Migration speed as a function of planet’s distance from the star in 3D simulations of discs with different viscosities (i.e. simulations M_3D, M_{3D α5}, M_{3D α4} and M_3Dα3; see Table 1). A running average procedure has been used to reduce fluctuations, with the consequence that all but the green curve start at about 5.1 au instead of the released distance of 5.2 au. In the α = 10⁻³ and 10⁻⁴ cases migration is always inwards (negative radial speed). Notice that we have divided by 10 the migration speed of M_{3D α3} in order to scale it proportionally to viscosity relatively to the α = 10⁻⁴ case. The migration pattern in the inviscid case does not respect this scaling and turns positive after a short phase of inward migration. The same happens in the M_{3D α5} simulation.