¹Tom Boonants,¹Steven Goderis,¹Bastien Soens,¹Flore Van Maldeghem,^2,3Stepan M. Chernonozhkin,²Frank Vanhaecke,⁴Matthias van Ginneken,¹Christophe Snoeck,¹Philippe Claeys
Meteoritics & Planetary Science (in Press)  Link to Article [https://doi.org/10.1111/maps.14188]
¹Archaeology, Environmental Changes and Geo-Chemistry, Vrije Universiteit Brussel, Brussels, Belgium
²Department of Chemistry, Atomic & Mass Spectrometry A&MS Research Unit, Ghent University, Ghent, Belgium
³Chair of General and Analytical Chemistry, Montanuniversität Leoben, Leoben, Austria
⁴Centre for Astrophysics and Planetary Science, School of Physical Sciences, University of Kent, Canterbury, UK
Published by arrangement with John Wiley & Sons

Upon passage through Earth’s atmosphere, micrometeorites undergo variable degrees of melting and evaporation. Among the various textural and chemical groups recognized among cosmic spherules, that is, melted micrometeorites, a subset of particles may indicate anomalously high degrees of vaporization based on their chemical and isotopic properties. Here, a selection of such refractory element-enriched cosmic spherules from Widerøefjellet (Sør Rondane Mountains, East Antarctica) is characterized for their petrographic features, major and trace element concentrations (N = 35), and oxygen isotopic compositions (N = 23). Following chemical classification, the highly vaporized particles can be assigned to either the “CAT-like” or the “High Ca-Al” cosmic spherule groups. However, through the combination of major and trace element concentrations and oxygen isotopic data, a larger diversity of processes and precursor materials are identified that lead to the final compositions of refractory element-enriched particles. These include fragmentation, disproportional sampling of specific mineral constituents, differential melting, metal bead extraction, redox shifts, and evaporation. Based on specific element concentrations (e.g., Sc, Zr, Eu, Tm) and ratios (e.g., Fe/Mg, CaO + Al2O3/Sc + Y + Zr + Hf), and variations of O isotope compositions, “CAT-like” and “High Ca-Al” cosmic spherules likely represent a continuum between mineral endmembers from both primitive and differentiated parent bodies that experienced variable degrees of evaporation.

¹Benjamin H. Gruber,^1,2Robert W. Nicklas,¹James M. D. Day,¹Emily J. Chin,³Minghua Ren,⁴Rachel E. Bernard
Meteortics & Planetary Science (in Press) Open Access Link to Artivcle [https://doi.org/10.1111/maps.14179]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
²Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, Massachusetts, USA
³Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, Nevada, USA
⁴Department of Geology, Amherst College, Amherst, Massachusetts, USA
Published by arrangement with John Wiley & Sons

Brachinites and brachinite-like achondrites are olivine-rich meteorites that represent materials after partial metal–silicate differentiation on multiple early Solar System bodies. Both meteorite types show macroscopic textures of olivine crystals, which make up >70 modal percent of their mineralogy. We investigated the orientations of olivine using electron backscatter diffraction (EBSD) and elemental compositions from paired brachinite-like achondrites and one brachinite. The olivine orientations are characterized by a strong concentration of [010] axes with maxima perpendicular to the foliation/layering and a concentration of [001] axes distributed in a girdle or, in a few samples, as point maxima. Trace element abundances of the olivine in these meteorites determined using laser ablation inductively coupled plasma–mass spectrometry have uniformly low concentrations of sodium (<300 μg g−1), aluminum (<70 μg g−1), and titanium (<40 μg g−1) that are distinct from olivine in chondrites or within terrestrial lavas. Instead, brachinite and brachinite-like olivine compositions broadly overlap those of olivine from melt-depleted mantle lithologies on Earth. Evidence from olivine trace element geochemistry, in conjunction with mineral fabrics, supports that these meteorites formed as melt residues on their host planetary body(ies).

