Normalized total orbital migration torque (Γ_tot∕Γ₀) vs. planetary mass and orbital radius in the reference model MREF, zoomed into the region inside 1 au. Inward migration is shown in blue, while outward migration is shown in red. The solid black line marks where the migration torque is zero, and hence where planets are trapped. Dotted lines indicate the pebble isolation mass, following Lambrechts et al. (2014; lower) and Bitsch et al. (2018; upper). The green dashed line indicates the location of the pebble trap, where the inward radial drift of solid particles halts. The gray shading at the top shows the gap-opening region according to Crida et al. (2006). Here, planets would modify the surface density structure strongly. The horizontal yellow dashed and dotted lines indicate the masses of Earth and Jupiter.