^1,2,3Jack Diab,³Mohit Melwani Daswani,³Julie Castillo-Rogez
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115339]
¹Southern Oregon University, 1250 Siskiyou Blvd., Ashland, OR 97520, USA
²University of California Los Angeles, 607 Charles E. Young Drive East. Box 951569, Los Angeles, CA 90095-1569, United States of America
³Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA
Copyright Elsevier

Ceres is the largest object in the asteroid belt and the only dwarf planet in the inner solar system. In 2015, carbon, and organic compounds, were found by the Dawn mission in high abundance in the surface of Ceres. Here, we use thermodynamic modeling with the goal of constraining the speciation, stability, and abundance of organic compounds formed via abiotic reactions in the early subsurface ocean of Ceres and its mud-bearing mantle. We vary environmental conditions such as temperature, pH, reduction potential, solution composition, and pressure to analyze the variables that lead to optimal formation of organics. Primary results predict that in-situ organic production is negligible for most cases in the subsurface ocean if Ceres primarily accreted CI carbonaceous chondrites yet may be more significant if Ceres formed from cometary material. Carbonate concentration is 3–6 orders of magnitude higher than organics in the chondritic models, while a cometary composition favors significant alcohol and carboxylic acid derivative production, among other organic species. Results also indicate that temperature and pH are drivers of organic formation by water-rock equilibrium, with temperature having the greatest effect. Further analysis reveals that a mixture of ≲ 80 wt% CI chondrite and ≳ 20 wt% cometary material is favorable to in situ organic production of reduced organics. Observational constraints from the Dawn mission indicate that our model results could be representative of the organic observations on the surface. While our models favor organic production in Ceres’ ocean with moderate amounts of cometary material, further studies into alternative mechanisms of production and concentration on the surface of Ceres are needed.

¹Huacheng Li,^2,6Zongyu Yue,²Yangting Lin,^3,6Kaichang Di,^1,4Nan Zhang,^5,6Jianzhong Liu
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115333]
¹Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China
²Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
³State Key Laboratory of Remote Sensing Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100101, China
⁴Earth Dynamics Group, School of Earth and Planetary Sciences, Curtin University, Perth, Australia
⁵Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China
⁶CAS Center for Excellence in Comparative Planetology, Hefei 230026, China
Copyright Elsevier

Mineral olivine and Mg-rich spinel observed in Das crater were previously attributed to the excavation from the lunar lower crust or even mantle. To test this hypothesis, we developed a three-dimensional hydrocode SALEc to simulate the formation of such an elliptical crater. The hydrocode SALEc was examined and verified by comparing its results with experimental data and another code iSALE-2D. Based on the comparison between our SALEc’s numerical results and observations, we found that Das crater can be formed by an impact with the projectile of 6.0 km in diameter, impact velocity of 10 km/s, and impact angle of 70° relative to the vertical. In the impact, the excavation depth of Das crater is ~3.0 km, much less than the lunar crust thickness, hence the mineral olivine and Mg-rich spinel observed in this crater is unlikely originated from lunar lower crust or mantle. Numerical simulation results also show that some projectile materials can survive in this impact and are distributed in the downrange crater floor. Given the abundant olivine in many asteroids, we propose that olivine observed in Das crater is most probably originated from projectile remnants instead of excavation from the depth.

¹Aleksandra N. Stojic et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115344]
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm – Klemm Str. 10, 48149 Münster, Germany
Copyright Elsevier

The effect of surface regolith gardening and melt layer production produced by space weathering (SW) (owing to micrometeorite [according to comment rev#1] bombardment) of surficial regolith layers of airless planetary surfaces was investigated in an experimental setup by using laser-induced ablation of powdered analog material (synthetic Fo100) under vacuum with a ns-pulsed infrared laser. The investigated analog pellets were prepared from the fine fraction (< 1 μm) up to a grain size of 280 μm, which resembles the uppermost regolith surface of many airless planetary bodies. The Fo-powder was pressed into shape to form a pellet. We focused here on nanometer-sized structural modifications that are induced in the relocated grains, sputtered off ejecta material and melt sprinkles that formed away from the craters caused by laser irradiation of the pressed pellet surface. The ejecta particles were redistributed over the entire pellet surface and beyond. The forming sputter film, melt sprinkles and ballistically ejected grains were caught on carbon film grids positioned nearby the craters. The grids were investigated with a transmission electron microscope (TEM) to discern between the distinct deposition types that were formed by ejecta condensate and partially molten ejected nanometer-size analog grains. Apart from a heavily modified pellet surface, we found that deposited droplets are mostly amorphous with minor nanocrystalline subdomains. Eight out of ten droplets show distinct incipient crystallization stages. This indicates at a relatively high amount of amorphous regolith material at the incipient stage of SW for airless bodies, if the regolith is altered via micrometeorite bombardment.

