¹R. Trappitsch, ¹F. J. Ciesla
¹Department of the Geophysical Sciences and Chicago Center for Cosmochemistry, The University of Chicago, Chicago, IL 60637

Solar cosmic-ray (SCR) interactions with a protoplanetary disk have been invoked to explain several observations of primitive planetary materials. In our own Solar System, the presence of short-lived radionuclides (SLRs) in the oldest materials has been attributed to spallation reactions induced in phases that were irradiated by energetic particles in the solar nebula. Furthermore, observations of other protoplanetary disks show a mixture of crystalline and amorphous grains, though no correlation between grain crystallinity and disk or stellar properties have been identified. As most models for the origin of crystalline grains would predict such correlations, it was suggested that amorphization by stellar cosmic-rays may be masking or erasing such correlations. Here we quantitatively investigate these possibilities by modeling the interaction of energetic particles emitted by a young star with the surrounding protoplanetary disk. We do this by tracing the energy evolution of SCRs emitted from the young star through the disk and model the amount of time that dust grains would spend in regions where they would be exposed to these particles. We find that this irradiation scenario cannot explain the total SLR content of the solar nebula; however, this scenario could play a role in the amorphization of crystalline material at different locations or epochs of the disk over the course of its evolution.

Reference
Trappitsch R, Ciesla FJ (2015) Solar Cosmic-ray Interaction with Protoplanetary Disks: Production of Short-lived Radionuclides and Amorphization of Crystalline Material. Astrophysical Journal 805, 5
Link to Article [doi:10.1088/0004-637X/805/1/5]

¹P. Beck, ¹B. Schmitt, ²E.A. Cloutis, ³P. Vernazza
¹Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France, CNRS, IPAG, F-38000 Grenoble, France
²Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, 6 Manitoba, Canada R3B 2E9
³Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France

The surface of Ceres, the most massive asteroid, presents a peculiar absorption band at 3.06 μm. This feature has been attributed to a number of candidate phases, including a magnesium hydroxide, brucite (Mg(OH)2). In order to gain insights into this possibility we have investigated the evolution of brucite reflectance spectrum under decreasing temperature (down to 93 K). Following early observation of brucite infrared spectra in transmission, a strong evolution of the reflectance spectrum of brucite is found under decreasing temperature. Small shifts of the band positions are found in particular at 1.36 and 1.39 μm, while the most important evolution is a decrease in intensity of the features at 2.82 and 3.06 μm. These observations can be seen in the light of the nature of these modes, which are transitions from excited states (difference bands) that are less populated under low-temperature. Such results provide a major test for the presence of brucite on Ceres from forthcoming DAWN observations, by searching for a possible evolution of the band with local time and then surface temperature. Based on the fact that the equivalent summation bands are not observed in Ceres spectra, brucite is not favored as the major constituent to the 3.06 μm feature. The possibility that this feature rather corresponds to ammoniated minerals (phyllosilicates or salts) is discussed.

Reference
Beck P, Schmitt B, Cloutis EA, Vernazza P (2015) Low-Temperature reflectance spectra of brucite and the primitive surface of 1-Ceres? Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.031]

Copyright Elsevier

^1,2 D. Dai, ¹ C. Zhou, ^1,3 X. Chen
¹Institute of Geology, Hunan University of Science and Technology, Xiangtan, China
²Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
³Hunan Provincial Key Laboratory of Shale Gas Resource Utilization, Xiangtan, China

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

Reference
Dai D, Zhou C, Chen X (2015) Ca-, Al-Rich Inclusions in Two New Carbonaceous Chondrites from Grove Mountains, Antarctica. Earth, Moon , and Planets (in Press)
Link to Article [DOI 10.1007/s11038-015-9470-1]

¹Ramakant R. Mahajan
¹Physical Research Laboratory, Ahmedabad-380009, India

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

Reference
Mahajan RR (2015) Lunar meteorite Yamato-983885: Noble gases, nitrogen and cosmic ray exposure history. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2015.05.003]

¹F. Zambona et al. (>10)*
¹INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, 00133 Rome, Italy
*Find the extensive, full author and affiliation list on the publishers website