^1,2Haiyang Xian,^1,2Jianxi Zhu,¹Yiping Yang,^1,2Shan Li,^1,2Jiaxin Xi,¹Xiaoju Lin,^1,2Jieqi Xing,¹Xiao Wu,^1,2Hongmei Yang,^1,2Hongping He,^2,3Yi-Gang Xu
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14174]
¹CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
²University of Chinese Academy of Sciences, Beijing, China
³State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
Published by arrangement with John Wiley & Sons

Charge disproportionation of ferrous iron has been considered as one of the mechanisms for the formation of metallic iron on the lunar surface. However, the detailed mechanism of the disproportionation reaction on the Moon is yet to be elucidated. We provide direct evidence for the ferrous disproportionation reaction that produces nano phase metallic iron (npFe0) during a rapid cooling process after splash melting from a lunar sample returned by China’s Chang’e-5 mission. Space weathering processes have resulted in the formation of three distinct zones at the rim of a pyroxene fragment, as observed through transmission electron microscopy. These zones, made up of splashed melts, newly formed melts from the substrate, and the mineral, are distinguished as I, II, and III. Quantitative analyses of the iron valence state by electron energy loss spectroscopy show that disproportionation reactions occurred in zone II at a low temperature of <570°C during a rapid cooling process. The reaction led to the production of α-structure npFe0 and Fe3+ reserve in the glass phase. The npFe0 produced by the disproportionation reaction has a larger grain size than those formed from solar wind irradiation, implying that micrometeoroid impacts mainly contribute to the darkening of visible and near-infrared reflectance. These findings reveal a novel rim structure by repeated space weathering and a universal formation mechanism of npFe0 during micrometeoroid impacts, suggesting that the disproportionation reaction could be widespread on airless bodies with impact-induced splash processes.

^1,2,3Phillip Gopon,^3,4James O. Douglas,^3,5Hazel Gardner,³Michael P. Moody,²Bernard Wood,^2,6Alexander N. Halliday,²Jon Wade
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14184]
¹Department of Applied Geosciences and Geophysics, University of Leoben, Leoben, Austria
²Department of Earth Science, University of Oxford, Oxford, UK
³Department of Materials, University of Oxford, Oxford, UK
⁴Department of Materials, Imperial College London, London, UK
⁵Culham Science Centre, UK Atomic Energy Authority, Abingdon, UK
⁶Earth Institute, Columbia University, New York, New York, USA
Published by arrangement with John Wiley & Sons

Millimeter-to-nanometer-sized iron- and nickel-rich metals are ubiquitous on the lunar surface. The proposed origin of these metals falls into two broad classes which should have distinct geochemical signatures—(1) the reduction of iron-bearing minerals or (2) the addition of metals from meteoritic sources. The metals measured here from the Apollo 16 regolith possess low Ni (2–6 wt%) and elevated Ge (80–350 ppm) suggesting a meteoritic origin. However, the measured Ni is lower, and the Ge higher than currently known iron meteorites. In comparison to the low Ni iron meteorites, the even lower Ni and higher Ge contents exhibited by these lunar metals are best explained by impact-driven volatilization and condensation of Ni-poor meteoritic metal during their impact and addition to the lunar surface. The presence of similar, low Ni-bearing metals in Apollo return samples from geographically distant sites suggests that this geochemical signature might not be restricted to just the Apollo 16 locality and that volatility-driven modification of meteoritic metals are a common feature of lunar regolith formation. The possibility of a significant low Ni/high Ge meteoritic component in the lunar regolith, and the observation of chemical fractionation during emplacement, has implications for the interpretation of both lunar remote-sensing data and bulk geochemical data derived from sample return material. Additionally, our observation of predominantly meteoritic sourced metals has implications for the prevalence of meteoritic addition on airless planetary bodies.

^1,2Naoya Imae et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14178]
¹National Institute of Polar Research (NIPR), Tachikawa, Tokyo, Japan
²The Graduate University for Advanced Studies (SOKENDAI), Tachikawa, Japan
Published by arrangement with John Wiley & Sons

Although CI chondrites are susceptible to terrestrial weathering on Earth, the specific processes are unknown. To elucidate the weathering mechanism, we conduct a laboratory experiment using pristine particles from asteroid Ryugu. Air-exposed particles predominantly develop small-sized euhedral Ca-S-rich grains (0.5–1 μm) on the particle surface and along open cracks. Both transmission electron microscopy and synchrotron-based computed tomography combined with XRD reveal that the grains are hydrous Ca-sulfate. Notably, this phase does not form in vacuum- or nitrogen-stored particles, suggesting this result is due to laboratory weathering. We also compare the Orgueil CI chondrite with the altered Ryugu particles. Due to the weathering of pyrrhotite and dolomite, Orgueil contains a significant amount of gypsum and ferrihydrite. We suggest that mineralogical changes due to terrestrial weathering of particles returned directly from asteroid occur even after a short-time air exposure. Consequently, conducting prompt analyses and ensuring proper storage conditions are crucial, especially to preserve the primordial features of organics and volatiles.

