¹Lingxi Zhang,^1,2Xiaohui Fu,^1,2Zongcheng Ling,¹Erbin Shi,¹Haijun Cao
Journal Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2023JE008157]
¹Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China
²CAS Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei, China
Published by arrangement with John Wiley & Sons

Akaganeite and jarosite were detected in two mudstone drill samples from Vera Rubin ridge (VRR), Gale crater by Chemistry & Mineralogy X-Ray Diffraction (CheMin). The co-occurrence of these two minerals is quite rare in both terrestrial and Martian aqueous environments. In order to confine the chemical conditions of paragenetic akaganeite and jarosite, and provide insight into late-stage diagenetic alterations at VRR, we synthesized akaganeite and jarosite with varying SO42− concentrations and initial pH levels. Synthetic samples were characterized using Field Emission Scanning Electron Microscopy, X-ray powder diffraction and Raman spectroscopy. Our study reveals that akaganeite and jarosite exist in equilibrium in the solution with 0.011–0.028 M SO42− with respect to 0.6 M Cl− and an initial pH of 1.3–2.2. In combination with the CheMin detection results, the chemistry and pH values of the fluids at VRR can be further constrained. Considering the absence of goethite and the relative higher portion of akaganeite than jarosite in the drill samples, the pH values should be 1.4–2 and the S/Cl molar ratio should be within the range of 0.018–0.042. Based on our laboratory results, we hypothesize that the presence of akaganeite and jarosite at VRR represents an individual episode of acidic groundwater activity. During the late-stage diagenetic process at VRR, upwelled acidic groundwater dissolved the local chlorides to form the Cl−-dominated fluids. Subsequent evaporation further concentrated the acid saline fluids and therefore resulted in an extremely acidic environment (1.4 ≤ pH＜2 with S/Cl molar ratio of 0.018–0.042), which produced akaganeite and jarosite.

^1,2Ery C. Hughes,²Katherine de Kleer,²John Eiler,³Francis Nimmo,⁴Kathleen Mandt,⁵Amy E. Hofmann
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE008086]
¹Te Pū Ao, GNS Science, National Isotope Centre and Avalon, Lower Hutt, Aotearoa New Zealand
²Division of Geological and Planetary Science, Caltech, Pasadena, CA, USA
³Earth & Planetary Sciences Department, University of California Santa Cruz, Santa Cruz, CA, USA
⁴NASA Goddard Space Flight Center, Greenbelt, MD, USA
⁵Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
Published by arrangement with John Wiley & Sons

Stable isotope fractionation of sulfur offers a window into Io’s tidal heating history, which is difficult to constrain because Io’s dynamic atmosphere and high resurfacing rates leave it with a young surface. We constructed a numerical model to describe the fluxes in Io’s sulfur cycle using literature constraints on rates and isotopic fractionations of relevant processes. Combining our numerical model with measurements of the 34S/32S ratio in Io’s atmosphere, we constrain the rates for the processes that move sulfur between reservoirs and model the evolution of sulfur isotopes over time. Gravitational stratification of SO2 in the upper atmosphere, leading to a decrease in 34S/32S with increasing altitude, is the main cause of sulfur isotopic fractionation associated with loss to space. Efficient recycling of the atmospheric escape residue into the interior is required to explain the 34S/32S enrichment magnitude measured in the modern atmosphere. We hypothesize this recycling occurs by SO2 surface frost burial and SO2 reaction with crustal rocks, which founder into the mantle and/or mix with mantle-derived magmas as they ascend. Therefore, we predict that magmatic SO2 plumes vented from the mantle to the atmosphere will have lower 34S/32S than the ambient atmosphere, yet are still significantly enriched compared to solar-system average sulfur. Observations of atmospheric variations in 34S/32S with time and/or location could reveal the average mantle melting rate and hence whether the current tidal heating rate is anomalous compared to Io’s long-term average. Our modeling suggests that tides have heated Io for >1.6 Gyr if Io today is representative of past Io.