The Av-13 (Tuccia) and Av-14 (Urbinia) quadrangles are located in the south-west region of Vesta. They are characterized by a large topographic variability, from the highest (Vestalia terra highlands) to the lowest (Rheasilvia basin). Many geological units in these quadrangle are not associated with mineralogical variability, as shown by the color-composite maps. Maps of mafic absorption band-center position reveal that the principal lithology is eucrite-rich howardite, but diogenite-rich howardite areas also are present, corresponding to particular features such as Antonia and Justina craters, which are also characterized by strong mafic absorptions. These quadrangles, especially Urbinia, are characterized by many bright ejecta, such as those of Tuccia crater, which are the highest reflectance materials on Vesta (Zambon et al., 2014). Dark areas are also present and correspond with regions with deeper OH-signature. The two quadrangle also contain many vertical ridge crests associated with the Rheasilvia impact. These ridges do not show mineralogical differences with respect to their surroundings, but have a distinctive appearance in color-ratio composite images.

Reference
Zambona F et al. (2015) Spectral Analysis of the Quadrangles Av-13 and Av-14 on Vesta. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.015]
Copyright Elsevier

¹A.J. King, ¹P.F. Schofield, ^2,3K.T. Howard, ¹S.S. Russell
¹Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
²Kingsborough Community College of the City University of New York, 2001 Oriental Boulevard, Brooklyn, New York, NY 11235, USA.
³Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA.

The CI chondrites are some of the most hydrated meteorites available to study, making them ideal samples with which to investigate aqueous processes in the early Solar System. Here, we have used position-sensitive-detector X-ray diffraction (PSD-XRD) to quantify the abundance of minerals in bulk samples of the CI chondrite falls Alais, Orgueil and Ivuna, and the Antarctic CI-like chondrites Y-82162 and Y-980115. We find that Alais, Orgueil and Ivuna are dominated by a mixed serpentine/saponite phyllosilicate (81 – 84 vol%), plus minor magnetite (6 – 10%), sulphides (4 – 7%) and carbonates (<3%). This reflects an extended period of aqueous alteration and the near-complete transformation of anhydrous phases into a secondary mineral assemblage. The similarity in total abundance of phyllosilicate suggests that the CI chondrites all experienced the same degree of aqueous alteration on the parent body. In contrast, Y-82162 contains a highly disordered serpentine/saponite phyllosilicate (68 vol%), sulphide (19%), olivine (11%) and magnetite (2%). This mineralogy is distinct from that of the CI chondrites, attesting to both a different starting mineralogy and alteration history. The structure and relatively low abundance of the phyllosilicate, and the high abundance of olivine, are consistent with previous observations that Y-82162 represents CI-like material that following aqueous alteration suffered thermal metamorphism at temperatures >500°C. Similarly, Y-980115 contains disordered serpentine/saponite (71 vol%), sulphide (19%), olivine (8%) and magnetite (2%), confirming that it too is a thermally metamorphosed CI-like chondrite. We suggest that the CI-like chondrites are derived from a different parent body than the CI chondrites, which underwent short-lived thermal metamorphism due to impacts and/or solar radiation.

Reference
King AJ, Schofield PF, Howard KT, Russell SS (2015) Modal mineralogy of CI and CI-like chondrites by X-ray diffraction. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.05.038]

Copyright Elsevier

The most popular papers on Cosmochemistry Papers in May were:

1-Liu N et al. (2015) Correlated Strontium and Barium Isotopic Compositions of Acid-cleaned Single Mainstream Silicon Carbides from Murchison. Astrophysical Journal 803,12 Link to Article [doi:10.1088/0004-637X/803/1/12]

2-Rubin AE (2015) Maskelynite in asteroidal, lunar and planetary basaltic meteorites: An indicator of shock pressure during impact ejection from their parent bodies. Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2015.05.010]

3-Tomeoka K, Ohnishi I (2015) Redistribution of chondrules in a carbonaceous chondrite parent body: A model. Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2015.05.012]

