¹Lv, Chaojia,^1,2Liu, Jin
Acta Geochimica (in Press) Link to Article [DOI 10.1007/s11631-021-00522-x]
¹Center for High Pressure Science and Technology Advanced Research, Beijing, 100094, China
²CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China

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¹Li, Chun-Hui
Acta Geochimica (in Press) Link to Article [DOI 10.1007/s11631-021-00517-8]
¹International Research Center for Planetary Science, College of Earth Sciences, Chengdu University of Technology, Chengdu, China

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^1,2A.P.Jordan,³A.W.Case,^1,2J.K.Wilson,¹C.-L.Huang
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115011]
¹Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA
²Solar System Exploration Research Virtual Institute, NASA Ames Research Center, Moffett Field, CA, USA
³Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
Copyright Elsevier

The standard view of space weathering on the Moon is that the solar wind and micrometeoroid impacts alter the optical properties of lunar soil. A third process—dielectric breakdown driven by solar energetic particles (SEPs)—has also been suggested to contribute to space weathering. It has been difficult to determine the relative roles of these processes. The Earth’s magnetotail, however, provides a way to distinguish between them, because it affects only charged particles. Earth’s magnetotail blocks the solar wind, and here we show that it also likely reduces the flux of SEPs traveling across the tail and impacting the tail-facing hemisphere of the Moon when it is entering or leaving. Consequently, we make two predictions that distinguish how the tail affects dielectric breakdown weathering patterns from how it affects solar wind weathering patterns. First, the magnetotail should create two minima in the total amount of breakdown weathering that has occurred: one near  and a deeper one near  longitude. Second, the tail should create east–west asymmetries in the breakdown weathering of crater walls, with the greatest asymmetries occuring at  longitude. Although the first prediction has proven difficult to test, we find that the second prediction is supported by observations. Therefore, we conclude that investigations of space weathering must consider, not only micrometeoroid and solar wind bombardment, but also dielectric breakdown.

¹William H.Farrand,²Christopher S. Edwards,²Christian Tai Udovicic
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115021]
¹Space Science Institute, 4765 Walnut Street, Suite B, Boulder, CO 80301, USA
²Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ 86011, USA
Copyright Elsevier

The Tacquet Formation (TF) was first identified in geologic mapping of southern Mare Serenitatis as a distinct low albedo region split by the linear Rimae Menelaus rilles. A distinct western dome, split by a linear rille and less distinct eastern dome (the Menelaus domes) are also present within the TF. Previous Earth-based radar analyses showed that the TF has a lower circular polarization ratio consistent with a pyroclastic mantle. In this study, compositional and spectroscopic parameters were derived from Moon Mineralogy Mapper (M3) data. Lunar Reconnaissance Orbiter Camera Wide Angle Camera (LROC WAC) and SELENE Kaguya Multiband Imager (MI) multispectral data were also utilized. FeO derived from MI data for the TF and Menelaus domes was elevated at levels consistent with pyroclastic glasses. While not diagnostic of pyroclastics, TiO2 derived from LROC WAC data over the TF and Menelaus domes was also elevated relative to the background materials. Analysis of 1 and 2 μm band parameters also show the TF and Menelaus domes as being distinct with a band center moderately longer than 1 μm and 2 μm band center shorter than the surroundings, characteristics consistent with pyroclastic glass and/or increased ilmenite. M3 data thermally corrected via two different thermal correction approaches indicate a moderately deeper band in the 3 μm region indicative of OH and/or H2O, a characteristic that is also potentially associated with pyroclastic deposits. These compositional findings are consistent with the Earth-based radar data suggesting that the TF is a pyroclastic mantle and potentially represents a previously unrecognized sub-class of pyroclastic deposits associated with lunar volcanic domes.

