PHYSICS OF INTERPLANETARY AND INTERSTELLAR DUST

Observations of dust in the solar system and in the diffuse interstell ar medium are summarized. New measurements of interstellar dust in the heliosphere extend our knowledge about micron-sized and bigger partic les in the local interstellar medium. Interplanetary grains extend fro m submicron- to meter-sized meteoroids. The main destructive effect in the solar system are mutual collisions which provide an effective sou rce for smaller particles. In the diffuse interstellar medium sputteri ng is believed to be the dominant destructive effect on submicron-size d grains. However, an effective supply mechanism for these grains is p resently unknown. The dominant transport mechanisms in the solar syste m is the Poynting-Robertson effect which sweeps meteoroids bigger than about one micron in size towards the sun. Smaller particles are drive n out of the solar system by radiation pressure and electromagnetic in teraction with the interplanetary magnetic field. In the diffuse inter stellar medium coupling of charged interstellar grains to large-scale magnetic fields seem to dominate frictional coupling of dust to the in terstellar gas.