¹David R. Frank,¹Gary R. Huss,²Michael E. Zolensky,¹Kazuhide Nagashima,³Loan Le
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14083]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, USA
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, Texas, USA
³Jacobs JETS, Houston, Texas, USA
Published by arrangement with John Wiley & sons

Cosmochemists have relied on CI carbonaceous chondrites as proxies for chemical composition of the non-volatile elements in the solar system because these meteorites are fine-grained, chemically homogeneous, and have well-determined bulk compositions that agree with that of the solar photosphere, within uncertainties. Here we report the discovery of a calcium-aluminum-rich inclusion (CAI) in the Ivuna CI chondrite. CAIs are chemically highly fractionated compared to CI composition, consisting of refractory elements and having textures that either reflect condensation from nebular gas or melting in a nebular environment. The CAI we found is a compact type A CAI with typical 16O-rich oxygen. However, it shows no evidence of 26Al, which was present when most CAIs formed. Finding a CAI in a CI chondrite raises serious questions about whether CI chondrites are a reliable proxy for the bulk composition of the solar system. Too much CAI material would show up as mismatches between the CI composition and the composition of the solar photosphere. Although small amounts of refractory material have previously been identified in CI chondrites, this material is not abundant enough to significantly perturb the bulk compositions of CI chondrites. The agreement between the composition of the solar photosphere and CI chondrites allows no more than ~0.5 atom% of CAI-like material to have been added to CI chondrites. As the compositions of CI chondrites, carbonaceous asteroids, and the solar photosphere are better determined, we will be able to reduce the uncertainties in our estimates of the composition of the solar system.

¹Alexander N. Krot,²Tasha L. Dunn,³Michail I. Petaev,⁴Chi Ma,¹Kazuhide Nagashima,⁵Jutta Zipfel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14080]
¹Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Mānoa, Honolulu, Hawaii, USA
²Department of Geology, Colby College, Waterville, Maine, USA
³Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
⁴Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
⁵Senckenberg Gesellschaft für Naturforschung, Frankfurt am Main, Germany
Published by arrangement with John Wiley & Sons

We report on the primary and secondary mineralogies of three coarse-grained igneous calcium-aluminum-rich inclusions (CAIs) (Compact Type A [CTA], Type B [B], and forsterite-bearing type B [FoB]) from the Northwest Africa (NWA) 5343 (CK3.7) and NWA 4964 (CK3.8) carbonaceous chondrites, compare them with the mineralogy of igneous CAIs from the Allende (CV3.6) chondrite, and discuss the nature of the alteration processes that affected the CK and CV CAIs. The primary mineralogy and mineral chemistry of the CK3 CAIs studied are similar to those from Allende; however, primary melilite and anorthite are nearly completely absent. Although the secondary minerals identified in CK CAIs (Al-diopside, andradite, Cl-apatite, clintonite, forsterite, ferroan olivine, Fe,Ni-sulfides, grossular, ilmenite, magnetite, plagioclase, spinel, titanite, and wadalite) occur also in the Allende CAIs, there are several important differences: (i) In addition to melilite and anorthite, which are nearly completely replaced by secondary minerals, the alteration of CK CAIs also affected high-Ti pyroxenes (fassaite and grossmanite) characterized by high Ti³⁺/Ti⁴⁺ ratio and spinel. These pyroxenes are corroded and crosscut by veins of Fe- and Ti-bearing grossular, Fe-bearing Al,Ti-diopside, titanite, and ilmenite. Spinel is corroded by Fe-bearing Al-diopside and grossular. (ii) The secondary mineral assemblages of grossular + monticellite and grossular + wollastonite, commonly observed in the Allende CAIs, are absent; the Fe-bearing grossular + Fe-bearing Al-diopside ± Fe,Mg-spinel, Fe-bearing grossular + Fe,Mg-olivine ± Fe,Mg-spinel, and Ca,Na-plagioclase + Fe-bearing Al-diopside + Fe-bearing grossular assemblages are present instead. These mineral assemblages are often crosscut by veins of Fe-bearing Al-diopside, Fe,Mg-olivine, Fe,Mg-spinel, and Ca,Na-plagioclase. The coarse-grained secondary grossular and Al-diopside often show multilayered chemical zoning with distinct compositional boundaries between the layers; the abundances of Fe and Ti typically increase toward the grain edges. (iv) Sodium-rich secondary minerals, nepheline and sodalite, commonly observed in the peripheral portions of the Allende CAIs, are absent; Ca,Na-plagioclase is present instead. We conclude that coarse-grained igneous CAIs from CK3.7–3.8 s and Allende experienced an open-system multistage metasomatic alteration in the presence of an aqueous solution–infiltration metasomatism. This process resulted in localized mobilization of all major rock-forming elements: Si, Ca, Al, Ti, Mg, Fe, Mn, Na, K, and Cl. The metasomatic alteration of CK CAIs is more advanced and occurred under higher temperature and higher oxygen fugacity than that of the Allende CAIs.