¹Masahiko Sato et al. (>10)
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007405]
¹The University of Tokyo, Tokyo, 113-0033 Japan
Published by arrangement with John Wiley & Sons

In this study, systematic rock magnetic measurements and saturation isothermal remanent magnetization (SIRM) paleointensity calibration experiments were conducted for the returned samples from C-type asteroid (162173) Ryugu and two carbonaceous chondrites (Orgueil and Tagish Lake) to evaluate the remanence carriers of the Ryugu sample and its ability as a paleomagnetic recorder. Our magnetic measurements show that Ryugu samples exhibit signatures for framboidal magnetite, coarse-grained magnetite, and pyrrhotite, and that framboidal magnetite is the dominant remanence carrier of Ryugu samples in the middle-coercivity range. The SIRM paleointensity constant was obtained for two Ryugu samples, and the median value was 3318 ± 1038 μT, which is close to the literature’s value based on the average among magnetite, titanomagnetite, pyrrhotite, and FeNi alloys and is widely used for SIRM paleointensity experiments. The paleointensity values estimated using the obtained SIRM paleointensity constant indicate a strong magnetic field of the protoplanetary disk, suggesting that Sun’s protoplanetary disk existed at the disk location of Ryugu’s parent planetesimal when framboidal magnetite precipitated from the aqueous fluid.

¹Liam D.Peterson,¹Megan E.Newcombe,²Conel M. O’D. Alexander,²Jianhua Wang,³Adam R.Sarafian,⁴Addi Bischoff,⁵Sune G.Nielsen
Geochimica et Cosmochimica acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.10.036]
¹Department of Geology, University of Maryland, College Park, MD 20740, United States
²Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, United States
³Corning, Corning, NY 14873, USA
⁴Institut für Planetologie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany
⁵NIRVANA Labs, Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, United States
Copyright Elsevier

The fate of highly volatile elements (H, C, F, Cl and S) during planetary accretion and differentiation is debated. Recent analyses of water in non-carbonaceous chondrites (RC, OC, EC) and achondrites (angrites, eucrites) have been used to argue that inner solar system parent bodies accreted and retained their highly volatile element budgets from their primary feedstock without substantial loss during accretion, metamorphism and differentiation. An alternative model posits that differentiated inner solar system parent bodies (e.g., the angrite parent body, 4 Vesta, Earth) derived the majority of their water from a carbonaceous chondrite-like source, delivered during the final stages of accretion.

In order to add new constraints to this debate, we have measured water in nominally anhydrous minerals, melt inclusions, and interstitial glass in ureilites, the largest group of primitive achondrites in the terrestrial meteorite collection. Primitive achondrites did not experience global melting and homogenization. Therefore, these meteorites capture part of the transition from chondritic to achondritic parent bodies, allowing us to constrain the fate of water during the earliest stages of differentiation. Our nano-scale secondary ion mass spectrometry (nanoSIMS) analyses allow us to assess the viability of ureilite-like material as a potential source of terrestrial water. Analyses of pigeonite in main group ureilites yield a range of 2.0 – 6.0 µg/g H2O, and analyses of high-Ca pyroxene and glass (glassy melt inclusions and interstitial glass) in the Almahata Sitta ureilitic trachyandesite yield ranges of 13 – 19 µg/g H2O and 44 – 216 µg/g H2O, respectively. Mass balance, incremental melting, and batch melting calculations yield a preferred ureilite parent body H2O content of 2 – 20 µg/g, similar to previous estimates of water in the eucrite parent body (4 Vesta), but lower than estimates of Earth’s water budget. With these data, we demonstrate that 1) the ureilite parent body is H2O-depleted relative to the Earth; 2) ureilite-like material is unlikely to be a primary source of H2O to the Earth; 3) C and H are not necessarily coupled elements during planetary accretion and thermal processing; and 4) accretion, heating, partial melting, and degassing of rocky planetesimals likely results in significant depletion of H2O.

^1,2C. J. Gimar,^2,1,3U. Raut,^2,3M. P. Poston,⁴A. Stevanovic,^5,2S. Protopapa,³T. K. Greathouse,^2,1,3K. D. Retherford,^2,3J. M. Friday,^2,3J. T. Grimes
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007508]
¹Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, 78249 United States
²Center for Laboratory Astrophysics and Space Science Experiments (CLASSE), Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, 78238 United States
³Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, 78238 United States
⁴Kleberg Advanced Microscopy Center, University of Texas at San Antonio, San Antonio, TX, 78249 United States
⁵Department of Space Studies, Southwest Research Institute, Boulder, CO, 80302 USA
Published by arrangement with John Wiley & Sons

