From outer space; Study of smallest 'dust' offers new challenge

Abstract

The probability that an extraterrestrial object will be captured without vaporization is a complex function of encounter velocity, direction, meteoroid mass, density and strength, among other factors. However, there are two 'windows' that admit material mo re or less intact. Through the big window, objects roughly 10 cm in diameter or larger make it to Earth's surface as meteorites. The small window admits objects of about 1 to 10 microns in size, which escape total vaporization because they rapidly radiate the frictional energy associated with atmospheric entry. Also, the smaller objects have much less kinetic energy, and they therefore slow down higher above Earth, where the atmosphere is less dense.

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