Space environment of an asteroid preserved on micrograins returned by the Hayabusa spacecraft
Space environment of an asteroid preserved on micrograins returned by the Hayabusa spacecraft
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DOI：
10.1073/pnas.1116236109
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发表时间：
2012-02
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通讯作者：
E. Nakamura;A. Makishima;T. Moriguti;K. Kobayashi;R. Tanaka;T. Kunihiro;T. Tsujimori;C. Sakaguchi-C.-Sakag
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作者：
E. Nakamura;A. Makishima;T. Moriguti;K. Kobayashi;R. Tanaka;T. Kunihiro;T. Tsujimori;C. Sakaguchi-C.-Sakag
在近地小行星 25143（糸川）回收的尘埃颗粒上发现了低至亚微米尺度的微陨石碰撞记录。由于这些颗粒是由隼鸟号航天器从小行星表面附近采集的，因此它们的表面反映了影响小行星外部物理性质的低重力空间环境。通过颗粒表面的描述来检查空间环境，并重建小行星场景。直径接近 50 μm 的 5 个岩屑颗粒的化学和 O 同位素组成表明，碎石堆结构的糸川的最上层主要由具有碰撞叠加效应的平衡 LL 普通球粒陨石状材料组成。晶粒表面以断裂为主，断裂面不仅含有亚微米级的凹坑，而且还含有大量亚微米级到几微米级的附着颗粒，其中一些颗粒由玻璃组成。粘附颗粒的尺寸分布和化学成分，以及亚微米级陨石坑的出现，表明纳米级微陨石的超高速碰撞形成，这是小行星表面恶劣的物理环境中预期的过程。我们描述了与撞击相关的现象，规模从 10-9 米到 104 米不等，展示了撞击过程在行星体长期演化中发挥的核心作用。撞击似乎是一个重要的过程，不仅塑造月球等大型行星体的外观，而且塑造小行星等低重力天体的外观。
Records of micrometeorite collisions at down to submicron scales were discovered on dust grains recovered from near-Earth asteroid 25143 (Itokawa). Because the grains were sampled from very near the surface of the asteroid, by the Hayabusa spacecraft, their surfaces reflect the low-gravity space environment influencing the physical nature of the asteroid exterior. The space environment was examined by description of grain surfaces and asteroidal scenes were reconstructed. Chemical and O isotope compositions of five lithic grains, with diameters near 50 μm, indicate that the uppermost layer of the rubble-pile-textured Itokawa is largely composed of equilibrated LL-ordinary-chondrite-like material with superimposed effects of collisions. The surfaces of the grains are dominated by fractures, and the fracture planes contain not only sub-μm-sized craters but also a large number of sub-μm- to several-μm-sized adhered particles, some of the latter composed of glass. The size distribution and chemical compositions of the adhered particles, together with the occurrences of the sub-μm-sized craters, suggest formation by hypervelocity collisions of micrometeorites at down to nm scales, a process expected in the physically hostile environment at an asteroid’s surface. We describe impact-related phenomena, ranging in scale from 10-9 to 104 meters, demonstrating the central role played by impact processes in the long-term evolution of planetary bodies. Impact appears to be an important process shaping the exteriors of not only large planetary bodies, such as the moon, but also low-gravity bodies such as asteroids.