![]() Models of dust propagation in the heliosphere show that interstellar particles have been size sorted by radiation pressure and Lorentz interactions within the heliosphere. Thus, the properties of ISM and LISM dust could vary significantly, and we should not claim a priori knowledge of what a particular grain from the LISM may look like. In addition, the Ulysses spacecraft has shown that dust reaching the inner system is significantly larger than the average dust size in the interstellar medium predicted by astronomical observations (Grün et al. These cases highlight the danger in predicting the properties of the LISM dust population from the context of galactic observations. Recent studies of the local interstellar medium (LISM) have shown significant chemical inhomogeneities on a parsec scale (Welsh and Lallement 2012), whereas studies of the galactic interstellar medium (ISM) have shown multiple dust populations throughout the Milky Way galaxy (Sandford et al. However, studies of dust crystallinity, grain size, and composition in the interstellar medium have focused on sight lines to the galactic center or similarly bright targets easily accessible to astronomers. With this and other information in hand, we may be tempted to form some ideas of the composition of our local interstellar medium-i.e., our immediate neighborhood containing particles that would be sampled by the Stardust interstellar collector. We expect that the dust population should comprise amorphous silicate and carbonaceous grains with an average size 1 μm grains are absent. Our current understanding of the interstellar medium is largely derived from astronomical observations. The discovery and projected direction of this dust stream was based on observations by dust detectors on the Galileo and Ulysses missions (Grün et al. During ≈ 200 days of the 7 yr of spaceflight, the mission controllers exposed a second aerogel collector to the interstellar dust stream. The secondary mission was to return the first solid samples of material from the local interstellar medium. The primary mission resulted in an analysis of cometary material captured from comet 81P/Wild 2 with unprecedented precision and detail (Brownlee et al. The primary mission was to return the first samples from a known comet to Earth for study using instruments far too bulky to be flown in space. It was effectively two missions in one spacecraft. The Stardust mission (Brownlee 2003 Tsou 2003) was a sample return mission flown as part of NASA's Discovery Mission program. An amorphous component appeared to be present in both these particles based on STXM and XRF results reported elsewhere. Two additional crystalline phases were present and remained unidentified. Orion also contained abundant spinel nanocrystals of unknown composition, but unit cell dimension a = 8.06 ± 0.08 Å (2σ). 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). It was polycrystalline with both mosaiced domains varying over ≈ 20 and additional unoriented domains, and contained internal strain fields < 1%. ![]() The second particle, I1043,1,30 (Orion), contained an olivine grain ≈ 2 µm in length and >500 nm in width. 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%. Using synchrotron-based X-ray diffraction measurements, we identified crystalline material in two particles of extraterrestrial origin extracted from the Stardust Interstellar Dust Collector.
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