¹Elishevah van Kooten,²Larissa Cavalcante,³Daniel Wielandt,³Martin Bizzarro
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1111/maps.13459]
¹Institut de Physique du Globe de Paris, Université de Paris, CNRS, UMR 7154, 1 rue Jussieu, 75238 Paris, France
²Institute of Chemistry, University of São Paulo, 03178 São Paulo, Brazil
³Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, DK‐1350 Copenhagen, Denmark
Published by arrangement with John Wiley & Sons

CM meteorites are dominant members of carbonaceous chondrites (CCs), which evidently accreted in a region separated from the terrestrial planets. These chondrites are key in determining the accretion regions of solar system materials, since in Mg and Cr isotope space, they intersect between what are identified as inner and outer solar system reservoirs. In this model, the outer reservoir is represented by metal‐rich carbonaceous chondrites (MRCCs), including CR chondrites. An important question remains whether the barrier between MRCCs and CCs was a temporal or spatial one. CM chondrites and chondrules are used here to identify the nature of the barrier as well as the timescale of chondrite parent body accretion. We find based on high precision Mg and Cr isotope data of seven CM chondrites and 12 chondrules, that accretion in the CM chondrite reservoir was continuous lasting <3 Myr and showing late accretion of MRCC‐like material reflected by the anomalous CM chondrite Bells. We further argue that although MRCCs likely accreted later than CM chondrites, CR chondrules must have initially formed from a reservoir spatially separated from CM chondrules. Finally, we hypothesize on the nature of the spatial barrier separating these reservoirs.

¹Max Collinet,¹Timothy L.Grove
Geochimcia et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.03.005]
¹Massachusetts Institute of Technology, Earth, Atmospheric and Planetary Sciences department, 77 Massachusetts avenue, 02139, MA, USA
Copyright Elsevier

We present the results of melting experiments on a suite of carbonaceous and ordinary chondritic compositions (CV, CM, CI, H and LL) performed at low pressure (0.1 to 13.1 MPa) and over a range of oxygen fugacity (log fO₂ – (log fO₂)_IW = -2.5 to -1 and +0.8, IW being the iron-wustite buffer). These experiments constrain the composition of partial melts (F = 5-25 wt.%) of chondritic planetesimals. Most experiments (IW -2.5 to -1) were conducted in Molybdenum-Hafnium Carbide pressure vessels, which prevented the loss of alkali elements from the melt. The results show that all planetesimals not significantly depleted in moderately volatile elements relative to the sun’s photosphere (e.g. CI, H and LL compositions) produced low-degree melts (<15 wt.%) rich in SiO₂, Al₂O₃ and alkali elements, regardless of the fO₂. Despite their high apparent viscosities (10^4-5 Pa.s), such low-density partial melts (2400-2500 kg/m³) were mobilized and, upon crystallizing, formed rocks containing up to 80 vol.% of plagioclase An_10-30 (i.e. oligoclase) such as the trachyandesite achondrites Graves Nunataks 06128/9, Northwest Africa 6698 and 11575, the Almahata Sitta clast ALM-A, as well as smaller “albitic clasts” in polymict ureilites and “alkali-silica-rich” inclusions in non-magmatic iron meteorites. We suggest that silica- and alkali- rich melts were widespread in small bodies of the early solar system but that much evidence was erased by subsequent stages of melting and planetary accretion and differentiation.

¹Max Collinet,¹Timothy L.Grove
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.03.004]
¹Massachusetts Institute of Technology, Earth, Atmospheric and Planetary Sciences department, 77 Massachusetts avenue, 02139, MA, USA
Copyright Elsevier

