Editing Planetary core (section)

==== Inner rocky planets ====
All of the rocky inner planets, as well as the moon, have an iron-dominant core. Venus and Mars have an additional major element in the core. Venus’ core is believed to be iron-nickel, similarly to Earth. Mars, on the other hand, is believed to have an iron-sulfur core and is separated into an outer liquid layer around an inner solid core.<ref name="stevenson 2001" /> As the orbital radius of a rocky planet increases, the size of the core relative to the total radius of the planet decreases.<ref name="solomon 1979" /> This is believed to be because differentiation of the core is directly related to a body's initial heat, so Mercury's core is relatively large and active.<ref name="solomon 1979" /> Venus and Mars, as well as the moon, do not have magnetic fields. This could be due to a lack of a convecting liquid layer interacting with a solid inner core, as Venus’ core is not layered.<ref name="de pater 2015" /> Although Mars does have a liquid and solid layer, they do not appear to be interacting in the same way that Earth's liquid and solid components interact to produce a dynamo.<ref name="stevenson 2001" />