Internal differentiation of planets occurs because elements have distinctive physical properties (density is most important in this case) and chemical affinities.

1) Iron are called siderophile (nickel, cobalt)

2) Sulphur are called chalcophile (copper, silver, zinc)

3) Oxygen are called lithophile (sodium, potassium, calcium, silicon)

Solar Energy is the energy a planet receives from the Sun. We like it (especially during this time of the year) but it is of no use to interior differentiation of the planet (potentially some effect during an earlier period of strong solar winds). It decreases with increasing distance to the sun.

Continuous flexing of a satellite within its orbit (remember Io) can lead to Tidal Heating. This can clearly be an important heat source but is not one that applies to many planets or satellites.

Accretionary Heat results from the conversion of the kinetic energy of impacts to heat. Very important early.

During Core formation gravitational potential energy of dense material is converted to heat as the dense material sinks to the core.

Radiogenic heat is produced by the breakdown of radioactive elements. We distinguish between isotopes that have short half-lives (Al, I) and those with long half-lives (K, U). Nuclear decay heats the interior with short-lived isotopes providing an early boost of energy and long-lived ones a more 'steady burn'.

Radiation - emission of electromagnetic waves (sun to planets)

Conduction - vibrational energy passed from atom to atom (transmission through rigid solid)

Convection - transfer of matter in which warm material rises and cooler denser material sinks downward (more efficient than conduction)

Planetary heat is ultimately radiated away from its surface. Since differentiation relies on heat, the degree to which a planet can ultimately differentiate also depends on the rate at which the planet looses its heat.

The rate of cooling depends of the Surface to Mass Ratio

Small planets run out of heat quickly and have a short active period.

As this Magma Ocean cools a shell of lighter silicate minerals forms on the surface (light scum rising to the surface). Iron accumulates, forming large (100km diameter) blobs, which sink to form the core.

Silicate rich magmas rise to the surface and volatiles are released to form atmospheres or hydrospheres.

The outer, colder shell of the planet, the Lithosphere will be mechanically more rigid.

Below the lithosphere is a layer that is much hotter and therefore mechanically softer, which is called the Asthenosphere.

The bulk of the metal's of the original planets will end up in the core.

Long-lived isotopes serve as the planetary heat source at this stage. (On Earth convection currents in the mantle bring hot material to the surface to cool down. This drives our system of plate tectonics).

As the planet looses more heat, the rigid outer shell becomes thicker until surface activity ceases. The ultimate fate of a terrestrial planet is to become a solid lump of rock.