¹K.Yumoto et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116122]
¹Department of Earth and Planetary Science, The University of Tokyo, Bunkyo, Tokyo, Japan
Copyright Elsevier

Asteroids (162173) Ryugu and (101955) Bennu observed by Hayabusa2 and Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) share many global properties, but high-spatial-resolution spectral observations by the telescopic Optical Navigation Camera (ONC-T) and MapCam detected subtle but significant differences (e.g., opposite space weathering trends), which may reflect differences in their origin and evolution. Comparing these differences on the same absolute scale is necessary for understanding their causes and obtaining implications for C-complex asteroids. However, ONC-T and MapCam have a large imager-to-imager systematic error of up to 15% caused by the difference in radiometric calibration targets. To resolve this problem, we cross calibrated albedo and colour data between the two instruments using the Moon as the common calibration standard. The images of the Moon taken by ONC-T and MapCam were compared with those simulated using photometry models developed from lunar orbiter data. Our results show that the cross-calibrated reflectance of Ryugu and Bennu can be obtained by upscaling the pre-cross-calibrated reflectance of Bennu by 13.3 ± 1.6% at b band, 13.2 ± 1.5% at v band, 13.6 ± 1.7% at w band, and 14.8 ± 1.8% at x band, while those for Ryugu are kept the same. These factors compensate for the imager-to-imager bias caused by differences in targets used for radiometric calibration and solar irradiance models used for data reduction. Need for such large upscaling underscore the importance of using the cross-calibrated data for accurately comparing the Ryugu and Bennu data. The uncertainty in these factors show that the reflectance of Ryugu and Bennu can be compared with <2% accuracy after applying our results. By applying our cross calibration, the geometric albedo of Bennu became consistent with those observed by ground-based telescopes and the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS). Our result can be simply applied by multiplying a constant to the publicly available data and enables accurate comparison of the optical spectra of Ryugu and Bennu in future studies.

^1,2R. L. Cheng,^1,2J. R. Michalski,^3,4K. A. Campbell
Journal of Geophyiscal Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE007999]
¹Department of Earth Sciences, The University of Hong Kong, Hong Kong, China
²Laboratory for Space Research, The University of Hong Kong, Hong Kong, China
³School of Environment, The University of Auckland, Auckland, New Zealand
⁴Te Ao Mārama—Centre for Fundamental Inquiry, Faculty of Science, The University of Auckland, Auckland, New Zealand
Published by arrangement with John Wiley & Sons

Siliceous hot spring deposits, or sinters, deposit from hot spring discharge at Earth’s surface and are sites of exceptional preservation of biosignatures. Their macro- and micro-textures are regarded as important evidence of past microbial activities in hydrothermal environments. However, biology mimics do occur, and bona fide microbial textures could be destroyed by subsequent diagenesis or other post-depositional processes. Thus, it is paramount to narrow the search for prospective Martian silica-rich deposits that may contain biosignatures from both orbital and rover-based perspectives. This study investigates hydrothermal deposits in Chile, which are analogs of high-silica deposits discovered in the Gusev crater on Mars, through remote sensing and laboratory analysis. Results indicate that compositional remote sensing based on multispectral data with a high spatial resolution of <4 m/pixel reflects various concentrations of silica, which assisted in identifying the direction of discharged hydrothermal flows from the vent to the apron. Micro-infrared mapping of sinters from similar hydrothermal fields linked spectral features to specific textures revealed by scanning electron microscope and chemical compositions confirmed by electron microprobe analysis, indicating that sinters with no shift in their emissivity minimum in the thermal infrared range were more likely to preserve cellular structures. An instrument for collecting multispectral data with higher spatial resolution could aid in characterizing the geologic settings of potential hot springs on Mars. Locating emissivity minima in the infrared regions of silica that do not shift to a lower position would suggest the potential for well-preserved microbial structures in Martian sinters, if life ever did exist there.

