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Space weathering is the damage that occurs to any object exposed to the harsh environment of outer space. Bodies without atmospheres (including the Moon, Mercury, the asteroids, comets, and most of the moons of other planets) incur many weathering processes: * collisions of galactic cosmic rays and solar cosmic rays, * irradiation, implantation, and sputtering from solar wind particles, and * bombardment by different sizes of meteorites and micrometeorites. Space weathering is important because these processes affect the physical and optical properties of the surface of many planetary bodies. Therefore, it is critical to understand the effects of space weathering in order to properly interpret remotely sensed data. == History == Much of our knowledge of the space weathering process comes from studies of the lunar samples returned by the Apollo program, particularly the lunar soils (or regolith). The constant flux of high energy particles and micrometeorites, along with larger meteorites, act to comminute, melt, sputter and vaporize components of the lunar soil, as well as to garden (or overturn) it. The first products of space weathering that were recognized in lunar soils were "agglutinates". These are created when micrometeorites melt a small amount of material, which incorporates surrounding glass and mineral fragments into a glass-welded aggregate ranging in size from a few micrometers to a few millimeters. Agglutinates are very common in lunar soil, accounting for as much as 60 to 70% of mature soils. These complex and irregularly-shaped particles appear black to the human eye, largely due to the presence of nanophase iron. Space weathering also produces surface-correlated products on individual soil grains, such as glass splashes; implanted hydrogen, helium and other gases; solar flare tracks; and accreted components, including nanophase iron. It wasn't until the 1990s that improved instruments, in particular transmission electron microscopes, and techniques allowed for the discovery of very thin (60-200 nm) patinas, or rims, which develop on individual lunar soil grains as a result of the redepositing of vapor from nearby micrometeorite impacts and the redeposition of material sputtered from nearby grains. These weathering processes have large effects on the spectral properties of lunar soil, particularly in the ultraviolet, visible, and near infrared (UV/Vis/NIR) wavelengths. These spectral changes have largely been attributed to the inclusions of "nanophase iron" which is a ubiquitous component of both agglutinates and soil rims. These very small (one to a few hundred nanometers in diameter) blebs of metallic iron are created when iron-bearing minerals (e.g. olivine and pyroxene) are vaporized and the iron is liberated and redeposited in its native form. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Space weathering」の詳細全文を読む スポンサード リンク
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