A differentiated object is one which has a layered internal structure sorted by the densities of the different components.

The layers inside a gravitationally differentiated object range from the most dense at the core, to the least dense in the crust. This is because the densest material sinks and the lighter material floats to the surface.

During the planetary formation stage of the early Solar System, the process of accretion produced homogeneous objects (planetesimals) which had the same composition throughout. Materials of different densities were able to co-exist throughout these bodies until a certain size (a diameter of approximately 200 km) was reached. At this point, the internal heat (generated through gravitational compression, energy from impacts, radioactive decay, and perhaps tidal forces) was sufficient to melt the interior of the object. When this happened, the densest material sunk towards the centre to form a core, while the lighter material floated to the surface to form a mantle and crust in a process called ‘gravitational differentiation’.