¹KATHERINE DE KLEER,^1,2ERY C. HUGHES,³FRANCIS NIMMO,¹JOHN EILER,⁴AMY E. HOFMANN,^5,6,7STATIA LUSZCZ-COOK,⁸KATHY MANDT
Science 384, 682-687 Link to Article [DOI: 10.1126/science.adj0625]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
²Earth Structure and Processes, Te Pū Ao | GNS Science, Avalon 5011, Aotearoa New Zealand.
³Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA 95064, USA.
⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
⁵Liberal Studies, New York University, New York, NY 10023, USA.
⁶Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA.
⁷Department of Astrophysics, American Museum of Natural History, New York, NY 10024, USA.
⁸NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
Reprinted with permission from AAAS

Jupiter’s moon Io hosts extensive volcanism, driven by tidal heating. The isotopic composition of Io’s inventory of volatile chemical elements, including sulfur and chlorine, reflects its outgassing and mass-loss history and thus records information about its evolution. We used submillimeter observations of Io’s atmosphere to measure sulfur isotopes in gaseous sulfur dioxide and sulfur monoxide, and chlorine isotopes in gaseous sodium chloride and potassium chloride. We find 34S/32S = 0.0595 ± 0.0038 (equivalent to δ34S = +347 ± 86‰), which is highly enriched compared to average Solar System values and indicates that Io has lost 94 to 99% of its available sulfur. Our measurement of 37Cl/35Cl = 0.403 ± 0.028 (δ37Cl = +263 ± 88‰) shows that chlorine is similarly enriched. These results indicate that Io has been volcanically active for most (or all) of its history, with potentially higher outgassing and mass-loss rates at earlier times.

¹Justin Filiberto,²Molly C. McCanta
American Mineralogist 109, 805-813 Link to Article [https://doi.org/10.2138/am-2023-9015]
¹Astromaterials Research and Exploration Science (ARES) Division, NASA Johnson Space Center, Houston, Texas 77058, U.S.A.
²Department of Earth and Planetary Sciences, University of Tennessee at Knoxville, Knoxville, Tennessee 37996, U.S.A.
Copyright: The Mineralogical Society of America

The surface of Venus is in contact with a hot (~470 °C), high pressure (92 bars), and caustic (CO2 with S, but little H2O) atmosphere, which should cause progressive alteration of the crust in the form of sulfate and iron-oxide coatings; however, the exact rate of alteration and mineral species are not well constrained. Different experimental approaches, each with its own limitations, are currently being used to constrain mineralogy and alteration rates. One note is that no experimental approach has been able to fully replicate the necessary conditions and sustain them for a significant length of time. Furthermore, geochemical modeling studies can also constrain surface alteration mineralogy, again with different assumptions and limitations. Here, we review recent geochemical modeling and experimental studies to constrain the state of the art for alteration mineralogy, rate of alteration, open questions about the surface mineralogy of Venus, and what can be constrained before the fleet of missions arrives later this decade.

Combining the new results confirms that basalt on the surface of Venus should react quickly and form coatings of sulfates and iron-oxides; however, the mineralogy and rate of alteration are dependent on physical properties of the protolith (including bulk composition, mineralogy, and crystallinity), as well as atmospheric composition, and surface temperature. Importantly, the geochemical modeling results show that the mineralogy is largely controlled by atmospheric oxygen fugacity, which is not well constrained for the near-surface environment on Venus. Therefore, alteration experiments run over a range of oxygen and sulfur fugacities are needed across a wide range of Venus analog materials with varying mineralogy and crystallinity.

