Planetary Differentiation: Iron Rain & Core Formation

A newly accreted rocky planet can be molten from surface to center — a magma ocean. Dense iron does not dissolve into the lighter silicate melt around it; it beads into droplets and rains downward, feeding a growing metallic core while the silicate fraction stays behind as the future mantle and crust. This simulator renders that separation in 3D: hundreds of iron droplets sink under Stokes' law drag through a translucent magma-ocean shell, merging into a solid core that visibly grows as differentiation proceeds. Grain size, mantle viscosity and surface gravity all feed the real terminal-velocity formula live, with readouts for settling speed, core radius and the fraction of iron that has differentiated out.