Stardust Interstellar Preliminary Examination V:XRFanalyses of interstellar dust candidates atESRF ID13
Authors: Brenker Frank E. , Westphal Andrew J. , Vincze Laszlo , Burghammer Manfred , Schmitz Sylvia , Schoonjans Tom , Silversmit Geert , Vekemans Bart , Allen Carlton , Anderson David , Ansari Asna , Bajt Saša , Bastien Ron K. , Bassim Nabil , Bechtel Hans A. , Borg Janet , Bridges John , Brownlee Donald E. , Burchell Mark , Butterworth Anna L. , Changela Hitesh , Cloetens Peter , Davis Andrew M. , Doll Ryan , Floss Christine , Flynn George , Fougeray Patrick , Frank David R. , Gainsforth Zack , Grün Eberhard , Heck Philipp R. , Hillier Jon K. , Hoppe Peter , Hudson Bruce , Huth Joachim , Hvide Brit , Kearsley Anton , King Ashley J. , Lai Barry , Leitner Jan , Lemelle Laurence , Leroux Hugues , Leonard Ariel , Lettieri Robert , Marchant William , Nittler Larry R. , Ogliore Ryan , Ong Wei Ja , Postberg Frank , Price Mark C. , Sandford Scott A. , Tresseras Juan‐Angel Sans , Simionovici Alexandre S. , Solé Vicente A. , Srama Ralf , Stadermann Frank , Stephan Thomas , Sterken Veerle J. , Stodolna Julien , Stroud Rhonda M. , Sutton Steven , Trieloff Mario , Tsou Peter , Tsuchiyama Akira , Tyliszczak Tolek , Von Korff Joshua , Wordsworth Naomi , Zevin Daniel , Zolensky Michael E. ,   >30,000 Stardust@home
Published: August 2014

Here, we report analyses by synchrotron X‐ray fluorescence microscopy of the elemental composition of eight candidate impact features extracted from the Stardust Interstellar Dust Collector (SIDC). Six of the features were unambiguous tracks, and two were crater‐like features. Five of the tracks are so‐called “midnight” tracks—that is, they had trajectories consistent with an origin either in the interstellar dust stream or as secondaries from impacts on the Sample Return Capsule (SRC). In a companion paper reporting synchrotron X‐ray diffraction analyses ofISPEcandidates, we show that two of these particles contain natural crystalline materials: the terminal particle of track 30 contains olivine and spinel, and the terminal particle of track 34 contains olivine. Here, we show that the terminal particle of track 30, Orion, shows elemental abundances, normalized to Fe, that are close toCIvalues, and a complex, fine‐grained structure. The terminal particle of track 34, Hylabrook, shows abundances that deviate strongly fromCI, but shows little fine structure and is nearly homogenous. The terminal particles of other midnight tracks, 29 and 37, had heavy element abundances below detection threshold. A third, track 28, showed a composition inconsistent with an extraterrestrial origin, but also inconsistent with known spacecraft materials. A sixth track, with a trajectory consistent with secondary ejecta from an impact on one of the spacecraft solar panels, contains abundant Ce and Zn. This is consistent with the known composition of the glass covering the solar panel. Neither crater‐like feature is likely to be associated with extraterrestrial materials. We also analyzed blank aerogel samples to characterize background and variability between aerogel tiles. We found significant differences in contamination levels and compositions, emphasizing the need for local background subtraction for accurate quantification.