Formation and Evolution of Lunar Soil from An Apollo Perspective

bodies like the Moon is almost entirely a function of meteorite and micro-meteorite (<1 mm) impact processing. With impacting velocities > 30,000 mph, even the micro-meteorites have great kinetic energy and cause 1) comminution (breaking), 2)agglutination (aggregates with melt-glass cement), and 3) vaporization (boiling of melt components). The first two competing processes cause decreases and increases in the particle size distribution of the soil, respectively, with a general trend to decreased grain size with increase exposure on the lunar surface. Soil formation is a stochastic process with successive impacts mixing larger and larger volumes of regolith. This is exemplified by the Apollo core samples in which traceable stratigraphy is not present – i.e., soil at 2 m depth may be younger than that at 1 m.

With higher energies of impacts, the soil is melted, and the temperatures generated can cause the super-heated melt to partially volatize. These vapors deposit as rims and rinds on the grains of many soil particles, as a silica-rich glass with a plethora of nano-sized, not connected, metallic Fe grains. With continued comminution and melting, particularly of this brittle glass, the nanophase Fe increases such that the finer size-fractions of the soil greatly increase in this impact-glass with its nanophase Fe. The presence of this nanophase metallic Fe in all lunar soils imparts unique properties many of which we are only recently beginning to appreciate. This ubiquitous metallic Fe gives the lunar soil unexpected ferromagnetic properties, useful for transporting lunar regolith. The microwave coupling of the nanophase Fe also can be used for road building, shelters, and landing pad construction.