4-Hartmann WK (2014) The giant impact hypothesis: past, present (and future?). Philosophical Transactions of the Royal Society A 13,372, 2024 Link to Article [doi: 10.1098/rsta.2013.0249]

5-Dauphas N, Pourmand A (2015) Thulium anomalies and rare earth element patterns in meteorites and Earth: Nebular fractionation and the nugget effect. Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2015.03.037]

^1,2Xiaojia Zeng, ¹Xiongyao Li, ¹Shijie Wang, ¹Shijie Li, ³Nicole Spring, ¹Hong Tang, ¹Yang Li, ¹Junming Feng
¹Lunar and Planetary Science Research Center, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 55002, China
²University of Chinese Academy of Sciences, Beijing 10049, China
³School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK

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

Reference
Zeng X, Li X, Wang S, Li S, Spring N, Tang H, Li Y, Feng J (2015) JMSS-1: a new Martian soil simulant.
Earth, Planets and Space 67:72
Link to Article [doi:10.1186/s40623-015-0248-5]

¹E. Ammannito
¹University of California Los Angeles, Earth Planetary and Space Sciences, Los Angeles, CA-90095, USA
*Find the extensive, full author and affiliation list on the publishers website

We present and describe the maps of spectral parameters such as pyroxene band centers and depths, reflectance at 1.4 μm and 2.8μm band depth in the Rheasilvia quadrangle. We found a broad anti-correlation between pyroxene band centers and depths while the reflectance is not correlated with the pyroxene spectral parameters. In addition, we found that the Rheasilvia quadrangle is free of OH absorption signatures. We also derived lithological maps with improvements in the spatial resolution with respect to previous lithological maps of the same region. We confirm that the central mound is dominated by eucritic/howarditic pyroxene while diogenitic lithology has been found mainly in a region delineated by Tarpeia, Severina and Mariamne craters. We found small scale variations in the composition of pyroxene. These variations identify lithological units that extend for tens of km, although small units of less than 1 km have also been found. We consider this fact as an indication of a high level of compositional heterogeneity within the Vestan crust.

Reference
Ammannito E et al. (2015) Compositional variations in the Vestan Rheasilvia basin. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.017]

Copyright Elsevier

¹Lidia Pittarello, ²Fabrizio Nestola, ³Cecilia Viti, ⁴Alvaro Penteado Crósta, ^1,5Christian Koeberl
¹ Department of Lithospheric Research, University of Vienna, Vienna, Austria
² Department of Geosciences, University of Padova, Padova, Italy
³ Department of Physics, Earth and Environmental Sciences, University of Siena, Siena, Italy
⁴ Institute of Geosciences, Campinas SP, Brazil
⁵ Natural History Museum, Vienna, Austria

Shatter cones are one of the most widely recognized pieces of evidence for meteorite impact events on Earth, but the process responsible for their formation is still debated. Evidence of melting on shatter cone surfaces has been rarely reported in the literature from terrestrial impact craters but has been recently observed in impact experiments. Although several models for shatter cones formation have been proposed, so far, no one can explain all the observed features. Shatter cones’ from the Vista Alegre impact structure, Brazil, formed in fine-grained basalt of the Jurassic-Cretaceous Serra Geral Formation (Paraná large igneous province). A continuous quenched melt film, consisting of a crystalline phase, mica, and amorphous material, decorates the striated surface. Ultracataclasites, containing subrounded pyroxene clasts in an ultrafine-grained matrix, occur subparallel to the striated surface. Several techniques were applied to characterize the crystalline phase in the melt, including Raman spectroscopy and transmission electron microscopy. Results are not consistent with any known mineral, but they do suggest a possible rare or new type of clinopyroxene. This peculiar evidence of melting and cataclasis in relation with shatter cone surfaces is interpreted as the result of tensile fracturing at the tip of a fast propagating shock-induced rupture, which led to the formation of shatter cones at the tail of the shock front, likely during the early stage of the impact events.

References
Pittarello L, Nestola F, Viti C, Crósta AP, Koeberl C (2015) Melting and cataclastic features in shatter cones in basalt from the Vista Alegre impact structure, Brazil. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12466]

Published by arrangement with John Wiley&Sons