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.
Read more about this topic: Space Weathering
Famous quotes containing the word history:
“A poet’s object is not to tell what actually happened but what could or would happen either probably or inevitably.... For this reason poetry is something more scientific and serious than history, because poetry tends to give general truths while history gives particular facts.”
—Aristotle (384–323 B.C.)
“For a transitory enchanted moment man must have held his breath in the presence of this continent, compelled into an aesthetic contemplation he neither understood nor desired, face to face for the last time in history with something commensurate to his capacity for wonder.”
—F. Scott Fitzgerald (1896–1940)
“The history of reform is always identical; it is the comparison of the idea with the fact. Our modes of living are not agreeable to our imagination. We suspect they are unworthy. We arraign our daily employments.”
—Ralph Waldo Emerson (1803–1882)