Symposium: Small meteoric particles in the earth's neighborhood: Measurements of distribution of interplanetary dust

Abstract

Of the various methods for investigating the distributions and particle streams with influx rates two orders of magnitude greater properties of interplanetary dust, direct measurements with than the average were detected. satellites and probes are the most effective for studying the The accretion of interplanetary material by earth is dominated characteristics of particles with radii less than lOOP. Since 1958, by dust particles with masses less than about and amounts more than a dozen major space vehicles have included such instru- to about 10 tons per day. The mass densities of the particles are mentation. At the present time, a significant amount of data has probably greater than 1 g . been accumulated and several characteristics of the interplanetary The direct measurements are compared to the information dust in the vicinity of the earth may be described. The cumulative derived from the studies of meteors and the zodiacal light. No distribution curve of the influx rate of dust particles as a function discernible evidence of significance exists in the space vehicle data of particle mass may be described approximately by the for a geocentric concentration. A comparison of the direct measure- equation ments with the spatial densities at 1 a.u. inferred from zodiacal- logI= -17.0-1.70 logm, light measurements indicates that the spatial density near the earth may be about 10 times greater than in interplanetary space. The direct measurements indicate that the particles are probably where I is the influx rate in particles secM and m is the mass in not in geocentric orbits. Various geocentric concentration mech- grams in the range from 10- < . The impact rates anisms are reviewed, and it is evident that additional measure- measured with satellites undergo large fluctuations in times of only ments are needed to demonstrate the existence and explain the a few hours. There is good evidence that on two occasions dust source of such a phenomenon.