^1,2Tomoya Obase,¹Daisuke Nakashima
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115290]
¹Division of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan
²Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
Copyright Elsevier

Astronomical observations of solar-like stars and theoretical predictions have proposed a high long-term average solar wind flux in the past, such as more than ~10 times higher than the present-day value at ~3 Ga. Solar-gas-rich meteorites are lithified asteroidal regolith materials that had been exposed to solar wind in the past and some of which may record the ancient solar wind. To test the hypothesis of dense solar wind in the past Solar System, we quantified the past solar wind 36Ar particle fluxes based on the correlations between the solar and cosmogenic noble gas concentrations in individual solar-gas-rich meteorites. As a result, the past solar wind fluxes recorded in six solar-gas-rich meteorites were comparable to the present-day value except for the R chondrite PRE 95410, showing a few times higher solar wind flux. The howardite Kapoeta perhaps records the solar wind flux at some time between ~1 and ~ 2 Ga, suggesting that the solar wind flux in the past at least ~1 Ga had been similar to the present-day value. These results may indicate that the past solar wind flux had been lower than that proposed by the astronomical observations and the theoretical predictions. Otherwise, the six meteorites would have acquired recent solar wind when the solar wind flux had already been down to the present-day level.

¹Matthew A. Pasek, ²Arthur Omran,¹Tian Feng,¹Maheen Gull,¹Carolyn Lang,¹Josh Abbatiello,¹Lyle Garong,¹Ray Johnston,¹Jeffrey Ryan,³Heather Abbott-Lyon
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.09.027]
¹School of Geosciences, University of South Florida, 4202 E Fowler Ave NES 204, Tampa, FL 33620, USA
²Department of Chemistry, University of North Florida, Jacksonville, FL 32224, USA
³Department of Chemistry, Kennesaw State University, Kennesaw, GA 30144, USA
Copyright Elsevier

A general assumption about the geochemical behavior of phosphorus (P) is that it exists exclusively in the +5 oxidation as phosphate. However, in extremely reducing environments, other oxidation states of phosphorus such as +3 may also be stable. Such environments—if prevalent globally—may determine planetary habitability, which is in part governed by nutrient availability, including the availability of the element phosphorus. Here we show a route to P liberation from water-rock reactions that are thought to be common throughout the Solar System. We report the speciation of phosphorus in several serpentinite rocks and muds to include the ion phosphite (HPO32- with P3+) and show that reduction of phosphate to phosphite may be predicted from thermodynamic models of serpentinization. Furthermore, the amount of phosphite exceeds the amounts predicted from thermodynamic models in three of nine samples analyzed. As a result, as olivine and other silicates in ultramafic rocks alter to serpentine minerals, phosphorus as the significantly more soluble and reactive phosphite ion should be released under low redox conditions, liberating this key nutrient for life. Thus, this element may be accessible to developing life where water is in direct contact with ultramafic rock, providing a source of this nutrient to potentially habitable worlds.

¹G.Munaretto,¹A.Lucchetti,¹M.Pajola,¹G.Cremonese,^1,2M.Massironi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115284]
¹INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio, Italy
²Department of Geosciences, University of Padova, Padova, Italy
Copyright Elsevier

The origin and formation mechanism of Mercury’s hollows, which are bright, often haloed, small, shallow, irregular, rimless and flat floored depressions, represent one of the major open science questions regarding the Hermean surface and the processes shaping it morphology. In this work, we perform a photometric modelling of multiangular and multiband images of Tyagaraja and Canova craters’ hollows to investigate the physical properties of their reflecting material. Thanks to such observations, we demonstrate that we can derive a better topographic correction when compared to the one obtained from the global photometric models of Mercury. Indeed, our parameters, which result from the inversion of the Hapke and Kaasalainen-Shkuratov models, can be useful for both future spectrophotometric analyses of Mercury and laboratory experiments aiming to identify hollows analogue materials. The analysis of our estimated model parameters imply that the Tyagaraja and Canova hollow walls are more backscattering and smoother than the crater floors, in agreement with independent phase ratio analyses. Our results suggest that the hollow forming material is made of roundish particles or particles with a high density of scattering centers, such as holes, vesicles or fractures, consistent with the release of volatiles as part of the hollows’ formation mechanism.

