Stardust Interstellar Preliminary Examination VIII: Identification of crystalline material in two interstellar candidates

Abstract : Using synchrotron-based X-ray diffraction measurements, we identified crystalline material in two particles of extraterrestrial origin extracted from the Stardust Interstellar Dust Collector. The first particle, I1047,1,34 (Hylabrook), consisted of a mosaiced olivine grain approximately 1 \textmum in size with internal strain fields up to 0.3%. The unit cell dimensions were a = 4.85 \textpm 0.08 \r A, b = 10.34 \textpm 0.16 \r A, c = 6.08 \textpm 0.13 \r A (2σ). The second particle, I1043,1,30 (Orion), contained an olivine grain ? 2 \textmum in length and 500 nm in width. It was polycrystalline with both mosaiced domains varying over ? 20 and additional unoriented domains, and contained internal strain fields 1%. The unit cell dimensions of the olivine were a = 4.76 \textpm 0.05 \r A, b = 10.23 \textpm 0.10 \r A, c = 5.99 \textpm 0.06 \r A (2σ), which limited the olivine to a forsteritic composition (2σ). Orion also contained abundant spinel nanocrystals of unknown composition, but unit cell dimension a = 8.06 \textpm 0.08 \r A (2σ). Two additional crystalline phases were present and remained unidentified. An amorphous component appeared to be present in both these particles based on STXM and XRF results reported elsewhere.