Variation of maximum temperature in the centre of a planetesimal with radius R and instant of formation t_form. Upper panel: completely consolidated bodies with porosity φ = 0. Lower panel: models of initially porous bodies with porosity φ_srf = 0.5 that consolidate in the interior during the course of their thermal evolution. The lines correspond to the indicated maximum central temperature. At temperatures above  ≈ 1400 K partial melting of the mineral mixture is expected. Temperatures exceeding 1500 K are excluded for this reason. Shown are models for three different initial ⁶⁰Fe/⁵⁶Fe abundance ratios: Left panel: without ⁶⁰Fe. Middle panel: the optimum-fit value of 4.1 × 10^-7 for the H chondrite parent body, see Sect. 8. Right panel: highest value of 1.6 × 10^-6 given in Table 5.