Acapulcoites-lodranites, ureilites, brachinites, brachinite-like achondrites and winonaites are the main groups of primitive achondrites. They are variably depleted in incompatible lithophile elements (Al, Na, K and rare earth elements) and siderophile/chalcophile elements relative to chondrites and are interpreted as the residual mantle of planetesimals from which silicate melts and sulfide/metal melts were extracted. We use a series of melting experiments conducted with various chondritic compositions (CV, CM, CI, H and LL) to constrain the oxygen fugacity (fO2), the temperature, extent of melting and the initial bulk composition of the parent bodies of primitive achondrites. They melted at different and variable fO2: ΔIW -0.5/-1.0 for brachinites, ΔIW -1.3/-2.5 for ureilites, ΔIW -1.6/-2.7 for acapulcoites/lodranites and ΔIW -2.5/-3.0 for winonaites (with ΔIW = log fO2 – (log fO2)IW; IW being the iron-wustite buffer). Those main groups of primitive achondrites, which have nucleosynthetic anomalies characteristic of the “non-carbonaceous” reservoir and the inner solar system, were not initially depleted in Na2O and K2O relative to the sun’s photosphere. This suggests, in accordance with the enrichment in the heavy isotopes of Zn, Rb and K in eucrites, that the depletion of moderately volatile elements in planetesimals that melted to a larger extent (e.g. Vesta, the angrite parent body) resulted from evaporative losses during partial melting. The depletion of moderately volatile elements in terrestrial planets is likely inherited from partial melting and differentiation of small planetary bodies rather than from the incomplete complete condensation of the solar nebula.

¹R.Brunetto,¹C.Lantz,²T.Nakamura,¹D.Baklouti,¹T.Le Pivert-Jolivet,²S.Kobayashi,³F.Borondics
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113722]
¹Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
²Division of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Japan
³SOLEIL Synchrotron, Gif-sur-Yvette, France
Copyright Elsevier

Solar wind ion irradiation continuously modifies the optical properties of unprotected surfaces of airless bodies in the Solar System. This alteration induces significant biases in the interpretation of the spectral data obtained through remote sensing, and it impedes a correct estimation of the composition of the sub-surface pristine materials. However, as the alteration of the surface is a function of time, an in-depth understanding of the phenomenon may provide an original way to estimate the weathering age of a surface. Laboratory experiments show that mid- and far-IR bands are very sensitive to space weathering, as they are significantly modified upon irradiation. These bands can thus constitute a reliable proxy of the time-bound effects of irradiation on an object. We show that the detection of irradiation effects is within the reach of IR spectral resolution of the OSIRIS-REx mission and of the future James Webb Space Telescope. Our results provide a possible evidence for space weathering effects in the IR spectrum of asteroid 101955 Bennu measured by OTES/OSIRIS-REx.

¹Gayantha R.L. Kodikara,²Lindsay J.McHenry
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113719]
¹Department of Geosciences, University of Wisconsin-Milwaukee, 3209 N. Maryland Avenue, Milwaukee, WI 53211, USA
²Department of Geosciences, University of Wisconsin-Milwaukee, 3209 N. Maryland Avenue, Milwaukee, WI 53211, USA
Copyright Elsevier

We examine the ability of machine learning techniques to determine the physical and mineralogical properties of lunar soil using reflectance spectra. We use the Lunar Soil Characterization Consortium (LSCC) dataset to train and asses the predictive power of classification models based on their type (Mare soil and Highland soil), particle size, maturity, and the dominant type of pyroxene (High-Ca and Low-Ca). Nine ML algorithms including linear methods, non-linear methods, and rule-based methods (three from each) were selected, representing a range of characteristics such as simplicity, flexibility, computational complexity, and interpretability along with their ability to handle different types of data. Fifteen spectral parameters were initially introduced to the models as input features and a maximum of four features was selected as the best feature combinations to classify lunar soils based on their types, particle size, maturity, and the type of pyroxene. The Support Vector Machine with radial basis function (svmRadial) and the penalized logistic regression model (glmnet) performed well for all target variables with high accuracies. Band depths and Integrated band depths at 1 μm, 1.25 μm and 2 μm, band position of the 1 μm band, along with four band ratios (band tilt, band strength, band curvature and olivine/pyroxene) are important features for classifying soil type, grain size, maturity, and type of pyroxene from reflectance spectra. This study shows that proper preprocessing and feature engineering techniques are crucial for high performance of the predictive models.

