Aspects of the mass distribution of interstellar dust grains in the solar system from in situ measurements

The in situ detection of interstellar dust grains in the solar system by th e dust instruments on-board the Ulysses and Galileo spacecraft as well as t he recent measurements of hyperbolic radar meteors give information on the properties of the interstellar solid particle population in the solar vicin ity. Especially the distribution of grain masses is indicative of growth an d destruction mechanisms that govern the grain evolution in the interstella r medium. The mass of an impacting dust grain is derived from its impact ve locity and the amount of plasma generated by the impact. Because the initia l velocity and the dynamics of interstellar particles in the solar system a re well known, we use an approximated theoretical instead of the measured i mpact velocity to derive the mass of interstellar grains from the Ulysses a nd Galileo in situ data. The revised mass distributions are steeper and thu s contain less large grains than the ones that use measured impact velociti es, but large grains still contribute significantly to the overall mass of the detected grains. The flux of interstellar grains with masses > 10(-14) kg is determined to be 1 x 10(-6) m(-2) s(-1) The comparison of radar data with the extrapolation of the Ulysses and Galileo mass distribution indicat es that the very large (m > 10(-10) kg) hyperbolic meteoroids detected by t he radar are not kinematically related to the interstellar dust population detected by the spacecraft.