Stardust Interstellar Preliminary Examination VI: Quantitative elemental analysis by synchrotron X-ray fluorescence nanoimaging of eight impact features in aerogel

Alexandre S. Simionovici , Laurence Lemelle (1) , Peter Cloetens , Vicente A. Sole , Juan-Angel Sans Tresseras , Anna L. Butterworth , Andrew J. Westphal , Zack Gainsforth , Julien Stodolna , Carlton Allen , David Anderson , Asna Ansari , Sasa Bajt , Nabil Bassim , Ron K. Bastien , Hans A. Bechtel , Janet Borg , Frank E. Brenker , John Bridges , Donald E. Brownlee , Mark Burchell , Manfred Burghammer , Hitesh Changela , Andrew M. Davis , Ryan Doll , Christine Floss , George Flynn , David R. Frank , Eberhard Gruen , Philipp R. Heck , Jon K. Hillier , Peter Hoppe , Bruce Hudson , Joachim Huth , Brit Hvide , Anton Kearsley , Ashley J. King , Barry Lai , Jan Leitner , Ariel Leonard , Hugues Leroux , Robert Lettieri , William Marchant , Larry R. Nittler , Ryan Ogliore , Wei Ja Ong , Frank Postberg , Mark C. Price , Scott A. Sandford , Sylvia Schmitz , Tom Schoonjans , Geert Silversmit , Ralf Srama , Frank J. Stadermann , Thomas Stephan , Veerle J. Sterken , Rhonda M. Stroud , Steven Sutton , Mario Trieloff , Peter Tsou , Akira Tsuchiyama , Tolek Tyliszczak , Bart Vekemans , Laszlo Vincze , Joshua von Korff , Naomi Wordsworth , Daniel Zevin , Michael E. Zolensky

1 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement

Hard X-ray, quantitative, fluorescence elemental imaging was performed on the ID22NI nanoprobe and ID22 microprobe beam lines of the European Synchrotron Research facility (ESRF) in Grenoble, France, on eight interstellar candidate impact features in the framework of the NASA Stardust Interstellar Preliminary Examination (ISPE). Three features were unambiguous tracks, and the other five were identified as possible, but not definite, impact features. Overall, we produced an absolute quantification of elemental abundances in the 15 = Z = 30 range by means of corrections of the beam parameters, reference materials, and fundamental atomic parameters. Seven features were ruled out as interstellar dust candidates (ISDC) based on compositional arguments. One of the three tracks, I1043,1,30,0,0, contained, at the time of our analysis, two physically separated, micrometer-sized terminal particles, the most promising ISDCs, Orion and Sirius. We found that the Sirius particle was a fairly homogenous Ni-bearing particle and contained about 33 fg of distributed high-Z elements (Z 12). Orion was a highly heterogeneous Fe-bearing particle and contained about 59 fg of heavy elements located in hundred nanometer phases, forming an irregular mantle that surrounded a low-Z core. X-ray diffraction (XRD) measurements revealed Sirius to be amorphous, whereas Orion contained partially crystalline material (Gainsforth et al. 2014). Within the mantle, one grain was relatively Fe-Ni-Mn-rich; other zones were relatively Mn-Cr-Ti-rich and may correspond to different spinel populations. For absolute quantification purposes, Orion was assigned to a mineralogical assemblage of forsterite, spinel, and an unknown Fe-bearing phase, while Sirius was most likely composed of an amorphous Mg-bearing material with minor Ni and Fe. Owing to its nearly chondritic abundances of the nonvolatile elements Ca, Ti, Co, and Ni with respect to Fe, in combination with the presence of olivine and spinel as inferred from XRD measurements, Orion had a high probability of being extraterrestrial in origin.

Domaines: Planète et Univers [physics]

Alexandre S. Simionovici, Laurence Lemelle, Peter Cloetens, Vicente A. Sole, Juan-Angel Sans Tresseras, et al.. Stardust Interstellar Preliminary Examination VI: Quantitative elemental analysis by synchrotron X-ray fluorescence nanoimaging of eight impact features in aerogel. Meteoritics and Planetary Science, 2014, 49 (9, SI), pp.1612--1625. ⟨10.1111/maps.12208⟩. ⟨hal-02351076⟩