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Gattacceca J.,French National Center for Scientific Research | Rochette P.,French National Center for Scientific Research | Lagroix F.,CNRS Paris Institute of Global Physics | Mathe P.-E.,French National Center for Scientific Research | Zanda B.,Laboratoire Of Mineralogie Et Cosmochimie Du Museum
Geophysical Research Letters

We present low temperature magnetic data (thermal demagnetization, hysteresis) obtained on thirty three ordinary chondrite meteorites. A magnetic transition is observed in the 40-80 K range (average 66 K), and is interpreted as a ferrimagnetic to paramagnetic phase transition. We present quantitative analyses of changes in magnetization across the magnetic phase transition and chemical elemental analyses to argue that chromite, a common accessory mineral in meteorites, is the mineral undergoing the phase transition, and not troilite or tetrataenite as proposed in previous studies. Moreover, we observe a correlation between the measured Curie temperature and chemical composition of chromites in ordinary chondrites. Low temperature magnetic measurement are thus a sensitive indicator of chromite composition in these meteorites, and as such a possible proxy to the understanding of their thermal metamorphism. Copyright 2011 by the American Geophysical Union. Source

Gattacceca J.,Aix - Marseille University | Gattacceca J.,Massachusetts Institute of Technology | Hewins R.H.,Laboratoire Of Mineralogie Et Cosmochimie Du Museum | Lorand J.-P.,CNRS Nantes Laboratory of Planetology and Geodynamics | And 13 more authors.
Meteoritics and Planetary Science

We present a description of opaque minerals, opaque mineral compositions, magnetic properties, and paleomagnetic record of the Tissint heavily shocked olivine-phyric shergottite that fell to Earth in 2011. The magnetic mineralogy of Tissint consists of about 0.6 wt% of pyrrhotite and 0.1 wt% of low-Ti titanomagnetite (in the range ulvöspinel 3-15 magnetite 85-97). The titanomagnetite formed on Mars by oxidation-exsolution of ulvöspinel grains during deuteric alteration. Pyrrhotite is unusual, with respect to other shergottites, for its higher Ni content and lower Fe content. Iron deficiency is attributed by an input of regolith-derived sulfur. This pyrrhotite has probably preserved a metastable hexagonal monosulfide solution structure blocked at temperature above 300 °C. The paleomagnetic data indicate that Tissint was magnetized following the major impact suffered by this rock while cooling at the surface of Mars from a post-impact equilibrium temperature of approximately 310 °C in a stable magnetic field of about 2 μT of crustal origin. Tissint is too weakly magnetic to account for the observed magnetic anomalies at the Martian surface. © The Meteoritical Society, 2013. Source

Mousis O.,University of Franche Comte | Hueso R.,University of the Basque Country | Beaulieu J.-P.,French National Center for Scientific Research | Bouley S.,University Paris - Sud | And 58 more authors.
Experimental Astronomy

Amateur contributions to professional publications have increased exponentially over the last decades in the field of planetary astronomy. Here we review the different domains of the field in which collaborations between professional and amateur astronomers are effective and regularly lead to scientific publications.We discuss the instruments, detectors, software and methodologies typically used by amateur astronomers to collect the scientific data in the different domains of interest. Amateur contributions to the monitoring of planets and interplanetary matter, characterization of asteroids and comets, as well as the determination of the physical properties of Kuiper Belt Objects and exoplanets are discussed. © 2014, Springer Science+Business Media Dordrecht. Source

Hewins R.H.,Laboratoire Of Mineralogie Et Cosmochimie Du Museum | Hewins R.H.,Rutgers University | Zanda B.,Laboratoire Of Mineralogie Et Cosmochimie Du Museum | Zanda B.,Rutgers University
Meteoritics and Planetary Science

Chondrule compositions suggest either ferroan precursors and evaporation, or magnesian precursors and condensation. Type I chondrule precursors include granoblastic olivine aggregates (planetary or nebular) and fine-grained (dustball) precursors. In carbonaceous chondrites, type I chondrule precursors were S-free, while type II chondrules have higher Fe/Mn than in ordinary chondrites. Many type II chondrules contain diverse forsteritic relicts, consistent with polymict dustball precursors. The relationship between finer and coarser grained type I chondrules in ordinary chondrites suggests more evaporation from more highly melted chondrules. Fe metal in type I, and Na and S in type II chondrules indicate high partial pressures in ambient gas, as they are rapidly evaporated at canonical conditions. The occurrence of metal, sulfide, or low-Ca pyroxene on chondrule rims suggests (re)condensation. In Semarkona type II chondrules, Na-rich olivine cores, Na-poor melt inclusions, and Na-rich mesostases suggest evaporation followed by recondensation. Type II chondrules have correlated FeO and MnO, consistent with condensation onto forsteritic precursors, but with different ratios in carbonaceous chondrites and ordinary chondrites, indicating different redox history. The high partial pressures of lithophile elements require large dense clouds, either clumps in the protoplanetary disk, impact plumes, or bow shocks around protoplanets. In ordinary chondrites, clusters of type I and type II chondrules indicate high number densities and their similar oxygen isotopic compositions suggest recycling together. In carbonaceous chondrites, the much less abundant type II chondrules were probably added late to batches of type I chondrules from different O isotopic reservoirs. © 2012 The Meteoritical Society. Source

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