The Meteorites

Meteorites range extraordinarily in size and weight. At the low end of the scale is cosmic dust, a term that designates particles smaller than 0.1 mm. These small particles are not melted by frictional heating during passage through the atmosphere. Due to their large surface to mass ratio, the generated heat is lost by radiation. There are also melted particles among these micrometeorites; they formed mainly by ablation from the molten surface of larger meteorites. The Earth accumulates about 10000 t of cosmic dust per year, but the problem for meteorite researchers is to distinguish it from the tremendous quantities of terrestrial dust. Two approaches to this problem have been found: 1.The capture of cosmic dust at high altitudes in the atmosphere;2.The recovery of cosmic spherules from deep-sea sediments, or from Arctic or Antarctic ice.