¹Chi Ma,¹John R. Beckett,²François L. H. Tissot,¹George R. Rossman
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13826]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
²The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
Published by arrangement with John Wiley & Sons

Paqueite (Ca3TiSi2[Al,Ti,Si]3O14; IMA 2013-053) and burnettite (CaVAlSiO6; IMA 2013-054) are new refractory minerals, occurring as euhedral to subhedral crystals within aluminous melilite in A-WP1, a type A Ca-Al-rich inclusion, and CGft-12, a compact type A (CTA) from the Allende CV3 carbonaceous chondrite. Type paqueite from A-WP1 has an empirical formula of (Ca2.91Na0.11)Ti4+Si2(Al1.64Ti4+0.90Si0.24V3+0.12Sc0.07Mg0.03)O14, with a trigonal structure in space group P321 and cell parameters a = 7.943 Å, c = 4.930 Å, V = 269.37 Å3, and Z = 1. Paqueite’s general formula is Ca3TiSi2(Al,Ti,Si)3O14 and the endmember formula is Ca3TiSi2(Al2Ti)O14. Type burnettite from CGft-12 has an empirical formula of Ca1.01(V3+0.56Al0.25Mg0.18)(Si1.19Al0.81)O6. It assumes a diopside-type C2/c structure with a = 9.80 Å, b = 8.85 Å, c = 5.36 Å, β = 105.6°, V = 447.7 Å3, and Z = 4. Burnettite’s general formula is Ca(V,Al,Mg)AlSiO6 and the endmember formula is CaVAlSiO6. Paqueite and burnettite likely originated as condensates, but the observed grains may have crystallized from local V-rich melts produced during a later thermal event. For CGft-12, the compositions of paqueite, clinopyroxene, and perovskite suggest that type As drew from two distinct populations of grains. Hibonite grains drew from multiple populations, but these were well mixed and not equilibrated prior to incorporation into type A host melilite.

¹S.A.Singerling,²L.R.Nittler,²J.Barosch,³E.Dobrică,⁴A.J.Brearley,¹R.M.Stroud
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.05.007]
¹U.S. Naval Research Laboratory, Code 6366, Washington, DC 20375, USA
²Carnegie Institution of Washington, Washington, DC 20015, USA
³University of Hawai’i at Mānoa, Honolulu, HI, 96822, USA
⁴University of New Mexico, Albuquerque, NM, 87131, USA
Copyright Elsevier

We investigated six presolar grains from very primitive regions of the matrix in the unequilibrated ordinary chondrite Semarkona with transmission electron microscopy (TEM). These grains include one SiC, one oxide (Mg-Al spinel), and four silicates. This is the first TEM investigation of presolar grains within an ordinary chondrite host (in situ) and the first TEM study to report on any presolar silicates (in or ex situ) from an ordinary chondrite. Structural and elemental compositional studies of presolar grains located within their meteorite hosts have the potential to provide information on conditions and processes throughout the grains’ histories.

Our analyses show that the SiC and spinel grains are stoichiometric and well crystallized. In contrast, the majority of the silicate grains are non-stoichiometric and poorly crystallized. These findings are consistent with previous TEM studies of presolar grains from interplanetary dust particles and chondritic meteorites. The individual silicates have Mg#’s ranging from 15 to 98. Internal compositional heterogeneities were observed in several grains, including Al in the SiC, Mg and Al in the spinel, and Mg, Si, Al, and/or Cr in two silicates. We interpret the poorly crystalline nature, non-stoichiometry, more Fe- rather than Mg-rich compositions, and/or compositional heterogeneities as features of the formation by condensation under non-equilibrium conditions.

Evidence for parent body alteration includes rims with mobile elements (S or Fe) on the SiC grain and one silicate grain. Other features characteristic of secondary processing in the interstellar medium, the solar nebula, and/or on parent bodies, were not observed or are better explained by processes operating in circumstellar envelopes. In general, there was very little overprinting of primary features of the presolar grains by secondary processes (e.g., ion irradiation, grain-grain collisions, thermal metamorphism, aqueous alteration). This finding underlines the need for additional TEM studies of presolar grains located in the primitive matrix regions of Semarkona, to address gaps in our knowledge of presolar grain populations accreted to ordinary chondrites.

