Caustics of Interstellar Dust Particles in the Heliosphere

Interstellar dust particles penetrate the heliosphere because of the relative motion of the Sun and the local interstellar medium. Inside the heliosphere, trajectories of dust grains deflect from the initial direction due to the action of three forces: gravitational attraction to the Sun, solar radiation pressure, and electromagnetic force. As a result, the distribution of dust grains becomes highly inhomogeneous. In our previous works, we demonstrated that under the influence of electromagnetic force, the envelopes of trajectories, or caustics, appear. We also studied the effects of velocity dispersion and the time-dependent magnetic field on the formation of caustics. The main goal of this work is to expand our knowledge about caustics. For this purpose, we apply two models of dust distribution in the heliosphere: 1) a kinetic model based on the solving of the kinetic equation for the velocity distribution function, and 2) a fluid cold gas model based on the solving of the continuity equation in the lagrangian form. For the first time, we perform simulations for particles of different sizes and discuss the physical reasons why the density singularities appear at the caustics. We also study the effects of combined gravity and solar radiation pressure on the dust distribution near the caustics.