Predicted envelope mass (in Earth masses, logarithmic scale) as a function of the envelope mass obtained by solving the internal structure equations (blue). The green and red points show the estimate of the envelope mass using the I00 and B15 accretion rate, respectively. This accretion rate is integrated on the disc lifetime, itself assumed to be randomly uniformly distributed between 0 and 5 Myr. Only envelope masses for core masses higher than 1 M_⊕ are represented. Left: using the ISM opacity from BL94. The envelope mass using I00 and B15 is computed assuming an opacity of 1 cm² g⁻¹. Right: reducing this opacity by a factor 100. The envelope mass using I00 and B15 is computed assuming an opacity of 0.01 cm² g⁻¹.