¹Kevin Zahnle,²James F. Kasting
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.09.023]
¹NASA Ames Research Center, Mails Stop 245-3, Moffett Field, 94043, CA, USA
²The Pennsylvania State University, State College,, PA, USA
Copyright Elsevier

We develop a new model of diffusively modulated hydrodynamic escape to predict oxygen isotopic fractionations caused by the loss of water from a steam atmosphere of Venus. The chief technical advance over previous work is including CO₂ as a major species. We find that ordinary (�18O) and mass-independent (Δ17O) fractionations depend mostly on the extent of lithospheric buffering and the ferocity of EUV heating when escape took place, and relatively little on the size of the lost ocean(s). It is likely that Δ17O evolved significantly from its birth state, not only in the atmosphere but also in the silicates of the crust and upper mantle. If both �18O and Δ17O of Venus are identical to Earth and Moon, we may conclude that Venus and Earth accreted from a common pool. But differences in �18O and Δ17O can be attributed to escape rather than to genetics. If the differences are large enough, they can be used to constrain when escape took place and the extent of volatile exchange with the lithosphere. Neon and argon systematics are most consistent with minimal escape, especially if an Ar-rich source, possibly derived from comets, is added. However, we also find a novel class of solutions in which Ne and Ar of Venus, Earth, and Mars are evolved from a common source material subject to different vigors of hydrodynamic escape, least extreme for Earth and most extreme for Mars. These alternative models require that Venus was always rather dry (<10% of an Earth ocean) and its water lost very early (before <100 Myrs). The two styles of escape – minimal or extreme – should be readily distinguished by an unambiguous measurement of the Ar/Kr ratio. Finally, we find that predicted D/H enrichments are of order 100 for almost all model parameters. This result, a direct consequence of diffusion-limited escape of H and D, provides support for the overall scenario.

^1,2Elizaveta Kovaleva, ³Hassan Helmy, ^4,5Said Belkacim,²Anja Schreiber, ²Franziska D.H. Wilke,²Richard Wirth
American Mineralogist 108, 1906-1923 Link to Article [http://www.minsocam.org/msa/ammin/toc/2023/Abstracts/AM108P1906.pdf]
¹Department of Earth Sciences, University of the Western Cape, Robert Sobukwe Road, 7535 Bellville, South Africa
²Helmholtz Centre Potsdam—GFZ German Research Centre for Geosciences, Telegrafenberg, D-14473 Potsdam, Germany
³Department of Geology, Minia University, 61519-Minia, Egypt
⁴LAGAGE Laboratory, Department of Geology, Faculty of Sciences, Ibn Zohr University, P.O. Box 28/S, 80 000, Agadir, Morocco
⁵Research Institute on Mines and Environment (RIME), Université du Québec en Abitibi-Témiscamingue, 445 Boul. Université, Rouyn-Noranda, Québec J9X 5E4, Canada
Copyright: The Mineralogical Society of America

The origin of Libyan Desert Glass (LDG) found in the western parts of Egypt close to the Libyan
border is debated in planetary science. Two major theories of its formation are currently competing:
(1) melting by airburst and (2) formation by impact-related melting. While mineralogical and textural
evidence for a high-temperature event responsible for the LDG formation is abundant and convincing, minerals and textures indicating high shock pressure have been scarce. This paper provides a
nanostructural study of the LDG, showing new evidence of its high-pressure and high-temperature
origin. We mainly focused on the investigation of Zr-bearing and phosphate aggregates enclosed within
LDG. Micro- and nanostructural evidence obtained with transmission electron microscopy (TEM) are
spherical inclusions of cubic, tetragonal, and orthorhombic (Pnma or OII) zirconia after zircon, which
indicate high-pressure, high-temperature decomposition of zircon and possibly, melting of ZrO2. Inclusions of amorphous silica and amorphous Al-phosphate with berlinite composition (AlPO4) within
mosaic whitlockite and monazite aggregates point at decomposition and melting of phosphates, which
formed an emulsion with SiO2 melt. The estimated temperature of the LDG melts was above 2750 °C,
approaching the point of SiO2 boiling. The variety of textures with different degrees of quenching immediately next to each other suggests an extreme thermal gradient that existed in LDG through radiation
cooling. Additionally, the presence of quenched orthorhombic OII ZrO2 provides direct evidence of
high-pressure (>13.5 GPa) conditions, confirming theory 2, the hypervelocity impact origin of the LDG.

