Earth's innermost layer is a 400-mile-wide ball of iron, new study suggests

This Blue Marble Earth montage — created from photos taken by the Visible/Infrared Imager Radiometer Suite (VIIRS) instrument on board the Suomi NPP satellite — shows stunning details.

(CNN)Scientists have long wondered what lies at the very center of the Earth, and the latest research is putting weight behind a theory that our planet has a distinct ball of iron within its metallic core.

Beneath the outermost crust, the mantle and the molten-liquid outer core lies the Earth's solid metal center — which actually has a hidden layer, or an "innermost inner core" within, according to a new study published Tuesday in the journal Nature Communications.
The monumental finding suggests the Earth has five major layers instead of four, and offered new details scientists could use to help unlock some of the oldest mysteries about our planet and how it was formed.
    Geoscientists first suggested that the Earth's core might have an additional, imperceptible layer about 20 years ago, according to a news release. Now, using new data sets collected by measuring the seismic waves of earthquakes as they passed through the Earth's center, researchers have finally detected that innermost core, the new study said.