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Magnetite in Comet Wild 2: Evidence for parent body aqueous alteration

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journal contribution
posted on 2018-04-23, 11:26 authored by L. J. Hicks, J. L. Macarthur, J. C. Bridges, M. C. Price, J. E. Wickham-Eade, M. J. Burchell, G. M. Hansford, A. L. Butterworth, S. J. Gurman, S. H. Baker
The mineralogy of comet 81P/Wild 2 particles, collected in aerogel by the Stardust mission, has been determined using synchrotron Fe-K X-ray absorption spectroscopy with in situ transmission XRD and X-ray fluorescence, plus complementary microRaman analyses. Our investigation focuses on the terminal grains of eight Stardust tracks: C2112,4,170,0,0; C2045,2,176,0,0; C2045,3,177,0,0; C2045,4,178,0,0; C2065,4,187,0,0; C2098,4,188,0,0; C2119,4,189,0,0; and C2119,5,190,0,0. Three terminal grains have been identified as near pure magnetite Fe 3 O 4 . The presence of magnetite shows affinities between the Wild 2 mineral assemblage and carbonaceous chondrites, and probably resulted from hydrothermal alteration of the coexisting FeNi and ferromagnesian silicates in the cometary parent body. In order to further explore this hypothesis, powdered material from a CR2 meteorite (NWA 10256) was shot into the aerogel at 6.1 km s -1 , using a light-gas gun, and keystones were then prepared in the same way as the Stardust keystones. Using similar analysis techniques to the eight Stardust tracks, a CR2 magnetite terminal grain establishes the likelihood of preserving magnetite during capture in silica aerogel.


We thank the NASA JSC Stardust Sample Curator for the loan of the Stardust aerogel track samples, prepared at the University of California at Berkeley and NASA‐JSC. The Diamond Beamline I18 staff Fred Mosselmans and Konstantin Ignatyev are thanked for the help in data acquisition, during beamtimes sp1833‐1 (Changela et al. 2012), sp7487‐1 (December 2011), sp9418‐1 (December 2013), sp10328‐1 (December 2014), and sp13690‐1 (July 2016). We also thank Graham Clark, Vinay Patel, and Lin Marvin of the University of Leicester for their support with SEM analysis of the meteorite samples. STFC is thanked for operation of the light‐gas gun and Raman spectrometer (University of Kent). EXAFS research involved the use of DL_EXCURV v1.01 via the SPECTRE High Performance Computing Facility at the University of Leicester. J. C. Bridges, M. J. Burchell, and M. C. Price acknowledge funding from STFC to support this work.



Meteoritics and Planetary Science, 2017, 52(10), pp. 2075–2096

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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