^1,2M.D. Suttle,²A.J. King,²C.S. Harrison,^1,3Q.H.S. Chan,⁴A. Greshake,⁵R. Bartoschewitz,⁶A.G. Tomkins,⁷T. Salge,²P.F. Schofield,²S.S. Russell
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.09.024]
¹School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
²Planetary Materials Group, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
³Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK
⁴Museum für Naturkunde, Leibniz-Institut für Evolutions und Biodiversitätsforschung, Invalidenstraße 43, 10115 Berlin, Germany
⁵Bartoschewitz Meteorite Laboratory, Weiland 37, D-38518 Gifhorn, Germany
⁶School of Earth, Atmosphere and Environment, Melbourne, Victoria, Australia
⁷Imaging and Analysis Centre, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
Copyright Elsevier

The CY chondrites are a group of thermally metamorphosed carbonaceous chondrites. Although they share similarities with the CM and CI chondrites, their primary properties argue for a distinct classification. Previous studies have highlighted their isotopically heavy bulk compositions (δ17O=10 ‰, δ18O=21 ‰, Δ17O=0 ‰) and exceptionally high sulphide abundances (10-30 vol%). In this work we explore their petrography and alteration history. The CYs accreted low abundances of chondrules (15-20 area%) with average apparent diameters slightly larger (∼320-340 µm) than the CM chondrites. In contrast to the CMs, the CYs record an early episode of brecciation prior to the main window of aqueous alteration. Subsequent fluid activity produced a range of alteration extents with both CY2 and CY1 chondrites documented. Phyllosilicate minerals in the CYs were a mix of serpentine and saponite (including occurrences of Na-saponite) with minor quantities of chlorite (within chondrules). An initial generation of Fe-sulphides formed by sulfidation of metal, and by precipitation from S-rich fluids. Three generations of carbonates are recognized, an early generation that infilled voids left by brecciation and co-precipitated with sulphide, a later generation that co-precipitated with magnetite and a final Fe-Mg-bearing generation which formed large (>100 µm) clasts. Only the first-generation carbonates are found in the CY2s, while the CY1s preserve all three generations. Phosphates occur as Ca-apatite or rarely as Mg-apatite and have hydroxylapatite compositions, indicating low halogen activities in the alteration fluids. Refractory oxides (ilmenite and Cr-spinel) occur as precipitates adhering to the margins of phyllosilicates. They formed late in the alteration sequence and attest to oxidizing conditions. During the late-stages of aqueous alteration Fe-sulphides were replaced by magnetite. Thermal metamorphism (Stage II-IV: ∼300-750 °C) overprinted aqueous alteration leading to dehydration and recrystallization of the phyllosilicate matrix and the decomposition of some carbonate phases. Most Fe-sulphide grains survived heating without decomposition as initial partial decomposition from pyrrhotite to troilite under closed system conditions led to elevated ƒS2 gas and resulted in a stabilizing effect. Retrograde reactions between trapped S2 gas and metal/magnetite formed a final generation of Fe-sulphides. The survival of Fe-sulphides and their stochiometric troilite compositions are evidence for near-closed system heating. Analysis of organic matter by Raman spectroscopy supports an interpretation of short-duration heating (on the scale of minutes to days), at peak temperatures between 750-900 °C. Thus, an impact event was the most likely cause of metamorphic heating.

