DUST PARTICLES BEYOND THE ASTEROID BELT - A STUDY BASED ON RECENT RESULTS OF THE ULYSSES DUST EXPERIMENT

Dust fluxes detected by the Ulysses dust experiment beyond the asteroi d belt, their possible sources and the possibilities of comparing them to observations of dust in the Zodiacal light are discussed. The dust fluxes detected at solar distances about r < 2.5 AU are compatible wi th a population of interplanetary dust particles moving on low eccentr icity and low inclination orbits. However, different orbital parameter s are required in order to explain the data obtained beyond this regio n. The analysis of impact directions and related inclinations of orbit s points to the existence of an interstellar dust stream (see Grun et al., Nature 362, 428-430, 1993) that makes up about 50% of the particl es detected in the outer solar system. Further components of the dust flux seem to be randomly oriented and on high eccentricity or unbound orbits. The activity of long period comets yields a possible source : from the analysis of radiation pressure particles of submicron size ar e expected to be in unbound orbits, whereas larger particles stay coup led to the solar system. Comparison to the out-of-ecliptic distributio n of dust derived from Zodiacal cloud models, shows that this outer du st cloud has only a small influence on the Zodiacal light brightness. However, it is shown, that detailed observations of the spectral varia tion in the infrared brightness could help for a better understanding standing. Also the compatibility of submicron dust, predominant in flu x data, and larger particles, predominant in brightness data, is shown to be not as clear in the outer dust cloud as in the inner solar syst em dust cloud.