College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan.
Science. 2011 Aug 26;333(6046):1121-5. doi: 10.1126/science.1207794.
The reflectance spectra of the most abundant meteorites, ordinary chondrites, are different from those of the abundant S-type (mnemonic for siliceous) asteroids. This discrepancy has been thought to be due to space weathering, which is an alteration of the surfaces of airless bodies exposed to the space environment. Here we report evidence of space weathering on particles returned from the S-type asteroid 25143 Itokawa by the Hayabusa spacecraft. Surface modification was found in 5 out of 10 particles, which varies depending on mineral species. Sulfur-bearing Fe-rich nanoparticles exist in a thin (5 to 15 nanometers) surface layer on olivine, low-Ca pyroxene, and plagioclase, which is suggestive of vapor deposition. Sulfur-free Fe-rich nanoparticles exist deeper inside (<60 nanometers) ferromagnesian silicates. Their texture suggests formation by metamictization and in situ reduction of Fe(2+).
最常见的陨石，即普通球粒陨石的反射光谱与丰富的 S 型（硅质的缩写）小行星的反射光谱不同。这种差异被认为是由于太空风化造成的，这是一种在没有大气层的天体暴露于太空环境时对表面的改变。在这里，我们报告了隼鸟号航天器从 S 型小行星 25143 糸川带回的颗粒上存在太空风化的证据。在 10 个颗粒中有 5 个发现了表面改性，这取决于矿物种类而有所不同。含硫的富铁纳米颗粒存在于橄榄石、低钙辉石和斜长石的薄（5 至 15 纳米）表层，这表明是蒸汽沉积的结果。无硫的富铁纳米颗粒存在于更深的铁镁硅酸盐内部（<60 纳米）。它们的结构表明是通过非晶化和原位还原 Fe(2+)形成的。