^1,2Andrew B. Foerder,¹Peter A.J. Englert,^3,4Janice L. Bishop,⁵Christian Koeberl,⁶Zachary F.M. Burton,^3,4Shital Patel,⁵Everett K. Gibson
American Mineralogist 109, 682-700 Link to Article [https://doi.org/10.2138/am-2022-8779]
¹Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, Honolulu, Hawai’i 96822-2336, U.S.A.
²Department of Earth, Environmental, and Planetary Sciences, University of Tennessee, Knoxville, Knoxville, TN, 37996-1526, U.S.A.
³SETI Institute, Mountain View, California 94043-5139, U.S.A.
⁴NASA Ames Research Center, Moffet Field, California 94035-1000, U.S.A.
⁵Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
⁶Department of Geological Sciences, Stanford University, Stanford, California, 94305, U.S.A.
⁷NASA Johnson Space Center, Houston, Texas 77058-3607, U.S.A.
Copyright: The Mineralogical Society of America

The McMurdo Dry Valleys of Antarctica provide a testbed for alteration processes on Mars due to the cold, arid, and windy conditions. Analysis of three sediment cores collected from Don Juan Basin, Wright Valley, Antarctica, reveals that surface sediment formation is primarily dominated by physical alteration. Chemical alteration occurs sporadically in this region and is frequently indicated by the accumulation of sulfates and Cl-bearing salts. We investigated the effects of physical and chemical alteration in Don Juan Basin by considering major and trace element abundances in the sediments based on depth and location. Our results indicate inversely related chemical- and physical-alteration gradients with proximity to Don Juan Pond where the current center of the pond represents a more chemically altering environment and the perimeter a more physically altering one. Comparing calculated sulfate abundances for Don Juan Basin cores to rock and soil samples taken by the rover Curiosity at Gale crater, we observed that the core from within Don Juan Pond best matches Curiosity soil sulfate abundances.

A new Chemical Index of Alteration equation that adjusts for salt dilution was also applied to the Antarctic cores and Curiosity rocks and soils. Our analysis indicates a significantly higher degree of chemical alteration than originally reported for most Antarctic and martian samples. Our investigation provides evidence for aqueous-based chemical alteration under cold, hyper-arid conditions in Don Juan Basin, Antarctica. Our work also demonstrates the analogous nature of terrestrial microenvironments to similar, local-scale sample sites on Mars, thereby supporting past or present chemical alteration on Mars.

^1,2Oriel A. Humes,³Audrey C. Martin,¹Cristina A. Thomas,¹Joshua P. Emery
The Planetary Science Journal 5, 5 108 Open Access Link to Article [DOI 10.3847/PSJ/ad3a69]
¹Northern Arizona University, Flagstaff, AZ 86011, USA; oriel.humes@tu-braunschweig.de
²Technische Universität Braunschweig, Braunschweig, NI 38106, Germany
³University of Central Florida, Orlando, FL 32816, USA

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

¹P.J.Gasda et al.(>10)
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE007923]
¹Los Alamos National Laboratory, Los Alamos, NM, USA
Published by arrangement with John Wiley & Sons

Manganese has been observed on Mars by the NASA Curiosity rover in a variety of contexts and is an important indicator of redox processes in hydrologic systems on Earth. Within the Murray formation, an ancient primarily fine-grained lacustrine sedimentary deposit in Gale crater, Mars, have observed up to 45× enrichment in manganese and up to 1.5× enrichment in iron within coarser grained bedrock targets compared to the mean Murray sediment composition. This enrichment in manganese coincides with the transition between two stratigraphic units within the Murray: Sutton Island, interpreted as a lake margin environment, and Blunts Point, interpreted as a lake environment. On Earth, lacustrine environments are common locations of manganese precipitation due to highly oxidizing conditions in the lakes. Here, we explore three mechanisms for ferromanganese oxide precipitation at this location: authigenic precipitation from lake water along a lake shore, authigenic precipitation from reduced groundwater discharging through porous sands along a lake shore, and early diagenetic precipitation from groundwater through porous sands. All three scenarios require highly oxidizing conditions and we discuss oxidants that may be responsible for the oxidation and precipitation of manganese oxides. This work has important implications for the habitability of Mars to microbes that could have used Mn redox reactions, owing to its multiple redox states, as an energy source for metabolism.