¹Devin L.Schrader,¹Jemma Davidson
Earth and Planetary Science Letters 589. 117552 Link to Article [https://doi.org/10.1016/j.epsl.2022.117552]
¹Buseck Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287, United States of America
Copyright Elsevier

The most abundant group of meteorites currently falling to Earth, ordinary chondrites, originate from S-type (Si-rich) asteroids and are thought to have originated in the inner Solar System. These asteroids typically underwent only minor aqueous alteration but experienced varying degrees of thermal metamorphism that altered their primary compositions and textures. However, some rare members remain unaltered and retain the pristine compositions they obtained in the protoplanetary disk prior to accretion of their parent asteroids. In contrast, comets formed in the icy reaches of the outer Solar System. Here we report on silicate minerals in pristine ordinary chondrites that are compositionally distinct from those in all other known chondrites but show similarities to those found in comet samples returned from Comet Wild 2 by NASA’s Stardust mission and those sourced from an unknown number of comets represented by interplanetary dusty particles. The identification of this material suggests that comets may have formed from diverse far-flung Solar System materials, including grains that migrated from the inner Solar System to the comet-forming region between ∼1 Myr and potentially ⪆3 Myr after the first Solar System solids formed. This finding suggests that migration from the inner to the outer Solar System lasted for millions of years and that comets are composed of residual materials from the entire early Solar System.

¹S.Iannini Lelarge,^1,2L.Folco,¹M.Masotta,³R.C.Greenwood,⁴S.S.Russell,⁴H.C.Bates
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.05.003]
¹Dipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria 53, Pisa, Italy
²CISUP, Centro per l’Integrazione della Strumentazione Università di Pisa, Lungarno Pacinotti 43 Pisa, Italy
³Planetary and Space Sciences, Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
⁴Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, United Kingdom
Copyright Elsevier

The cosmochemistry of meteorites provides unique clues on asteroids accretion, differentiation, collisional break-up and reassembly, processes of critical importance for understanding planet formation in the early solar system. Mesosiderites are a complex group of achondrites whose nearly 50:50 metal-silicate composition is interpreted in the literature as resulting from the mixing of core and crustal materials derived from differentiated asteroid(s). Because of their complex nature and contrasting geochemical, isotopic, and spectroscopic data, the formation mechanism of mesosiderites is still poorly understood and is open to a large variety of planetary differentiation scenarios and collisional histories. In this study, based on new petrographic and geochemical data of 16 mesosiderites, we investigate in detail the proposal that mesosiderites are related to the howardite-eucrite-diogenite (HED) meteorite group, whose parent body is widely considered to be asteroid 4 Vesta (∼500 km diameter), the target of the recent NASA’s Dawn mission. We present the first high precision oxygen isotope analyses on the matrix of a set of mesosiderite samples, coupled with new chemical and petrographic analyses of mesosiderites Um Hadid, Estherville, and Mount Padbury. Concordant Δ17O values between mesosiderites (–0.241 ± 0.015 (2σ)) and howardite-eucrite-diogenites (−0.241 ± 0.017‰ (2σ)) indicate that they derived from the same oxygen isotope reservoir, but petrological evidence, in particular the distinctly lower Fe/Mn ratios and the larger lithological diversity in mesosiderites, indicates that they formed within different parent bodies. This suggests that mesosiderites and howardite-eucrite-diogenites originated in distinct parent bodies that accreted in the 4 Vesta source region but experienced different geologic evolution in terms of crustal differentiation and impact history, which were more complex and catastrophic in the mesosiderite parent body.

¹Matthias van Ginneken,²Vinciane Debaille,³Sophie Decrée,⁴Steven Goderis,⁵Alan B. Woodland,¹Penelope Wozniakiewicz,³Marleen De Ceukelaire,³Thierry Leduc,³Philippe Claeys
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13818]
¹Centre for Astrophysics and Planetary Science, School of Physical Sciences, Ingram Building, University of Kent, Canterbury, CT2 7NH UK
²Laboratoire G-Time, Université Libre de Bruxelles, Brussels, BE1050 Belgium
³Geological Survey of Belgium, Royal Belgian Institute of Natural Sciences, rue Vautier 29, Brussels, BE1000 Belgium
⁴Analytical, Environmental, and Geochemistry, Vrije Universiteit Brussel, Pleinlaan 2, Brussels, BE1050 Belgium
⁵Institut für Geowissenschaften, Goethe-Universität Frankfurt, Altenhöferallee 1, Frankfurt am Main, D-60438 Germany
Published by arrangement with John Wiley & Sons