We have characterized the far-ultraviolet (FUV) spectro-photometric response of lunar soil simulants JSC-1A and LMS-1, reporting notable differences from our previous results for Apollo soil 10084 (Raut et al., 2018). While JSC-1A and LMS-1 were designed to emulate the geotechnical and compositional properties of a low-Ti and high-Ti mare soil respectively, these terrestrial simulants lack “space weathering” attributes such as the nanophase iron present in the weathered rims of Apollo grains and glassy agglutinates. Photometric analyses of the JSC-1A phase curves reveal a ∼ 3-4 fold increase in single scattering albedo (SSA) and a forward scattering behavior compared to 10084. LMS-1 is shown to have SSA nearly twice that of 10084 and a near isotropic reflectance. Additionally, both JSC-1A and LMS-1 spectra present a blue slope in the FUV, with the JSC-1A slope ∼ 10× larger than that reported for the 10084 soil. Our analyses imply that low-Ti content, corroborated using energy dispersive x-ray spectroscopy, correlates to brighter FUV reflectance and a greater spectral blue slope for JSC-1A, while space weathering components likely contribute to the backscattering of FUV light by the Apollo soil relative to both simulants. Further work with an extended set of Apollo soils is warranted to deconvolute the relative contributions of weathering and composition to their FUV spectro-photometric response.

^1,2Anthony Gargano,³James Dottin,⁴Sean S. Hopkins,^1,2Zachary Sharp,⁵Charles Shearer,^4,6lex N. Halliday,⁴Fiona Larner,^3,7James Farquar,⁸Justin I. Simon
American Mineralogist 107, 1985-1994 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2022/Abstracts/AM107P1985.pdf]
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131-0001, U.S.A.
²Center for Stable Isotopes, University of New Mexico, Albuquerque, New Mexico 87131-0001, U.S.A.
³Department of Geology, University of Maryland, College Park, Maryland, 20742, U.S.A.
⁴Department of Earth Sciences, University of Oxford, OX1 3AN, U.K.
⁵Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico 87131-0001, U.S.A.
⁶The Earth Institute, Columbia Climate School, Columbia University, New York, New York 10025, U.S.A.
⁷Earth System Science Interdisciplinary Center, College Park, Maryland 20742, U.S.A.
⁸Center for Isotope Cosmochemistry and Geochronology, Astromaterials Research and Exploration Science Division,
The Lyndon B. Johnson Space Center, National Aeronautics and Space Administration, Houston, Texas 77058, U.S.A
Copyright: The Mineralogical Society of America

We compare the stable isotope compositions of Zn, S, and Cl for Apollo mare basalts to better constrain the sources and timescales of lunar volatile loss. Mare basalts have broadly elevated yet limited
ranges in δ66Zn, δ34S, and δ37ClSBC+WSC values of 1.27 ± 0.71, 0.55 ± 0.18, and 4.1 ± 4.0‰, respectively,
compared to the silicate Earth at 0.15, –1.28, and 0‰, respectively. We find that the Zn, S, and Cl
isotope compositions are similar between the low- and high-Ti mare basalts, providing evidence of
a geochemical signature in the mare basalt source region that is inherited from lunar formation and
magma ocean crystallization. The uniformity of these compositions implies mixing following mantle
overturn, as well as minimal changes associated with subsequent mare magmatism. Degassing of
mare magmas and lavas did not contribute to the large variations in Zn, S, and Cl isotope compositions found in some lunar materials (i.e., 15‰ in δ66Zn, 60‰ in δ34S, and 30‰ in δ37Cl). This reflects
magma sources that experienced minimal volatile loss due to high confining pressures that generally
exceeded their equilibrium saturation pressures. Alternatively, these data indicate effective isotopic
fractionation factors were near unity.
Our observations of S isotope compositions in mare basalts contrast to those for picritic glasses
(Saal and Hauri 2021), which vary widely in S isotope compositions from –14.0 to 1.3‰, explained by
extensive degassing of picritic magmas under high-P/PSat values (>0.9) during pyroclastic eruptions.
The difference in the isotope compositions of picritic glass beads and mare basalts may result from
differences in effusive (mare) and explosive (picritic) eruption styles, wherein the high-gas contents
necessary for magma fragmentation would result in large effective isotopic fractionation factors during
degassing of picritic magmas. Additionally, in highly vesiculated basalts, the δ34S and δ37Cl values of
apatite grains are higher and more variable than the corresponding bulk-rock values. The large isotopic
range in the vesiculated samples is explained by late-stage low-pressure “vacuum” degassing (P/PSat ~ 0)
of mare lavas wherein vesicle formation and apatite crystallization took place post-eruption. Bulk-rock
mare basalts were seemingly unaffected by vacuum degassing. Degassing of mare lavas only became
important in the final stages of crystallization recorded in apatite—potentially facilitated by cracks/
fractures in the crystallizing flow. We conclude that samples with wide-ranging volatile element isotope compositions are likely explained by localized processes, which do not represent the bulk Moon.