Postdoc fellowship – Museo Nazionale dell'Antartide, Siena, Italy 1 – Antarctic cosmic spherules from differentiated asteroids Cosmic spherules are extraterrestrial particles < 1mm in size captured by the Earth's gravitational field and that underwent severe melting during their penetration through the atmosphere. They are mainly chondritic in composition and only very few of them are related to differentiated asteroids. My research first focused on the geochemical investigation of these differentiated cosmic spherules. The purpose was to establish chemical markers that can be easily analyzed by in situ methods in these small-sized glassy particles (electron microprobe for major elements and laser ablation-inductively coupled plasma-mass spectrometry for trace elements); and to use these markers to identify further differentiated cosmic spherules and to discuss their origin. To calibrate the chemical markers, I used the differentiated cosmic spherules previously reported in the South Water Well collection in Antarctica (collaboration, S. Taylor, CRREL, US). These proxies allowed me to identify more than ten new differentiated cosmic spherules in the micrometeorites trapped over the last million years on the summits of the nunataks of the Transantarctic Mountains, Antarctica. The differentiated spherules show three major chemical distinctions with the chondritic particles: they have high Fe/Mg ratio, due to their low Mg contents reflecting magma extraction from the asteroid mantle through time; they have strong siderophile element depletions, reflecting the segregation of these elements in the core of the parent asteroid; and they have high contents in incompatible elements, concentrated in the magmas produced during magmatic processes occurring on the parent body. Three main parent bodies can be envisaged for these spherules: the Moon, Mars, and a differentiated asteroid, 4 Vesta. The Moon can be disregarded because of the higher Fe/Mn ratio of the lunar meteorites when compared to the studied spherules. To distinguish between an origin from Mars and 4 Vesta, I used elements that are sensitive to redox conditions, as Mars is known to be a more oxidating environment. For these elements (i.e., V, Co, and volatile elements), the differentiated cosmic spherules share the signature of the eucrites, the basaltic meteorites coming from 4 Vesta. This conclusion is supported by oxygen isotope compositions acquired for a few spherules. Oxygen isotope compositions, even if modified during the flight of the particles through the atmosphere, retain some strong constraints about the parent body of the extraterrestrial material. The differentiated spherules that I analyzed fall along a mixing line between a 4 Vesta composition and the atmospheric oxygen. The results were presented at two international conferences (the Lunar and Planetary Science Conference, March 2010 and the Meeting of the Meteoretical Society, July 2010) and gathered in a paper accepted for publication in Geochimica and Cosmochimica Acta. 2 – Ni abundance in cosmic spherules Currently, I am working on cosmic spherules with barred-olivine (skeletal bars of olivine set in a glassy matrix speckled with magnetite microcrystals) and porphyritic (olivine microphenocrysts set in a glassy mesostasis with magnetite microcrystals with olivine relics that survived atmospheric entry melting) textures. Barred-olivine and porphyritic cosmic spherules studied in this work. The aim of this work is to understand the variability of the NiO content in both the olivines and the bulk spherules. One of the main issues is to understand if the NiO content in olivine could be used to distinguish between meteorite ablation debris (that detached from fusion crust of meteorites) from cosmic spherules. We also explore the role of variable redox conditions during the atmospheric entry and of variable precursor type to explain the Ni variability. The results are in review for Meteoritics and Planetary Science and will be presented at the Lunar and Planetary Science Conference (March 2011). 3 – Craters and meteorites viewed from the field I also took part to three field trips in the Egyptian, Tunisian and Australian deserts, to study the structure of the newly discovered Kamil Crater in Egypt and to hunt for meteorites (Tunisia and Western Australia). During the Italian-Egyptian geophysical survey of the Kamil crater, my tasks were to search for both microscopic and macroscopic fragments of the impacting meteorite. With the collected samples, I plan to study the spatial distribution, the abundance and the mineralogical and chemical composition of the magnetic microscopic particles to help to constraint the mass of the impactor. I also plan to study the impact melt glassy objects and the relation between glasses derived from the basement and the impactor. The Kamil Crater, Southern Egypt (Folco et al., 2011) The discovery of the crater has been published in Science (Folco et al., 2010) and a more detailed description of the crater structure will be published soon (Folco et al., 2011, in press). More information can be found at the following links: The meteorite: http://tin.er.usgs.gov/meteor/metbull.php?code=52031 A general overview of the field trip: http://www.mna.it/Kamil http://news.nationalgeographic.com/news/2010/07/100722-science-space-egypt-kamil-crater-meteor-meteorite-impact-hazard/ http://news.discovery.com/space/meteorite-impact-crater-google.html Analytical support CNR-IGG Unità operativa di Padova, Italy (EPM) INVG, Rome, Italy (FEG-SEM and EPM) CNR-IGG Unità operativa di Pavia, Italy (LA-ICPMS) CEREGE, Aix en Provence, France (oxygen isotope measurements) My publications during the period of my Origins fellowship - Folco and the Kamellers (2011, in press) The Kamil Crater (Egypt): ground truth for small-scale meteorite impacts on Earth. Geology. - Folco and the Kamellers (2010) The Kamil Crater in Egypt. Science. 329, 804. - Cordier C., Folco L., Taylor S (accepted) Vestoid cosmic spherules from the South Pole Water Well and Transantarctic Mountains (Antarctica): A major and trace element study. Geochim. Cosmochim. Act. - Cordier C., van Ginneken M., Folco L. (submitted) Nickel abundance in stony cosmic spherules: constraining precursor material and formation mechanisms. Meteorit. Planet. Sci. - van Ginneken M., Folco L., Cordier C. , Rochette P. (submitted) Chondritic micrometeorites from the Transantarctic Mountains. Meteorit. Planet. Sci.