¹L.C.Cheek,¹J.M.Sunshine
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113718]
¹Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
Copyright Elsevier

A major goal of the Dawn mission to Vesta was to test and refine current models of the asteroid’s formation by characterizing the distribution of mineral components on its surface. Detection of the mineral olivine by the Visible and Infrared Mapping spectrometer (VIR) and the Framing Camera (FC) onboard Dawn was a key milestone in this effort, and was expected to help resolve a debate regarding the dominant mode of Vesta’s petrologic evolution (i.e., magma ocean vs. serial magmatism). However, the subtleties of the olivine spectral signature combined with the small size of individual olivine-rich exposures (tens of meters) prohibits detailed mapping of this petrologically significant mineral component when the data from either instrument are evaluated independently. As a result, the particular role of these olivine exposures in Vesta’s geologic history remains largely unresolved.
Here, we fully characterize the type locality of Vesta’s olivine-rich materials, the northern hemisphere craters Bellicia and Arruntia, using a novel data fusion approach for linking the VIR and FC datasets. Specifically, we have leveraged a spectral mixture analysis framework to create a new dataset that maps, or “extrapolates”, full resolution spectra, derived from VIR data, onto the higher spatial resolution of FC. When used as an exploratory tool in conjunction with the original FC and VIR data, the new “extrapolated” dataset reveals important new details about the distribution of olivine around Bellicia and Arruntia craters.
There are clear compositional distinctions between the exposures at the two craters, with a much stronger olivine component in the walls of Bellicia than Arruntia. The proximal Arruntia ejecta appear more consistent with high proportions of an evolved high‑calcium pyroxene (as in eucrites) than with an enhanced olivine component. Examples of diogenite-rich howardite also occur in the region. Further, we leverage Arruntia’s role as the freshest large crater in the northern hemisphere, and thus a rare window into the Vesta’s northern hemispheric crust, to suggest an overall stratigraphy for the region: a thin veneer of howardite overlies a sequence of diogenite-rich (near surface), olivine-rich (intermediate), and eucrite-rich materials (at depth). The manner of exposure of these various components in a marked stratification point to a plutonic model for emplacing these mineralogically unique components in the near surface of Vesta.

^1,2Jordi Llorca,^3,4Marc Campeny,⁵Neus Ibáñez,⁶David Allepuz,⁷Josep Maria Camarasa,⁸Josep Aurell‐Garrido
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13455]

¹Institute of Energy Technologies, Department of Chemical Engineering, Barcelona, Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, EEBE, Eduard Maristany 10‐14, E‐08019 Barcelona, Catalonia, Spain
²Institut d’Estudis Catalans, Carrer del Carme 47, E‐08001 Barcelona, Catalonia, Spain
³Departament de Mineralogia, Museu de Ciències Naturals de Barcelona, Passeig Picasso s/n, E‐08003 Barcelona, Catalonia, Spain
⁴Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, Martí i Franquès s/n, E‐08028 Barcelona, Catalonia, Spain
⁵Botanic Institute of Barcelona, IBB, CSIC‐Ajuntament de Barcelona, Passeig del Migdia s/n, E‐08038 Barcelona, Catalonia, Spain
⁶Sant Julià de Vilatorta Observatory, E‐08514 Sant Julià de Vilatorta, Catalonia, Spain
⁷Seminari d’Història de la Ciència Joan Francesc Bahí. Fundació Carl Faust. Passeig Carles Faust, 9. E‐17300 Blanes, Catalonia, Spain
⁸Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Columnes s/n, Campus de la UAB, E‐08193 Cerdanyola del Vallès, Catalonia, Spain
Published by arrangement with John Wiley & Sons

On Christmas Day 1704, at 17 h (UT), a meteorite fell in Terrassa (about 25 km NW of Barcelona). The meteorite fall was seen and heard by many people over an area of several hundred kilometers and it was recorded in several historical sources. In fact, it was interpreted as a divine sign and used for propaganda purposes during the War of the Spanish Succession. Although it was believed that meteorite fragments were never preserved, here we discuss the recent discovery of two fragments (49.8 and 33.7 g) of the Barcelona meteorite in the Salvador Cabinet collection (Botanic Institute of Barcelona). They are very well preserved and partially covered by a fresh fusion crust, which suggests a prompt recovery, shortly after the fall. Analysis of the fragments has revealed that the Barcelona meteorite is an L6 ordinary chondrite. These fragments are among the oldest historical meteorites preserved in the world.

