Pressure versus depth inside the nucleus, for different initial sizes of the nucleus (radius R = 2.2, 3.0, 5.0 or 7.0 km). The pressure increases with depth. The blue range corresponds to the best value of 30−150 Pa for the compressive strength of the surface materials we see today (30−150 Pa). The red line at 2 km indicates the current size of the nucleus, which is what we see today. For an initial radius of 2.2−3.0 km, slightly larger than today, the pressure inside the nucleus exceeds the compressive strength of the layers we see today.