Study on the evolution of the surface of solar system body: Effect of iron

S型小行星的光谱比普通小行星的光谱有更大的损耗和红化，吸收带也更弱。这些光谱失配被解释为所谓的“空间风化”。13高速尘埃粒子撞击以及太阳风溅射将是产生纳米铁粒子的原因。我们的研究组成功地利用纳秒脉冲激光辐照模拟高速尘埃撞击，再现了预期的空间风化光谱变化。我们证实了纳米铁粒子的形成内的气相沉积边缘的激光辐照橄榄石和辉石颗粒使用TEM。本研究开发了含铁陨石的粉碎方法，并成功地将铁颗粒粉碎。Hayabusa航天器观测了S型小行星（25143）Itokawa。在光学上，丝川的表面分为较亮（较蓝）的区域和较暗（较红）的区域。在粗糙地带，深色的巨砾表面通常会叠加在明亮的物质上。我们可以解释说，由于撞击或行星遭遇引起的震动，黑暗的太空风化的富含巨石的表面物质被清除，应该会导致下面相对新鲜的明亮区域暴露出来。高分辨率图像显示，漂砾被风化的细颗粒牢固地覆盖，或者漂砾的表面被光学风化。在真空条件下，用脉冲激光辐照陨石碎片，切割出平整的表面。正如预期的那样，在颗粒样品的照射下观察到显著的变暗和变红。这是首次通过空间风化证实岩石表面的光性变化。具有硅酸盐成分的小型少风化层小行星也可能通过空间风化改变其亮度和颜色，尽管它们的风化程度比风化层覆盖的小行星弱。

S-type asteroids show more overall depletion and reddening of spectra, and more weakening of absorption bands than ordinary chondrites. These spectral mismatches are explained by the so-called "space weathering". High-velocity dust particle impacts as well as sputtering by solar wind would be responsible for the production of nano-iron particlesOur group succeeded in reproducing the spectral change expected as space weathering, using nanosecond pulse laser irradiation simulating high-velocity dust impacts. We confirmed the formation of nanophase iron particles within the vapor-deposited rim of laser-irradiated olivine and pyroxene grains using TEM. In the present study, we developed the comminution method of iron-bearing meteorites and succeeded in grinding the iron particles. We confirmed the optical change of ordinary chondrite powder samples.Hayabusa spacecraft observed the S-type asteroid (25143) Itokawa. Optically, the surface of Itokawa is divided into brighter (and bluer) areas and darker (and redder) areas. In rough zones, dark boulder-rich surfaces usually superpose on bright materials. We can interpret that removal of dark space-weathered boulder-rich surface materials by shaking caused by impacts or planetary encounters should lead to exposure of underlying relatively fresh bright area. High resolution images indicate that boulders are firmly covered with weathered fine particles or boulders' surface are optically weathered. We irradiate pulse laser on meteorite fragments with cut flat surface under vacuum. As expected, significant darkening and reddening are observed under the irradiation of pellet samples. This is the first confirmation of optical change of rock surface by space weathering. Small less-regolith asteroids with silicate composition may also change its brightness and color by space weathering, although their weathering degree would be weaker than regolith-covered asteroids.