Geologists estimate that the Earth’s core is a sweltering 5,700 K (5,427° C, 9,800° F), putting it about on par with the surface of the Sun – and yet the inner core is a solid ball of iron. Why it doesn’t liquify is a bit of a mystery, but now a study from KTH Royal Institute of Technology puts forward a new theory, simulating how solid iron can remain atomically stable under such extreme conditions.
Here on the surface of the Earth, iron atoms arrange themselves into cubes, in what’s known as a body-centered cubic (BCC) phase. Since this state is a product of room temperature and normal pressure, scientists have long believed that iron couldn’t exist in this form in the broiling temperatures and intense pressure at the planet’s center. Under those conditions, the crystal architecture of iron was expected to take on the shape of a hexagon, in a state called the hexagonal close-packed (HCP) phase.
Using the Swedish supercomputer Triolith, the new study from KTH crunched larger volumes of data than had previously been analyzed. The data indicated that the core was likely composed of 96 percent pure iron, with the remaining four percent made up of nickel and some light elements. But most importantly, the study found that BCC iron can indeed exist in the core, with its crystal structure remaining stable thanks to the very characteristics that were previously assumed to destabilize it.
“Under conditions in Earth’s core, BCC iron exhibits a pattern of atomic diffusion never before observed,” says Anatoly Belonoshko, one of the study’s authors. “It appears that the experimental data confirming the stability of BCC iron in the core were in front of us – we just did not know what that really meant.”