meteorite groups and the affinity of ungrouped chondrites, documenting temporal/spatial variability in the solar nebula, and exploring the effects of parent body processing. Many of the recently reported sizes of chondrules within the CM carbonaceous chondrites differ significantly from the established literature average and are more closely comparable to those of chondrules within CO chondrites. Here, we report an updated analysis of chondrule dimensions within the CM group based on data from 1937 chondrules, obtained across a suite of CM lithologies ranging from petrologic subtypes CM2.2 to CM2.7. Our revised average CM chondrule size is 194 μm. Among the samples examined, a relationship was observed between petrologic subtype and chondrule size such that chondrule long-axis lengths are greater in the more highly aqueously altered lithologies. These findings suggest a greater similarity between the CM and CO chondrites than previously thought and support arguments for a genetic link between the two groups (i.e., the CM-CO clan). Using the 2-D and 3-D data gathered, we also apply numerous stereological corrections to examine their usefulness in correcting 2-D chondrule measurements within the CM chondrites. Alongside this analysis, we present the details of a standardized methodology for 2-D chondrule size measurement to facilitate more reliable inter-study comparisons.

¹L.E. McGraw,¹J.P. Emery,¹C.A. Thomas,²A.R. Rivkin
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.116252]
¹Northern Arizona University, Department of Astronomy and Planetary Science, P.P. Box 6010, Flagstaff, AZ 86011, USA
²JHU/APL, 211100 Johns Hopkins Road, Laurel, MD 20723, United States of America
Copyright Elsevier

Near-Earth Asteroids (NEAs) are excellent laboratories for processes that affect the surfaces of airless bodies. Most NEAs were not expected to contain OH/H2O on their surfaces because they are primarily S-complex objects and sourced from the inner Main Belt, which is interior of the frost line, and their surface temperatures are high enough to remove these volatiles. However, a 3-μm feature typically indicative of OH/H2O was identified on other seemingly dry bodies in the inner Solar System, such as the Moon and Vesta, and more recently on the NEAs (433) Eros, (1036) Ganymed, and (3122) Florence. The most likely sources for OH/H2O on these bodies include carbonaceous chondrite impacts or interactions with protons implanted by solar wind. We investigated the causes of band depth and shape variations on NEAs by comparing new observations of Eros and Ganymed to those previously published and conducting a rotationally-resolved spectral study on Florence. All spectra discussed were collected by SpeX on NASA’s IRTF using the LXD_short (1.67–4.2 μm) mode to characterize the 3-μm region. Some observations also used the prism (0.7–2.52 μm) mode to characterize asteroid spectral type and investigate silicate composition dependencies. All three asteroids possess exogenously sourced OH/H2O and have spectra that show potential spatially correlated variations in band depth or shape. Eros’ band is slightly wider at the poles than at lower sub-observer latitudes, possibly due to its high obliquity, which ensures that each polar region is oriented toward the Sun over a significant part of its orbit. Ganymed’s trends in hydration band depth with sub-solar longitude and band I center suggest a carbonaceous or cometary impactor that struck the surface around 0° relative longitude, excavating a relatively magnesium- and olivine-enriched layer. Florence’s total hydrogen concentration remains stable across the surface even as the OH-to-H2O ratio changes as the asteroid rotates. These three examples suggest that non-native OH/H2O on other bodies will likely also be spatially dependent, regardless of delivery mechanism.

¹J.O. Edgar,²J.A. Gould,³K. Badreshany,²S.P. Graham,¹J. Telling
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.116238]
¹School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
²Faculty of Sciences, Agriculture and Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom
³Department of Archaeology, Durham University, Durham DH1 3LE, United Kingdom
Copyright Elsevier

The aeolian transport of sand generates fine material through abrasion. On Mars this process occurs at lower temperatures than on Earth, however, there is minimal data on the effects of temperature on aeolian abrasion rates. Here, results are reported of laboratory experiments where a suite of single-phase, Mars relevant minerals (feldspar, olivine, pyroxene, quartz and opal) were exposed to conditions simulating aeolian abrasion at temperatures common to the Martian surface (193 to 293 K). Our results suggest that mineral specific differences in solid phase parameters result in non-similar changes in abrasion rates with temperature. We propose this will ultimately exert a control on the composition and reactivity of the Martian surface.