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 of the material in the heliosphere emanates from the Sun itself.
The solar wind streams away from the Sun in all directions at speeds of several hundred km/s (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 is 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 precise distance to, and shape of, the heliopause is still uncertain. Interplanetary spacecraft such as Pioneer 10 and Pioneer 11 and Voyager 1 and Voyager 2 are traveling outward through the solar system and will eventually pass through the heliopause.
The solar wind consists of particles, ionized atoms from the solar corona, and fields, in particular magnetic fields. 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.
In March 2005 it was reported that measurements by the Solar Wind Anisotropies (SWAN) instrument onboard the Solar_and_Heliospheric_Observatory (SOHO) have shown that the heliosphere, the solar wind filled volume which prevents the solar system from becoming embedded in the local (ambient) interstellar medium, is not axisymmetrical, but is distorted, very likely under the effect of the local galactic magnetic field.
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- ^ "The Distortion of the Heliosphere: Our Interstellar Magnetic Compass." ESA news. Accessed on March 18, 2005.