^1,2,3ShiYong Liao,²Birger Schmitz
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115285]
¹Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, China
²Astrogeobiology Laboratory, Department of Physics, Lund University, Lund, Sweden
³CAS Center for Excellence in Comparative Planetology, Hefei, China
Copyright Elsevier

The breakup of the L-chondrite parent body (LCPB) in the asteroid belt at 466 Ma ago is the largest asteroid breakup documented in Earth’s geological record for the past ca. three billion years. Recovery of abundant macroscopic fossil L chondrites in mid-Ordovician marine sediments as well as reconstructions of the flux of micrometeoritic chrome spinel through the ages have given much new information on the precise timing of the breakup and its effects on Earth. In the present study, we focus on the flux of large micrometeorites to Earth shortly (in the 2 Ma time interval) before the LCPB breakup (pre-LCPB), which may be crucial for understanding the dynamical evolution of the asteroid belt leading up to the breakup. We present chrome-spinel data (32–355 μm grain size) from two mid-Ordovician limestone sections in Sweden (Kinnekulle and Öland, 300 km apart) and one section in western Russia (Lynna River), ca. 1100 km from Kinnekulle. One aim is also to test the level of reproducibility of chrome-spinel flux reconstructions between different sites.

Between 300 and 600 kg of limestone were collected from each section in the stratigraphic interval corresponding to ca. 2 Ma before up to immediately before the LCPB breakup. The relations between H, L and LL meteorites from Kinnekulle (38.7 ± 6.3%, 33.2 ± 6.1% and 28.1 ± 5.8%), Öland (46.0 ± 5.6%, 31.2 ± 3.1% and 24.5 ± 4.8%) and Lynna River (38.2 ± 5.5%, 32.8 ± 5.3% and 29.0 ± 5.1%) sections are indistinguishable from each other within uncertainties, revealing a globally homogeneous influx of H, L and LL meteorites. This gives support for the validity of previous reconstructions for the meteorite flux based on chrome spinel reconstructions for fifteen time windows through the Phanerozoic.

All the pre-LCPB samples from the three regions show a collective dominance of H-chondritic grains (42 ± 3%) over L (31 ± 3%) and LL grains (27 ± 3%), largely similar to the Phanerozoic background flux. Intriguingly, the presence of background concentrations of L-chondritic material also in the pre-LCPB flux demonstrates that the idea of a largely intact LCPB still existing before the final breakup may be far from reality. Apparently, a substantial amount of equilibrated chondritic material from deep levels of an L-chondritic body reached Earth even before the inferred catastrophic disruption at 466 Ma ago. This would concur with a “rubble pile” structure of the L-chondrite parent body and exposure of abundant deep-seated material as a result of earlier disruption and re-accretion events. The LL-chondritic contribution in the pre-LCPB flux is higher than at other Phanerozoic time windows, including the Cambrian. This anomalously enhanced flux thus cannot be ascribed to the Neoproterozoic breakup of the large LL-chondritic Flora asteroid. Previously observed high concentrations of chrome-spinel grains of achondritic origin can be reproduced only in our samples from immediately (< 1 Ma) before the LCPB breakup. We speculate that this, together with the high LL percentage before the breakup, may be explained by dynamic perturbations, possibly in the near-Earth region, leading up to the LCPB event.