^1,2,3Xuhang Zhang et al. (>10)
Earth and Planetary Science Letters 637, 118725 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.118725]
¹State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
²Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
³College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Copyright Elsevier

The extent of volatile elements on the surface and interior of the Moon remains a highly debated topic. Previous studies conducted on bulk lunar soil samples and solar wind samples collected by the Genesis mission indicate a discernible isotope mass- or non-mass-dependent fractionation of krypton and xenon. However, a detailed investigation of these processes is missing, particularly in determining the possible incorporation of cometary volatiles in the lunar regolith. New lunar soil samples returned by the Chang’e-5 mission provide a chance to answer these key questions. In this study, noble gas isotopes of nine subsamples from a Chang’e-5 scooped sample were analysed through stepwise-heating and total fusion laser extraction. The results reveal that a simple binary mixture of solar wind and cosmogenic components did not explain alone the isotopic composition of these samples. The Xe data shows insignificant amounts of atmospheric Xe and presents clear evidence of cometary contributions to the lunar regolith, with a significant depletion of 134,136Xe compared to that in the solar wind. Additionally, a meteoritic component is identified. Compared to the Apollo results, our findings further validate the theory of Earth’s atmospheric escape, substantiate the plausibility of these exogenous admixtures to elucidate the isotopic fractionation mechanisms of Kr and Xe within the lunar regolith, and provide novel insights into long-term constancy in the solar wind composition.

^1,2Larry R Nittler et al. (>10)
Earth and Planetary Science Letters 637, 118719 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.118719]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
²Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, USA
Copyright Elsevier

We report the H, C, and N isotopic compositions of microscale (0.2 to 2 µm) organic matter in samples of asteroid Ryugu and the Orgueil CI carbonaceous chondrite. Three regolith particles of asteroid Ryugu, returned by the Hayabusa2 spacecraft, and several fragments of Orgueil were analyzed by NanoSIMS isotopic imaging. The isotopic distributions of the Ryugu samples from two different collection spots are closely similar to each other and to the Orgueil samples, strengthening the proposed Ryugu-CI chondrite connection. Most individual sub-μm organic grains have isotopic compositions within error of bulk values, but 2–10 % of them are outliers exhibiting large isotopic enrichments or depletions in D, 15N, and/or 13C. The H, C and N isotopic compositions of the outliers are not correlated with each other: while some organic grains are both D- and 15N-enriched, many are enriched or depleted in one or the other system. This most likely points to a diversity in isotopic fractionation pathways and thus diversity in the local formation environments for the individual outlier grains. The observation of a relatively small population of isotopic outlier grains can be explained either by escape from nebular and/or parent body homogenization of carbonaceous precursor material or addition of later isotopic outlier grains. The strong chemical similarity of isotopically typical and isotopically outlying grains, as reflected by synchrotron x-ray absorption spectra, suggests a genetic connection and thus favors the former, homogenization scenario. However, the fact that even the least altered meteorites show the same pattern of a small population of outliers on top of a larger population of homogenized grains indicates that some or most of the homogenization occurred prior to accretion of the macromolecular organic grains into asteroidal parent bodies.

^1,2,3D. P. Moriarty III,¹N. E. Petro
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE008266]
¹NASA GSFC, Greenbelt, MD, USA
²University of Maryland, College Park, MD, USA
³Center for Research and Exploration in Space Science and Technology, College Park, MD, USA
Published by arrangement with John Wiley & Sons

The lunar south pole is a region of focused scientific and exploration interest, with several crewed and robotic missions to this region planned within the next decade. Understanding the mineralogy of the region is essential to inform landing site characterization and selection and provides the key context for interpreting samples and in situ observations. At high latitudes, extreme illumination conditions (high phase angles) can negatively impact the data quality of orbital instruments. This is especially true for passive near-infrared spectrometers such as the Moon Mineralogy Mapper (M3) and the Kaguya Spectral Profiler, which measure the spectral properties of the surface using reflected sunlight. Using Moon Mineralogy Mapper data, we observed that the south polar region is associated with a detectable mafic signature consistent with the presence of pyroxenes. The strongest mafic signatures are associated with the South Pole—Aitken Basin, suggesting that impact melt and basin ejecta from the lower crust and upper mantle are present within this region. This observation is validated in several ways: (a) comparisons between M3 data acquired during different mission phases, (b) comparisons between multiple spectral parameters sensitive to the presence of mafic minerals, (c) comparisons between the north and south lunar polar regions, and (d) comparisons with publicly available Kaguya polar mineralogy maps and Lunar Prospector elemental abundances. We also investigate the nature of an anomalous high-albedo region within 2–3° of the south pole observed in Lunar Orbiter Laser Altimeter reflectance data exhibiting a spatially conflicting apparent FeO abundance pattern between several data sets.

