How are the core of the planets made?

Answer 1

So far as we can tell, the cores of the planets formed as dense materials sank and light materials floated through the material of the planet, under the influence of the planet's own gravity.

In the case of the terrestrial planets (Mercury, Venus, Earth, Mars) the dense material forming the cores would seem to be mostly iron, iron sulphide, nickel, and various other elements that mix well with iron and are called "siderophiles", with elements that combine readily with sulphur ("chalcophiles") above them, elements that combine well with silicates (lithophiles) forming the crust, and elements that tend to form compounds that are liquids, gases, and vapours (atmophiles) either on top of that or drifting away to space.

In the case of the giant planets the light fraction is a mixture of hydrogen and helium along with a few other gases and vapours, and teh core, if any, it rather mysterious. There might be a ball of iron wrapped in sulphides and silicates in the middle, but we can't tell at present. It seems clear though, that in the case of Uranus and Neptune there is a significant ball or layer of water ice.

The larger, spherical moons of the giant planets are interesting. They seem to be differentiated into layers like the terrestrial planets except that the layer of water is frozen, or at least the top of it is.

As for the dwarf planets, I don't think we can tell yet. They certainly have enough gravity to achieve a spheroid shape, but whether they all have enough to differentiate themselves into layers we don't know.

Answer 2

The core of planets, including Earth, formed through a process called differentiation during the planet's early stages of formation. This process involved the denser materials sinking to the center to form the core, mainly composed of iron and nickel, while lighter materials accumulated in the outer layers. Heat generated by radioactive decay and impact events also played a role in shaping the composition and temperature of a planet's core.