Meteors and interplanetary dust

Abstract

The contribution of meteor observations to our knowledge of meteoroids and interplanetary dust is reviewed under four headings — flux, mass distribution, physical structure and chemical composition. For lower limits of particle mass ranging from 1 g to 10⁻⁵ g the mean cumulative flux into the earth's atmosphere varies from 2 × 10⁻¹⁵ to 6 × 10⁻⁹ particles m⁻² s⁻¹ (2πster)⁻¹, and the mean size distribution of these particles is given by log N = C − 1.3 log M, where N is the cumulative number of particles counted down to a lower mass limit M, and C is a constant. The physical structure of meteoroids in the above range is essentially fragile, with generally low mean bulk densities that tend to increase with decrease in mass. A minor fraction, about 10 or 15 percent, with orbits lying inside that of Jupiter, have densities several times the average densities, approaching those of the carbonaceous chondrites. The mean chemical composition of meteoroids seems to be similar to the bronzite chondrites for the elements heavier than number 10, but with the probable addition of extra quantities of the light volatiles H, C and O.