¹Laura B. Seifert,¹Pierre Haenecour,^1,2Thomas J. Zega
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13811]
¹Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd, Tucson, Arizona, 85721 USA
²Department of Materials Science and Engineering, University of Arizona, 1235 E. James E. Rogers Way, Tucson, Arizona, 85721 USA
Published ba arrangement with John Wiley & Sons

We report the structural and chemical analyses of six presolar silicate grains identified in situ in the CO3.0 carbonaceous chondrite Dominion Range (DOM) 08006. Two of the grains have O-isotopic compositions consistent with origins in the circumstellar envelopes of low-mass (<2M☉) asymptotic giant branch (AGB)/red giant branch (RGB) stars, although without Mg-isotopic data, origins in supernovae (SNe) cannot be ruled out. The other four grains have O-isotopic compositions consistent with origins in the ejecta of type-II SNe. Transmission electron microscopy analyses reveal that all grains are crystalline (single crystal or polycrystalline) and have varied compositions. The analyzed AGB/RGB grains include an Fe-rich crystalline olivine with an Fe-sulfide inclusion and a chemically zoned olivine grain that also contains an Fe-oxide rim. The grains derived from SNe include two polycrystalline assemblages with structures that overlap with both olivine and pyroxene, an assemblage composed of both a single crystal of forsterite and polycrystalline forsterite, and an orthopyroxene grain with an embedded Fe-sulfide crystal. The thermodynamic origins of both AGB/RGB and SN grains are also diverse. The structure and compositions of two grains are consistent with equilibrium thermodynamic predictions of condensation, whereas four are not, suggesting formation through nonequilibrium or multistep processes. Our observations of presolar silicate grains suggest that the circumstellar envelopes of AGB/RGB stars and the ejecta of SNe can produce grains with comparable structures and compositions.

¹Nicolas P. Walte,²Gregor J. Golabek
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13810]
¹Heinz Maier-Leibnitz Center for Neutron Science (MLZ), Technical University Munich, Garching, 85748 Germany
²Bayerisches Geoinstitut (BGI), University of Bayreuth, Bayreuth, 95447 Germany
Published by arrangement with John Wiley & Sons

Olivine aggregates, bodies found in pallasites that consist of olivines with coherent grain boundaries and minor amounts of Fe-Ni and troilite, likely represent well-preserved samples of different mantle regions of pallasite parent bodies (PPBs). We investigated olivine aggregates from the main group pallasites Fukang, Esquel, Imilac, and Seymchan and compare their textures with results from deformation experiments. Our measurements reveal an inverse relationship between the grain size of olivines and the primary metal fraction inside olivine aggregates, which is explained by simultaneous grain growth retarded by Zener pinning in different mantle regions. Textural evidence indicates that the mantle has remained at high temperatures before initial cooling occurred shortly after pallasite formation that was likely caused by an impact. Different degrees of annealing of the deformation textures suggest that the postcollisional cooling occurred in the order Seymchan, Imilac, Esquel, and Fukang. We interpret this observation with an increasing burial depth after the collision. We also demonstrate that the mantle has not been convecting before the impact despite being at high temperature. Using the minimum critical Rayleigh number, we estimate PPB radii assuming different core radii. Our results question the recent ferromagmatism hypothesis for pallasite formation and support a multistage formation process that includes one or several impacts.

¹Michael Zolensky et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13808]
¹Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

Our goal was to devise a bridge between shock determinations of asteroid regolith grains by standard light optical petrography, synchrotron X-ray diffraction (SXRD), and electron backscattered diffraction (EBSD). We determined the optimal conditions under which to measure the shock stage of olivine crystals in astromaterial grains by EBSD. We applied this EBSD procedure to the shock stage determination of four regolith grains from asteroid Itokawa, returned to earth by the Hayabusa spacecraft. Interpretation of these data required a parallel examination of three ordinary chondrite standards that exhibited shock histories ranging from stage 2 to stage 4, using all three techniques. Standard light optical petrography indicated shock stage of S2/3 for the 24 Itokawa grains analyzed. SXRD results for seven Itokawa grains indicate a shock stage of S2. EBSD maps of four Itokawa grains indicate shock stage S3. Thus, the different techniques indicate slightly different shock stages, probably due to small sampling populations for EBSD and SXRD. We therefore recommend that significantly more than seven regolith grains should be separately analyzed by any shock determination technique, probably between 10 and 20. In any case, Itokawa regolith grains have been shocked to stage S2/3, or approximately 5–10 GPa. Finally, we investigated the crystallinity of one Itokawa olivine by SXRD, determining that the 5–10 GPa shock it had experienced did not appreciably alter the size of the unit cell, contrary to some previous suggestions.

