Since there is a continual loss of micrometeoritic material in space because of the radiation effects, there must be a continual replenishment: otherwise, micrometeorites would have disappeared from interplanetary space. There are several possible sources. According to Whipple (1955), cometary debris is sufficient to replenish the material spiraling into the sun, maintaining a fairly steady state. Asteroidal collisions are also thought to contribute material. It is also possible that some of the dust in the vicinity of the Earth originated from meteoritic impacts upon the moon.

One cannot make a very satisfactory guess about the micrometeorite flux in space. Even in the neighborhood of the Earth, where information has been obtained both directly and indirectly, the derived flux values vary by at least four orders of magnitude. This large discrepancy demonstrates the inadequacies of the experimental methods and the lack of understanding of the various phenomena involved. Beyond a few million kilometers from the Earth, but still in the region of the Earth's orbit, a prediction of the flux of dust is even more unreliable. At greater distances from the sun, the situation is still less certain.

There are several sources of evidence on the micrometeorite environment. Direct information has been obtained from rockets and satellites equipped with impact sensors. In addition, the size distribution obtained from visual and radar observations of meteors may be extrapolated to the micrometeorite domain. From the brightness of the F component of the solar corona and the brightness of the zodiacal light, an estimate of the particle sizes, concentrations, and spatial distribution can be derived for regions of space near the ecliptic plane. Another important source of evidence only recently receiving much attention is the analysis of atmospheric dust for a meteoritic component. The cores of deep sea sediments and content of collectors in remote regions are valuable in this category. The data provide a measure of the total mass of cosmic material incident upon the Earth.