¹Qinting Jiang,¹Shun-ichiro Karato,^2,3Thilo Bissbort,³Varvara Foteinou
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.115958]
¹Department of Earth and Planetary Science, Yale University, 210 Whitney Avenue, New Haven, CT 06520, USA
²Department of Earth and Environmental Sciences, Ludwig-Maximilians-University, Theresienstr. 41, 80333 Munich, Germany
³Central Unit for Ionbeams and Radionuclides RUBION, Ruhr-University Bochum, Universitätsstraße 150, 44801 Bochum, Germany
Copyright Elsevier

The solar wind is a possible source for hydrogen and other volatiles on planetary bodies. To better understand the role of the solar wind during the volatile acquisition of planetary materials, we conducted hydrogen implantation experiments on olivine, orthopyroxene, quartz single crystals. Depth profiles of hydrogen concentration after implantation are determined by the Nuclear Resonance Reaction Analysis. We find that energetic hydrogen particles penetrate into the sample and accumulate at a certain depth. The hydrogen concentration increases with the hydrogen fluence until a “saturation level” is attained. Hydrogen saturation level (e.g., ~10–20 at.% in olivine, equivalent to 0.5–1.2 wt%) far exceeds the equilibrium solubility in the bulk crystal at a similar thermodynamic condition (~10−22 wt%). The results of olivine show that the hydrogen penetration depth increases whereas the saturation level decreases (weakly) with the beam energy. Hydrogen saturation level also depends on the mineral species in the order: olivine > orthopyroxene > quartz. The experimental results can be applied to explain some observations on the high surface water content of some planetary bodies including Itokawa asteroid and the Moon. We also explore the possibility of hydrogenated dusts by the solar wind implantation as a source for water on terrestrial planets. We conclude that if all dusts were exposed to the solar wind and all implanted hydrogen were converted to water, then >10 ocean masses would have been acquired for Earth by ~100 years. However, the main part of the proto-planetary disk was not exposed to the solar wind and dusts could have been hydrogenated only when they were far from the equatorial plane of the disk. We discuss a possible mechanism to transport the hydrogenated dusts to the disk interior via turbulent mixing. Also, our experimental results and the mass dependence of the particle energies in the solar wind suggest that the D/H ratio of the dusts exposed to the solar wind will be higher than the solar wind value.

¹Zaicong Wang et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.01.002]
¹State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
Copyright Elsevier

Sulfides are accessory phases in lunar rocks but are important for understanding lunar interior processes as well as impacts on the lunar surface. Whether or not the lunar mantle had achieved sulfide saturation during magma ocean evolution and displays homogeneous sulfur isotopes remains under debate. The Chang’e-5 (CE-5) mission returned young (2.0 Ga) basalts from a mare terrain in the northern Oceanus Procellarum. Here we study chemical and sulfur isotopic compositions (δ34SV-CDT) of sulfides from CE-5 basaltic fragments and combine them with δ34S of other young (3.1–3.0 Ga) lunar low-Ti basalt (NWA 10597 and NWA 4734) and gabbro meteorites (NWA 6950) to compare them with Apollo low-Ti and high-Ti mare basalts. The sulfides in basaltic fragments of CE-5 are troilites (FeS) with low abundances of Ni, Co, and Cu (e.g., Ni < 0.04 wt.% and Ni/Co < 0.3). Textures and chemical compositions indicate that most troilites are late-stage crystallization products from the highly evolved CE-5 basalts. Several troilites occur in the matrices of impactite clasts and are intergrown with Fe–Ni metal (12–36 wt.% Ni, Ni/Co of 12–39). These troilites are distinct from the major population of troilites with noticeably higher Ni abundances (mostly >0.2 wt.% with Ni/Co of 1–3) and reconcile with the addition of meteoritic materials into the impact melts.

