Penetration of interstellar dust into the solar system

Reference is made to Bertaux and Blamont (Astr. Astrophys. 11:200 (1971)) who suggested that interstellar dust grains streaming into the solar system are focused by the gravitational attraction of the Sun and that, as a consequence, the density of these grains is strongly peaked on a line extending from the Sun backwards in the downstream direction. Comparisons of the predictions of this focusing model with direct observations of the dust, which do not show this large peak, led to the suggestion that the dust particles are underabundant in the solar system by a factor of about 100 compared with the usual assessment, and a number of possible explanations offered by the above authors for this are mentioned. It is pointed out here that an effect hitherto not considered may offer a natural explanation of the observations, in that grains will in general carry a net electrical charge and the Lorentz force will be strong enough to destroy gravitational focusing. Processes that contribute to the charging of grains in space are discussed. (U.K.)