SOUTH-NORTH AND RADIAL TRAVERSES THROUGH THE INTERPLANETARY DUST CLOUD

Identical in situ dust detectors are flown on board the Galileo and Ul ysses spacecraft. They record impacts of micrometeoroids in the eclipt ic plane at heliocentric distances from 0.7 to 5.4 AU and in a plane a lmost perpendicular to the ecliptic from -79 degrees to +79 degrees ec liptic latitude. The combination of both Ulysses and Galileo measureme nts yields information about the radial and latitudinal distributions of micron- and submicron-sized dust in the Solar System. Two types of dust particles were found to dominate the dust flux in interplanetary space. Interplanetary micrometeoroids covering a wide mass range from 10(-16) to 10(-6) g are recorded mostly inside 3 AU and at latitudes b elow 30 degrees. Interstellar grains with masses between 10(-14) and 1 0(-12) g have been positively identified outside 3 AU near the eclipti c plane and outside 1.8 AU at high ecliptic latitudes (>50 degrees). I nterstellar grains move on hyperbolic trajectories through the planeta ry system and constitute the dominant dust flux (1.5 X 10(-4) m(-2) se c(-1)) in the outer Solar System and at high ecliptic latitudes. To co mpare and analyze the Galileo and Ulysses data sets, a new model is de veloped based on J. Geophys. Res. 98, 17029-17048, Divine's (1993, ''f ive populations of interplanetary meteoroids'' model. Both models desc ribe the interplanetary meteoroid environment in terms of dust populat ions on distinct orbits. Taking into account the measured velocities a nd the effect of radiation pressure on small particles (described by t he ratio of radiation pressure force to gravity, beta), we define four populations of meteoroids on elliptical orbits and one population on hyperbolic orbit that can fit the micrometeoroid flux observed by Gali leo and Ulysses. Micrometeoroids with masses greater than 10(-10) g an d negligible radiation pressure (beta = 0) orbit the Sun on low to mod erately eccentric orbits and with low inclinations (less than or equal to 30 degrees). Populations of smaller particles with mean masses of 10(-11) g (beta = 0.3), 10(-13) g (beta = 0.8), and 5 X 10(-15) g (bet a = 0.3), respectively, have components with high eccentricities and h ave increasingly wider inclination distributions with decreasing mass. Similarities among the orbit distributions of the small particle popu lations on bound orbits suggest that all are genetically related and a re part of an overall micrometeoroid complex that prevails in the inne r Solar System. The high-eccentricity component of the small particle populations may actually be beta-meteoroids which are not well charact erized by our measurements. Our modeling suggests further that the int erstellar dust flux is not reduced at Ulysses' perihelion distance (1. 3 AU) and that it contributes about 30% of the total dust flux observe d there. (C) 1997 Academic Press.