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Interplanetary dust measurements near the Earth
Author(s) -
Bandermann L. W.,
Singer S. Fred
Publication year - 1969
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/rg007i004p00759
Subject(s) - zodiacal light , interplanetary dust cloud , physics , interplanetary spaceflight , cosmic dust , isotropy , interplanetary medium , computational physics , solar system , astrobiology , astronomy , solar wind , optics , quantum mechanics , magnetic field
The impact of dust particles on space vehicles near the earth gives important information about interplanetary dust. Satellite impact measurements have been made with two types of detectors: acoustic and penetration detectors. These types of detectors correspond to momentum and energy restrictions, respectively, on the impact rate of dust. The early acoustic data showed a greatly enhanced rate near the earth, which suggested that there was a high concentration near the earth (‘dust belt’). Quite to the contrary, from theory no sensible enhancement in concentration can be derived but, instead, a moderate enhancement in impact rate, depending on the geocentric velocity of the particles. The dust belt would therefore exist only as a consequence of the measurement technique. Here we review the theory that allows us to calculate the following, for a given geocentric velocity of dust particles and a distribution of velocities (all isotropic) : (1) the concentration; (2) the flux; and (3) the impact rate (momentum‐ and energy‐limited) at various distances from the earth and for various detector velocities so as to bracket all possible experimental situations. With the use of these results, it is then possible to analyze and compare results from different experiments. Of the experimental data reviewed, both U. S. and Russian, only certain are selected for a more detailed analysis. The theory accounts well for the observed penetration data in space vehicles flown near the earth and the moon; they lead to a zodiacal dust model similar to van de Hulst's model, having a particle population predominantly in the micron and decamicron size range (rather than submicron), with a flat (rather than steep) size distribution, and with geocentric velocities of 5 to 15 km/sec. A theoretical analysis is also presented for a nonisotropic velocity distribution. This is of practical importance for very small particles, which are partly supported by solar radiation pressure and therefore develop a streaming velocity with respect to the earth; in addition, the earth itself introduces an asymmetry, since its orbital velocity varies throughout the year. Numerical results are given for predicted asymmetries in concentration, influx of dust into the atmosphere, and in the satellite impact rates. Impact rates from some satellites exhibited such asymmetries, and these cases support the hypothesis that the heliocentric dust orbits have small inclination and small eccentricity. These results are inconclusive because the data are scant; a systematic analysis of all available impact data with respect to asymmetries is needed.