Top row: examples of solar proton trajectories, dimensionless, initially flowing from the right to the left. No particle can enter into the cavity, the central disk of radius r_cav ≈ 0.28 r_E. Bottom row: the shape of the caustic created by particles coming from infinity, using the same spatial scale for three different heliocentric distances, as developed by Saillenfest et al. (2018). The corresponding values of r_E are, from left to right: 27, 165 and 714 km. Near the origin, the caustic wraps around the cavity. The nucleus position is displayed by a black cross in all plots.