Åke V.Rosén^a, Jonas Pape^b, Beda A. Hofmann^a,b Edwin Gnos^c Marcel Guillong^d
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.11.016]
^aInstitute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
^bNatural History Museum Bern, Bernastrasse 15, 3005 Bern, Switzerland
^cNatural History Museum of Geneva, 1, Route de Malagnou, 1208 Geneva, Switzerland
^dInstitute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland
Copyright Elsevier

Ureilites are the second largest group of achondrite meteorites but consensus is still lacking on the nature of their precursors, melting processes, and the genetic relationship between monomict ureilites and brecciated ureilites. The recently found ureilite Ramlat as Sahmah 517 is of special interest in this context. This meteorite lacks shock features in its primary silicates and belongs to a rare augite- and chromite-bearing subset of the monomict ferroan ureilites. It hosts abundant intergranular glass veinlets speckled with pyroxene and metal globules. Detailed petrographic investigations show that the Si-Al rich glass represents quenched anatectic melt that was present prior to formation of the reduced olivine rims by incomplete low-pressure equilibration (smelting) of carbon and silicates. The melt facilitated smelting which, along with rapid crystallization of secondary pyroxene, modified the originally trachyandesitic melt. Melt-silicate equilibrium preceding these events is constrained by modelling using MELTS and the first reported in-situ measurements of LREE-enriched glass that is largely complementary to the depleted mafic silicates in monomict ureilites. The inferred major element composition of the partial melt that formed in RaS 517 is similar to that of trachyandesite in Almahata Sitta but RaS 517 lacks phosphates which are abundant in the Almahata Sitta trachyandesite and in alkali-rich feldspathic clasts in polymict ureilites. The LREE-depletion in the dominant monomict ferroan ureilite population can be explained by the formation of melt fractions similar to the glass in RaS 517 after initial rapid melting of phosphates. These finds provide evidence for a genetic relationship between ferroan ureilites and lithologies similar to the Almahata Sitta trachyandesite and further suggest that these ureilites formed by partial melting of P- and alkali-rich precursors with trace element concentrations similar to equilibrated ordinary chondrites. Quenched Si-Al rich glass also occurs in magnesian ureilites but has lower concentrations of alkalis and LREE-depleted trace element signatures which can reflect more depleted compositions at the onset of partial melting. The evidence presented here favors a scenario in which the primary ureilite differentiation was driven by gradual heating from radioactive decay with resulting temperatures (>1100 °C) being maintained until disruption of the ureilite parent asteroid.

R. L. PALMA^1,2, R. O. PEPIN², A. J. WESTPHAL³, E.F€URI⁴, D. J. SCHLUTTER², Z.S.GAINSFORTH³, and D. R. FRANK⁵
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13189]
¹Department of Physics and Astronomy, Minnesota State University, Mankato, Minnesota 56001, USA
²School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
³Space Sciences Laboratory, University of California, Berkeley, California 94720–7450, USA
⁴Centre de Recherches Petrographiques et Geochimiques, CNRS-UL, 54501 Vandoeuvre-les-Nancy Cedex, France
⁵Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, Hawai’i 96822, USA
Published by arrangement with John Wiley & Sons

Helium and neon distributions are reported for a variety of Stardust comet 81P/Wild 2 samples, including particle tracks and terminal particles, cell surface and subsurface slices from the comet coma and interstellar particle collection trays, and numerous small aerogel blocks extracted from comet cells C2044 and C2086. Discussions and conclusions in several abstracts published during the course of the investigation are included, along with the relevant data. Measured isotope ratios span a broad range, implying a similar range for noble gas carriers in the Wild 2 coma. The meteoritic phase Q‐²⁰Ne/²²Ne ratio was observed in several samples. Some of these, and others, exhibit ²¹Ne excesses too large for attribution to spallation by galactic cosmic ray irradiation, suggesting exposure to a solar proton flux greatly enhanced above current levels in an early near‐Sun environment. Still others display evidence for a solar wind component, particularly one C2086 block with large abundances of isotopically solar‐like helium and neon. Eighty‐nine small aerogel samples were cut from depths up to several millimeters below the cell C2044 surface and several millimeters away from the axis of major track T41. A fraction of these yielded measurable and variable helium and neon abundances and isotope ratios, although none contained visible tracks or carrier particle fragments and their locations were beyond estimated penetration ranges for small particles or ions incident on the cell surface, or for lateral ejecta from T41. Finding plausible emplacement mechanisms and sources for these gases is a significant challenge raised by this study.

Pinghui Huang^1,2,3, Andrea Isella⁴, Hui Li³, Shengtai Li³, and Jianghui Ji¹
Astrophysical Journal 867, 3 Link to Article [DOI: 10.3847/1538-4357/aae317]
¹CAS Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, People’s Republic of China
²University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
³Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
⁴Department of Physics & Astronomy, Rice University, 6100 Main Street, Houston, TX 77005, USA

Several nearby protoplanetary disks have been observed to display large-scale crescents in the (sub)millimeter dust continuum emission. One interpretation is that these structures correspond to anticyclonic vortices generated by the Rossby wave instability within the gaseous disk. Such vortices have local gas overdensities and are expected to concentrate dust particles with a Stokes number around unity. This process might catalyze the formation of planetesimals. Whereas recent observations showed that dust crescents are indeed regions where millimeter-size particles have abnormally high concentration relative to the gas and smaller grains, no observations have yet shown that the gas within the crescent region counterrotates with respect to the protoplanetary disk. Here we investigate the detectability of anticyclonic features through measurement of the line-of-sight component of the gas velocity obtained with ALMA. We carry out 2D hydrodynamic simulations and 3D radiative transfer calculations of a protoplanetary disk characterized by a vortex created by the tidal interaction with a massive planet. As a case study, the disk parameters are chosen to mimic the IRS 48 system, which has the most prominent crescent observed to date. We generate synthetic ALMA observations of both the dust continuum and ¹²CO emission around the frequency of 345 GHz. We find that the anticyclonic features of the vortex are weak but can be detected if both the source and the observational setup are properly chosen. We provide a recipe for maximizing the probability of detecting such vortex features and present an analysis procedure to infer their kinematic properties.

^1,2Britvin, S.N.,¹Murashko, M.N., ³Vapnik, Y., ¹Polekhovsky, Y.S., ^1,2Krivovichev, S.V., ¹Vereshchagin, O.S., ⁴Vlasenko, N.S., ⁴Shilovskikh, V.V., ¹Zaitsev, A.N.
Physics and Chemistry of Minerals (in Press) Link to Article [DOI: 10.1007/s00269-018-1008-4]
¹Institute of Earth Sciences, Saint-Petersburg State University, Universitetskaya Nab. 7/9, St. Petersburg, 199034, Russian Federation
²Nanomaterials Research Center, Kola Science Center of Russian Academy of Sciences, Fersman Str. 14, Apatity, Murmansk Region 184209, Russian Federation
³Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, POB 653, Beersheba, 84105, Israel
⁴Geomodel Resource Center, Saint Petersburg State University, Ulyanovskaya Str. 1, St. Petersburg, 198504, Russian Federation

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