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 µ m in size with internal strain fields up to 0.3%. The unit cell dimensions were a = 4.85 ± 0.08 Å, b  =  10.34 ± 0.16 Å, c  =  6.08 ± 0.13 Å (2σ). The second particle, I1043,1,30 (Orion), contained an olivine grain ≈ 2 µ m 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 ± 0.05 Å, b  =  10.23 ± 0.10 Å, c  =  5.99 ± 0.06 Å (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 ± 0.08 Å (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.