¹Tarunika Ramprasad,^1,2Venkateswara Rao Manga,²Laura B. Seifert,³Prajkta Mane,^1,2Thomas J. Zega
Geochimica et Cosmochmica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.04.028]
¹Department of Materials Science and Engineering, University of Arizona, 1235 E. James E. Rogers Way, Tucson, AZ 85721, United States
²Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721, United States
³Lunar and Planetary Institute (USRA), 3600 Bay Area Blvd., Houston, TX 77058, United States
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) are the first formed solids in our solar system. Information regarding their formation and alteration is imprinted within their crystal structures, and so analysis of CAIs can provide insight into the early stages of solar system formation. Here we report on micrometer-sized metal grains that occur inside of fluffy type A (FTA) CAIs in the NWA 8323 and Leoville CV3 chondrites. Transmission electron microscopy (TEM) shows that the ultra-refractory metal assemblages contain subhedral grains of alloys of Pt, Os, Ir, Ru, Fe, Ni, and Mo with minor amounts of oxides and silicates inclusions and are crystalline. These assemblages occur in melilite and are surrounded by or adjacent to spinel and perovskite. TEM analysis shows that the majority of the alloys present in the assemblages are significantly enriched in Pt-group elements, with compositions of 75 wt % Pt in some Fe-Ni-Pt grains, and >90 wt % Pt-group elements in Os-Ir-Ru grains. Electron diffraction shows that the alloys occur predominantly in a hexagonal (HCP) structure, with a minority of the grains exhibiting cubic (FCC) and tetragonal lattices. To support these findings, we present a thermodynamic model for the formation of hexagonal (HCP) and cubic (BCC and FCC) ultra-refractory alloys. We use an Fe-Os-Ir ternary system to approximate the various compositions and crystal structures observed in the metal grains. Modeling results indicate a condensation temperature for the alloys as high as 1831 K (HCP, 10−4 bar), placing them well above those predicted for the major CAI phases that surround them. Based on the spatial relationships of the refractory metal grains to their host CAIs, our thermodynamic predictions, and prevailing astrophysical models of the solar protoplanetary disk, the data imply that the grains could have formed inward of the regions where CAI materials condensed. We hypothesize that the refractory metal grains were transported radially outward to the part of the disk where CAIs formed and provided a nucleation site for the condensation of CAI phases such as melilite, hibonite, perovskite, and spinel.

¹Fabre, Sébastien,²Bêche, Eric,³Esvan, Jérôme,³Thébault, Yannick,¹Munsch, Pascal,¹Quitté, Ghylaine
ACS Earth and Space Chemistry 8, 174, 193 Link to Article [DOI 10.1021/acsearthspacechem.3c00083]
¹IRAP, Université Paul Sabatier, CNRS, Observatoire Midi-Pyrénées, 14 Av. Edouard Belin, Toulouse, 31400, France
²PROMES, CNRS, Centre du Four Solaire Félix Trombe, Font-Romeu, 66120, France
³CIRIMAT, CNRS-UPS-INPT, ENSIACET, 4 Allée Emile Monso, Toulouse, 31030, France

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¹Yang, Jing,²Zheng, Dewen,²Wu, Ying,¹Chen, Hong,^1,3Yang, Li,⁴Zhang, Bin
Science China Earth Sciences 67, 641-656 Link to Article [DOI 10.1007/s11430-023-1245-8]
¹Key Laboratory of Active Tectonics and Geological Safety, Ministry of Natural Resources, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing, 100081, China
²State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, 100029, China
³Institute of Earth Sciences, China University of Geosciences, Beijing, 100083, China
⁴Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China

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¹Neeraja S. Chinchalkar,¹Gordon R. Osinski,²Timmons M. Erickson,³Cyril Cayron
Earth and Planetary Science Letters 636, 118714 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.118714]
¹Department of Earth Sciences, University of Western Ontario, 1151 Richmond St, London, ON N6A 3K7, Canada
²Jacobs-JETS II, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Mailcode XI3, Houston, TX 77058, USA
³Laboratory of ThermoMechanical Metallurgy (LMTM), PX Group Chair, École Polytechnique Fédérale de Lausanne (EPFL), Rue de la Maladière 71b, 2000 Neuchâtel, Switzerland
Copyright Elsevier

