The heliosphere is a bubble in space produced by the solar wind. Although electrically neutral atoms from interstellar space can penetrate this bubble, virtually all the material in the heliosphere emanates from the Sun itself. The solar wind streams off of the Sun in all directions at speeds of several hundred kilometers per second (about 1,000,000 mph in the Earth's vicinity). At some distance from the Sun, well beyond the orbit of Pluto, this supersonic wind must slow down to meet the gases in the interstellar medium. It must first pass through a shock, the termination shock, to become subsonic. It then slows down and gets turned in the direction of the ambient flow of the interstellar medium to form a comet-like tail behind the Sun. This subsonic flow region is called the heliosheath. The outer surface of the heliosheath, where the heliosphere meets the interstellar medium, is called the heliopause.
The solar wind consists of particles, ionized atoms from the solar corona, and fields (magnetic fields in particular). As the Sun rotates once in about 27 days, the magnetic field transported by the solar wind gets wrapped into a spiral. Variations in the Sun's magnetic field are carried outward by the solar wind and can produce magnetic storms in the Earth's own magnetosphere.
Image Credit: Lunar and Planetary Institute
Credit: Lunar and Planetary Institute