¹Christopher K. Junium,²Aubrey L. Zerkle,³James D. Witts,¹Linda C. Ivany,⁴Thomas E. Yancey,⁵Chengjie Liu,²Mark W. Claire
Proceedings of the National Academy of Science of the USA (PNAS) 119 (14) e2119194119 Link to Article [https://doi.org/10.1073/pnas.2119194119]
¹Department of Earth and Environmental Sciences, Syracuse University, Syracuse, NY13244
²School of Earth and Environmental Sciences,Centre for Exoplanet Science, University of St Andrews, StAndrews KY16 9AL, United Kingdom
³School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom
⁴The College of Geosciences, Texas A&MUniversity, College Station, TX 77483
⁵Ellington Geological Services, Houston, TX 77043

Sulfate aerosols have long been implicated as a primary forcing agent of climate change and mass extinction in the aftermath of the end-Cretaceous Chicxulub bolide impact. However, uncertainty remains regarding the quantity, residence time, and degree to which impact-derived sulfur transited the stratosphere, where its climatic impact would have been maximized. Here, we present evidence of mass-independent fractionation of sulfur isotopes (S-MIF) preserved in Chicxulub impact ejecta materials deposited in a marine environment in the Gulf Coastal Plain of North America. The mass anomalous sulfur is present in Cretaceous–Paleogene event deposits but also extends into Early Paleogene sediments. These measurements cannot be explained by mass conservation effects or thermochemical sulfate reduction and therefore require sulfur-bearing gases in an atmosphere substantially different from the modern. Our data cannot discriminate between potential source reaction(s) that produced the S-MIF, but stratospheric photolysis of SO₂ derived from the target rock or carbonyl sulfide produced by biomass burning are the most parsimonious explanations. Given that the ultimate fate of both of these gases is oxidation to sulfate aerosols, our data provide direct evidence for a long hypothesized primary role for sulfate aerosols in the postimpact winter and global mass extinction.

^1,2Valerie Payre,¹Rajdeep Dasgupta
Geochimica et Cosmochimica acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.03.034]
¹Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, Texas 77005
²Present address: Department of Physics and Planetary Sciences, Northern Arizona University, Flagstaff, Arizona
Copyright Elsevier

Phosphorus is estimated to be ten times more enriched in the martian mantle compared to the terrestrial mantle. Yet, its effects on primary melt composition and melting phase relations in martian systems is unknown. We performed piston-cylinder experiments at a constant upper mantle pressure of 2 GPa and temperatures of 1210-1450 °C using a model martian primitive mantle composition with P2O5 content of 0 and 0.5 wt.%. All experiments produced an assemblage of olivine + orthopyroxene + melt ± pigeonite ± apatite ± spinel. Our experimental results, in combination with a previous study at similar P-T conditions and major element bulk composition but containing 0.2 wt.% bulk P2O5, show that the addition of phosphorus dramatically increases the abundance of more polymerized residual mineral such as orthopyroxene while decreasing the proportion of less polymerized residual phases such as olivine, especially at low extent of melting (∼11 wt.%). Such effects lead to lower SiO2 concentrations in the near-solidus melt by up to 10 wt.% for mantle P2O5 of 0.2 and 0.5 wt.%. Increasing bulk P2O5 to 0.5 wt.% also leads to elevated CaO/Al2O3 ratio and increased FeO* concentration in mantle-derived melts with the latter likely due to formation of Fe-O-P complexes in the liquid. Our study suggests that elevated phosphorus in the martian mantle has important consequences regarding the composition and mineralogy of the crust, partly made with primary melts, and of the upper mantle. Because of elevated P, variably melt-depleted upper mantle of Mars is likely to be richer in orthopyroxene compared to the terrestrial mantle and the elevated P content is partly responsible for several geochemical attributes of martian basalts compared to those on Earth. Extrapolating our experimental results to a range of pressures, we suggest a depletion of P in the mantle through time, which likely contributed to major elemental compositional differences between ancient Gusev and Gale crater basalts and more recent martian meteorites.

¹Chennaoui Aoudjehane H.
Advances in Science, Technology and Innovation 978, 345 – 348 Link to Article [DOI 10.1007/978-3-030-72547-1_74]
¹GAIA Laboratory, Faculty of Sciences Ain Chock, Hassan II University of Casablanca, km8 Route d’El Jadida, 20150, Casablanca, Morocco

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