^1,2S. S. Rout,³J. Storz,⁴A. Davydok,³A. Bischoff,⁵T. John,⁴C. Krywka,⁶M. Ritter
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14082]
¹School of Earth and Planetary Sciences, National Institute of Science Education and Research, Khorda, India
²Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai, India
³Institut für Planetologie, University of Münster, Münster, Germany
⁴Institute of Materials Physics, Helmholtz-Zentrum Hereon, Outstation DESY, Hamburg, Germany
⁵Freie Universität Berlin, Institut für Geologische Wissenschaften, Berlin, Germany
⁶Electron Microscopy Unit, Hamburg University of Technology, Hamburg, Germany
Published by arrangement with John Wiley & Sons

The origin of diamond in ureilites has been frequently debated. We investigated carbon phase assemblages (CPAs) in five ureilitic samples of the brecciated asteroid 2008 TC3, found within the Almahata Sitta (AHS) strewn field, by transmission electron microscopy, Raman spectroscopy, synchrotron X-ray diffraction, and cathodoluminescence. Samples MS-MU 006, MS-187, and MS-170, are of low to moderate shock degree (U-S2 and U-S3), and samples MS-MU 027 (U-S4) and MS-MU 045 (U-S5) have a higher shock degree. In MS-MU 006 and MS-187, we did not find any diamond grains. MS-170 contains disordered and distorted graphite with diamond grains up to 12 μm in size and containing inclusions of Fe,Ni-metal, FeS, Fe-phosphide, and Cr,Fe-oxide. These diamond grains formed under relatively low (5–15 GPa) shock pressures through a catalytic process in the presence of a Fe,Ni,Cr,S,P-rich melt. The highly shocked and fine-grained ureilites MS-MU 027 and MS-MU 045 have three different types of CPAs, namely a nanopolycrystalline assemblage of diamond and defect-rich diamond/lonsdaleite, disordered and distorted graphite, and polycrystalline diamond with abundant Fe-rich mineral inclusions. The CPAs that have only diamond and planar defect-rich diamond (e.g., MS-MU 027) most likely formed through martensitic transformation of graphite to diamond and lonsdaleite at >15 GPa and >2000 K. The assemblage of diamond, defect-rich diamond, and disordered and distorted graphite (e.g., MS-MU 045) formed by martensitic transformation of graphite to diamond and lonsdaleite, followed by back-transformation to disordered graphite. We did not find any conclusive evidence to support the formation of diamond grains under high static pressure.

¹Fabian Zahnow,¹Tido Stracke,¹Tommaso di Rocco,²Thilo Hasse,¹Andreas Pack
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14084]
¹Geowissenschaftliches Zentrum, Universität Göttingen, Göttingen, Germany
²Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
Published by arrangement with John Wiley & Sons

In this study, we present a method for high precision Δ′17O (Δ′17ORL = ln(δ17O + 1) – λRL ln(δ18O + 1)) analysis of small mass silicate and oxide materials. The analyses were conducted by laser fluorination in combination with gas chromatography and continuous flow isotope ratio monitoring gas spectrometry. We could analyze the oxygen isotope composition of samples down to 1 μg, which corresponded to about 13 nmol O2. The analytical error (we report the 1σ external reproducibility of a single analysis) in δ18O increases with decreasing sample sizes from ~0.2‰ for ~20 μg samples to ~0.9‰ for 1 μg samples. For Δ′17O, we achieved an external reproducibility of 0.04‰ for a sample mass range between 1 and 27 μg. The uncertainty in Δ′17O is smaller than the uncertainty in δ18O due to the correlated errors in δ17O and δ18O. We applied the method to urban micrometeorites, that is, small meteorites (<2 mm) that were sampled from a rooftop in Berlin, Germany. A total of 10 melted micrometeorites (S-type cosmic spherules, masses between 11 and 22 μg) were analyzed. The oxygen isotope compositions are comparable to that of modern Antarctic collections, indicating that the urban micrometeorites sample the same population. No indication for terrestrial weathering had been identified in the studied set of urban micrometeorites making them suitable materials for the study of micrometeorite origins.

¹S. Loehle,²J. Vaubaillon,³P. Matlovič,³J. Tóth
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115817]
¹High Enthalpy Flow Diagnostics Group, Institute of Space Systems, University of Stuttgart, Pfaffenwaldring 29, 70569 Stuttgart, Germany
²IMCCE, Observatoire de Paris, PSL, 77 Av. Denfert Rochereau, Paris, 75014, France
³Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
Copyright Elsevier

The paper reports the determination of luminous efficiency values from ground testing of a comprehensive set of meteorite samples. The ground testing data is translated with commonly used ground to flight extrapolation analogies from atmospheric entry maneuver’s engineering into values of a night observation. This results in a meteor at an altitude of 80 km with a flight speed of 11.7 km/s of a 34.8 mm diameter spherical meteoroid. A method is developed to determine the total luminous efficiency
in the bands U, B, V, R, and I from the radiance data and the measured mass loss. For the first time, a measurement of luminous efficiency became possible for known materials. The values itself are in the range of 0.01% to
1%, which is in the range of previous studies from meteor measurements.