The δ34SV-CDT of large troilite grains (>10 μm) from the CE-5 basaltic fragments and lunar meteorites were obtained by high-precision, high-spatial-resolution femtosecond laser ablation MC-ICP-MS which achieved external uncertainty (0.65‰, 2SD at 8-μm laser spots) like nano-SIMS. Sulfur degassing during surficial effusive lava flow likely led to a slight decrease in δ34S (by ∼1‰) for some basaltic fragments; however, such effects were limited to the scale of bulk rock samples, consistent with previous results. The mean δ34S of troilites in CE-5 basaltic fragments (0.35±0.25‰, 2SE, n = 45) is similar to those of ancient (3.8–3.1 Ga old) Apollo low-Ti and high-Ti mare basalts and the young gabbro cumulate NWA 6950 (0.56 ± 0.21‰, 2SE, n = 10). The paired NWA 10597 and NWA 4734 show consistent δ34S, lower than most values by ∼0.5‰. Current data thus indicate that most mantle sources of lunar basalts would be homogeneous for δ34S (0.6 ± 0.3 ‰) and minor regions may be different. The overall homogenous δ34S from different mantle sources with variably low sulfur content supports sulfide-undersaturated accumulation of the lunar magma ocean, which was inherited from strong volatile loss and evaporative fractionation during the formation of the Moon.

¹Zachary A. Torrano,¹Conel M.O’D. Alexander,¹Richard W. Carlson,²Jan Render,²Gregory A. Brennecka,¹Emma S. Bullock
Earth and Planetary Science Letters 627, Link to Article [https://doi.org/10.1016/j.epsl.2023.118551]
¹Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, United States
²Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA, United States
Copyright Elsevier

Amoeboid olivine aggregates (AOAs) are the most abundant type of refractory inclusions found in most carbonaceous chondrite groups. AOAs are thought to be genetically related to calcium-aluminum-rich inclusions (CAIs) and potential chondrule precursor components, although the precise physical and temporal details of AOA formation and their relationship to other chondritic components remain unclear. In this study, we measured the chromium and titanium isotopic compositions of eight AOAs from four different CV chondrites with the goal of evaluating potential genetic links between AOAs, CAIs, and chondrules. These are the first Cr and Ti isotopic data reported beyond a single AOA previously measured for Cr and a different single AOA previously measured for Ti. The results presented here show that the ε54Cr and ε50Ti isotopic compositions of AOAs are indistinguishable from those of CAIs, suggesting that AOAs and CAIs formed from a common region of the disk. We also demonstrate, based on the comparison of the Cr and Ti isotopic composition of AOAs to previously measured chondrules, that mixing between AOAs and an NC compositional endmember alone cannot fully explain the range of measured chondrule compositions. Although AOAs may have been important chondrule precursor components along with AOA olivine, CAIs, fragments of earlier generation chondrules, and fine-grained matrix material, this observation requires another currently unknown component to be involved in chondrule formation.

¹C. Maurel,¹J. Gattacceca,¹M. Uehara
Earth and Planetary Science Letters 627, 118559, Open Access Link to Article [https://doi.org/10.1016/j.epsl.2023.118559]
¹CNRS, Aix Marseille Univ, IRD, INRAE, CEREGE, Aix-en-Provence, France
Copyright Elsevier

The JAXA Hayabusa 2 mission returned 5.4 g of material from the C-type asteroid Ryugu. The Mn-Cr ages of dolomite in the returned samples indicate that Ryugu’s parent body experienced aqueous alteration sometimes between <1.8 and 6.8 Myr after CAI formation. Because this time range overlaps with the lifetime of the solar nebula, we investigate the possibility that magnetite and pyrrhotite, which are aqueous alteration products found in Ryugu samples, acquired a remanent magnetization reflecting the nebula field intensity. We analyze the intrinsic magnetic properties and paleomagnetic record of three Ryugu samples of 0.82, 0.97 and 21.87 mg. None of the samples exhibit a stable natural remanent magnetization. This indicates that the aqueous alteration of Ryugu’s parent body took place either in a field of a few µT, or in a very weak to null field. In the former scenario, the solar nebula field is the most likely magnetizing field, implying that aqueous alteration occurred before its dissipation, i.e., before ∼5 Myr after CAI formation. In the latter scenario, aqueous alteration must have occurred either after the dissipation of the nebula, or at an earlier epoch and a large heliocentric distance (> 5 au). The similarities between Ryugu samples and CI chondrites favor this second hypothesis. Our results contrast with another paleomagnetic study of two Ryugu samples, arguing for a paleofield intensity of 40 to 390 µT. Our interpretation of this discrepancy is that these samples were exposed to artificial magnetic fields (> mT) during preceding experiments. This highlights the importance of conducting, as much as possible, the paleomagnetic investigations of returned samples before any other experiment. We also demonstrate that the ratio of NRM over low-field magnetic susceptibility is a powerful, non-destructive indicator of magnetic contamination. We recommend measuring this ratio routinely before paleomagnetic investigations of meteorites and returned samples.