Evolution of impact melt in terms of initial melt temperatures, melt transport, and cooling history, is a process that remains to be fully understood. Theoretical predictions had suggested that impact melts can experience temperatures far exceeding those in endogenous igneous settings. Direct evidence of the hottest temperatures recorded in impactites was observed recently at the Mistastin Lake impact structure, Canada. The former presence of cubic zirconia, a polymorph of ZrO2 that forms at >2370 °C, was documented within impact glass. In this work, we investigated the zircon and zirconia microstructures and crystallographic orientation relationships with electron backscatter diffraction in two impact glass samples from West Clearwater Lake impact structure in Quebec, Canada. Here we present the first report of the former presence of cubic zirconia, indicating a superheated melt temperature of >2370 °C in one of two impact glass samples analysed. Our results make West Clearwater Lake impact structure the second terrestrial structure with confirmed evidence of former cubic zirconia. Furthermore, we found evidence of melt superheating to temperature of 1673 °C in the other impact glass sample. We also document the first occurrence of former reidite in granular neoblastic (FRIGN) zircon grains in the two impact glass samples analysed in this work, giving us a minimum shock pressure estimate of 20 GPa. This study highlights the heterogeneous thermodynamic (high temperature/low pressure, high pressure, and low temperature/ low pressure) conditions recorded within impact glass from West Clearwater Lake impact structure.

¹Samuel Ebert,²Kazuhide Nagashima,²Alexander N. Krot,¹Markus Patzek,¹Addi Bischoff
The Astrophysical Journal 966, 10 Open Access Link to Article [DOI 10.3847/1538-4357/ad2ea8]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany,
²Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, Honolulu, HI 96822, USA

Calcium, aluminum-rich inclusions (CAIs) are the oldest solids dated that formed in the solar system. Most CAIs in unmetamorphosed chondritic meteorites (chondrites; petrologic type ≤3.0) have uniform solar-like ¹⁶O-rich compositions (Δ¹⁷O ∼ −24‰) and a high initial ²⁶Al/²⁷Al ratio [(²⁶Al/²⁷Al)₀] of ∼(4–5) × 10⁻⁵, consistent with their origin in a gas of approximately solar composition during a brief (<0.3 Ma) epoch at the earliest stage of our solar system. The nature of O-isotope heterogeneity in CAIs (Δ¹⁷O range from ∼−24 up to ∼+5‰) from weakly metamorphosed chondrites (petrologic type >3.0) remains an open issue. This heterogeneity could have recorded fluctuations of O-isotope composition of nebular gas in the CAI-forming region and/or postcrystallization O-isotope exchange of CAI minerals with aqueous fluids on the chondrite parent asteroids. To obtain insights into possible processes resulting in this heterogeneity, we investigated the mineralogy, rare-earth element abundances, and O- and Mg-isotope compositions of a CAI from the CO3.1 chondrite Dar al Gani 083. This concentrically zoned inclusion has a Zn-hercynite core surrounded by layers of (from core to edge) grossite, spinel, melilite, and Al-diopside. The various phases have heterogeneous Δ¹⁷O (from core to edge): −2.2 ± 0.6‰, −0.9 ± 2.1‰, −13.7 ± 2.1‰, −2.6 ± 2.3‰, and −22.6 ± 2.1‰, respectively. Magnesium-isotope compositions of grossite, spinel, melilite, and Al-diopside define an undisturbed internal Al–Mg isochron with (²⁶Al/²⁷Al)₀ of (2.60 ± 0.29) × 10⁻⁶. We conclude that the variations in Δ¹⁷O of spinel and diopside recorded fluctuations in O-isotope composition of nebular gas in the CAI-forming region prior to injection and/or homogenization of ²⁶Al at the canonical level. The ¹⁶O depletion of grossite and melilite resulted from O-isotope exchange with asteroidal fluid, which did not disturb Al–Mg isotope systematics of the CAI primary minerals.