Interstellar dust in the solar system: model versus in situ spacecraft data

Abstract

Context. In the early 1990s, contemporary interstellar dust penetrating deep into the heliosphere was identified with the in situ dust detector on board the Ulysses spacecraft. Later on, interstellar dust was also identified in the data sets measured with dust instruments on board Galileo, Cassini, and Helios. Ulysses monitored the interstellar dust stream at high ecliptic latitudes for about 16 yr. The three other spacecraft data sets were obtained in the ecliptic plane and cover much shorter time intervals. Aims. To test the reliability of the model predictions, we compare previously published in situ interstellar dust measurements, obtained with these four spacecraft, with predictions of an advanced model for the dynamics of interstellar dust in the inner solar system (Interplanetary Meteoroid environment for EXploration; IMEX). Methods. Micrometer and sub-micrometer-sized dust particles are subject to solar gravity, radiation pressure and the Lorentz force on a charged dust particle moving through the interplanetary magnetic field. These forces lead to a complex size-dependent flow pattern of interstellar dust in the planetary system. The IMEX model was calibrated with the Ulysses interstellar dust measurements and includes these relevant forces. We study the time-resolved flux and mass distribution of interstellar dust in the solar system. Results. The IMEX model agrees with the spacecraft measurements within a factor of 2–3, including time intervals and spatial regions not covered by the original model calibration with the Ulysses data set. The model usually underestimates the dust fluxes measured by the space missions which were not used for the model calibration, i.e. Galileo, Cassini, and Helios. Conclusions. A unique time-dependent model, IMEX is designed to predict the interstellar dust fluxes and mass distributions for the inner and outer solar system. The model is suited to study dust detection conditions for past and future space missions.