¹Matthias van Ginneken et al. (>10)
Earth and Planetary Science Letters 627, 118562 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2023.118562]
¹Centre for Astrophysics and Planetary Science, School of Physical Sciences, University of Kent, Ingram Building, Canterbury CT2 7NH, UK
Copyright Elsevier

Airbursts are estimated to be the most frequent and hazardous type of impact events. Yet, confirmation of these events are elusive, resulting in a major gap in the impact record of Earth. The recent discovery of igneous chondritic spherules produced during a new type of touchdown airburst 430 thousand years (kyr) ago over Antarctica, in which a projectile vapor jet interacts with the Antarctic ice sheet, provided the first trace of such an impact in the geological record. In terms of petrology and geochemistry, particles constituting the BIT-58 dust horizon, which was found in surface ice at near Allan Hills in Antarctica, are almost identical to those produced 430 kyr ago. We demonstrate here that BIT-58 particles were indeed formed during a touchdown event between 2.3 and 2.7 million years (Myr) ago. This represents the oldest record of an airburst on Earth identified to date. Slight geochemical differences with 430 kyr old airburst spherules provide additional constraints on spherule condensation in large airburst plumes. Finding confirmation of airbursts in the paleorecord can provide insight into the frequency of the most hazardous impacts and, thus, has implications for planetary defence.

¹Christian A. Jansen,^1,2Christoph Burkhardt,³Yves Marrocchi,^1,2Jonas M. Schneider,^1,2Elias Wölfer,^1,2Thorsten Kleine
Earth and Planetary Science Letters 627, 118567 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.118567]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, Münster D-48149, Germany
²Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, Göttingen D-37077, Germany
³Centre de recherches pétrographiques et géochimiques (CRPG), CNRS, UMR 7358, F-54000, Nancy, France
Copyright Elsevier

Refractory inclusions in chondritic meteorites, namely amoeboid olivine aggregates (AOAs) and Ca-Al-rich inclusions (CAIs), are among the first solids to have formed in the solar system. The isotopic composition of CAIs is distinct from bulk meteorites, which either results from extreme processing of presolar carriers in the CAI-forming region, or reflects an inherited heterogeneity from the Sun’s parental molecular cloud. Amoeboid olivine aggregates are less refractory than CAIs and provide a record of how the isotopic composition of solid material in the disk may have changed in time and space. However, the isotopic composition of AOAs and how this composition relates to that of CAIs and later-formed solids is unknown. Here, using new O, Ti, and Cr isotopic data for eight AOAs from the Allende CV3 chondrite, we show that CAIs and AOAs share a common isotopic composition, indicating a close genetic link and formation from the same isotopic reservoir. Because AOAs are less refractory than CAIs, this observation is difficult to reconcile with a thermal processing origin of the isotope anomalies. Instead, the common isotopic composition of CAIs and AOAs is readily accounted for in a model in which the isotopic composition of infalling material from the Sun’s parental molecular cloud changed over time. In this model, CAIs and AOAs record the isotopic composition of the early infall, while later-formed solids contain a larger fraction of the later, isotopically distinct infall. This model implies that CAIs and AOAs record the isotopic composition of the Sun and suggests that the nucleosynthetic isotope heterogeneity of the solar system is predominantly produced by mixing of solar nebula condensates, which acquired their distinct isotopic compositions as a result of time-varied infall from the protosolar cloud.

¹E. Dobrica,²K.A. McCain,³A.J. Brearley
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.01.017]
¹Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science, and Technology, University of Hawai‘i at Mānoa, Honolulu, HI
²Jacobs Jets II Contract, NASA-Johnson Space Center, Houston, TX, USA
³Department of Earth and Planetary Sciences, MSC03-2040, 1University of New Mexico, Albuquerque, NM
Copyright Elsevier