¹Carolyn A. Crow,¹Cynthia Tong,²Timmons M. Erickson,³Desmond E. Moser,¹Aaron S. Bell,⁴Nigel M. Kelly,⁵Tabb C. Prissel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14162]
¹Department of Geological Sciences, University of Colorado Boulder, Boulder, Colorado, USA
²NASA JSC\Jacobs Technology, Houston, Texas, USA
³Western University, London, Ontario, Canada
⁴Bruker Corporation, Billerica, Massachusetts, USA
⁵NASA JSC, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

Investigations of trapped melt inclusions in minerals can yield insights into the compositions and conditions of parent magmas. These insights are particularly important for detrital grains like many of the lunar zircons found in samples returned by the Apollo missions. However, unlike their terrestrial counterparts, lunar zircons have potentially been exposed to billions of years of impact bombardment. Samples from terrestrial impact structures and impact shock experiments have revealed that deformation during an impact event produces melt and glass blebs that can mimic igneous melt inclusions in both morphology and composition. We have undertaken a geochemical and textural investigation of zircons from Apollo impact melt breccia 14311 to assess their formation mechanisms. The association of trapped melts with shock microtwins and monomineralic melt compositions suggests some inclusions formed as a result of the high pressures and temperatures of impact shock. All other inclusions in this study are associated with curviplanar features, planar features, crystal plastic deformation, or embayments (large regions in contact with adjacent melts or minerals) suggesting that they are not igneous melt inclusions. While these textures can be produced in tectonic environments, impacts are a likely formation mechanism since impacts are the main driver of tectonics on the Moon. The results of this study demonstrate that a combination of textural and compositional analyses can be employed distinguish between igneous melt inclusions and melt blebs in zircons from impact environments.

¹Ko Hashizume et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14175]
¹Faculty of Science, Ibaraki University, Mito, Japan
Published by arrangement with John Wiley & Sons

The nitrogen isotope compositions of two samples returned from the asteroid Ryugu were determined using a stepwise combustion method, along with Ivuna (CI) and Y-980115, a CI-like Antarctic meteorite, as references. The two Ryugu samples A0105-07 and C0106-07 showed bulk δ15N values of +1.7 ± 0.5‰ and +0.2 ± 0.6‰, respectively, significantly lower than Ivuna with +36.4 ± 0.4‰, but close to Y-980115 with +4.0 ± 0.3‰. The Ryugu samples are further characterized by C/N and 36Ar/N ratios up to 3.4× and 4.9× the value of Ivuna, respectively. Among all Ryugu samples and CI chondrites, a positive correlation was observed between nitrogen concentrations and δ15N values, with samples with lower nitrogen concentrations exhibiting lower δ15N. This trend is explained by a two-component mixing model. One component is present at a constant abundance among all CI-related samples, with a δ15N value around 0‰ or lower. The other varies in abundance between different samples, and exhibits a δ15N value of +56 ± 4‰. The first 15N-poor endmember is seemingly tightly incorporated into a carbonaceous host phase, whereas the 15N-rich endmember can be mobilized and decoupled from carbon, potentially because it is in the form of ammonia. Asteroid materials with volatile compositions that are similar to those reported here for the Ryugu samples are attractive candidates for the volatile sources among Earth’s building blocks.

^1,2Maree McGregor,^1,2John G. Spray,²Christopher R. M. McFarlane
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14172]
¹Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick, Canada
²Department of Earth Sciences, University of New Brunswick, Fredericton, New Brunswick, Canada
Published by arrangement with John Wiley & Sons

In situ LA-ICP-MS/MS U-Pb and Rb-Sr geochronology combined with geochemical analysis and electron microscopy have been performed on ejecta components sampled from the Mid-to-Late Triassic Mercia Mudstone Group at Churchwood Quarry, SW England. The layer comprises altered impact spherules, melt-rich and fragment-rich accreted grain clusters (AGCs), along with shocked mineral phases. Late Triassic ages are obtained: a U-Pb age of 219 ± 72 Ma from variably shock-metamorphosed apatite and a Rb-Sr age of 213 ± 31 Ma from melt-rich AGCs. A post-depositional U-Pb age of 200 ± 7.5 Ma obtained from the carbonate host matrix correlates with an early Jurassic dolomitization event associated with regional marine transgression. Several links to the Manicouagan impact structure, Canada, are identified that complement previous provenance studies: (1) rare earth element compositions of impact spherules and melt-rich AGCs match those of the Manicouagan impact melt sheet; (2) the preservation of Archean and Paleo- to Neoproterozoic target rock U-Pb ages in zircon and apatite match those recorded within Manicouagan basement lithologies; and (3) impact spherules and melt-rich AGCs record initial 87Sr/86Sr compositions that overlap with those of the Manicouagan impact melt sheet and the target rocks involved in their generation.

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.