¹A. Nakamura,¹M. Miyahara,^2,3H. Suga,⁴A. Yamaguchi,⁵D. Wakabayashi,⁵S. Yamashita,^5,6Y. Takeichi,¹K. Kukihara,²Y. Takahashi,⁷E. Ohtani
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2023JE007951]

¹Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima, Japan
²Department of Earth and Planetary, Graduate School of Science, The University of Tokyo, Tokyo, Japan
³Japan Synchrotron Radiation Research Institute, Hyogo, Japan
⁴National Institute of Polar Research, Tokyo, Japan
⁵Institute of Materials Structure Science, High-Energy Accelerator Research Organization (KEK), Tsukuba, Japan
⁶School of Engineering, Osaka University, Osaka, Japan
⁷Department of Earth Sciences, Graduate School of Science, Tohoku University, Sendai, Japan
Published by arrangement with John Wiley & Sons

Alteration minerals in one of the Martian meteorite nakhlites, Yamato (Y) 000802, were studied to understand the alteration process and conditions. Mn-precipitates are discovered between altered plagioclase grains in Y 000802. Mn-precipitates consist of hausmannite (), manganite (γ-Mn³⁺OOH), rhodochrosite (Mn²⁺CO₃), and a trace amount of Mn⁴⁺O₂ mineral. Jarosite ) is also found. Mn²⁺ dissolved from olivine contributes to the formation of Mn-precipitates. A weakly acidic-neutral fluid containing a trace amount of  altered the olivine, and Mn²⁺ was dissolved into the fluid. The fluid also reacted with plagioclase and probably induced dealkalization of plagioclase, causing a local strong alkaline environment. Plagioclase was altered to ferroan saponite-nontronite + amorphous SiO₂ under alkaline conditions. Simultaneously, Mn^2+/3+-precipitates were formed from the Mn²⁺-containing fluid in the interstices between the altered plagioclase grains under the strong alkaline reducing environment. These alterations occurred in the deep part of the nakhlite body, where they are isolated from Martian subsurface water, including strong oxidants. The formation of Mn^2+/3+-precipitates may have been triggered by the melting of permafrost caused by an impact event around ∼633 Ma. Later, the nakhlite body was probably excavated by another impact, making it susceptible to water including strong oxidants. Pyrrhotite was dissolved and a highly acidic oxidizing fluid was formed, which would induce the formation of jarosite and the Mn⁴⁺O₂ mineral between ∼633 Ma and ∼11 Ma.

¹R. Ravichandran,¹S. Loehle,¹F. Hufgard,¹D. Leiser,⁴F. Zander,⁵L. Ferrière,²J. Vaubaillon,³P. Matlovič,³J. Tóth
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115818]
¹High Enthalpy Flow Diagnostics Group, Institute of Space Systems, University of Stuttgart, Pfaffenwaldring 29, 70569 Stuttgart, Germany
²IMCCE, Observatoire de Paris, PSL, 77 Av. Denfert Rochereau, Paris, 75014, France
³Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
⁴Institute of Advanced Engineering and Space Sciences, University of Southern Queensland, Toowoomba 4350, Queensland, Australia
⁵Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria
Copyright Elsevier

Optical emission spectra between 522-580 nm of ablating meteorites have been recorded at frame rates as high as 1 kHz for the first time during ground testing with simultaneous spatial and temporal resolution. A novel high frame rate emission spectroscopy arrangement has been developed and employed to diagnose the ablating meteorites in several experimental campaigns. In addition to the identification of species from emission lines detected, the resulting high-speed spectral data were used to study the temporal and spatial evolution of melting droplets and the associated spectral signatures. The time history of radiance from the atomic species emission was used to interpret the fragmentation behavior of various meteorites. Chelyabinsk meteorite exhibit almost constant radiance over time indicating steady droplet detachment whereas Ragland meteorite shows infrequent radiance peaks corresponding to random fragmentation/droplet detachment of varying sizes. A gradual rise in radiance history from iron meteorite Mount Joy shows that it takes finite time for melting and accumulation of droplets.