Planetary and Space Science 55 (2007) 966–973 In-situ Fe XANES of extraterrestrial grains trapped in aerogel collectors: An analytical test for the interpretation of Stardust samples analyses F. Grossemy a,Ã , J. Borg a , Z. Djouadi a , A. Simionovici b , L. Lemelle b , D. Eichert c , D. Deboffle a , A.J. Westphal d , C.J. Snead d a Institut d’Astrophysique Spatiale (IAS), CNRS, Univ. Paris-Sud, UMR8617, Orsay Cedex F 91405, France b Laboratoire des Sciences de la Terre (LST), UMR CNRS 5570, ENS Lyon, 46 alle´e d’Italie, 69364 Lyon, France. c ESRF, X-ray micro spectroscopy beamline ID21, BP220, 38043 Grenoble Cedex, France d Space Science Laboratory, University of California, Berkeley, CA 94720, USA Received 14 July 2006; received in revised form 13 November 2006; accepted 13 November 2006 Available online 12 January 2007 Abstract On 15 January 2006, the NASA Stardust Capsule Sample Return came back to Earth with its load of cometary and contemporary interstellar grains trapped in aerogel collectors. These cometary grains are the first samples of known parent body and their study in the laboratory will give new clues on the nature of the cometary materials. Using Synchrotron X-ray Microscopy (SXRM), some analogues of Stardust’s samples were analysed. The aim was to develop an analytical protocol and to study the effects of the slowing down of hypervelocity particles into aerogel on the physical and chemical properties of the collected grains. Our samples originate either from the NASA Orbital Debris Collection Experiment (ODCE) deployed outside the MIR station, or from light gas gun shots of Allende meteorite grains into aerogel at velocities of 6 km/s. They consist of grains trapped in pieces of aerogel, a few hundreds of microns large. Using synchrotron X-ray microbeam, micro-fluorescence mappings and X-ray absorption near-edge structure (XANES) spectra were performed, bringing information on elemental analysis, repartition and speciation of Fe in our samples. In particular, the XANES studies obtained at the iron K-edge show that iron is present in different oxidation states in the samples, rather in a ferric form at the track entrance while rather in a ferrous form at the end of the track as well as in the final grain. The tests performed on the Allende meteorite dust grains for which the Fe 2+ /Fe 3+ ratio is a priori known, tend to show that the final particle presents the same oxidation state as the initial incident one, a very encouraging clue for the validity of the future interpretation of Stardust samples analyses. r 2006 Elsevier Ltd. All rights reserved. Keywords: Aerogel; Stardust; Keystone; XANES; Micro-fluorescence 1. Introduction Made of ice and dust, comets are ‘‘icy dirtballs’’ that formed in the early times of the solar nebula, some 4.6 billion years ago. Two reservoirs of comets exist in the Solar System, the Oort Cloud and the Kuiper Belt. The current comets formation models indicate that the Oort Cloud, a 50 000 A.U. radius shell, is composed of comets formed at 20–30 A.U. from the Sun that were ejected in the outer part of the Solar System by gravitational perturba- tions of the giant planets. The Kuiper Belt reservoir, placed between 30 and 100 A.U. from the Sun, contains objects that never left their region of formation and stayed in quite cold areas. As comets remained in the outer parts of our Solar System they presumably survive as unique witnesses of the chemical composition and the physical conditions in the solar nebula and its early evolution. In spite of their great astrophysical interest, comets are still not well known, essentially because they spend most of their time in the outer part of the Solar System. In the perspective of a better understanding of the conditions prevailing in the ARTICLE IN PRESS www.elsevier.com/locate/pss 0032-0633/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.pss.2006.11.004 Ã Corresponding author. Tel.: +33 1 69 85 86 83; fax: +33 1 69 85 86 75. E-mail address: faustine.grossemy@ias.u-psud.fr (F. Grossemy).