^1,2L.Krämer Ruggiu et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.09.020]
¹Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
²Analytical-, Environmental- and Geo-Chemistry, Vrije Universiteit Brussel, Brussels, Belgium
Copyright Elsevier

We discuss if the detection of aqueous alteration depends on the techniques that are used. We apply different methods to estimate the extent of aqueous alteration on four ungrouped carbonaceous chondrites showing limited aqueous alteration and thermal metamorphism: Chwichiya 002, El Médano (EM) 200, Northwest Africa (NWA) 12957 and NWA 11750, classified as C3 or C3.00-ung. The aim is to propose a reliable methodology to identify the most primitive chondrites. Chwichiya 002, NWA 11750 and NWA 12957 display very primitive matrices and could be amongst the most primitive chondrites currently known, similar to the least altered lithologies of the CM chondrites Paris (CM2.9) and Asuka (A) 12085 (CM2.8), A 12236 (CM2.9) and A 12169 (CM3.0). The structure of organic matter and Cr2O3 in ferroan olivines show that the four meteorites have been less heated than the least metamorphosed standard/reference type 3 chondrite, Semarkona (LL3.00), with Chwichiya 002, NWA 12957 and NWA 11750 similar to the CO3.0s, Acfer 094 (C2-ung) and Paris meteorites. Chwichiya 002 and NWA 12957 show similar alteration phases and degree of alteration, with high abundances of amorphous material with embedded metal and sulfide, resembling Glass with Embedded Metal and Sulfide (GEMS)-like materials, and tochilinite-cronstedtite intergrowths (TCIs) as the major alteration phases. The matrix in NWA 11750 contains aggregates of nanoscale olivine crystals and abundant carbonates, observed as micrometer-sized carbonate veins surrounding chondrules, and as nanoscale carbonates mixed with the fine-grained materials. It also contains abundant grains of metal and a low abundance of phyllosilicates. El Medano 200 shows a high abundance of magnetite (∼ 10 vol%), nanoscale phyllosilicates, troilite, and organic matter. The variability of the secondary alteration phases in the meteorites suggests different alteration mechanisms, likely depending on both the starting composition of the meteorites and the composition of the fluids of alteration.

Scanning and transmission electron microscopy (SEM and TEM) allow the identification of primitive phases and the composition and spatial distribution of the secondary phases. X-ray diffraction (XRD) can detect alteration products, including some amorphous phases, although this is limited by the small coherence domains of small TCIs and other phyllosilicates. Transmission infrared (IR) spectroscopy can detect phyllosilicate and carbonate, but is ineffective for the detection of amorphous phases, metal, or sulfide. Both matrix defocused electron microprobe analyses (EMPA) and thermogravimetric analysis (TGA) allow detection of hydrated minerals, such as phyllosilicates and carbonates, but are strongly influenced by the presence of organic matter and do not reflect the overall alteration state of a meteorite. We conclude that the assessment of the primitivity of a chondrite is highly technique dependent. We propose a combination of XRD and the Cr2O3 in ferroan olivines or Raman spectroscopy for a rapid characterization of the alteration state of a chondrite and the detection of the most primitive meteorites. Finally, the combination of XRD and TEM allows for the detection of all primary and secondary phases and represents an ideal methodology for the characterization and detailed study of primitive chondrites and the different types of incipient aqueous alteration.

¹Rajdeep Dasgupta,¹Emily Falksen,¹Aindrila Pal,^1,2Chenguang Sun
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.09.012]
¹Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, USA
²Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78712
Copyright Elsevier

