In the Gundam anime metaseries, the Earth Sphere refers to Earth, the Moon, and all artificial satellites orbiting them. Space colonies are located at areas of gravitational stability known as Lagrange points. In light of the colonization prevalent in Gundam, the term essentially encompasses humanity's expanded habitat.
Nearly all Gundam stories take place exclusively within the Earth Sphere, though a few involve events around Mars, Jupiter, and the asteroid belt.
In the Cosmic Era of Gundam SEED the area includes the Lagrange points, the space settlements known as PLANTs, military bases, and a ring of orbiting space junk known as the Debris Belt.