It has, however, another key difference from Earth. The entire surface of Erna is wrapped in a powerful energy field known as the Fae. The Fae is a type of energy that comes up to the surface from the core of the planet via the plethora of volcanoes and earthquakes that rock the planet's surface. This is an energy that the native animals of Erna sense, and utilize to a small extent to help them survive (i.e. the Fae is often able to tell a Sensitive individual when an earthquake is coming, or if the tides are about to shift). This energy field that encompasses the planet is likened to Earth's magnetic field. Author C.S. Friedman explains how her idea of the Fae was shaped by Isaac Asimov's essay arguing that if magic existed, it would be a natural force governed by consistent rules. "Like fire, it should be useful when controlled, dangerous if uncontrolled," she says. "The fact that we build windmills does not mean we stop fearing hurricanes."