HELIOPAUSE

boundary of the heliosphere, the teardrop-shaped region around the Sun that is filled with solar-magnetic fields and outward-moving solar gas consisting of protons and electrons. Outside the heliopause lies the heliosheath, a region of transition between the heliosphere and the hydrogen atoms and galactic magnetic fields of the local interstellar medium. The tail of the heliopause is theoretically estimated to be between 50 and 100 astronomical units from the Sun. The shape of the heliopause fluctuates and is influenced by a wind of interstellar gas produced by the Sun's motion through it. The orbits of all the major planets, including the Earth, lie well within the heliopause.