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



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 µm 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 µm in length and >500 nm in width. It was polycrystalline with both mosaiced domains varying over ≈ 20math formula 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 math formula (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.