The inner core of the Earth is made up of iron and nickel in an alloy represented with the chemical formula NiFe. The inner core is believed to be solid, and it is under intense pressure, which keeps it solid despite high temperatures. The temperature at the inner cores surface is estimated to be around 5,200° Celsius (9,392° Fahrenheit) . The inner core is growing slowly as the Earth cools. Although there is still no direct evidence about the composition of the inner core, it is believed to consist primarily of an iron-nickel alloy based on the relative prevalence of various chemical elements in the Solar System, the theory of planetary formation, and constraints imposed or implied by the chemistry of the rest of the Earths volume.