^1,2Masayuki Ikeda,^2,3,4Ryuji Tada
Earth and Planetary Science Letters 537, 116168 Link to Article [https://doi.org/10.1016/j.epsl.2020.116168]
¹Department of Geosciences, Graduate School of Science, Shizuoka University, Shizuoka, 790-8577, Japan
²Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo, 113-0033, Japan
³The Research Center for Earth System Science, Yunnan University, Chenggong District, Kunming, Yunnan Province 650500, China
⁴Institute for Geo-Cosmology, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan
Copyright Elsevier

Astronomical solutions for planetary orbits beyond several tens of million years (Myr) ago have large uncertainties due to the chaotic nature of the Solar System, mainly Myr-scale cycles related with the Earth-Mars secular resonance. Our only accessible archive for unraveling the Earth’s orbital variations in the geologic past are sedimentological records, yet their reliability and uncertainties are still debated. Here, we describe Myr-scale orbital signals of early Mesozoic monsoon records from two different sedimentary settings (lake level records of the equatorial Pangea and biogenic silica burial flux of deep-sea Panthalassa), along with a marine carbon isotope compilation. Although most of the dominant multi-Myr cycles are not exactly of the same frequency, 1.8 Myr cycles during ∼216–210 Ma are detected from the two mutually-independent sedimentary settings, and differ from available astronomical solutions. This finding provides not only convincing evidence for the chaotic nature of the Solar System in the geological past, but also additional constraints on astronomical models. On the other hand, besides the orbital cycles, tectonic forcing and consequent climatic perturbations could also have affected the proxies on multi-Myr timescales during episodes of large igneous province emplacement, such as Siberian trap volcanism (252–245 Ma), Wrangellia (233–225 Ma), Central Atlantic Magmatic Province (202–200 Ma), and Karoo-Ferrar volcanism (184–180 Ma). If we can distinguish orbital signals from other effects, such as tectonic and volcanic processes, the multi-Myr cycles in geologic records have the potential to reconstruct the chaotic evolution of the Solar System.

¹S. Kommescher,^1,2R.O.C. Fonseca,^1,3F. Kurzweil,^1,3M.M. Thiemens,¹C. Münker,^1,4P. Sprung
Geochemical Perspectives 13, (In Press) Link to Article [doi: 10.7185/geochemlet.2007]
¹Institut für Geologie und Mineralogie, Universität zu Köln, Germany
²Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Germany
³G-TIME Laboratory, Université Libre de Bruxelles, Belgium
⁴Hot Laboratory Division (AHL), Paul Scherer Institut, Villigen, Switzerland

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2Peter Jenniskens et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13452]
¹SETI Institute, 189 Bernardo Ave, Mountain View, California, 94043 USA
²NASA Ames Research Center, Moffett Field, California, 94035 USA
Published by arrangement with John Wiley & Sons

The trajectory and orbit of the LL7 ordinary chondrite Dishchii’bikoh are derived from low‐light video observations of a fireball first detected at 10:56:26 UTC on June 2, 2016. Results show a relatively steep ~21° inclined orbit and a short 1.13 AU semimajor axis. Following entry in Earth’s atmosphere, the meteor luminosity oscillated corresponding to a meteoroid spin rate of 2.28 ± 0.02 rotations per second. A large fragment broke off at 44 km altitude. Further down, mass was lost to dust during flares at altitudes of 34, 29, and 25 km. Surviving meteorites were detected by Doppler weather radar and several small 0.9–29 g meteorites were recovered under the radar reflection footprint. Based on cosmogenic radionuclides and ground‐based radiometric observations, the Dishchii’bikoh meteoroid was 80 ± 20 cm in diameter assuming the density was 3.5 g/cm³. The meteoroid’s collisional history confirms that the unusual petrologic class of LL7 does not require a different parent body than three previously observed LL chondrite falls. Dishchii’bikoh was ejected 11 Ma ago from parent body material that has a 4471 ± 6 Ma U‐Pb age, the same as that of Chelyabinsk (4452 ± 21 Ma). The distribution of the four known pre‐impact LL chondrite orbits is best matched by dynamical modeling if the source of LL chondrites is in the inner asteroid belt in a low inclined orbit, with the highly inclined Dishchii’bikoh being the result of interactions with Earth before impacting.