Meteorites are prone to errestrial weathering not only after their fall on the Earth’s surface but also during storage in museum collections. To study the susceptibility of this material to weathering, weathering experiments were carried out on polished sections of the H5 chondrite Asuka 10177. The experiments consisted of four 100-days cycles during which temperature and humidity varied on a twelve hours basis. The first alteration cycle consisted of changing the temperature from 15 to 25 °C; the second cycle consisted of modifying both humidity and temperature from 35 to 45% and 15 to 25 °C, respectively; the third cycle consisted of varying the humidity level from 40 to 60%; and the fourth cycle maintained a fixed high humidity of 80%. Weathering products resulting from the experiments were identified and characterized using scanning electron microscopy–energy dispersive spectroscopy and Raman spectroscopy. Such products were not observed at the microscopic scale after the first cycle of alteration. Conversely, products typical of the corrosion of meteoritic FeNi metal were observed during scanning electron microscope surveys after all subsequent cycles. Important increases in the distribution of weathering products on the samples were observed after cycles 2 and 4 but not after cycle 3, suggesting that the combination of temperature and humidity fluctuations or high humidity (>60%) alone is most detrimental to chondritic samples. Chemistry of the weathering products revealed a high degree of FeNi metal corrosion with a limited contribution of troilite corrosion. No clear evidence of mafic silicate alteration was observed after all cycles, suggesting that postretrieval alteration remains limited to FeNi metal and to a lesser extent to troilite.

¹J.-Y.Chaufray,¹F.Leblanc,¹A.I.E.Werner,¹R.Modolo,²S.Aizawa
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115081]
¹LATMOS-IPSL, CNRS, Sorbonne-Université, Paris-Saclay, Paris, France
²IRAP, CNRS, Toulouse, France
Copyright Elsevier

We simulate the seasonal variations of the Mg 285.3 nm and Ca 422.7 nm brightness and compared our results to the MESSENGER/MASCS observations at dawn. Our results are consistent with the previous studies of Ca while for Mg we used another seasonal variation for the g -value (excitation frequency) at 285.3 nm. We find that both emissions are well reproduced from micrometeoroid impacts when the true anomaly angle (TAA) of Mercury is larger than 80°. For true anomaly angle lower than 80°, an additional source is needed to reproduce the Ca observations in agreement with previous studies, and possibly the Mg observations. We compare several solar spectra (observed or modeled) to study the Mg g-value and found that the seasonal variation of the g-value peaking near TAA = 60° used by previous studies to analyse the MESSENGER observations of Mg may be due to an artefact not present in the solar spectrum. The observed seasonal variations of the Mg brightness are better reproduced without this artefact. However, observations of the solar spectrum near 285.3 nm at a spectral resolution of ~20 mA would be needed to better estimate the seasonal variations of the Mg excitation frequencies and then to better understand the possible differences in the source of these two species in the exosphere of Mercury.

¹Prabhakar Alok Verma,¹Mamta Chauhan,¹Prakash Chauhan
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115075]
¹Indian Institute of Remote Sensing, Indian Space Research Organisation, Dehradun, India
Copyright Elsevier

This paper presents the methodology for correction of thermal emission from the Imaging Infrared Spectrometer sensor data onboard the recently launched Chandrayaan-2 spacecraft. The sensor provides extended spectral range of 0.8–5 μm and a spectral resolution of ~20 nm. The Imaging Infrared Spectrometer measures the reflected and emitted radiation of the Moon at a spatial resolution of ~80 m and has an advantage over the previous sensors in complete and clear characterization of OH/H2O feature. The thermal removal method follows calculation of the mean surface temperature at a fixed emissivity to obtain thermally corrected spectra. Further, the data have been utilized to generate temperature map of the Moon from the available data strips. The data after thermal correction can be further utilized to understand and derive the radiative and thermophysical properties of regolith and volatiles on the Moon.

