Lab experiments show that planets do not have identical cores because of how nickel reacts with iron in the core. Work by Elardo and Shahar of Carnegie Institution of Science, US studied this reaction to understand the difference in cores.
During early solar system, the planets started forming as matter accumulated around them. During this accumulation, the heavier elements started sinking in to form the core. One such element was iron. Under different conditions of pressure and temperature, nickel reacts with different isotopes of iron to segregate them into heavier and lighter isotopes.
What are isotopes? Each element has a fixed number of protons in its atom. But the number of neutrons can vary. This leads to the formation of isotopes of that element.
The experiment helped in understanding that heavier isotopes tended to form the core of the planets and lighter isotopes the mantle, which was the layer around the core. Moon, Mars and asteroid Vesta depicted this segregation.
But Earth’s core showed different results. Because of extremely high temperatures, nickel did not segregate iron isotopes to that extent in the Earth’s core. That is the reason there are differences in lavas from Earth and other planets.