The two groups of planets based on their composition are the terrestrial planets, and the jovian planets. The terrestrial planets are small, and their composition is different than that of the jovian planets. The terrestrial planets have a solid iron inner core, liquid iron outer core, silicate mantle, and silicate crust. The jovian planets are also called gas giants because they are much larger and are gassy, not hard as the terrestrial planets. These planets have a silicate inner core, ice outer core, liquid metallic hydrogen layer, liquid hydrogen layer, and on the top gaseous hydrogen.