Evolution of nitrogen (N), a life-essential volatile element, in highly reduced magmatic systems is a key for the origin of N on rocky planets formed via accretion of reduced chondritic parent body materials, planetesimals, and embryos that underwent partial or complete differentiation. However, the storage capacity of N in phases relevant for reduced silicate systems undergoing thermal processing is poorly known. To investigate the stability of N-bearing phases in partially molten silicate-rich systems as well as solubility of nitrogen in silicate melts and minerals, we performed laboratory experiments on a 80:20 synthetic basalt-Si3N4 mixture at 1.5-3.0 GPa and 1300-1600 °C in graphite capsules, yielding oxygen fugacity ranging from ∼IW– 3.0 to ∼IW – 4.0. All experiments produced silicate melt + nierite + Fe-rich alloy melt + N-rich vapor ± sinoite ± cpx. Sinoite was restricted to above while cpx was restricted below 1400-1500 °C. Nitrogen solubility and Nitrogen Concentration at Silicon-Nitride Saturation (NCNS) in silicate melts increases with increasing pressure and temperature and ranges between 3.6 and 9.5 wt %. Using our high pressure N solubility data and similar data at ambient and lower pressures, we derived a new N solubility model in silicate melts. Solubility of nitrogen in cpx was between 1.51 and 2.05 wt% and resulted in cpx/silicate melt partition coefficients for nitrogen, of ∼0.4 to ∼0.2. These are distinctly higher than those previously estimated at more oxidizing conditions, suggesting N maybe much less incompatible during thermal processing of rocky reservoirs at highly reducing conditions. Partition coefficient of N between Fe-rich alloy melt and cpx, was found to be between 1.6 and 2.1. The application of our N solubility data and model suggests that mobilization of N from the deeper, partially molten reservoirs to shallower reservoirs is possible in reduced planetesimals and internally differentiated meteorite parent bodies – leading to net loss of N via melt degassing or reprecipitation of N-bearing solid phases, depending on whether the surficial shell is oxidized or reduced, respectively. Similarly, comparison of the first measured values from our highly reducing experiments with those estimated at more oxidizing conditions suggest that N would be much less incompatible during internal and external magma ocean processing of rocky bodies under highly reducing conditions. Therefore, enrichment of N in the atmospheres of Earth and Venus is likely a result of more oxidizing penultimate phase of accretion, which would lead to N being more readily partitioned to residual liquid, which would also more readily degas at oxidizing conditions.

Michael Zolensky¹, Takashi Mikouchi², Kenji Hagiya³, Kazumasa Ohsumi^4,5, Mutsumi Komatsu⁶, Andrew Cheng⁷, Loan Le⁸
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13909]
¹ARES, NASA Johnson Space Center, Houston, Texas 77058, USA
²University Museum, University of Tokyo, Tokyo 113-0033, Japan
³Graduate School of Life Science, Universtiy of Hyogo, Hyogo 678-1297, Japan
⁴Japan Synchrotron Radiation Research Institute (JASRI), Hyogo 679-5198, Japan
⁵Japan and High Energy Accelerator Research Organization (KEK), Ibaraki 305-0801, Japan
⁶The Graduate University for Advanced Studies, SOKENDAI, Kanagawa 240-0193, Japan
⁷The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20723, USA
⁸Jacobs JETS, Johnson Space Center, Houston, Texas 77058, USA
Published by arrangement with John Wiley & Sons

We explore impact shock processing of the regolith of parent asteroids of carbonaceous chondrites, which has not been considered a major process for hydrous carbonaceous chondrites. We describe shock-produced minerals and features found in brecciated CI, CM, and CV chondrites, including agglutinates, a glassy melt pod, a shock melt vein, and melted sulfides. We also reexamine cognate clasts present in the Vigarano CV3 chondrites which appear to derive from asteroid ponds and exhibit cross-bedded dish structures.

Tarunika Ramprasad¹, Pierre Haenecour², Kenneth Dominik², Thomas J. Zega^1,2
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13910]
¹Department of Materials Science and Engineering, University of Arizona, 1235 E. James E. Rogers Way, Tucson, Arizona
²Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd, Tucson, Arizona 85721, USA
85721, USA
Published by arrangement with John Wiley & Sons

