Interstellar dust in the heliosphere
Mann, I.; Morfill, G. E.; Gruen, E.; Baguhl, M.; Zook, H. A.; Gustafson, B.; Staubach, P.; Taylor, A.
Germany, United States, United Kingdom
Abstract
A flow of μm-sized interstellar grains has been identified with the Ulysses dust detector in the outer solar system at about 5 AU from the Sun. The observed flux is 1.5x10^-4^m^-2^/s of particles of mean mass 3x10^-13^g, which corresponds to a mass flux of 5x10^-17^g/m^2^/s. The particles on hyperbolic trajectories have radiants which are compatible with the flow of interstellar gas, although some velocity dispersion occurs. The grains are on average a factor 30 more massive than the classical interstellar grains which cause stellar extinction. However, these smaller grains have not been detected by Ulysses. It is demonstrated that radiation pressure and interaction of the charged grains with the interplanetary magnetic field prevent these small grains from penetrating down to the distance of Ulysses. The spatial density of interstellar grains is compatible with zodiacal light observations. Some consequences arising from the existence of big grains in the interstellar medium are discussed.