The satellites, three identical spacecraft collectively known as Swarm, were launched in 2013 to study’s the Earth’s many magnetic signals. These signals create a magnetic field that can be likened to an enormous cocoon, a shield that protects the planet from cosmic radiation and charged particles from solar wind.

The planet’s molten iron core generates the majority of the magnetic field, according to ESA. The remaining 6 percent is created, in part, by electrical currents in space that surround Earth, as well as by magnetized rocks in the upper lithosphere, an area encompassing Earth’s crust and upper mantle. [50 Amazing Facts About Planet Earth]

After three years of collecting data, the Swarm satellites were able to plot the highest-resolution map to date of the lithosphere’s relatively weak magnetic signals.

“By combining Swarm measurements with historical data from the German CHAMP satellite, and using a new modeling technique, it was possible to extract the tiny magnetic signals of crustal magnetization,” project lead researcher Nils Olsen, a professor of geomagnetism at the Technical University of Denmark, said in a statement.