Planetary growth tracks and evolution of the capture radii. Left: planet mass versus semimajor axis evolution for Jupiter (J) and Saturn (S) in gas accretion scheme 1 and 2. Large dots indicate a time of 2 and 3 Myr, and small dots are separated by 0.2 Myr. We started the simulation at the time when Jupiter reached the pebble isolation mass (t_iso), and further included the growth and migration of Saturn’s core. In scheme 1 the contraction of the envelope occurs on a short timescale, resulting in fast gap opening and little migration. In scheme 2 this phase is significantly longer, and thus the planets migrate a further distance before coming to a halt due to gap opening. Right: capture radius versus time for the growth tracks presented in the left panel, calculated using a planetesimal radius of 100 km. The approximation for the capture radius has three regimes: before gas accretion is initiated, the capture radius is equal to the core radius; during the first phase of gas accretion, the envelope is enhanced, resulting in a large capture radius; and after the onset of runaway gas accretion, the capture radius decreases by roughly two orders of magnitude, and it takes on a value of about 1.5 times the current Jupiter radius.