Based on measurements of the dust detector onboard Ulysses, we determine the flux of -meteoroids to at solar distances from 1 to 1.6 AU within the ecliptic plane for the first 65 days of the mission. This is in agreement with a previous analysis of the Ulysses measurements within the ecliptic (Baguhl, 1993) and it is also in agreement with other previous measurements (Berg & Grün, 1973). For the out-of-ecliptic part of the mission the flux amounts to in the region between 1.8 and 2.7 AU and helioecliptic latitudes between and . The mass distribution of detected -meteoroids is slightly different from the mass distribution of the (presumably) interplanetary dust component in the data. Taking into account the uncertainties in the speed determination as well as the unreliability in the impact direction a clear distinction between prograde and retrograde motion was not possible for the single impact event. However, from the discussion of the selection effects we can conclude that the detected -meteoroids are moving predominantly on prograde orbits. As expected from the flux geometry the flux of -meteoroids decreases with increasing solar distance. The study of the orbits of particles tends to indicate that the particles are produced at at solar distances less than 0.5 AU. However, the present data does not allow for a real determination of the orbital parameters of the particles. We conclude that the main mechanism that has influenced the particles that were identified as -meteoroids in the Ulysses data set, is most probably the influence of the radiation pressure force. However further studies will be needed to investigate the influence of the solar magnetic field on these small particles.
© European Southern Observatory (ESO) 1999
Online publication: November 26, 1998