Compact type A calcium-aluminum-rich inclusions (CTA CAIs) are believed to have experienced partial melting that erased all information on their original nebular condensation. To investigate this question, we report new microstructural data on a CTA CAI, composed primarily of melilite, spinel, and perovskite, in the Northwest Africa 5028 CR2 chondrite. The melilite grains contain low (5–10 mole%) åkermanite contents and are not compositionally zoned. Spinel and perovskite each occur as near endmember compositions MgAl₂O₄ and CaTiO₃ and contain minor V and Al, respectively. A continuous rim composed of melilite, spinel, and perovskite, with minor hibonite grains occur around the CAI. We extracted two regions of interest from the interior CAI and two from the rim using focused ion beam techniques for detailed analysis using transmission electron microscopy. Evidence for thermal processing occurs as a perovskite–spinel–spinel triple junction in an interior section and a spinel inclusion within perovskite in a rim section. Evidence for parent-body alteration occurs in the form of Fe-rich sheet silicates in the rim, and localized amstallite in the interior of the CAI. While previous work suggested that many CTA CAIs experienced thermal processing in the solar nebula, including partial melting, our data show that signatures of primary condensation can be preserved in the form of more refractory phases contained within less refractory minerals, namely melilite and perovskite grains within spinel, and hibonite grains within perovskite, respectively. The inclusion we report on here has a complex history involving gas-phase condensation, nebular thermal processing, and parent-body alteration.

Dilyara M. Kuzina¹, Jérôme Gattacceca², Natalia S. Bezaeva³, Dmitry D. Badyukov³, Pierre Rochette², Yoann Quesnel², François Demory², Daniel Borschneck²
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13906]
¹Institute of Geology and Petroleum Technologies, Kazan Federal University, 4/5 Kremlyovskaya Str, 420008 Kazan, Russia ²CNRS, Aix Marseille Univ, IRD, INRAE, Aix-en-Provence, France
³Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19 Kosygin Str, 119991 Moscow, Russia
Published by arrangement with John Wiley & Sons

We present a paleomagnetic study of the ~10 km diameter Karla impact structure in Russia. We sampled the target carbonate rocks, and a yet undocumented fragmental melt-bearing lithic breccia layer. This impact breccia, which contains carbonate melt, is enriched in stoichiometric magnetite by a factor of ~15 compared to the target lithologies, and carries a stable natural remanent magnetization. The weak remanent magnetization and the presence of both normal and reverse polarities down to the centimeter scale indicate that the breccia does not carry a thermoremanent magnetization (TRM), but rather a chemical remanent magnetization (CRM). The presence of stoichiometric magnetite and the absence of TRM suggest that the magnetite was formed during relatively low-temperature postimpact hydrothermalism that affected the porous impact breccia layer. During this process, the breccia acquired a CRM. The paleomagnetic direction is compatible with a Cenozoic age for the impact event, but cannot bring more precise constraint on the age because of the stable position of the Eurasian plate over the last 60 Myr. However, the presence of both polarities indicates that mild hydrothermalism took place over a period of time long enough to span at least one reversal of the geomagnetic field, that is, over a time scale of the order of 100 kyr. This confirms that protracted hydrothermal systems associated with impact craters are long lived, even in relatively small craters such as Karla, and are key features of the geologic and environmental effects of impacts on Earth.

Bidong Zhang¹, Nancz L. Chabot¹ and Alan E. Rubin¹
Science Advances – Link to Article [https://www.science.org/doi/full/10.1126/sciadv.abo5781]
¹Department of Earth, Planetary and Space Sciences, University California, Los Angeles, CA 90095-1567, USA.
²Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
Copyright Elsevier

The parent cores of iron meteorites belong to the earliest accreted bodies in the solar system. These cores formed in two isotopically distinct reservoirs: noncarbonaceous (NC) type and carbonaceous (CC) type in the inner and outer solar system, respectively. We measured elemental compositions of CC-iron groups and used fractional crystallization modeling to reconstruct the bulk compositions and crystallization processes of their parent asteroidal cores. We found generally lower S and higher P in CC-iron cores than in NC-iron cores and higher HSE (highly siderophile element) abundances in some CC-iron cores than in NC-iron cores. We suggest that the different HSE abundances among the CC-iron cores are related to the spatial distribution of refractory metal nugget–bearing calcium aluminum–rich inclusions (CAIs) in the protoplanetary disk. CAIs may have been transported to the outer solar system and distributed heterogeneously within the first million years of solar system history.