^1,2He, Yuyang^3,4Zhou, You,⁵Wen, Tao,⁶Zhang, Shuang,⁷Huang, Fang,⁸Zou, Xinyu,⁹Ma, Xiaogang,¹⁰Zhu, Yueqin
Applied Geochemistry 140, 105273 Link to Article [DOI 10.1016/j.apgeochem.2022.105273]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
²State Key Laboratory of High Temperature Gas Dynamics, Institute of Mechanics, Chinese Academy of Sciences, Beijing, 100190, China
³International Research Center for Planetary Science, College of Earth Sciences, Chengdu University of Technology, Chengdu, 61005, China
⁴CAS Center for Excellence in Comparative Planetology, Hefei, 230026, China
⁵Department of Earth and Environmental Sciences, Syracuse University, Syracuse, 13244, NY, United States
⁶Department of Oceanography, Texas A&M University, College Station, 77843, TX, United States
⁷CSIRO Mineral Resources, Kensington, 6151, WA, Australia
⁸Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
⁹Computer Science Department, University of Idaho, 875 Perimeter Drive, MS 1010, Moscow, 83844-1010, ID, United States
¹⁰National Institute of Natural Hazards, Ministry of Emergency Management of the People’s Republic of China, Beijing, 100085, China

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¹M.M.Hirschmann
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.04.005]
¹Dept. of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455 USA
Copyright Elsevier

The mantles of both Earth and Mars are more oxidized than would be expected based on low pressure equilibration of molten silicate and alloy during their magma ocean stages. High pressure silicate-alloy equilibration in a magma ocean can produce appreciable ferric iron in the silicate, leading to comparatively oxidized near surface conditions and overlying atmospheres. Upon crystallization, this may feasibly be sufficient to account for oxygen fugacities prevailing in basalt source regions of Earth and Mars. Experiments and first principles studies affirm that Fe3+ is stabilized at high pressure, but to date there has been no model that accounts accurately for the combined effects of melt composition, temperature, pressure, and oxygen fugacity on magma ocean Fe3+/FeT. We calibrate a new model for Fe3+/FeT as a function of temperature, pressure, melt composition, and fO2 which reproduces Fe3+/FeT for experimental peridotite liquids and which incorporates differences in FeO and Fe2O3 liquid heat capacities into a potentially realistic temperature function. For the effects of pressure, two versions of the model are implemented based on recent equations of state (EOS), though only the EOS of Deng et al. (2020) is applicable to pressures relevant to metal-silicate equilibration in a deep terrestrial magma ocean. For Earth, metal-silicate equilibration at 28-53 GPa, 2300-4100 K, and fO2 set by plausible mantle and core compositions produces Fe3+/FeT between 0.034 and 0.10, with variation mostly owing to differences in assumed temperatures. For Mars, different proposed mantle compositions produce Fe3+/FeT ratios that range from 0.026 for FeO* of 13.5 wt.% up to 0.038 for FeO* of 18.1 wt.%.

Although significant Fe3+ may be present in magma oceans owing to high pressure equilibration with alloy, the budget of Fe2O3 in crystallized mantles is expected to be modified from that in the molten state. An important additional factor is the influence of Cr, which is Cr2+ in molten silicate equilibrated with alloy and Cr3+ in terrestrial upper mantles. Production of Cr3+ and Fe2+ by reaction with Cr2+ and Fe3+ during crystallization can destroy much of the Fe2O3 present during the magma ocean stage. Considering the stability of Cr2+ in olivine and the temperature-dependent partitioning of Cr3+ between mantle silicates, we construct an empirical model for the fraction of Cr that is Cr2O3 in solid spinel peridotite as a function of temperature and fO2. For Earth, at least 0.35 wt.% Fe2O3 is destroyed by oxidation of magma ocean CrO and for Mars, more than 0.55 wt.% Fe2O3 should be destroyed. Consequently, either the terrestrial and martian magma oceans were significantly more enriched in Fe2O3 than their present-day upper mantles or other processes contributed to oxidation of the latter. Over-enrichment of Fe2O3 in the magma oceans is plausible only if terrestrial metal-silicate equilibration occurred above 3300 K and if the martian mantle contains >17 wt.% FeO*. Subsolidus disproportionation of ferrous iron may have contributed to the present-day redox state of the Earth’s mantle, and late accretion of chondrite-like material and hydrogen degassing also likely affected the solidified mantles of both Earth and Mars.

¹Ray D.,¹Panda D.K.,¹Arora G.,^bGhosh S.,³Murty S.V.S.,⁴Chakraborty S.
Journal of the Geological Society of India 98, 323-328 Link to Article [DOI 10.1007/s12594-022-1983-4]
¹Physical Research Laboratory, Ahmedabad, 380 009, India
²54/3 M.B. Road, Kolkata, 700 072, India
³Lad Society Road, Ahmedabad, 380 015, India
⁴Department of Chemistry, University of California, Urey Hall 5112, San Diego, La Jolla, 92093-0356, United States

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