Interplanetary dust: Sources, sinks and dynamics

Lunar microcrater and in situ measurement data on the dynamics of interplanetary dust are summarized. Lunar microcrater studies and simulation experiments produce flux diagrams for the dust at 1 AU in the mass range between 10 to the minus 17th power and 10 to the minus 3rd power g. Microcrater morphologies prove the existence of low density particles. In situ experiments reveal that 90% of the particles are on direct orbits around the Sun at 20 to 25 km/sec heliocentric velocities (apex particles) and 10% at a speed of 50 km/sec (antiapex particles). The antiapex particles are low-density. A submicron-sized particle stream comes from the direction of the Sun. Comets provide most of the particles in the solar system dust cloud. Due to the Poynting-Robertson effect, the young low density cometary dust particles spiral towards the Sun. When these particles are old and on quasicircular orbits around the Sun, their densities could be 1g/cu cm.