We have investigated different carbonate minerals (calcite, aragonite, and ankerite) from two meteorites with different shock metamorphic stages (Boriskino, CM2 − ∼S3-S4 and Murchison CM2.5-2.2 − S1-S2) using various electron microscope techniques. Our detailed transmission electron microscopy study shows that carbonates are valuable recorders of the shock metamorphic environment and help interpret shock metamorphic conditions on the chondrite parent asteroids. We show the occurrence of fine-scale complex microstructures (dislocations, modulations, mosaic blocks, and microfractures) in all carbonates analyzed, indicating that they were modified during deformation processes at a variable degree. The presence of shock features in all generations of carbonates (Type 0, 1, and 2) indicates that shock deformation event/(s) occurred after the precipitation of all types of carbonates. In Boriskino, the most shocked meteorite analyzed, carbonates record very distinct microstructures compared to Murchison, an unshocked or very weakly shocked sample. We divided these microstructures into two different categories as a function of the degrees of deformation, and several features could be used as diagnostic tools for low and high shock pressures in meteorites. Deformation features are pervasive in calcites, aragonites (Type 1 and 2 Ca carbonates), and ankerites from Boriskino. However, the abundance and distribution of these deformation features are minimal in all calcite crystals analyzed from Murchison and one Type 0 Ca carbonate from Boriskino. This suggests the presence of a correlation between these microstructural features and the degree of shock metamorphic stages of the samples analyzed. The low amount of deformation features in the Type 0 calcite from Boriskino could indicate that the least altered lithologies from Boriskino were not subject to high-intensity impacts.

^1,2S. A. Singerling,³C. M. Corrigan,⁴A. J. Brearley
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14132]
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
²Department of Geosciences, Goethe University Frankfurt, Altenhoeferallee 1, 60438 Frankfurt am Main, Germany.
³Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
⁴Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

We have carried out a SEM-EPMA-TEM study to determine the textures and compositions of relict primary iron sulfides and their alteration products in a suite of moderately to heavily altered CM1 carbonaceous chondrites. We observed four textural groups of altered primary iron sulfides: (1) pentlandite+phyllosilicate (2P) grains, characterized by pentlandite with submicron lenses of phyllosilicates; (2) pyrrhotite+pentlandite+magnetite (PPM) grains, characterized by pyrrhotite–pentlandite exsolution textures with magnetite veining and secondary pentlandite; (3) pentlandite+serpentine (PS) grains, characterized by relict pentlandite exsolution, serpentine, and secondary pentlandite; and (4) pyrrhotite+pentlandite+magnetite+serpentine (PPMS) grains, characterized by features of both the PPM and PS grains. We have determined that all four groups were initially primary iron sulfides, which formed from crystallization of immiscible sulfide melts within silicate chondrules in the solar nebula. The fact that such different alteration products could result from the same precursor sulfides within even the same meteorite sample further underscores the complexity of the aqueous alteration environment for the CM chondrites. The different alteration reactions for each textural group place constraints on the mechanisms and conditions of alteration with evidence for acidic environments, oxidizing environments, and changing fluid compositions (Ni-bearing and Si-Mg-bearing).

¹Ted M Johnson,¹Beth L. Klein,²D. Koester,³Carl Melis,¹B. Zuckerman,¹M. Jura
The Astrophysical Journal 941, 113 Open Access Link to Article [DOI 10.3847/1538-4357/aca089]
¹Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1562, USA; tedjohnson12@g.ucla.edu
²Institut fur Theoretische Physik und Astrophysik, University of Kiel, D-24098 Kiel, Germany
³Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093-0424, USA

Ultraviolet and optical spectra of the hydrogen-dominated atmosphere white dwarf star G238-44 obtained with FUSE, Keck/HIRES, HST/COS, and HST/STIS reveal 10 elements heavier than helium: C, N, O, Mg, Al, Si, P, S, Ca, and Fe. G238-44 is only the third white dwarf with nitrogen detected in its atmosphere from polluting planetary system material. Keck/HIRES data taken on 11 nights over 24 yr show no evidence for variation in the equivalent width of measured absorption lines, suggesting stable and continuous accretion from a circumstellar reservoir. From measured abundances and limits on other elements, we find an anomalous abundance pattern and evidence for the presence of metallic iron. If the pollution is from a single parent body, then it would have no known counterpart within the solar system. If we allow for two distinct parent bodies, then we can reproduce the observed abundances with a mix of iron-rich Mercury-like material and an analog of an icy Kuiper Belt object with a respective mass ratio of 1.7:1. Such compositionally disparate objects would provide chemical evidence for both rocky and icy bodies in an exoplanetary system and would be indicative of a planetary system so strongly perturbed that G238-44 is able to capture both asteroid and Kuiper Belt–analog bodies near-simultaneously within its <100 Myr cooling age.