Comparison of models with different core masses but when applying the same temperature offset. The calculations use the SR2018 phase diagram with T_offset = 350 K. Displayed quantities are at t = 4.56 Gyr. Left panel: atmospheric helium mass fraction as a function of the temperature offset. The horizontal dashed lines show the upper and lower bounds of the observed value of Y₁. Right panel: planetary adius as a function of the 1 bar temperature. The black errorbars show the observed radii and 1 bar temperatures of Jupiter and Saturn (see Fig. B.1 for details about these measured values). The dashed lines show the possible range of models with core masses that fall between the two values we considered here.